Renewable and Sustainable Energy Reviews 43 (2015) 244–263

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Renewable and Sustainable Energy Reviews

journal homepage: www.elsevier.com/locate/rser

Biorefining in the prevailing energy and materials crisis: a review

of sustainable pathways for biorefinery value chains and sustainability
assessment methodologies
Ranjan Parajuli a,n, Tommy Dalgaard a, Uffe Jørgensen a, Anders Peter S. Adamsen b,
Marie Trydeman Knudsen a, Morten Birkved c, Morten Gylling d, Jan Kofod Schjørring e
a
Department of Agroecology, Aarhus University, Blichers Allé 20, DK-8830 Tjele, Denmark
b
Department of Engineering, Aarhus University, Hangøvej 2, DK-8200 Aarhus N, Denmark
c
Department of Manufacturing Engineering and Management, Technical University of Denmark, Building 424, DK-2800 Lyngby, Denmark
d
Department of Food and Resource Economics, University of Copenhagen, Rolighedsvej 25, DK-1958 Frederiksberg C, Denmark
e
Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark

art ic l e i nf o a b s t r a c t

Article history: The aim of the current paper is to discuss the sustainability aspect of biorefinery systems with focus on
Received 31 January 2014 biomass supply chains, processing of biomass feedstocks in biorefinery platforms and sustainability
Received in revised form assessment methodologies. From the stand point of sustainability, it is important to optimize the
20 August 2014
agricultural production system and minimize the related environmental impacts at the farming system
Accepted 1 November 2014
Available online 25 November 2014
level. These impacts are primarily related to agri-chemical inputs and the related undesired environ-
mental emissions and to the repercussions from biomass production. At the same time, the biorefineries
Keywords: need a year-round supply of biomass and about 40–60% of the total operating cost of a typical bio-
Biorefinery refinery is related to the feedstocks chosen, and thus highlights on the careful prioritization of feedstocks
Biomass feedstock
mainly based on their economic and environmental loadings. Regarding the processing in biorefinery
Sustainability
platforms, chemical composition of biomasses is important. Biomasses with higher concentrations of
Biobased product
Environmental performances cellulose and hemicelluloses compared to lignin are preferred for bioethanol production in the
Economic performances lignocellulosic biorefinery, since the biodegradability of cellulose is higher than lignin. A green
Life Cycle Assessment biorefinery platform enables the extraction of protein from grasses, producing an important alternative
to importing protein sources for food products and animal feed, while also allowing processing
of residues to deliver bioethanol. Currently, there are several approaches to integrate biorefinery
platforms, which are aimed to enhance their economic and environmental sustainability. Regarding
sustainability assessment, the complexities related to the material flows in a biorefinery and the delivery
of alternative biobased products means dealing with multiple indicators in the decision-making process
to enable comparisons of alternatives. Life Cycle Assessment is regarded as one of the most relevant tools
to assess the environmental hotspots in the biomass supply chains, at processing stages and also to
support in the prioritization of any specific biobased products and the alternatives delivered from
biorefineries.
& 2014 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
2. Biorefinery processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
2.1. Biorefinery platforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
2.2. Potential biorefinery feedstocks and products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
2.3. Biomass to biobased products and processes involved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
2.4. Description of material flows in a biorefinery, an example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
3. Sustainability themes in biorefineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

n
Corresponding author. Tel.: þ 45 71606831.
E-mail address: ranjan.parajuli@agro.au.dk (R. Parajuli).

http://dx.doi.org/10.1016/j.rser.2014.11.041
1364-0321/& 2014 Elsevier Ltd. All rights reserved.
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 245

3.1. Material inputs in biorefinery pathways: at farm gate level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

3.2. Agricultural management and environmental impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
3.3. Inputs and outputs of materials in a biorefinery system-at processing level, an illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
3.4. Sustainability dimensions of biorefinery value chains with biofuel as an example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
3.4.1. Production economics of bioethanol generated with different biorefinery technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
3.4.2. Environmental performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
4. Methodological concepts for the sustainability assessment of biorefineries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
4.1. Sustainability assessment framework and tools. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
4.2. Assessment criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
4.2.1. Selection and weighting of criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
4.3. Integrating sustainability assessment procedures and tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
4.3.1. Application of LCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
4.3.2. Evaluation approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
5. Biorefinery in the context of the Danish agricultural and energy systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
5.1. Background for biorefinery setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
5.2. Research perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
6. Conclusions and way forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

1. Introduction
transportation biofuels (bioethanol and biodiesel) replaces conven-
The societal need of energy and materials is predicted to reach a tional diesel and gasoline. One of the crucial issues related to the 1st
crisis point in the near future [1]. This is because of the coupling generation biofuel production is the belief that it accelerates the
between escalating demand and cost of fossil fuels upon which the competition among the food and feed industries for agricultural land.
production of chemicals, materials and energy conversions still Furthermore, issues related to indirect landuse changes (iLUC) are also
depend. The high energy intensity in material production has sustain- increasingly included in the studies related to sustainable agro-
ability impacts on the energy sector, environment and economy [2]. ecological management and aiming to assess the negative impacts
Currently fossil fuels contribute about 80% of the global energy on Greenhouse gas (GHG) emissions, biodiversity loss and socio-
demand, and even if the current political commitments and strategies economic impacts [22]. In this context, a wider range of innovations,
to tackle the issues of climate change and energy insecurity, as including the biorefinery, is now emerging to create new ways of
envisioned by different countries are in place, the global energy generating bioenergy and explore entirely new types of products in
demand in 2035 is still projected to rise by 40% with fossil fuels new value chains [23]. Biorefining is regarded as a sustainable
contributing 75% [3]. The consequences of such dependency of fossil processing of a biomass or a combination of different types of
fuels in the agriculture system has resulted hikes in the prices of the biomasses [24] to produce a spectrum of marketable products and
raw ingredients for food and feedstuffs [4,5], since fossil fuel is one of energy [17] at a potentially better economic return [24–26]. Never-
the principal raw material in the modern agriculture [6]. theless, it is important to ensure the sustainable supply of biomass
Amid concerns about the sustainability of the energy sector without compromising the prevailing land use, soil nutrient loss and
initiatives, the production of biofuel is gaining ground in various the wider environmental and economic sustainability [27,28]. This
economic regions, ranging from developing countries [7] to more demands a comprehensive analysis of biorefinery value chains; cover-
developed economies [8]. Currently, there are regulations in Europe on ing the entire flows of material inputs and also including the
the substitution of non-renewable sources with biofuels for transpor- sustainability features of agriculture system upon which production
tation. The European Commission [9] has also focused on biofuels such of biorefinery feedstocks are connected.
as bioethanol, biodiesel, biogas, biomethanol, synthetic biofuels, bio- The current study undertakes a review of fundamental aspects
hydrogen and pure vegetable oil [10] to promote greener transporta- of sustainable biorefining pathways, concentrating on three major
tion fuel. Despite biomass being important source of bioenergy sources areas: (i) introduction to the processes and platforms of biorefin-
issues concerning their environmental impacts, security and stability ery, potential biobased products markets, (ii) discussion of key
and diversification of their uses also exist [11–13]. Regarding the sustainability parameters, such as relevance of considering poten-
debates on biofuels, they are primarily based on the advantages and tial influences of the input materials (energy and non-energy) at
disadvantages of the classified biofuels, i.e., 1st versus 2nd or 3rd the farming system level and at the stages of biorefining processes,
generation fuels. Biofuel production chains based on starch and sugar as discussed in Sections 2 and 3, and (iii) outlining possible
from corn and sugarcane respectively, and including the liquid fuels methodological considerations for the sustainability assessment
derived from animal and vegetable fat using conventional technologies of biorefining processes, as discussed in Section 4. Based on these
are regarded as 1st generation biofuels [14]. Biofuels based on reviews, the current study also outlines research perspectives in
lignocellulosic feedstock (e.g. straw, grasses, willow) [15] are classified the specific context of Danish agricultural and energy systems,
under the 2nd generation types. Algae and advanced processing of the which is discussed in Section 5.
2nd generation biofuels have been defined as 3rd generation biofuels
[16]. The main advantage of the 1st generation biofuel production is
primarily the high sugar or oil content in the raw material and the 2. Biorefinery processes
conversion process to energy is relatively easy [17]. Regarding the
environmental performances of biofuel production chains, studies 2.1. Biorefinery platforms
including Refs. [18–21] have made the comparisons of the environ-
mental differences of them with the corresponding fossil fuels. For In the current era, the biorefinery concept is aimed at replacing
instance, a reduction in the global warming potential (GWP) and the ‘petroleum refineries’ [29] and to reduce the fossil fuel
increase in fossil fuel savings could be achieved if the most common intensity in different production areas [30]. The replacement of
246 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

fossil-fuel-based products is generally possible if their alternatives market [10,34]. The green juice is a potential raw material for
(e.g. biochemicals, transportation fuels and fuels for the generation the production of high quality fodder and cosmetic proteins,
of heat and electricity delivered from biorefineries) [30,31] are human nutrition, chemicals (e.g. lactic acid and lysine), or can
available in the market. According to René and Bert [24], the alternatively be used as a substrate for biogas production [10].
current biorefinery classification system is in a developing stage, Another advantage of green biorefinery is its ability to utilize
where categories have until now been differentiated based mainly versatile and abundant green biomasses [34]. Further descriptive
on: (i) raw material inputs (e.g. green biorefinery, whole-crop information of the outlined biorefinery classifications can be found
biorefinery, lignocellulosic biorefinery, marine biorefinery), (ii) in studies including Refs. [10,24,35]. Table 1 provides information
type of technology (e.g. biochemical, thermo-chemical biorefin- about different types of biorefinery platforms along with the
ery), (iii) status of technology (conventional and advanced bior- possible biobased products.
efinery, 1st and 2nd generation biorefinery), and (iv) main
(intermediate) product produced (syngas platform, sugar platform,
lignin platform). 2.2. Potential biorefinery feedstocks and products
The four main technological processes involved in biorefineries
include: thermochemical, biochemical, mechanical/physical and A wider variations on the utilization of bioenergy crops can be
chemical processes [17]. In general biorefinery can also be grouped found across the world [30]; e.g. corn (maize) is the main crop for
in two categories: biochemical platform and thermochemical the 1st generation bioethanol production in North America, and in
platform. The former type normally focuses on the fermentation Brazil soybean is the main feedstock for biodiesel production and
of sugars, e.g. extracted from lignocellulosic feedstocks. In this sugarcane for bioethanol production [37]. If the governmental
kind of platform after the preparation of feedstocks (e.g. size interest to upscale the production capacity of bioethanol, e.g. as
reduction), the feedstocks are subjected to three basic steps of currently considered by different developed countries continues,
conversions: (i) conversion of raw biomass to sugar or other by 2020 its demand could exceed 125 billion l. The major con-
fermentation feedstock, (ii) bioconversion of feedstock intermedi- sequences of such situation are primarily on the feedstock market
ates using biocatalysts and (iii) processing to deliver added value and on the global capacity of the agricultural system to maintain
chemicals, fuel-grade ethanol and other fuels, heat and/or elec- the bulk biomass demand [38], which pinpoint on the up-scaling
tricity. Likewise, in the case of the thermochemical platform, of biomass production and the diversification of their uses.
biorefineries primarily focus on gasification (heating biomass with The selection of feedstocks for biorefining is primarily con-
about one-third of oxygen necessary for complete combustion, cerned with the issue of sustainable year-round supplies
producing syngas), and/or pyrolysis (heating biomass in absence of [14,39,40]. It is also important to optimize the production costs
oxygen, producing a pyrolysis oil). The syngas and pyrolysis oil are of biobased products, since generally about 40–60% of the total
regarded as cleaner and more efficient fuels than solid biomass. It operating costs of a typical biorefinery are spent on the feedstock
should be noted that they can also be chemically converted to [41]; on a per-gallon basis of ethanol production this equates to
other valuable fuels and chemicals. In the thermochemical plat- 30–32% of the total production cost [42]. Furthermore, its rele-
forms the basic processing steps include: (i) feedstock preparation vancy is also signified by the chemical compositions of different
(drying, size reduction), (ii) conversion of biomass starting with types of biomass (e.g. Table 2), since these compositions are the
feeding, gasification and/or pyrolysis, and (iii) product delivery basic elements that undergo transformation processes to deliver
with cleaning and conditioning [32]. Currently in order to ensure different valuable products [43]. Galbe et al. [44] made a compar-
the environmental and economic sustainability, at several stages ison of biorefinery based on lignocellulosic feedstocks and starch-
of these platforms are integrated. containing biomasses. They pointed out that the lignocelluloses
The lignocellulosic biorefinery type, is generally suited for possess some physical barriers, such as complex structures, pre-
producing products in an industrial scale, utilizing a variety of sence of various hexose and pentose sugars making the fermenta-
raw material (e.g. straw, reed, grass, wood, paper-waste, etc.) tion process complicated, and the presence of lignin or other
available with low prices [33]. Green biorefinery is increasingly compounds inhibiting the fermenting organisms. These limita-
becoming popular in several northern European countries. In this tions are further related with a higher energy demand and thus
type of biorefinery the green biomass is separated into a fibre-rich increasing the production costs. However, there have been recent
press cake and a protein-rich press juice [10]. The bulk chemical advancements in processing technologies that have more or less
contents contained in the press cake (e.g. cellulose, starch and addressed such issues; and are discussed in Section 2.3. Nonetheless,
dyes) and green juice (e.g. proteins, free amino acids, organic acids, due to land use and other socio-economic and environmental issues,
enzymes and minerals) are valuable products in the current lignocelluloses are preferable to the starch-containing materials [44].

Table 1
Classification of biorefinery, platforms and products.

Types Processes Feedstocks Products

Energy Materials

One-platforma (C6 sugars) Hydrolysis, fermentation Starch crops (Corn) Bioethanol Animal feed
One-platforma (Oil) Pressing, transesterification Oil crops (Rapeseed) Biodiesel Animal feed (rape
cake), glycerine
One-platforma (Syngas) Pre-treatment, gasification, FT synthesis, Lignocellulosic residues (straw) Synthetic biofuels Fischer– Chemicals (alcohols)
alcohol synthesis Tropsch (FT-fuels)
b
Two-platform (Sugar and Biochemical conversion (sugar platform), Biomasses (with 75% Conditioning gas, fuels Chemicals, polymers
syngas) thermochemical (syngas) carbohydrate, on average)
Four-platforma (C6/C5 sugars, Pre-treatment, hydrolysis, fermentation, Lignocellulose crops FT-fuels, Bioethanol Animal feed
lignin, syngas) gasification, FT- synthesis (switchgrass)

a
Cherubini et al. [35].
b
Kamm et al. [36].
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 247

Table 3 shows typical examples of potential biobased feed- Commission taskforce [52] produced a report on the estimated
stocks for biorefining and the alternative fossil fuel-based products potential market for bio-based products in European Union (EU)
available in the current market. For example, succinic acid is a and also a comprehensive market analysis of public interest in
fermentable product derived from glucose and is used in food, biobased products, such as those based on lignin. In 2005, within
chemical and pharmaceutical productions [46,47]. Likewise, a the chemical sector the market for bio-based products accounted
biochemical such as lactic acid and amino acids are also alter- for about 7% of the global sales, equivalent to US $77 billion, and
natives to the current raw materials used in food industries. Other the EU industry contributed approximately 30% to the global sales.
commercially available biobased chemicals produced from bior- By 2020, the value of biobased products is expected to be
efining include adhesives, cleaning compounds, detergents, dielec- approximately US $250 billion (i.e. 20% of the chemical industry
tric fluids, dyes, hydraulic fluids, inks, lubricants, packaging output will be biobased by that time) [52]. Similarly, the recent
materials, paints and coatings, paper and box board, plastic fillers, study of International Energy Agency (IEA)-Bioenergy (Task 42
polymers, solvents and sorbents [26]. Biorefinery) has shown that there is a massive demand of biobased
The global market for the special biochemicals (enzymes, chemicals and has also highlighted on the growing future market
flavours and fragrances, biopesticides, thickening agents, plant [53].
growth promoters, essential amino acids, vitamins, etc.) based on
biomasses is currently several billion US dollars per year and is
growing at a rate of 10–20% per year [33]. In 2007 a European 2.3. Biomass to biobased products and processes involved

The conversion of a raw biomass into marketable biobased

Table 2
Percentage of dry weight composition of the selected biomasses (based on [30,45]).
products, such as in a lignocellulosic biorefinery system, occurs in
four major steps: (i) pretreatment of the raw biomass, (ii) hydro-
Feedstock Cellulose Hemicellulose Lignin lysis, (iii) fermentation, and (iv) product recoveries. A detailed
description of these key steps can be found in FitzPatrick et al.
Bagasse 41 23 18
[54].
Bamboo 26–43 15–26 21–31
Banana Waste 13 15 14 In a lignocellulosic biorefinery, pretreatment is necessary to
Barley straw 32 26 23 convert the strong lignocellulosic structure into reactive cellulosic
Coffee pulp 35 46 19 intermediates and is a high energy-consuming process [44]. The
Corn cobs 45 35 15
cellulose is structurally strong with a long chains of glucose
Corn stalks 43 24 17
Corn stover 40 22 18
molecules (C6 sugar) linked with β-1,4 glycosidic linkages, giving
Grasses 25–40 25–50 10–30 a crystalline structure which is difficult to break down (hydrolyze)
Rye grass (early leaf) 21 16 3 compared to starch with α-1,4 glycosidic linkages [55]. A typical
Switchgrass 45 31 12 composition of agricultural residues constitute of cellulose
Hardwood bark 22–40 20–38 30–55
35–50%, hemicellulose 23–35% and lignin 14–20% [30,45]
Hardwood stem 40–50 24–40 18–25
Softwood stem 45–50 25–35 25–35 (Table 2). The compositions of a biomass are significantly changed
Sorted plant refuse 60 20 20 after undergoing a pretreatment process. For instance, in ligno-
Leaves 15–20 80–85 – celluloses the cellulose fraction increases from 43% to 85%,
Millet husk 33 27 14
whereas hemicellulose and lignin reduce from 34% and 22% to
Wheat straw 39 24 16
Rice husk 31 24 14
6% and 9%, respectively [56]. Removal of potassium chloride (KCl)
Rice straw 37 23 14 is an important part of the pretreatment of straw, as Larsen et al.
Rye grass (seed setting) 27 26 7 [57] has reported that about 90% of the KCl is found in the liquid
Rye straw 33–35 27–30 16–19 fraction of the straw-based biorefinery and can be recovered in the
Pine wood 39 24 20
biorefining processes. On a per-gallon basis, the pretreatment
Poplar wood 35 17 26
Sweet sorghum bagasse 45 25 18 represents about 19–22% of the production cost of bioethanol
Newspaper 40–55 25–40 18–30 [42]. The cellulose content of a biomass is hydrolyzed to break
Waste papers from chemical pulps 60–70 10–20 5–10 down into glucose (by cellulases in the enzymatic treatment, or
Nut shells 25–30 25–30 30–40 chemically by sulphuric or other acids). It should be noted that
Swine waste 6 28 –
Solid cattle manure 1.6–4.7 28 –
after the pretreatment process, the C5 sugars (mainly pentose,
xylose and arabinose) are also liberated, and the source of

Table 3
Overview of suitable biorefinery feedstocks with significant related chemical value chains.

Biobased products Maize Sugarcane Rice Barley Potato Other lignocellulose Vegetable oils Oilseed (e.g. rapeseed, sunflower)

1,3 -Propanediol a √ √
Succinic acid b √ √ √ √ √ √
Adhesives, solvents, Surfactantsc √ √ √
Ethyl lactate d √ √ √ √ √
Erucic acid e √
Amylose ethers f √ √ √ √

a
A building block of polymer (mostly from maize syrup) [46].
b
Fermentation of glucose and applied in food production, chemical industry and pharmaceutics [46,47].
c
Surfactants is an important product used in detergents, cosmetics and manufacturing processes, and are still primarily derived from petroleum [48]. Vegetable oils
(sunflower, rapeseed), coconut oil, and palm oil are also suitable [49].
d
A lactic acid derivative, produced from alcohols and fatty acids through fermentation of carbohydrates. It can be used in pharmaceuticals, paints and ink manufacturing
[46,47]. Rapeseed and sunflower oils are major sources of fatty acids.
e
Applied as industrial oil products (high-quality lubricants and hydraulic oils) [49,50].
f
Alternatives for polyethylene and polystyrene, required to produce bioplastics [46,51]. Processing of sugar or starch to produce alternative biochemicals to the
competing fossil reference polymers [48].
248 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

C6 sugars (cellulose) is subjected to hydrolysis. Moreover, under technology that can reduce the cellulase cost for the cellulose-to-
normal conditions, the pretreated biomass should be cooled to a ethanol process from US$5.40 gal  1 (1 US gallon ¼3.8 l) of ethanol
much lower temperature to assist enzymatic hydrolysis in order to to approximately 20 cents/gal [66]. Pan et al. [67], along a similar
liberate C6 sugars, which costs time and money. In the meantime, line also aired the similar prospect of reducing the cost of
with the lower temperature there is a high chance of contaminat- manufacturing enzymes by using modern biotechnologies.
ing the fermentation process due to extraneous organisms [58]. It Removal of lignin in the initial processing of biomass facilitates
should be noted that the yield of ethanol only from the C6 sugars enzymatic hydrolysis processes, as a higher concentration of lignin
produced after the fermentation process is normally low [15]. inhibits the process of hydrolysis [68,69]. An additional advantage
Regarding the case of starch-containing materials, e.g. corn or of lignin removal is that it represents about 40% of the heat
wheat, liquefaction of the starch fraction is accomplished by content in biomass and can thus can be treated as a fuel [69], as
adding hydrolytic enzymes (α-amylases) at temperatures of have been used in the process of producing cellulose from wood
around 90 1C; after this stage the starch molecules are further for paper and cardboard [70]. In spite of this, the limitation of
hydrolyzed by the addition of glucoamylases, producing sugars. In lignin is that it is highly contaminated with acid, and therefore
general, sugars are readily fermented by yeast, e.g. Saccharomyces hard to utilize even for conversion to energy in a profitable way
cerevisiae, to produce bioethanol and co-products like animal feed [31], which definitely has negative consequences in the sustain-
and fractions of proteins and fibre, which is also referred to as ability of biobased products production [71]. Catalytical processing
distillers dried grains with solubles (DDGS) [44]. of biomass is regarded one of the solutions to enable lignin
From a techno-economic perspective, all the available pretreat- valorization [72] and facilitates the conversion process to produce
ment processes have both advantages and disadvantages. For bulk chemicals. Comprehensive information about catalytic lignin
instance, (i) the lime pretreatment process (though claimed to valorization can be found in Ref.[72]. Moreover, conversion of
be the most effective) also requires the input of pressurized lignin to potential bulk chemicals (e.g. aromatic compounds)
oxygen [59], upping the cost, (ii) the organic solvent pretreatment [72,73] instead of burning as fuel, not only displaces fossil-fuel-
requires additional catalysts and the solvents need to be removed based chemicals and their related environmental impacts but also
after the use to avoid inhibitory effects on saccharification and adds new value chains in the spectrum of biobased products.
fermentation [60], (iii) dilute sulphuric acid pretreatment solubi- Organosolv extraction processes can be used to separate lignin and
lizes the majority of the hemicellulose and a small amount of other useful materials from biomass [74]. In Holladay et al. [75]
lignin, but at higher temperatures it facilitates the production of potential lignin-based products are further listed and described in
polysaccharide-degradation products that inhibit the fermentation detail.
process [61], (iv) steam pretreatment can be used for different The fermentation process is normally performed either in a
biomasses but requires impregnating agents to improve yields separate fermenting tank, the process generally being referred to
[62], (v) ionic pretreatment, claimed to address the above- as “separate hydrolysis and fermentation” (SHF), or simulta-
mentioned limitations of the other pretreatment processes, is neously with the hydrolysis of the cellulose chains, also called
relatively costly [42]. Comparative performances of the different “simultaneous saccharification and fermentation” (SSF). In the
types of pretreatment processes can be found in Refs. [63,64]. case of fermenting the pentose sugars, the process is also referred
Next stage of processing is the hydrolysis of the feedstock. to as “simultaneous saccharification and cofermentation” (SSCF)
Hydrolysis process is important to yield sugar from both hemi- [44]. The relative advantages of fermentation along with the
cellulose and cellulose, and is one of the critical parameters for hydrolysis processes, with respect to bioethanol production, are
ensuring economic viability of the ethanol production [65]. Hydro- discussed in Section 3.4.1.
lysis of biomass can be carried out in two different ways, acid
hydrolysis and enzymatic hydrolysis. A dilute acid hydrolysis is 2.4. Description of material flows in a biorefinery, an example
generally conducted in two steps (pre-hydrolysis and main hydro-
lysis) [61]. The limitation of the acid hydrolysis process is a A schematic process of “Inbicon” biorefinery model is discussed
somewhat lower ethanol yield and the need to use resistant in this section. The Inbicon biorefinery model was built in 2009 in
materials to avoid corrosion by acid at high temperatures, thereby Denmark as a demonstration plant after several years of research
increasing the production costs. Furthermore, acid neutralization and development at laboratory and pilot scale. The reason for
is also necessary to avoid formation of large amounts of gypsum, selecting this model are threefold: (i) straw, an agriculture residue,
calcium sulphate and other disposable compounds [44]. The has been one of the principal sources of biomass for bioenergy and
impact of a higher temperature on enzymatic hydrolysis and of a a potential source of feedstock for biorefining in Denmark [57],
lower temperature on the fermentation process, as discussed and the biorefinery plant uses this biomass; (ii) the plant uses the
above, can be addressed by the use of special fungi as a source enzymatic hydrolysis process (particularly the cellulase enzyme at
of cellulase enzymes [58]. Cellulolytic enzymes [66], generally the current stage), which is attractive as it leads to better yield and
produced by microorganisms can potentially be used to remove with a lower production cost of bioethanol compared to the acid-
short sugar units from the cellulose chain. The enzymatic process catalyzed hydrolysis [44]; (iii) the plant is claimed to produce
tends to be slower if the biomass is not pretreated before the bioethanol, C5 molasses, lignin pellets on a commercial scale [76],
hydrolysis process and it is also operated under milder processing which may be of interest to wider research platforms.
conditions, but gives relatively higher yields and less toxic pro- Larsen et al. [76] stated that the handling of the biomass in the
ducts compared to the acid hydrolysis process [44]. The cellulase Inbicon plant is initiated with pre-processing of the biomass
enzyme is thermophilic by nature, i.e. it can work at temperatures residue ((cutting and dry matter (DM) adjustment)) (Fig. 1).
up to 65 1C (close to pasteurization temperature), thus reduces the Condensate containing acetic acid back from the evaporation step
cost of lowering the temperature compared to acid hydrolysis is used to adjust the DM content. The pre-processed biomass is
process. Most importantly, the ability of this enzyme to work at hydrothermally treated at different temperatures for different
the higher temperature makes the fermentation process less prone periods of time, which solubilizes the hemicellulose and reorga-
to contamination from extraneous organisms [58]. However, the nizes the lignin on the cellulose surface, thus rendering the
production cost of the cellulase enzyme is a crucial element, cellulose more accessible for enzymatic hydrolysis. The pretreated
despite the claim that the biotechnology companies Genencor biomass is separated into fibres and liquid streams; the former is
International and Novozymes Biotech have recently developed a subjected to hydrolysis (e.g. enzymatic) after washing and pH
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 249

Biomass feedstocks
(e.g. straw)

Condensate with acetic acid

Pre-processing Pre-treatment
(Chopping, dry matter adjustment) (e.g. hydrothermal)

Fiber particles
Fiber particles recycling Hydrolytic treatment
Fibers and liquid separation (e.g. enzymatic)

Enzyme recycling
Liquid particles
Fermentation
Evaporation

Animal feed C5 molasses

Distillation
Further processing alternatives
Bioethanol
Biogas production
Separation
Liquid particles
Heat Solid particles
Electricity CHP Lignin Pellets Drying and pelletizing

Fig. 1. Illustrative flow of biomass to biovalue products in a biorefinery process, modified after the Ref. [76].

Table 4
Estimated mineral fertilizer (N, P, K) and lime requirements for selected crops horizontal fermentation where commercial dry yeast is added to
grown in temperate climate zones (kg/ha/yr). convert C6 sugars into bioethanol, whilst C5 sugars (e.g. xylose) are
not converted in this stage. In the Inbicon model, after the
Crops N P K prehydrolysis, the C6 sugars are fermented in a SSF. Yeast for the
Winter Wheat a
192 22 87
fermentation is normally added before the enzymatic hydrolysis is
Maizeb 228 59 208 completed and hence the breakdown of cellulose continues along
Sorghumb 130 60 40 with the fermentation of glucose to ethanol [57]. In the distillation
Triticaleb 87 76 50 process, the concentration of ethanol is maintained (above 4–6
Rape (seed)d 230 39 347
w/w %) to reduce the energy requirement in the distillation
Sunflowerd 70 – –
Soybeand 40 – – process [57]. The concentration is maintained by passing it firstly
Potatoesc 140 43 140 through a rectifying column and then through a molecular sieve
Sugar beetc 120 21 42 [76]. The residual product from the bottom of the distillation
Clover/grassc 64 28 37 column is collected, constituting both solid and liquid particles.
Reed canary grassc 110 19 23
Miscanthus (autumn harvest)a,e 90–107 6–15 45–75
The solid particles are dried and pelletized into lignin pellets and
Willowa,c 100–120 6–15 45–50 used as fuel (e.g. co-firing in a CHP plant to produce heat/
Barleya 136 22 62 electricity). It should be noted that an alternative to the use of
Rye grassa 387 42.5 239 lignin as a fuel is its further processing to produce potential bulk
chemical derivatives [72,73,77,78], as discussed in Section 2.3.
Data sources:
a
The liquid particles since are enriched with C5 sugars and partly
For Sandy loam soil-Denmark [81].
b
[80]. cellulases, and enzymes are recycled for hydrolysis processes. It should
c
[82]. be noted that the C5 molasses produced in a biorefinery is suitable for
d
[83]. cattle feed, but stabilization of quality for this purpose is crucial [57]. A
e
[84]. comparative analysis of C5 molasses with beet and cane molasses was
presented by Larsen et al. [76]. The alternative use of C5 molasses is as
Table 5 a biogas booster in a manure-based biogas production process.
Annual energy input in the cultivation and initial processing of biomass in a Another sustainable solution could be the conversion of C5 sugars to
temperate climate and estimated production and economically optimal use of
boost the bioethanol yield, which is highlighted in section 3.3.
synthetic fertilizers and pesticides [84].

Particulars Unit Corn Miscanthus Willow

3. Sustainability themes in biorefineries
Field preparation MJ/ha 933 100 300
Planting MJ/ha 108 100 100
3.1. Material inputs in biorefinery pathways: at farm gate level
Fertilizer application MJ/ha 72 72 50
Pesticide application MJ/ha 108 25 25
Harvestþ transport MJ/ha 1795 2190 1150 The choice of feedstock primarily depends on the local climatic
Total MJ/ha 3016 2487 1625 and weather conditions, socio-economic issues and national/
Yield tDM/ha 10.12 12.7 11.18
regional policies that drive the use of available biomasses for
Energy ratio (output/input) (GJ/GJ) 7.2 6.9 7.3
specific purposes [79]. Moreover, it is important to assess the
socio-economic and environmental performance related to the
adjustment. The hydrolyzed liquefied fibres are pumped from the production of relevant biomass feedstocks and prioritize them
hydrolysis reactor through a heat exchanger to the fermentation based on the minimum environmental impacts and higher eco-
process. In a conventional system, the pretreated biomass usually nomic returns. In the sustainability assessment of an agriculture
undergoes the fermentation process in two stages: firstly, the system, often the material inputs (e.g. fuel and agrichemical, as
250 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

shown in Tables 4 and 5) are of prime importance. The amount of rapeseed had a greater impact than soybean as a raw material, but
fertilizer inputs however could not be the only basis to decide upon since the productivity of soy is lower, it requires a larger area to
one type of crop, but it is important while introducing efficient produce the same amount of biodiesel [90]. Also here the use of
agriculture management practices in order to fulfil the increased fertilizers (mainly N) had the greatest environmental impact,
biomass demand. For instance, introduction of catch crops (clover/ followed by pre-processing and transportation of the biomass
grass, reed canary grass, ryegrass etc.) and their prioritization can be leading to increase the environmental loads in the biomass
made based on N-fertilizer input, preferably lower, and in such case, conversion processes. Assessment of the net energy and green-
based on Table 4 clover/grass could be the best alternatives. It is house gas balances of producing ethanol from corn grain shows
evident that agri-chemicals inputs are responsible to increase envir- inconsistent findings [91–94]. Based on varying corn yields,
onmental loadings, as suggested in many life cycle impact assess- fertilizer manufacturing efficiencies, corn-to-fuel conversion tech-
ment studies, and are discussed in the following. In the similar nologies, fertilizer application rates and evaluation of by-products
prospects, based on the amount of pesticides required for the and energy inputs, net energy input was found lower than the net
cultivation of crops, e.g. among maize, sorghum, triticale and mis- energy output of fuel ethanol, as reported by Shapouri et al. and
canthus, as suggested in Blengini et al. [80] maize is the preferable Saricks et al. [91,92], but Pimentel [93,94] found the opposite. Kim
one. Pesticides inputs for cultivating maize, sorghum, triticale and and Dale [95] claimed that it might not be appropriate to compare
miscanthus are respectively, 0.37, 0.49, 0.37 and 0.43 kg/ha/year. biomass feedstocks in terms of cumulative energy and the related
In the same manner, Table 5 shows an example of primary energy GWP, because different agricultural and forestry biomasses have
consumption for biomass cultivation for annual and perennial crops, different chemical properties that can be transformed into differ-
based on which miscanthus is preferable among others with high ent valuable products, and if these products are considered as
energy output to input ratio. Dalgaard et al. [85] gave comprehensive alternatives to fossil fuel-based products they pursue different
information on the primary energy input for biomass production and displacement effects of the environmental impacts.
processing, and these inputs are pertinent in a sustainability assess- Another important parameter in the context of N-fertilizer
ment at the farming system level, e.g. in the assessment of economic input is nitrogen cycling and losses. A significant rise in the risk
and environmental performances of biomass production. of nitrate leaching can take place with increasing amounts of
As coined earlier about the N-fertilizer inputs and their applied N within a specific cropping system [96]. However, the
implications to the agro-environment, Heller et al. [86] reported ploughing period, choice of rotational crops versus perennial crops
that in the willow cultivation inorganic N-fertilizer application are among the important factors to impact N-mineralization and
would increase the environmental loadings. About 37% of the non- seasonal N-uptake, and thereby nitrate leaching can be minimized
renewable energy (NRE) used in willow cultivation is primarily by manipulating these factors rather than fertilization per se. For
related to N-fertilizer input (mainly manufacturing and applica- instance, after the establishment period, willow and miscanthus
tion), and they argued that substitution of inorganic N-fertilizer showed very low leaching (between 1 and 15 kg N/ha) [97]. Nitrate
with sewage sludge could increase the net energy ratio of the leaching reduction is further linked with a reduction in the
willow production by more than 40%. Furthermore, the signifi- emission of nitrous oxide (a GHG), and genereally its emission is
cance of such assessments could be useful to assess the environ- claimed to be occuring at the rate of 0.75% of the leached nitrogen
mental and economic hotspots at the farming system level. These [98-99], and with respect to reduced N-fertiliser inputs it takes
hotspots principally guide to implement the preventive measures place at 1% of the reduced input [100].
to reduce the anticipated impacts. Introduction of catch crops (e.g. rape, oil radish or ryegrass) is
Parajuli et al. [87], while assessing the environmental perfor- regarded to play a vital role to reduce the nitrate leaching occuring
mance of miscanthus as a fuel input to a combined heat and power with the annual crop production. In Denmark, catch crops are
(CHP) plant stated that of the gross NRE used calculated in the generally sown for up-taking nitrogen during the autumn and
conversion of the biomass to 1 MJ of district heat, manufacturing winter, and is incorporated into the soil in the spring, and is
process of agri-chemicals alone covers about 43%. Similarly, of the always followed by a spring sown crop. In the Danish agriculture
gross GWP related to conversion of miscanthus to heat and power system there are generally two levels of catch crops based on
in the CHP plant, manufacturing process of agri-chemicals covered manure application: (i) if animal manure greater than 80 kg N/ha
about 55%. In the same manner, in another study, Parajuli et al. are applied, farmers have to establish catch crops in at least 14% of
[88] calculated the consequences of removing 1 ton (t) of straw the ‘catch crop base area’, and this results in offsetting 25 kg N/ha
(with 85% DM) and stated that the process would lead to a GWP of from the specific quota of the following crops (ii) if animal manure
1331 kg CO2-eq. The calculation also took into account of the corresponding to less than 80 kg N/ha are applied, catch crops
emissions from the agri-residue undergoing a decaying process should cover at least 10% of the ‘catch crop base area’, resulting an
that is avoided because of straw removal from field (otherwise, offset of 17 kg N/ha from the specific quota of the following crops
143 kg CO2-eq, if only emission reduction potential related to soil C [101]. It reveals that in the course of optimizing the agriculture
buildup is considered). For the same quantity of agri-residue, NRE system in order to cope the increased demand of biomass, catch
use was reported to be 217 MJ-primary. However, the fact that the crops play vital role primarily to reduce the undesired emission to
straw ashes may be recycled after combustion and was not taken the environment. Furthermore, assessment of related environ-
into account at this stage, but was accounted for when assessing mental impacts of such crops also facilitate to priortize among
the overall consequences in the entire life cycle process of straw them as biorefinery feedstocks.
utilization [88]. In most of the impact categories, as discussed
above, manufacturing of N-fertilizers is the major source of the 3.2. Agricultural management and environmental impacts
impact, also in this case (e.g. of the 13% of the total GWP related to
chemical fertilizers, the N-fertilizer alone covers the 8%), but it In the context of maximizing the biomass supply to meet the
must be noted that there are large differences, dependent on the year-round supply to biorefineries, substantial land use change is
fertilizer manufacturing technology (typically coal, natural gas, expected to occur. For instance, changes in the agricultural system
nuclear, or hydropower), and major improvements in these tech- may include: land use change (e.g. from annual cropping to forest
nologies are being implemented over the years [89]. or grassland), and these processes may lead to changes in GHG-
Tsoutsos et al. [83] stated that for the environmental impacts of emissions to the atmosphere, and consequences may include also
biodiesel production expressed per unit area, the cultivation of indirect effects on land use elsewhere [102]. Furthermore, the
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 251

process of carbon (C) accumulation and decay are convertible, and yeasts normally only consume C6 sugars. The DONG Energy and
the amount of C that can be stored in the soil is limited [102]. the since the Royal Dutch DSM (the Dutch Life Sciences and
Significance of such environmental concerns are primarily related Materials Sciences Company) have demonstrated combined fer-
in the context of agricultural management practices, where soil C mentation of C6 and C5 sugars from wheat straw on an industrial
sequestration and maintenance of soil health are also in high scale, with the result purportedly giving a 40% increase in
interest, despite the management practice aims to increase crop/ bioethanol yield per ton of straw with the use of advanced yeast
biomass yields. Glendining and Powlson [103] discussed that [107]. This is expected to lead to a significant drop in the
fertilizers (especially N) increase crop yields and returns of organic production cost of second-generation bioethanol.
C in roots and residues to soil; in the vast majority of situations Likewise, Kaparaju et al. [108] analysed the bioethanol, biohy-
this leads to a modest increase in soil organic carbon (SOC). drogen and biogas products of a wheat-straw-based biorefinery.
In contrast to the argument for the positive changes in SOC They calculated the mass flow of the biomass with respect to the
resulting from fertilizer application, Johnston et al. and Powlson amount of sugars and conversions to different products. The
et al.[102,104] argued that other GHG's may offset the benefit. pretreated solid particles undergo the hydrolysis-fermentation
They expected that the application of N fertilizer (at and distillation processes, finally producing bioethanol from the
144 kg N ha  1 yr  1 (in addition to P, K, Mg and lime)) would lead fermentation broth along with other products. The same study
to an increased SOC by about 50 kg C ha  1 year  1, before reaching [108] revealed that the total bioethanol production from the input
new equilibrium (generally after 50 years), but commented that it of 0.92 t DM of straw is about 0.13 t DM. The stillage products
may not be logical to imply that increased fertilization can (residues obtained from the distillation of the ethanol broth) are
decrease net GHG-emission, since annual emissions associated also suitable feed material to the biogas digestion process. The
with N fertilizer (including manufacturing and application) is pretreated liquid particles (primarily C5 sugars) are convertible to
calculated to be four-fold higher than annual SOC increase (5 kg bio-hydrogen [109], and effluents from the same liquid stream are
CO2-equivalent kg  1 N (200 kg C ha  1 vs 50 kg C ha  1 respec- also used to produce biogas, similar to stillage [108]. The stillage
tively)) [102]. This further emphasizes the significance of consid- fraction of the straw input is reported to be 0.29 t DM and effluent
ering efficient utilization of N fertilizer [105] in the agricultural is 0.17 t DM [108]. In this biorefinery framework, it is argued that
system. the use of straw to produce a range of biofuels including biogas is
Guo and Gifford [106] argued that with the land use change more energetically efficient than producing bioethanol only. It
from pasture to plantation, the soil C stocks decline at about  10%, emphasizes that the sustainability of biorefining also needs careful
and from native forest to plantation ( 13%), native forest to crop consideration on how waste streams can be capitalized in the
(  42%), and pasture to crop land (  59%). Whilst, increment in the entire conversion process.
soil C stocks with the land use changes follows þ8% (from native From the above cases of straw conversion in biorefinery, it is found
forest to pasture), þ 19% (from crop to pasture), þ18% (crop to that production of bioethanol is generally about 14–23% (on mass
plantation) and from crop to secondary forest is þ53%. The basis) of the biomass input, and this widens up the necessity to further
importance of SOC build-up is related to the reducing the emission process lignin and cellulosic content of biomass to other marketable
reduction potential in a life cycle perspective of a farming system. products to ensure a higher return on the investment. In the same
It is thus concluded that increased biomass supply through context, Uihlein and Schebek [61] argued that conversion of lignin to
agricultural intensification and expansions should consider the both heat and electricity was not economically attractive compared to
potential changes in the soil health. This is further connected with the conversion to acrylic binder. Another case related to the extent of
the rationality of prioritizing biomass feedstocks keeping in mind material processing may include the use of C5 molasses as biogas
about: material inputs (energy and non-energy), undesired emiss- feedstocks or further processed to make them suitable as a feed
sion (related to agri-chemicals), changes in the soil C pool (in the material for ruminants and or conversion to increase the yield of
course of changing the land cover) etc at the farming system level. bioethanol. These cases open the perspectives of assessing the
performance of biorefinery with respect to the extent of material
3.3. Inputs and outputs of materials in a biorefinery system-at processing, i.e. whether some of the products should be instanta-
processing level, an illustration neously used, or processed further to derive other valuable biobased
products, and in the process to examine: how environmental and
We have presented two cases of hydrolysis processes (acid and socio-economic performances would change.
enzymatic) to discuss on the mass flow that generally take place in
a lignocellulosic biorefinery. In the acid hydrolysis process, as 3.4. Sustainability dimensions of biorefinery value chains with
argued in Uihlein and Schebek [61], processing of 1 t straw as a biofuel as an example
feedstock (as input) would lead to deliver outputs including
ethanol (about 225 kg), lignin (300 kg), xylite (254 kg), and pro- 3.4.1. Production economics of bioethanol generated with different
cess heat and electricity production (varying under different biorefinery technologies
scenarios of lignin utilization). Furthermore, for the same input According to Wright and Brown [110], the production of grain-
they presented two scenarios of lignin utilization: (i) conversion to based bioethanol is relatively more energy-intensive than cellu-
process heat (3.2 GJ), and (ii) conversion to electricity (3.46 GJ), losic bioethanol. Energy outputs other than biofuels (e.g. process
and also considering the variation in the rate of acid recovery. heat, electricity), and distillers' dried grains are claimed to offset
As an example for a biorefinery involving the enzymatic the operating costs. If ranked in the order of the lowest capital cost
hydrolysis process, we have taken a case of the Inbicon biorefinery then the order of preferences for the thermochemical conversion
plant (see Section 2.4 about the plant). Larsen et al. [76] reported of cellulosic biofuels was hydrogen, methanol, and lignocellulosic
that processing of 4 t (86% DM) of straw per hour would lead to ethanol and F-T diesel. From this comparison, one may claim that
hourly productions of 0.57 t bioethanol, 1.49 t C5 molasses (65% both biochemical and thermo-chemical platforms have opportu-
DM) and 1.74 t lignin pellets (90% DM). Furthermore, in Inbicon nities to compete against grain ethanol, if the price of grain were
[107] it is reported that the output of ethanol may be further to increase in the market. Furthermore, at the operational level the
boosted through the use of an advanced yeast technology that cost of biomass feedstock covers the major portion of the cost
facilitates simultaneously consumption of both C6 and C5 sugars [111,112]. Lange [5] also argued that the conversion of biomass to
and liberate bioethanol. It should be noted that the traditional biofuels in a biorefinery is significantly influenced by the cost of
252 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

the feedstock and the technology used. For instance, cost of methyl changes in the demand for biomass, despite of the claim that even
hydro-oxide (MeOH) or Fischer–Tropsch synthesis and biofuel with recovering the protein from the carbohydrate content of
derived from lignocellulosic biomasses are technology-dominated, forage crops substantial amounts of bioethanol might be pro-
whilst the vegetable-oil-based biofuel production is mostly influ- duced, and this would result to minimal or no changes in the total
enced by cost of feedstocks. Furthermore, the production cost is occupancy of agricultural land [33]. However, the increased
also influenced by the simplicity in the route of feedstock conver- demand of biomass possibly stress that gap in the production
sion to final product, e.g. feedstocks such as vegetable oil may be volume of cereals in an economy which should be compensated by
expensive (US $ 13–18/GJ or US $ 500–700/t DM), but they are producing somewhere else through intensification, expansion of
easy to convert, whilst lignocellulose may be cheap (US $ 2–4/GJ or agricultural land (linked with deforestation), crop displacement
US $ 34–70/t DM), but is very difficult to convert [113,114]. Similar [123] etc.
variations in the production economics can be assumed to occur
with the biochemical routes under the similar technological
constraints. 4. Methodological concepts for the sustainability assessment
Based on the Iogen technology [115], Galbe et al. [44] have of biorefineries
shown relative advantages of different biomass conversions (of
hardwood, softwood and corn stover) to bioethanol, using differ- 4.1. Sustainability assessment framework and tools
ent types of hydrolysis and fermentation processes. The maximum
raw material handling capacity turned out to be with “consoli- The complexity associated with biorefinery technologies is
dated bio-processing” (CBP) (i.e. using an advanced microorgan- primarily related to the multiple material flows, and this has
ism) and produced 3.1 Mt DM per year of hardwood [44], with a meant dealing with multiple indicators in the decision-making
capital cost of 820 Million USD resulting in a net production cost of process to compare one product with another. It also highlights
$0.2 l  1 of ethanol. The lowest production cost was for enzymatic the need for an integrated framework of evaluation of alternatives,
SSCF at US $0.13 l  1 with hardwood as the feedstock. The as also widely experienced in other types of sustainability assess-
production cost of acidic-hydrolyzed bioethanol ranged from US ment studies, e.g. in energy planning studies [124]. The sustain-
$0.36–0.53 l  1. For the biofuel production, it is of course impor- ability assessment of a biorefinery process can be categorized into
tant to optimize the cost of raw materials and the feedstock mainly three stages: (i) feedstock supply: primarily to determine
conversion process, as also reported in Refs. [5,33]. the suitability and adequacy of potential biomass feedstocks for
the transformation process, (ii) biorefinery process performances:
to determine the input-output balance of material flows, and (iii)
3.4.2. Environmental performance biobased products production: to measure responses to overall
To compare the advantages of biorefineries with petroleum sustainability aspects (environmental, economic and social)
refineries, life cycle impact assessment (LCIA) method has been because of the delivery of biobased products from a biorefinery.
used in many studies [17,20,29]. Most of these studies focused on a The latter case is relevant in the cases where there are opportu-
single type of feedstock. However, it is of increasing importance to nities of displacing fossil fuel-based products (e.g. petro-chemi-
identify and assess the relative advantages of different biorefinery cals, petroleum products, food/fibres, etc.) by biobased products,
processes, involving different feedstocks and processing technol- and has significant impact on the sustainability of biorefineries.
ogies. Schaidle et al. [116] discussed on the sustainability assess- Sammons Jr. et al. [125] proposed a general systematic framework
ment of (i) biochemical production of ethanol from grain and for optimizing the product portfolio and process configuration of
cellulosic biomasses, and (ii) the thermochemical production of biorefineries. They have discussed on the economic aspects of
F-T diesel from biomass-derived syngas. As Table 6 demonstrates, delivering biobased products and further encapsulated the opti-
the environmental performances of a biorefinery (with biofuel as a mization framework to enable the decision-making process pri-
main product) vary significantly depending on the types of feed- marily concerned with whether a certain product should be sold
stock used. It is claimed that cellulosic ethanol refineries are or further processed, or with which processing route to pursue if
relatively more sustainable than the grain ethanol and F-T diesel multiple production pathways exist for a special product.
refineries, if greenhouse gas (GHG) emissions is considered as an The typology of sustainability assessment tools [126] can thus
indicator of the comparison. in brief be categorized as: monetary, biophysical and indicator
The major question in an assessment of the sustainability of tools (Table 7), and the tools can either be applied in an
biorefinery in today's world is also whether a comparative assess- independent or in a combined/integrated manner, depending on
ment of biobased products (biofuels, biochemicals and protein) the complexity of the production system/services to be assessed.
can be carried out. Furthermore, it remains important to assess the The monetary tools primarily compare the market prices,
land use change impacts, particularly the iLUC effects in relation to transfer of benefits, economic modelling of alternatives

Table 6
Life cycle impact of fuel generated from different types of biorefinery.

Biorefinery types Energy efficiency (Fossil) (energy input/energy in fuel) GHG emissions (g CO2-eq/MJ biofuel) SOX emissions (g/MJ) NOx emissions (g/MJ)

a a b
Grain ethanol 0.33–0.42 44–57 0.066–0.081 0.12–0.25b
Cellulose ethanol 0.08 to 0.13b,c;  0.01 to 0.15d  5 to 23c,d 0.014–0.51c,d 0.05–0.65d,e,f
F-T diesel 0.05–0.22b  5 to 19c,f 0.009–0.11b,f 0.03–0.1b,f

Data sources:
a
[118].
b
[116,119].
c
[120].
d
[121].
e
[122].
f
[117].
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 253

Table 7
Sustainability assessment tools and possible indicators essential for the assessment.

Tools Measures used References used

Monetary tools
Economic cost basis  Cost-Benefit Analysis Economics: [7,127-134]
(e.g.):
 Investment analysis  Net present value
 Revenue to feedstock  Annualized cost
ratio
 Revenue to main  Payback period
product ratio  Valuation of material choice or production system
Eco-cost (e.g.)  Changes in the eco-cost due to alternative choices and production system Eco-cost and EVR: [135,136]
 Pollution prevention Indicators of material depletion: [137]
eco-cost
 Eco-cost of energy
 Eco-cost of material
depletion

Bio-physical tools
 Material flow analysis  Mass balance, energy balance, exergy analysis Technical: [127,128,138,139]
 Product substitution  Economic and environmental differences between choices/ alternative production chains Environmental: [127,138–143]
effects

Indicator tools
Resource indicators  Weighing of the indicators based on the region/country/local sustainability goal settings and LCA for environment impact
(e.g.) ecological management initiatives. characterization: [140,144]
 Fuel consumption
 Material extraction
 Fuel depletion  Quantification of impacts (LCA)
Environmental
indicators (e.g.)
 Land-use (direct/  Monetization of impacts (LCCA)
indirect)
 Environmental impact  Aggregating the criteria (Multi-Criteria Assessment)
categories
 (as used in LCA
studies).
Social indicators (e.g.) Social aspects: [145-148]
 Social acceptance
 Waste disposal
 Participation
 Health impacts
 Aesthetic impacts
 Employment

[126,149], as well as the aggregation of cost benefits analysis [150], products in a commercial scale and the assessment of the related
full cost accounting and sustainability assessment modelling [151]. material inputs for the processing.
The advantage of such tools in the case of biorefineries is in the Furthermore, Ness et al. [154] broadly classified the sustain-
assessment of cost optimization opportunities and comparison of ability assessment tools as indicator-based assessment, product-
different products. The biophysical tools generally consider the related assessment and integrated assessment. The indicator-
dynamics of the material flows [152], estimation of ecological based assessment was further classified into non-integrated and
footprints [153], fossil energy balances [85] or exergy and emergy integrated indicators. The former basically reflects the compre-
analysis [154,155] in a production system. In the case of biorefin- hensive list of environmental pressure indicators (EPIs) developed
ery, significance of this tool is primarily related to quantify the by the statistical office of the European Communities (Eurostat)
mass of materials under transformation (e.g. how cellulose, hemi- and the indicators developed by the United Nations Commission
cellulose and lignin contents in the biomass are transformed to on Sustainable Development (UNCSD). The EPI indicator sets are
final products and what are the facilitating material inputs for the being used in economic and social policy-making in European
process) and in turn correlating their nexus with their socio- communities covering the issues of resource depletion, waste
economic and environmental paradigms. Similarly, the indicator- management, dispersion of toxic substances, air and water pollu-
based tools primarily involve the process of defining/assigning the tion, etc. [157]. The UNCSD has put forward 50 core sets of
composite indicators and evaluation of alternatives via multi- indicators, representing 14 sustainability themes [158]. Prioritizing
criteria assessment [156]. In spite of wider application of of such indicators however may require the review of national/
indicator-based tool in the sustainability assessment of biorefining regional interests to address the environmental impacts, e.g.
processes (primarily to identify the most vulnerable stages of environmental impacts may occur at the regional level in the flow
biomass conversions under the broader socio-economic and envir- of substances (chemical compounds) [159], thus requiring con-
onmental categories), the challenges with the use of such tools are siderations of regional commitments on such issues.
(i) the extent and availability of the disaggregated data required
for the assessment at different stages of a product value chains, 4.2. Assessment criteria
and (ii) possibility of monetizing the environmental indicators
along the product value chains. Nevertheless, there have been Wang et al. [160] summarized the principles of criteria selec-
efforts globally to assess the production volumes of biobased tion aimed at supporting the decision-making process, primarily
254 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

for sustainable energy choices. This included the following five square method, the Delphi method, the consistent matrix analysis
major types of principle: (i) the systems principle: reflecting the and the analytical hierarchy process (AHP) [165,166]. This involves
characteristics and performance of a whole system, (ii) the con- the ranking and prioritizing of one indicator against another (or
sistency principle: highlighting the consistency with the research rating of indicators), as also described in Refs. [167,168]. The
objectives, or product system goals in the decision-making pro- objective weighing method uses the measured data and informa-
cess, (iii) the independency principle:freedom for assessing per- tion, thereby assessing their degree of variation [165,169–171].
formances of products/services considering different aspects of Some of the examples of objective weighting methods, as described
alternatives, (iv) the measurability principle: measuring conveni- in Wang et al. [160], are methods for entropy assessment, the
ence of enumerating the quantitative and qualitative values of the technique for order of preference by similarity to ideal solution
criteria, and (v) the comparability principle: possibility to normal- (TOPSIS) method and the vertical and horizontal method [172], etc.
ize the criteria and compare among the alternatives. Such princi- The entropy method primarily shows to what extent the criterion
ples can also be utilized in the case of a biorefinery to investigate reflects the information of the system and the uncertainties
its economic and ecological dimensions, as elaborated in Table 8. associated with criteria. The vertical and horizontal method is an
optimal weighing method, where weighing of a product system can
be answered through mathematic models [160]. In regard to the
4.2.1. Selection and weighting of criteria
sustainability assessment of biorefinery, which necessarily involves
The most common methods to select relevant sustainability
comparison among biobased products and between biobased
assessment criteria, according to Wang et al. [160], can be based on
products and fossil-fuel based products, a pair-wise comparison
the principles of the sustainability assessment as discussed above,
seems effective, as it allows entertaining stakeholder preferences on
and on the ‘major’ and ‘minor’ sustainability interests of a political/
the qualified sustainability indicators. This aspect is further dis-
economic regimes, for instance as detailed in EPI, UNCSD. The
cussed in Section 4.3.2.
Delphi method (devised by a group of experts) [161] is often applied
for identifying criteria. Generally, this method assesses the overall
rankings of the criteria collected from individuals, and then aggre- 4.3. Integrating sustainability assessment procedures and tools
gates them into a single collective framework [162]. Application of
the Delphi method in the process of sustainability assessment of a 4.3.1. Application of LCA
biorefinery process may involve selecting, weighting and evaluating LCA can be regarded as an important tool to capture complex
the assessment criteria (and/or setting up the relevant indicators). features and interdependency of material flows of a production
This approach might be applied starting from the farming system system, process and product. Life Cycle Impact Assessment (LCIA)
level to prioritize the suitable biomass feedstock and further when starts with defining a functional unit, so that environmental
deciding the determinant biobased products that can be delivered performances of any process or production system can be com-
from a biorefinery. In addition, there are a number of statistical pared with the alternatives. The functional unit determines how
methods that can be applied in the process of selecting sustain- the final results should be expressed. It also facilitates to compare
ability assessment criteria. For instance, the least mean square the environmental impacts of biomass conversion pathways, e.g.
method, which is primarily relevant when one of the criteria of environmental loadings among the cases: firing straw in a CHP
the assessment does not respond significantly and the perfor- plant, gasifying them in a gasification technology, or converting to
mances of alternative criteria turn out to be more important in produce bioethanol. In such cases, the heat content of the biomass
the evaluation process [160]. Another method, the min–max could be a basis for defining a functional unit. The complexities
deviation method [163] can also be applied to weigh the sustain- with defining the functional unit lie primarily in the necessity to
ability criteria and respective indicators when looking at the consider ‘the main’ or ‘the co-products’, when there are multiple
deviation of the values of the assessment criteria. This method products from a single processing technology. In such case, it is
has been applied to determine a framework for integrating envir- difficult to prioritize the determinant products among the mix of
onmental, economic and technical factors for establishing an different products; however market analysis of such products
ethanol refinery in Canada, as discussed in Ref. [164]. The correla- helps in the process. There are some cases where more than one
tion coefficient of the criteria can also be determined to prioritize functional unit is considered. An example of such is the study for
the possible best parameters [163]. Furthermore, weighing of assessing the environmental performances of wood-based biore-
sustainability criteria/indicators can be grouped into three cate- finery initiatives (Borregaard, Sarpsborg) [173] in Norway. As
gories: (i) subjective weighing, (ii) objective weighing and (iii) reported in Ingunn and Bjørn [173], the terms as such ‘main
combination weighing. Some of the most commonly used tools product’ or ‘co-products’ are not used, but all products cellulose,
for the subjective weighing are pair-wise comparison, the least- ethanol, lignin (liquid and powder) and vanillin were assessed.

Table 8
Five major principles (elaborated from Wang et al. [160]) in relation to sustainability assessment of biorefinery processes and examples on the related criteria for decision-
making.

Principles Criteria/dimensions of the assessment

(i) The Systems Principle Technical and process design of biorefinery: processing efficiency, mass flow, aims for the potential substitution/displacement of fossil-fuel-
based products by biobased products.
(ii) The Consistency In coherence with the national/regional/global strategies on sustainable development, e.g. the EU–biofuel [9] and bioeconomy strategy [52].
Principle Resource management and diversification of use in relation to sustainability goals.
(iii) The Independency Comparative economic and environmental performance of the biomass conversion in biorefinery with respect to alternatives (e.g.
Principle combustion, thermochemical, gasification etc.). Socio-economic and environmental differences with respect to biorefinery pathways but
differing the feedstocks supply scenarios, and differing products scenarios (extent of processing).
(iv) The Measurability Qualitative and quantitative analysis of the process and product system. Quantification of sustainability assessment criteria/indicators (e.g.
Principle GWP per kg of bioethanol, annualized cost of producing 1 kg of ethanol, animal feed etc., potential employment generation per kg of ethanol
etc.).
(v) The Comparability In relation to the principle (iii) as stated above, ecological and socio-economic aspects of utilizing various inputs to produce marketable
Principle products in a biorefinery process.
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 255

They introduced the functional unit as 1 t for cellulose, lignin and biorefinery). Mass allocation in their study showed that the largest
vanillin, and 1 m3 for ethanol. Borrion et al. [174] summarized the contribution to the environmental impact (GHG emissions) was
LCIA studies of lignocellulose biomass based bioethanol produc- from bioethanol, since the approach only accounted for the
tion, and have outlined different functional units that can be used products (non-energy) and excluded the energy products (heat
for the assessment of the like. It is found that the functional unit and electricity). In the same manner, the energy allocation
primarily depends on the biomass types, such as m3 of hard approach is argued as not being appropriate, since it excludes
woodchips (for wood chips based bioethanol production), 1 t co-products which do not have any energy value. Cherubini et al.
ethanol (based on willow), and for wheat based bioethanol [178] argued that the exergy and economic portioning methods
production the functional unit were 1 l of fuel, or simply 1 t straw may be more appropriate for covering the effects of both materials
input. In Cherubini et al. [12] assessment of energy and GHG and energy flows. Furthermore, the economic allocation method is
balances of bioenergy systems based on dedicated energy crops arguably more rational, especially in a system characterized by a
are discussed, and the functional unit for the assessment is based production of high volume but low market-value products (e.g.
on the land area needed to deliver a specific output. They argued straw, animal feed and others). In conclusion, the selection and use
that this approach could connect with the land use issues, of a specific allocation method is determined by how the sustain-
particularly if LCIA related to biofuel production have to be carried ability assessment of the biorefinery process could best fit the
out. They further suggested that the functional unit of the assess- designed research question of a particular study [178].
ment could be expressed in relation to land use (e.g. 1 m2-year, Another important aspect related to the sustainability of a
1 ha-year, etc.), or to the biomass input (e.g. t DM or MJ of production system is the approach of integrating environmental
biomass) with respect to producible outputs. and economic performances, weighing them and evaluating them.
Another way of determining a functional unit could be based The Life Cycle Cost Analysis (LCCA) method can be used for
on the objective of implementing biorefineries in a local and estimating the life cycle cost of a production system, and is
macro-economic setting. In Uihlein and Schebek [61] LCIA is relevant when assessing how best a production system can be
presented for a straw-based biorefinery and is compared with optimized [179]. It covers all the relevant costs related to the
the alternatives in a relatively simplified manner. The assessment different stages of conversion of materials (e.g. biomass conversion
was initiated by defining both the reference flow of feedstock and covering the cultivation, handling, transportation, processing and
functional unit as 1 t of straw. The environmental performances production of valuable products). This accountancy also helps to
were assessed with the formulation of an input-output matrix of compare with the alternative product systems that intend to fulfil
the reference flow of the feedstock, involving material inputs (e.g. the same performance requirements, but differ among themselves
chemicals, fuels) in the input matrix and the final products (e.g. with respect to economic costs in a suitable duty cycle.
bioethanol, lignin, xylite, process heat and electricity) in the Furthermore, Bidoki and Wittlinger [180] have argued that the
output matrix. In such approach, when normally accountancy of eco-efficiency analysis could integrate the economic and life cycle
the mass flow is carried out the use of a physical quantity of a environmental effects of a production system, providing them
biomass feedstock (e.g. t of straw) can be regarded as a with equal weighting. It involves the quantification of sustain-
functional unit. ability criteria in the entire product life cycle, starting from
Another important aspect in the LCA of a production system is concept development to design and finally the end-of-life. Com-
the debates on the application of either attributional LCA (ALCA) bining such sustainability criteria may thus rely on subjective
or consequential LCA (CLCA) approaches [175]. Normally, the ALCA weighing to normalize economic and ecological factors and come
approach is used to describe e.g. the pollution and resource flows up with a value that gives a purposeful comparison. However, as
within a chosen system attributed to the delivery of a specified discussed before, there are debates on the validity and transpar-
amount of the functional unit [175,176]. In contrast, the CLCA ency required when assigning weights to these criteria, as also
estimates how the same pollution and resource flows within a discussed in Ref. [181]. The World Council for Sustainable Devel-
system change in response to a change in output of the functional opment has voiced its concern about improving the ecological
unit [176,177]. For example, in the case of a biorefinery it would be efficiency while delivering competitively priced goods and ser-
relevant to assess the environmental impacts of land use changes vices to satisfy the human needs in a qualitative manner [135], and
due to changes in the demand for biomass (e.g. straw and grasses) has also brought attention to the concepts of ecological economics
compared to their existing use. In this context, importance defin- to signify the introduction of an alternative against other options
ing the “main” and “co-products” may evolve. The reason behind [182]. Eco-costs are basically the ‘virtual cost’, employed to
such consideration is that in the case of allocation process, the measure changes both in the overall economic costs and ecological
calculated environmental impacts are allocated for different cor- costs due to recycling/re-use of a product, which is in contrast to
responding products; whilst in the consequential method a system the conventional approach where the end-of-life is not monetized
expansion is done, emphasizing that the environmental impacts in terms of economic and ecological values [136].The eco-cost is
related to the co-products are substituted with the corresponding thus the sum of the ‘marginal prevention costs’ of each stage of
average/marginal supplies. Cherubini et al. [178] discussed the substitution or prevention of pollution, and also prevention of
categorization of environmental impacts of biorefinery products costs related to material and energy resource depletion [135,136].
taking GHG emissions as an impact category. In the assessment, One of the main advantages of the eco-cost method is the
bioethanol was assumed to be the main product and co-products garnering of environmental impacts (e.g. assessed with LCA
included heat, electricity and phenols. They also presented the approach) into a single indicator. The single indicator is categor-
annual GHG emissions of a biorefinery, based on either the main ized based on whether the issue dealt with is: (i) a single issue
products or co-products. They argued that the partitioning could based – e.g. carbon footprint (measured in terms of CO2-eq per
be done through (i) system expansion, (ii) allocation (by mass, unit production but does not cover the cost of material depletion),
energy values and economic values of co-products), and (iii) a (ii) damage-based – it aware the producer and consumer to
hybrid approach. In the case of the system expansion approach, optimize the consumption level and maximize the cleaner produc-
assuming bioethanol as the main product, the co-products were tions, but it is complex as it applies subjective weighting principles
assigned the function of displacing fossil fuel reference products and is generally based on single indicators, and (iii) prevention-
(e.g. natural gas as the source of fuel to produce heat/electricity based – it facilitates relatively simplified and transparent calcula-
was displaced by the co-produced heat/electricity from the tions and monetizes the results [183]. Furthermore, since the
256 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

classical way to calculate a ‘single indicator’ in LCA is to collect the platforms) or for the biobased products. Let us say that in
potential emissions in separate groups (e.g. GWP, acidification, Scenario-x, a willow crop is evaluated. In the evaluation procedure,
eutrophication), the eco-cost determination therefore utilizes a initially environmental performance of cultivating the respective
multiplier (a characterization factor, often a marginal prevention feedstocks can be assessed with the use of the LCIA methods,
cost) to measure the relative significance of environmental cate- involving environmental impact categories (ranging from 1 to ‘n’)
gories [183]. These environmental impact categories are summed- (e.g. GWP, NRE use, AP, EP, material extractions…. ‘n’). These
up to the level of their ‘midpoint’ effect, which is generally done by indicators can be weighted by adopting the suitable weighing
‘normalisation’ (e.g. comparison with the pollution in a country or methods, as discussed in Section 4.2.1 (say the Delphi Method).
a region) and weighting. Eco-cost determination can be carried out Another possibility of identifying the weighting factor is to assess
as an extended form of LCA of a biorefinery process. The eco-cost the comparative significance of each indicator with respect to as
of material depletion can be estimated by assessing the life-cycle the most critical impacts to the ecosystem, e.g. the EU Environ-
impact of material inputs, resource use (resource depletions), mental Policies focus on GHG emissions, biodiversity and chemical
savings in fossil fuel consumption, anticipated after the imple- pollution as the most critical factors [185]. For the similar biomass
mentation of biorefinery process compared to the alternative scenarios, as discussed above, economic evaluations can be carried
biomass conversion technologies and also displacing the corre- out with the aid of economic indicators (e.g. see Table 7). In the
sponding fossil fuel reference products. same manner, evaluations for Scenario-y (e.g. straw) and Scenario-
z (e.g. a poplar crop) can be carried out. These scenarios are further
compared on the basis of calculated environmental and socio-
4.3.2. Evaluation approach economic burdens. While using the value-based method each
In Sections 2 and 3 we discussed that in the course of parameters of the sustainability assessment (e.g. environmental
sustainability assessment of biorefining processes, different stages and socio-economic) are separately weighed and the weighted
of biomass processing (starting from farming system level to average of the assessed impact are calculated to derive a sustain-
thermochemical and/or biochemical conversions in a biorefinery ability index, which can be used to compare among the alternative
plant) are to be handled, and these processes have different level scenarios. Whilst in the case of the out-ranking methods a pair-
of socio-economic and environmental impacts mostly influenced wise comparison of alternatives is carried out to assess the
by the material inputs (chemicals, fuel and energy). This implies preferences of stakeholders on available alternatives. The detail
that the framework of sustainability assessment of biorefining steps of evaluating the alternatives based on the out-ranking
processes constitute of a wide range of indicators. These indicators methods are discussed in Refs. [186,187].
should be weighed and evaluated and the process might be guided
∑nind ¼ 1 quantif icationindicators  Weight indicators
by the principles of the sustainability assessment, e.g. as elabo- Evaluationf eedstock ðenvÞ ¼
∑weight indicators
rated in Wang et al. [160] and in Table 8. Dalgaard et al. [184] have
ð1Þ
also discussed a procedure to evaluate and compare alternatives,
e.g. in the case of potential improvements of the different path- In the same manner, depending on the types of feedstocks and
ways towards a more sustainable economy and have dealt with a the biorefineries, evaluation of alternative biobased product sce-
number of sustainability indicators. A ‘traffic light’ approach has narios can be carried out. The alternative scenarios of biobased
been proposed: green light categorized as an improvement, yellow products may include, e.g. in the case of lignocellulosic biorefinery
as status quo, and red as a negative development compared to the bioethanol can be regarded as the main products and the co-
reference situation. The evaluation was made with respect to an products as C5 molasses (i.e. protein content) and heat/electricity
extra area unit of specific land-use configurations and technolo- (e.g. conversion of lignin in a cogeneration unit), whilst in the case
gies, while developing a bioeconomy in rural landscapes. of green biorefinery may include extracted protein as the main
In the following, we have discussed a simplified approach of product and co-product as bioethanol. In the process, LCIA can be
quantifying the selected indicators (e.g. as shown in Table 7) and used for accounting the environmental impacts related to the
also the process of evaluating them (e.g. Table 9 and Eq. (1)). For conversion of biomass starting from the farming system level to
example, scenarios (‘x’, ‘y’ and ‘z’), as shown in Table 9 can be the delivery of biobased products, and economic viability can be
chosen for the feedstock types or for biorefinery process (types of assessed using economic tools for the similar route of biomass
conversions. Furthermore, integration of both environmental and
Table 9 economic parameters may be necessary to put forward a compar-
Schematic matrix of evaluation process. able sustainability index among available alternatives. For such
requirements LCC estimates of the entire value chains and assess-
Evaluation schemes (e.g.) Weight Quantification of impact e.g. per
indicators tDM ment of ecological cost, as discussed in Section 4.3.1 are the
possible methods. The latter case involves the monetization of
Scenario- Scenario- Scenario- calculated differences (e.g. eco-cost of reduced material deple-
‘x’ ‘y’ ‘z’
tions) when an alternative is preferred over other. These complex-
Criteria /indicators: environmental (env.) ities in the material processing entail that sustainability
GWP assessment of biorefinery system needs to deal with multiple
Non-renewable energy parameters, including socio-economic and environmental impacts.
use Multi-criteria decision analysis (MCDA) methods, mainly using
Acidification potential
Eutrophication
value-based methods and outranking- based methods [160] are
potential important in the process of sustainability assessment of biorefin-
Material extraction ery value chains, since the evaluation can entertain both qualita-
… tive and quantitative information in relation to the selected
‘n’.
indicators. The former method basically deals with the assigned
Criteria /indicators: economics ratings (or scores) to an alternative, on the way to signify its
e.g. Cost benefit ratio suitability based on the criteria developed. The range of the rating
…
‘n’.
scale is arbitrary and can be selected to meet the desires of the
decision makers. However, once a rating scale is defined, rating
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 257

values assigned to each of the alternatives for a specific criterion for the diversified enduse including the production of heat and
need to be carefully applied so that scores appropriately reflect the power. There is therefore a risk that biomass could be significantly
differences in the alternatives. The most common value-based limited in the existing land use pattern of Denmark [197]. However,
MCDA alternative ranking methods are the ‘Weighted Average the recent study on the Danish biomass availability. ‘The þ10 million
Method’ and the ‘Discrete Compromise Programming Method’. In tonnes study’ [198] has highlighted that the biomass supply in
the case of outranking method e.g. PROMETHEE method (Prefer- Denmark from agriculture and forestry could be increased by up to
ence Ranking Organization Method for Enrichment Evaluations), 10 Mt per annum without substantially affecting the existing food
the ELECTRE methods (Elimination et choice translating reality ), a and feed productions.
pair-wise comparison of alternatives is performed in order to rank So far, the most common biomass resources in Denmark
them with respect to a number of criteria [188]. The ELECTRE include lignocellulose (e.g. wood and straw), waste, manure and
method mainly considers the preference and ignores the differ- a minor proportion from grass, with particular focus on the high-
ence level between alternatives when determining the ranking volume types of straw and on wood-based fuels [199]. The average
order, whilst the PROMETHEE introduces the preference functions annual production of straw in Denmark was about 3.5 Mt between
to measure the difference between two alternatives for any criteria the period of 2000–2011, of which about 97% was from cereal
[160]. crops [199]. In 2010, cereal crops represented 55% of the agricul-
tural land (i.e. about 2.6 Mha) of the country. Based on the current
composition of biomass supplies, if a Danish future energy system
5. Biorefinery in the context of the Danish agricultural and is to be based on a higher proportion of biomass, dependency on
energy systems cereal crops and their residues might be very high. Although there
is good availaility of straw, it is equally necessary to consider a
5.1. Background for biorefinery setting situation where the demand for straw for fuel exceeds its supply.
The application sides of Danish recovered straw are 49% as fuel,
Denmark has made a significant shift to the use of more 32% for fodder, and 19% as bedding materials in livestock houses
sustainable energy after the energy crisis of the 1970s [189]. The [198]. This reveals that cases of over-exploitation of biomass (e.g.
share of renewable energy on the total primary energy (TPE) straw) for energy purposes, or the production of materials could
production of the country in 2011 had increased almost two-fold be an issue and has to be taken seriously, if straw-based biorefi-
compared to year 2000 [190], but 31% of the renewable energy neries are going to be a fundamental platform of a Danish
production was based on imported sources. The use of biodiesel and bioeconomy. The consequences of directing too much of the
bioethanol in the country started in respectively 2005 and 2009 recovered straw to a single purpose must be diligently examined,
[190], and was in coherent with the aim of the Biofuels Directive for instance impacts on supply of animal feed, soil carbon build-up
[191] to promote the use of biofuel in the transport sector. In June and related land-use implications in different economies. It may
2010, Denmark forwarded its national strategy to the European have resulted that because of such concerns in European countries
Commission to fulfil its target of achieving 10% renewable energy borefineries are gaining attention, not only to deliver energy
in transport by 2020 [189,192], and also highlighted that biofuel products, but also to sustainably cope with the increasing demand
could make a higher contribution to renewable energy by that time of high-value proteins. Denmark has an annual net import of
[193,194]. Furthermore, the country has a long-term sustainable 1.6 Mt soybean (average 2006–11) [200], corresponding to 0.8 Mt
energy goal, which aims to be finally free of fossil fuels by 2050 protein. Totally, Europe has a net import of about 22 Mt soybean
[195]. In such a transition, Hvelplund et al. [193] reported that the cake (11 Mt protein) and 14.5 Mt soybeans (6 Mt protein) (average
TPE consumption of Denmark by 2050 could be 480 PJ, of which 2006–11) [200], mainly from South America. South America
biomass and waste are expected to cover 49%, and rest by other (primarily Brazil) is the major supplier for most of European
renewable sources/technologies (wind, photovoltaic, solar thermal soybean protein import volumes [200]. In the past five decades,
and wave energy). Due to the fluctuating nature of wind power, one every year 2.4 Mha of forest and forest grassland has been
of the challenges in the future Danish energy mix is to increase the replaced by soybean fields in South America. Furthermore, esti-
flexibility in power production to improve the balance between mates show that in 2020 around 22 Mha of forest and forest
supply and demand [196]. Biomass is the most ‘valuable’ resource as grassland in South America could be converted into soy fields,
a fuel for transport sector in such transitions [193], and one of the which has significant impact on soil carbon stocks [201]. The high
challenge in such circumstances is maintaining a sustainable supply import of soybean is primarily to maintain the livestocks

Fig. 2. Production and export of soybeans from Brazil and gross import of soybean products to Europe and China (Mt DM per year) [200].
258 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263

production. However, Europe is not the only region with a high ruminants and also a depletion of the soil carbon content and
demand for soybean protein, as the import of soybeans to China nutrient availability [207,208]. It is thus essential to assess the
has also grown by three-fold during the last decade (Fig. 2). sustainable quantity of biomass that can be used as feedstocks for
Brazil supplies approximately 40% of the soybean demand of biorefineries without exacerbating the aforesaid issues. Further-
China [200]. Due to the high demand, the soybean production in more, it is important to identify the possible interactions with the
Brazil has almost doubled during the last decade and the prices have biorefinery products and agricultural inputs – for instance, oppor-
as a result risen three-fold [200], also driven by an increased tunities to recycle nutrients content in waste water streams of
domestic consumption of soybeans for Brazil's own livestock pro- biorefinery to farmers' field, as also suggested by Ahring and
duction (Fig. 2). The European and Danish livestock productions are Westermann [209] and Langeveld et al. [49]. LCIA of feedstocks
vulnerable to increasing prices of soy protein and combined with the supply scenarios are thus relevant to assess: (i) environmental and
environmental concern related to the production of soybeans, economic hotspots in the entire biomass supply chains (ii) poten-
alternative and more sustainable protein sources from e.g. biorefi- tial measures to be taken to optimize the production cost and
neries are very attractive to the European and Danish livestock reduce the environmental loadings (iii) potential land use change
sector. This makes relevant to convert green grasses and alike to impacts due to increased demand of biomasses (iv) suitability of a
extract protein sources (as main product) from green biorefinery. In particular feedstock in relation to the prioritized biobased pro-
this aspect, it might be interesting to assess how the feed values of ducts and so on.
the biomass, as available conventionally and delivered from bior- Beyond the farm gate level, at the stages of processing in a
efinery would differ from environmental and economic returns. biorefinery, economic and environmental performances can be
Regarding the biorefinery initiatives in Denmark, Bentsen et al. studied in relation to (i) interaction between the chemical proper-
[202] studied on the energy balance of 2nd generation bioethanol ties of biomass and biobased products, and how they differ among
production using Danish winter wheat (considering whole crop). crops with respect to volume and quality of products production,
In the study they estimated that with the agricultural production (ii) displacement of corresponding fossil-fuel-based products, and
as of 2006 and to meet the 2010 obligation of the biofuel Directive the ecological benefits behind such displacement/substitutions,
(i.e. 2003/30/EC) fulfilling the 5.75% of the transportation fuels (iii) utilization of by-products, e.g. whether lignin based pellets
(gasoline and diesel) about 0.125 Mha of wheat land is required should be burnt to produce heat/power or further processed to
(equivalent to occupying about 5% of the total Danish agriculture produce biochemicals, and the ecological benefits between two
land as of reported in 2010). Other commerical biorefinery facilities pathways. Likewise, it is also relevant to assess the potentiality of
in Denmark include (i) Agroferm: utilizes green juices and produces recovering the protein from the carbohydrate content of forage
lysins for animal feeds (by fermentation of green juices from green crops to reduce the import volume of protein sources. Likewise,
pellet production), (ii) Dangrønt: utilizes grasses to produce green sustainability of biorefinery can also carried out considering the
fodder pellets and green juices (green juice is useable asa raw variations in the treatment, hydrolysis and fermentation processes,
material for the fermentation process [203]), and (iii) Daka biodiesel: e.g. comparing enzymatic hydrolysis with acid hydrolysis, com-
utilizes animal fats from slaughterhouses to produce biodiesel, bined production of ethanol fermenting both C5 and C6 sugars
glycerol and potassium sulphate [204]. Currently, a bioethanol plant and so on.
based on straw and municipal waste is being planned in Måbjerg, Furthermore, while working with the wider scope of biomass
West Jutland, which is until now expected to be the largest conversion through biorefinery platforms, it is also important to
biorefinery project in the country. Here the Inbicon model is a review (i) national or regional policies, formulated to enhance the
forerunner for the Måbjerg plant. Furthermore, the BioRefining bioeconomy via biorefineries, so that market volume of biobased
Alliance, formed with participation from Dong Energy, Novozymes, products can be identified and their underlying economic and
the Danish Agriculture & Food Council, Haldor Topsøe, University of environmental performances can be quantified, (ii) whether any
Copenhagen, Technical University of Denmark and Aarhus University incentives are also required to maximize the biomass supply,
[205] collectively facilitates the transfer of know-how and the (iii) the ethics related to such incentives; is it, for example, a good
development of biorefineries in Denmark. In addition, Bio-Value idea to provide incentives to upscale the yield of potential feed-
SPIR [206] provides an important platform to develop and accumu- stocks for biorefining in the current climate of increasing prices for
late the innovative conversions of biomass to marketable biobased food and other consumables, and (iv) potential opportunities to
products. The platform is supported financially by the Danish increase the yield of biomasses without affecting the market of
Council for Strategic Research and the Danish Council for Technology food and feed. Other important sustainability aspects could be
and Innovation [206]. The Bio-Value SPIR platform embraces major related to social dimensions: technology exposures, willingness to
Danish universities and companies that are joining forces to develop pay by consumers, acceptability, etc., which might be influenced
new biomass supply chains and sustainable technological solutions by the marketability of such processes and products. A well-
for refining plant material, so that it can be used as a feedstock for coordinated and integrated framework of a development model
production of chemicals, polymers, feed and food ingredients. is also important to ensure better harmonization between sectors
Specific activities within the Bio-Value SPIR platform are dedicated and actors within the platforms of biorefinery value chains.
to assessing the socio-economic, environmental and ethical aspects Regarding the willingness to pay, a general belief is that the
of using biomass as a raw material for production of high-value bio- “European consumer behaviour is increasingly affected by these
based products. The project “Socioeconomics, sustainability and ‘green’ product qualities, and recent research shows consumers'
ethics (SeSE)” under Bio-Value SPIR [206] has also outlined the willingness to pay a premium for more sustainable products” [52].
necessity of linking the research and innovation activities of bior- In spite of this, it might be necessary to educate all the stake-
efineries in a more holistic manner, bringing together different holders and to identify their potential roles and responsibilities in
production/value chains of biorefineries into a system-wide frame- the entire value chain, as also indicated by Dale [33].
work of the sustainability assessment.

5.2. Research perspectives 6. Conclusions and way forward

Consequences of increased demand of biomass in material Biorefinery is increasingly becoming popular to produce spec-
production could lead to a shortage of feed materials for trum of biobased products with minimum socio-economic and
 R. Parajuli et al. / Renewable and Sustainable Energy Reviews 43 (2015) 244–263 259

environmental repercussions compared to the ‘petroleum refi- sustainability of biorefinery processes, as it facilitates the
neries’. The important feature of biorefinery is its ability to deliver system-wide assessment and evaluation of related physical and
products that has positive effects while displacing the correspond- socio-economic parameters. These parameters are often assessed
ing fossil-fuel based products and thus the environmental effects with the use of the sustainability assessment tools including,
related to them. Biorefinery is regarded as a promising emerging bio-physical (e.g. mass balance), economic (e.g. production cost
technology for sustainable biomass value chain development, and benefits) and social (e.g. acceptance, employment opportu-
primarily considering the prospects of: (i) reducing the fossil fuel nities). In the decision making process of the alternatives (e.g.
intensity in the material productions, e.g. conversion of biomass to straw versus grasses as feedstocks, fossil fuel-based products
biofuel and recirculation of produced energy within the biorefin- versus biobased products, or lignin pellets versus acrylic binder),
ery production system, (ii) optimizing the biomass conversion one has to utilize different types of methods to prioritize, weigh
pathways, e.g. diversified conversion of biomass to a multiple and evaluate the sustainability parameters. In such cases, value-
products to ensure better economic and environmental returns, based methods and outranking-based methods are useful tools.
and (iii) enhancing the sustainability of agricultural production These methods are constructed on the basis of scoring process of
system, e.g. minimizing the prevailing issues of food, feed and fuel the assessment parameters. Furthermore, in the sustainability
sectors and a wider land use issue. Moreover, prioritization of a assessment process, often decision makers have to involve the
specific biorefineries type/platform may depend on the market preferences of stakeholders on alternatives, which emphasize the
demand of biobased products and strategies that a country use of out-ranking method.
accustoms to deal its energy and wider socio-economic and Finally, in the course of sustainability assessment of biorefinery
environmental issues. The advantage of the green biorefinery is processes it will be necessary to investigate and forward suggestions
related to the possibility of separating green biomasses into a for: (i) viable innovation of the farming system to maintain sustain-
fibre-rich press cake and a protein rich press juice, while ligno- able feedstock supply, including increased harvest of biomass without
cellulosic biorefinery to the capability of delivering products (e.g. affecting the net production of feed and food and without increasing
bioethanol, C5 molasses and lignin based products) at an industrial environmental impacts, (ii) viable innovation in biomass conversion
scale based on a versatile input of raw materials available at lower routes (i.e. biochemical versus fuel-oriented) to produce competitive
prices. Furthermore, in light of maintaining a sustainable and year- biobased products compared with fossil-fuel-based products.
round supply of biomass to biorefinery, feedstocks should be
thoughtfully prioritized, as they represents about 40–60% of the
total operating cost of a typical biorefinery. Acknowledgements
Concerning the sustainability aspects of biorefinery value
chains, it is important to judiciously manage the available biomass The current article is written as part of a PhD study at the
resources with respect to the demand of different biobased Department of Agroecology, Aarhus University (AU), Denmark. The
products. It also entails to the risk that a substantial rise in the first author would like to thank the Graduate School of Science and
use of biomass from agriculture, forestry and waste for producing Technology (GSST) of AU for the PhD scholarship. The study is co-
energy or materials would possess negative ecological impacts, funded by the Bio-Value Platform (http://biovalue.dk/), funded
socio-economic impacts and additional GHGs emissions. As a part under the SPIR initiative by The Danish Council for Strategic
of the sustainability of the agricultural system, prioritization of Research and The Danish Council for Technology and Innovation,
biomass is thus imperative, so that bulk volume of biomass can be Case no: 0603-00522B. Head of the section (SYSTEM), John E.
supplied with minimum negative ecological impacts. The signifi- Hermansen of the same department at AU is also highly acknowl-
cance of such prioritization is also related to reduce the direct and edged for providing necessary supports while developing this
indirect land use change impact while optimizing the agricultural article. Thanks to Margit Schacht (from Agro Business Park) for
system. Assessment of environmental and socio-economic perfor- providing necessary support in editing this article. We are also
mances related to choices of feedstocks is also vital, since different grateful to the editor and two anonymous reviewers for their
biomasses response differently to the farm inputs and their valuable and critical reviews.
impacts (e.g. N-fertilizer inputs and related emissions to the
environment, changes in the soil C pools etc.). Likewise, the References
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