Accepted Manuscript

Review

Emerging Technologies for the Pretreatment of Lignocellulosic Biomass

Shady S. Hassan, Gwilym A. Williams, Amit K. Jaiswal

PII: S0960-8524(18)30622-9
DOI: https://doi.org/10.1016/j.biortech.2018.04.099
Reference: BITE 19879

To appear in: Bioresource Technology

Received Date: 23 March 2018

Revised Date: 23 April 2018
Accepted Date: 24 April 2018

Please cite this article as: Hassan, S.S., Williams, G.A., Jaiswal, A.K., Emerging Technologies for the Pretreatment
of Lignocellulosic Biomass, Bioresource Technology (2018), doi: https://doi.org/10.1016/j.biortech.2018.04.099

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Emerging Technologies for the Pretreatment of Lignocellulosic Biomass

Shady S. Hassan1,2, Gwilym A. Williams2 and Amit K. Jaiswal1*

1
School of Food Science and Environmental Health, College of Sciences and Health, Dublin

Institute of Technology, Cathal Brugha Street, Dublin 1, Republic of Ireland.

2
School of Biological Sciences, College of Sciences and Health, Dublin Institute of

Technology, Kevin Street, Dublin 8, Republic of Ireland.

*Corresponding author:

Email: amit.jaiswal@dit.ie; akjaiswal@outlook.com

Tel: +353 1402 4547

1
Abstract

Pretreatment of lignocellulosic biomass to overcome its intrinsic recalcitrant nature prior to

the production of valuable chemicals has been studied for nearly 200 years. Research has

targeted eco-friendly, economical and time-effective solutions, together with a simplified

large-scale operational approach. Commonly used pretreatment methods, such as chemical,

physico-chemical and biological techniques are still insufficient to meet optimal industrial

production requirements in a sustainable way. Recently, advances in applied chemistry

approaches conducted under extreme and non-classical conditions has led to possible

commercial solutions in the marketplace (e.g. High hydrostatic pressure, High pressure

homogenizer, Microwave, Ultrasound technologies). These new industrial technologies are

promising candidates as sustainable green pretreatment solutions for lignocellulosic biomass

utilization in a large scale biorefinery. This article reviews the application of selected

emerging technologies such as ionizing and non-ionizing radiation, pulsed electrical field,

ultrasound and high pressure as promising technologies in the valorization of lignocellulosic

biomass.

Keywords: Lignocellulose; pretreatment; green technology; emerging technology; advanced

biorefinery.

Abbreviations: LC, lignocellulose; MW, microwaves; US, ultrasound; HHP, high

hydrostatic pressure; HPH, high pressure homogenization; UHPH, ultra-high pressure

homogenization; PEF, pulsed-electric field; EB, electron beam.

2
1 Introduction

Since the industrial revolution 250 years ago, the world has pursued a linear economic model

of “take, make & dispose” that was built on the presumption of plentiful and inexpensive

natural resources. Contrasting with this approach, the new “Bioeconomy” economic model of

the 21st century encourages the reuse and recovery of resources, instead of the mere use of

natural non-renewable resources, in order to achieve economic prosperity and ecological

survival. In this context, the biorefinery is the economic engine propelling society to achieve

a sustainable economy by conversion of the abundantly available, renewable and non-edible

lignocellulosic biomass, such as agricultural residue and food industry waste, into usuable

energy, fuels and chemicals.

However, due to the complex hierarchical structure and recalcitrant nature of lignocellulosic

biomass, pretreatment steps present the most critical challenge to biomass utilization prior to

conversion. The principal treatment regimes available for lignocellulosic biomass

pretreatment may be categorized as biological, chemical, physical or physicochemical

approaches (Kumar and Sharma, 2017). Generally, currently used pretreatment approaches

suffer significant disadvantages in the goal to achieve cost effective, industrial scale, eco-

friendly production.

The harsh chemicals and high conventional heating methods used for biomass pretreatment

require extensive amounts of energy and are not environmentally friendly. Furthermore, these

pretreatment strategies lead to the formation of numerous undesirable compounds, such as

aliphatic acids, vanillic acid, uronic acid, 4-hydroxybenzoic acid, phenol, furaldehydes,

cinnamaldehyde, and formaldehyde, which may all interfere with the growth of the

fermentative microorganisms during fermentation (Ravindran and Jaiswal, 2016). This

encouraged the movement from non-sustainable conventional pretreatments (e.g. chemical

3
and physiochemical pretreatments) to sustainable green pretreatments (e.g. biological

pretreatments). However, long treatment times, low yields and loss of carbohydrate during

pretreatment are considered to be the major challenges in biological pretreatment by

microorganisms (Saha et al., 2016). Furthermore, pretreatment processes can cost more than

40% of the total processing cost, and represent the most energy intensive aspects in biomass

conversion to value added products (Sindhu et al., 2016). Thus, the challenge of low

efficiency production associated with green pretreatments encouraged the investigation of

using large scale technologies that are now available on the market as scalable green

pretreatments to achieve sustainable and efficient pretreatment process of lignocellulosic

biomass.

In recent years, advances in applied research within the field of chemistry, and featuring

extreme and non-classical conditions, has led to the development of novel food processing

technologies that are now available on a commercial scale. Interestingly, some of these

technologies hold promise as green approaches for the pretreatment of lignocelluosic

biomass, with possible advantages of lower cost and higher productivity within the context of

a commercial-scale biorefinery. Numerous articles have reviewed common biomass

pretreatment methods (Chen et al., 2017; Kumar and Sharma, 2017), green technologies

(Capolupo and Faraco, 2016), and emerging technologies (Singh et al., 2016). However, a

review of all emerging pretreatment technologies is missing in the current literature. This

article reviews the application of selected emerging technologies for pretreatment of

lignocelluosic biomass, including non-ionizing radiation (microwaves), ionizing radiation

(gamma ray, electron beam), pulsed-electric field, high pressure (high hydrostatic pressure,

high pressure homogenization) and ultrasound.

4
2 Lignocellulosic biomass

Lignocellulosic biomass refers to plant biomass that can be divided into four categories:

hardwood, softwood, agricultural wastes and grasses. Interestingly, agricultural residues are

being produced in very large amounts (billions of tons) each year around the world, but the

majority of these residues are either discarded or burned. Food waste is defined as any

discarded food (including inedible parts), removed from the food supply chain and which

may be either recovered for alternative use or disposed (including composted, crops ploughed

in/not harvested, anaerobic digestion, bio-energy production, co-generation, incineration,

disposal to sewer, landfill or discarded to sea) (Östergren et al., 2014). In the EU-28

countries, it is estimated that an average of 9 to 10 kg of waste is generated for every tonne of

food in the primary production sector, while an average of 22 kg of food waste is generated

for every tonne in the food processing sector (Stenmarck et al., 2016). The latter EU figures

do not include by-products destined for animal feed and bio-based products. Lignocellulosic

wastes generated from agriculture and food processing can be utilized as feedstock for the

second generation of sustainable biorefineries.

Plant biomass is composed mainly of polysaccharides (cellulose, hemicellulose) and lignin.

Polysaccharides are polymers of sugars and therefore a potential source of fermentable

sugars, while lignin can be used for the production of chemicals. Generally, cereal residues

(e.g. rice straw, wheat straw, corn stover, and sugarcane bagasse) contain a large fraction of

lignocellulose substances and represent the favourite feedstock for biorefineries, while

grasses, fruit and vegetable wastes have less lignocellulosic content.

The ECN Phyllis2 database (www.phyllis.nl) is an open literature facility which is readily

available to users and documents the composition of biomass and waste. Furthermore, table 1

shows the chemical composition of different lignocellulosic feedstocks based on recent

5
literatures published in 2016, 2017 and 2018. Biomass on a dry weight basis generally

contains cellulose (50%), hemicellulose (10–30% in woods, or 20–40% in herbaceous

biomass) and lignin (20–40% in woods or 10–40% in herbaceous biomass) (Sharma et al.,

2015). However, these ratios between cellulose, hemicellulose and lignin within a single

plant will vary with different factors like age, harvesting season and culture conditions.

Pretreatment of lignocellulosic biomass is a necessary step to convert biomass into

fermentable sugars and to enable enzymatic hydrolysis to break the lignin and hemicellulose

structures and to free the buried cellulose (Sun et al., 2016). Pretreatment steps should be

simple, eco-friendly, cost-effective and economically feasible (Ravindran et al., 2018). In

addition, the pretreatment process should not give rise to inhibitory compounds or loss in the

fraction of interest (polysaccharide or lignin). Moreover, to date, there is no harmonised

pretreatment strategy to suit all types of lignocellulosic biomass, and the pretreatment process

depends mostly on the type of lignocellulosic biomass and the desired products. However, the

use of a combination of two or more pretreatment strategies can significantly increase the

efficiency of the process, and represents an emerging approach in this field of study.

3 Conventional approaches for pretreatment of lignocellulosic biomass

Generally, each of the common pretreatment approaches that fall under the four categories of

physical, chemical, physio-chemical and biological methods work differently to break the

complex structure of the lignocellulosic material. As a result, different products and yields

can be obtained from each pretreatment approach, and each method has its advantages and

disadvantages that are summarized in Table 2. While some of the methods listed have

successfully made the transition from research platform to the industrial stage, significant

challenges remain, including in some cases the generation of environmentally hazardous

6
wastes and/or high energy inputs; there is a pressing need for green technology solutions to

this challenge (Capolupo and Faraco, 2016).

4 Green approaches for pretreatment of lignocellulosic biomass

In recent years, the concept of “Green Chemistry” has gained increasing interest as a possible

approach to the challenge of developing a viable biorefinery concept. Central to achieving

this goal is the development of technology that uses raw materials more efficiently,

eliminates waste and avoids the use of toxic and hazardous materials. Selected green methods

currently being pursued for pretreatment of lignocellulosic biomass are summarised in Table

3. Although these green methods are environmentally friendly, problems exist regarding high

production costs and poor efficiency, as well as lack of availability of commercial equipment

suited to industrial scale processing. However, the more widespread adoption of such

technology by the food industry, with anticipated decreases in initial capital cost and

increased scale of operation, may encourage uptake for pretreatment of lignocellulosic

biomass.

5 Emerging technologies for pretreatment of Lignocellulosic biomass

Chemical approaches conducted under extreme or non-classical conditions are currently a

dynamically developing area in minimal food processing. Microwaves, ultrasound, gamma

ray, electron beam, pulsed-electric field, high hydrostatic pressure, and high pressure

homogenization are non-thermal food processing technologies that also being investigated for

pretreatment of lignocellulosic biomass.

7
5.1 Microwave Irradiation

Microwaves are an electromagnetic radiation with wavelengths ranging from 1 mm to 1 m.

They are located between 300 and 300,000 MHz on the electromagnetic spectrum and are a

nonionizing radiation that transfers energy selectively to different substances (Huang et al.,

2016a). Microwaves have attracted renewed interest since the 1980s, when Gedye et al.

(1986) reported the increase of hydrolysis, oxidation, alkylation and esterification processes

by energy efficient microwave heating. Researchers have reported good lignocellulosic

pretreatment performance using microwave radiation over the past 30 years, and have

gradually moved from laboratory to pilot scale (Li et al., 2016a). Currently, microwave-

assisted pretreatment technologies of lignocellulosic biomass can be classified into two main

groups: (a) Microwave-assisted solvolysis under mild temperatures (<200 °C) that

depolymerises the biomass to produce value-added chemicals, and (b) Microwave-assisted

pyrolysis of lignin without oxygen, under high temperatures (>400 °C) to convert biomass to

bio-oil or bio-gases. Each of the two groups of technologies might be accomplished with

catalysts. However, microwave-assisted pyrolysis is discussed largely due to energy shortage

and sustainability plans of most of the Countries.

Compared with conventional heating, microwave radiation has significant advantages such

as: (a) fast heat transfer, short reaction time, (b) selectivity and uniform volumetric heating

performance (c) easy operation and energy efficient and (d) low degradation or formation of

side products. In addition, microwave hydrothermal pretreatment removes more acetyl groups

in hemicellulose, which may be raised from the hot spot effect of microwave irradiation (Dai

et al., 2017).

In the case of conventional heating, energy is transferred from the outside surface of the

material inwards to the core of the material by conduction. Thus, overheating can occur on

8
the outside surface whilst still maintaining a cooler inner region. Contrasting with this,

microwaves induce heat at the molecular level by direct conversion of the electromagnetic

energy into heat. Energy is therefore uniformly dissipated throughout the material.

Materials can be grouped into three categories according to their response to microwaves:

insulators, absorbers, and conductors. Insulators are materials which are transparent to

microwaves (e.g., glass and ceramics), conductors are materials which show high

conductivity and thus reflect microwaves from the surface (e.g., metals), while absorbers or

dielectrics are materials that can absorb microwaves and convert microwave energy into heat

(Huang et al., 2016b). Most biomass is generally considered as low lossy materials, and they

need to be supported with materials that achieve rapid heating, such as graphite, charcoal,

activated carbons and pyrites.

Interestingly, Salema et al. (2017) studied the dielectric properties of different biomass from

agriculture and wood-based industries (including oil palm shell, empty fruit bunch, coconut

shell, rice husk, and sawdust) and reported that all were low loss dielectric materials. Such

materials do not absorb microwaves well during microwave-assisted pyrolysis until the char

is formed, and the microwave absorption will then be significantly higher.

5.1.1 Microwave-assisted solvolysis (pretreatment of lignocellulosic biomass)

In conventional heating methods, the lignocellulosic biomass is ground into small particles to

prevent large temperature gradients and then heated by indirect heat conduction or high

pressure steam injection up to 160–250 °C. Therefore, fermentable sugar recovery and

conversion might be affected by degradation of the hemicellulose into furfural or humic acids

(Li et al., 2016a). Alternatively, microwave heating is reported to enhance enzymatic

9
saccharification through fibre swelling and fragmentation (Diaz et al., 2015) as a result of the

internal uniform and rapid heating of large biomass particles. Almost no effect is observed in

plant fibre material when treated with microwaves under temperatures that are equal to or

below 100 °C (Chen et al., 2017).

The performance of microwaves depends on the dielectric properties of biomass which

represent the ability of the material to store electromagnetic energy and to convert this energy

into heat. Although, biomass usually is a low microwave absorber, the presence of relatively

high moisture and inorganic substances can improve the absorption capacity of biomass (Li et

al., 2016b). The increasing commercial availability of flow-through microwave systems may

be of particular relevance to lignocellulosic pretreatment.

Choudhary et al. (2012) evaluated the pretreatment of sweet sorghum bagasse (SSB) biomass

through microwave radiation, and reported that about 65% of maximal total sugars were

recovered when 1 g of SSB in 10 ml water was subjected to 1000 W for 4 minutes. Scanning

electron microscope analysis of microwave-assisted pretreatment of corn straw and rice husk

in alkaline glycerol showed clear disruption of the plant cell structure (Diaz et al., 2015).

Recently, Ravindran et al. (2018) reported that microwave-assisted alkali pretreatment was

the best pretreatment method for brewers’ spent grain (1g of BSG in 10 ml 0.5% NaOH was

pretreated using 400 W for 60 seconds), as compared with dilute acid hydrolysis, steam

explosion, ammonia fiber explosion, organosolv and ferric chloride pretreatment. The authors

found that BSG after microwave-assisted alkali pretreatment yielded 228.25 mg of reducing

sugar/g of BSG which was 2.86-fold higher compared to untreated BSG (79.67 mg/g of

BSG). Others have also found that microwave radiation for lignocellulosic pretreatment

10
possesses the advantage of low capital cost, easy operation and significant energy efficiency

(Kostas et al., 2017).

5.1.2 Microwave-assisted pyrolysis of lignocellulosic biomass

In this technique, microwave irradiation is used as a pretreatment method followed by

biological conversion of biomass into biofuel, as well as a thermo-chemical pyrolysis of

biomass. Pyrolysis is the conversion of biomass to liquid (bio-oil), solid (bio-char) and

gaseous (syn-gas) fractions, by heating the biomass in the absence of air to high temperatures.

Pyrolysis can convert the lignocellulosic biomass into biofuels or chemicals more completely

and more quickly (Huang et al., 2016b). Microwave-assisted pyrolysis can convert fifty

percent of lignocellulosic biomass processed into bioenergy gas products (Huang et al.,

2015). Oil obtained from the fast pyrolysis of lignocellulosic materials contains a complex

mixture of phenolic compounds derived primarily from lignin (Bu et al., 2011). Huang et al.

(2016a) compared the heating rate of both microwave and conventional pyrolysis methods

using the same input power level. They reported that the heating rate of microwave pyrolysis

was higher by up to 42 % when compared with the heating rate of conventional processes;

this means that microwave pyrolysis requires less time to reach the target temperature,

indicating superior performance over conventional heating.

When converting agricultural biomass to higher value products using pyrolysis, the process

may be tailored to meet either qualitative or quantitative objectives, such as maximizing the

yield of solids, liquids or gases, as well as improving the energy density of chars or producing

good quality syngas for the synthesis of bio-based chemicals. Calculations of the Energy

Return On Investment (EROI) for microwave pyrolysis by Lo et al. (2017) provided evidence

for the energetic efficiency and economic feasibility of microwave pyrolysis of

11
lignocellulosic biomass. The authors reported that when microwave pyrolysis is conducted on

biomass feedstock (rice straw, rice husk, corn stover, sugarcane bagasse, bamboo leaves,

sugarcane peel, or waste coffee grounds) with a heating value of 16 MJ/kg using microwave

power of 500 W for 30 min, the EROI was be approximately 3.56. This finding may support

the feasibility of the process, considering that minimum EROI for sustainable society is 3.0

(Hall et al., 2009). EROI is the ratio of the energy supplied to society and the energy invested

to capture and deliver that energy (Hall et al., 2013).

5.2 Ultrasound

Over 90 years ago, Wood and Loomis (1927) reported the effects of the ultrasonic treatment

on cellular biomass, such as floc fragmentation, cell rupture and destruction. Ultrasound in

the range of 20 kHz to 1 MHz is used in chemical processing, while higher frequencies are

used in medical and diagnostic applications. Ultrasound pretreatment of biomass results in

alteration of the surface structure and production of oxidizing radicals that chemically attack

the lignocellulosic matrix (Luo et al., 2013). Additionally, ultrasound can disrupt α-O-4 and

β-O-4 linkages in lignin (Shirkavand et al., 2016) which results in the splitting of structural

polysaccharides and lignin fractions by formation of small cavitation bubbles (Kumar and

Sharma, 2017). The bubbles formed grow to a certain critical size and then become unstable,

collapsing violently, and achieving pressures up to 1,800 atmospheres and temperatures of

2,000–5,000 K (Kunaver et al., 2012). Hence, ultrasonic disruption may represent an

effective green technology for the pretreatment of lignocellulosic biomass.

Kunaver et al. (2012) studied the utilization of forest wood wastes to produce valuable

chemicals using high energy ultrasound at a power of 400 W and amplitudes ranging from

20% to 100%, and reported shorter reaction times (by a factor of up to nine). Sun et al.,

12
(2004) reported that ultrasound irradiated sugarcane bagasse achieved 90% hemicellulose and

lignin removal at an ultrasound power of 100 W and sonication time for 2 hours in distilled

water at 55° C. The ultrasound was found to attack the integrity of cell walls, cleaving the

ether linkages between lignin and hemicelluloses, and increasing the accessibility and

extractability of the hemicelluloses. This is in agreement with another study for ultrasound-

assisted alkaline pretreatment of sugarcane bagasse using 400 W microwave power for 47.42

minutes in 2.89% NaOH and 70.15° C, where the theoretical reducing sugar yield recovered

was about 92% (Velmurugan, 2012).

Ultrasound-assisted, alkali pretreatment can enhance lignin degradation and enzymatic

saccharification rates by breaking hydrogen bonds between molecules of lignocellulosics and

lowering its crystallinity. However, the ultrasonic vibration energy is too low to change the

surface conformation of the raw material biomass particles (Zhang et al., 2008). Subhedar et

al. (2017) recently investigated the ultrasound-assisted delignification and enzymatic

hydrolysis of three biomass types (groundnut shells, pistachio shell and coconut coir) and

reported an approximate 80–100% increase in delignification over conventional alkali

treatments, where biomass loading was 0.5%, ultrasound power was 100 W and duty cycle

was 80% for 70 minutes. Additionally, reducing sugar yields in the case of ultrasound-

assisted enzymatic hydrolysis under optimised conditions of enzyme loading at 0.08% w/v,

substrate loading at 3.0% w/v, ultrasound power of 60 W and duty cycle of 70% for 6.5h,

were 21.3, 18.4 and 23.9 g/L for groundnut shells, pistachio shells and coconut coir

respectively, significantly more than that found for alkali hydrolysis (10.2, 8.1 and 12.1 g/L).

It was also reported that reducing sugar yield was increased by a factor of approximately 2.4

by the application of ultrasound at a power of 60 W and duty cycle of 70 % for pretreatment

of lignocellulosic waste paper at substrate loading of 3.0% (w/v) and cellulase loading of

13
0.8% (w/v) for 6.5 hours (Subhedar et al., 2015). Moreover, acoustic cavitation was found to

successfully decrease the crystallinity of the microcrystalline cellulose, enabling enhanced

enzymatic digestibility (Madison et al., 2017).

Combining ultrasound with ammonia pre-treatment of sugarcane bagasse (sonication time of

45 minutes in 400 w power, 100% amplitude and 24 kHz frequency, biomass loading of 1 g

per 10 ml of 10% ammonia and temperature of 80° C) resulted in a cellulose recovery of

95.78%, with 58.14% delignification (Ramadoss and Muthukumar, 2014). Additionally, the

synergistic effect of combining ammonia with ultrasound reduced by-product formation,

enabled the treatment to be conducted at moderate temperature and reduced cellulose

crystallinity. This is with an agreement with recent work carried out on ultrasound-assisted

dilute aqueous ammonia (2.0% w/v aqueous ammonia) pretreatment of corn cob, corn stover

and sorghum stalk using ultrasound at 90 W power and 50 kHz frequency (Xu et al., 2017);

the highest enzymatic hydrolysis sugar yield was approximately 81% in corn cob (70° C, 4h),

66% in corn stover (60° C, 2 h) and 57% in sorghum stalk (50° C, 4 h). Similarly,

pretreatment of spent coffee waste by ultrasound assisted potassium permanganate (biomass

loading of 1.0 g at 10 ml of 4% KMnO4 for 20 minutes, ultrasonic frequency of 47 kHz and

power of 310 W) resulted in 98% cellulose recovery and 46% lignin removal (Ravindran et

al., 2017).

5.2.1 Combination of Microwave and Ultrasound

Both microwaves and ultrasound are energy that may be applied to biomass to reduce the

size, increase the exposed surface area and increase availability of cellulose, hemicellulose

and oligosaccharides present in the biomass, facilitating further processing to produce target

chemicals (Dunson et al., 2006). Ultrasonication and microwave pretreatments were found to

accelerate hydrolysis and biodegradability of agriculture wastes (grape pomace and olive

14
pomace) and wastewater sludges used to produce biogas. The author concluded also that

ultrasonication was found to be more effective pretreatment method than microwaves alone

(Alagöz et al., 2016) . The applicability of the combination of microwaves with ultrasound

for pretreatment of biomass has been considered in a number of patents (Olsen, 2011;

Augustin et al., 2012; Gjermansen, 2014). Such a hybrid approach was found to selectively

degrade waxes and lignin, and microwaves were reported to remove the waxy layer from the

surface of biomass to increase the surface area available for enzymic action.

In hemicellulose degradation, the combination of ultrasound and microwave energy was

found to provide a supplemental method of heating the biomass internally, which rapidly

hydrolyzed the hemicellulose (North, 2016). Hydrothermal pretreatment of corncobs was also

achieved using ultrasound (20 and 60 kHz for 10 and 20 minutes respectively), and

microwaves (400 w and 600 w for 1 and 130 minutes respectively) to produce a high yield of

xylose maize hydrolyzate core (Junli et al., 2016).

Most recently, patent inventors reported on the superimposed dual-energy of an ultrasound

and microwave-assisted ionic liquid. A microwave power of 15~1000W (frequency of

1500~3000 MHz) combined with ultrasound (200 ~ 1000W and 15 ~ 30KHz) effectively

removed lignin, could enhance the efficiency of enzyme hydrolysis of cellulose, and

significantly increased fermentable sugar (glucose and xylose) yield (Xing et al., 2017).

5.3 Gamma ray

Gamma ray radiation is obtained from radioisotopes (Cobalt-60 or Cesium-137) and has also

been tested as a lignocellulosic pretreatment. Ionizing radiation can easily penetrate the

15
lignocellulosic structure, causing modification of the lignin and a breakdown of cellulose

crystal regions. The latter effect is facilitated by the formation of free radicals which decay

quickly from the amorphous regions after the termination of radiation, while decay at a

certain period from the crystalline regions also causes further degradation of the biomass

(Hyun Hong et al., 2014).

Liu et al. (2015) studied the effect of γ-irradiation on the bioconversion efficiency of

microcrystalline cellulose (MCC), as compared with other pretreatment methods (ionic

liquids - ILs, acidic aqueous ionic liquids, 1% HCL, and 1% H2SO4). They reported that the

most effective irradiation dose (891 kGy) possessed almost the same efficiency of MCC

bioconversion as ILs pretreatment, and higher than that of other tested pretreatment methods.

As a promising pretreatment technology, numerous articles have demonstrated that γ-

irradiation pretreatment can enhance enzymatic hydrolysis of lignocellulosic biomass (Li et

al., 2016c; Liu et al., 2016; Zhou et al., 2016; Liu et al., 2017). Gamma irradiation of

rapeseed straw at 1200 kGy was found to induce a series of changes in the physical and

chemical properties of the material. The latter included alteration of the linkage between the

carbohydrates and lignin in the plant biomass, decreases in particle size, narrowing of the

distribution range, increases in the specific surface area, and decreases in the thermal stability

of the treated biomass (Zhang et al., 2016a).

5.4 Electron beam (EB) irradiation

EB ionising radiation is obtained from a linear accelerator. This pretreatment uses accelerated

beams of electrons to irradiate lignocelluosic biomass in order to disrupt the structure of cell

wall polymers (lignin, cellulose, hemicellulose) by such processes as production of free

16
radicals, inducing cross-link formation or chain scission, decrystallization, and/or decreasing

the degree of polymerization (Grabowski, 2015).

EB irradiation of sugar maple (at dosages up to 1000 kGy) was found to depolymerize

cellulose and hemicellulose structures to varying degrees, and increased the yield of

phenolics (Mante et al., 2014). Yang et al. (2015) reported that the optimal EB irradiation

was 500 kGy to treat Korean Miscanthus sinensis prior to enzymatic hydrolysis for

fermentable sugar production. EB is mainly effective on depolymerizing cellulose, and so

therefore there is a requirement for use in combination with other pretreatments, such as

steam explosion or alkali, for hydrolyses of hemicellulose and lignin (Leskinen et al., 2017;

Xiang et al., 2017).

5.5 Pulsed-electric field

Pulsed-electric field (PEF) processing uses a simple device without moving parts that treats

plant biomass or bio-suspensions between two electrodes to voltage pulses, with an electrical

field strength of 0.1–80kV/cm for a very short time (10−4 and 10−2 s). Under the effect of

PEF, the biological membrane is disrupted and local structural changes occur which result in

a loss of semi-permeability, allowing the passage of intracellular compounds to the

surrounding solution (Barba et al., 2015). This also facilitates the entry of hydrolytic enzymes

through the pores of the treated plant cell membrane (Kumar and Sharma, 2017). Kumar et al.

(2011) found that pretreatment of lignocellulosic materials (wood chip and switchgrass) with

2000 pulses at field strength of 10 kV/cm could improve the cellulose hydrolysis for

conversion to fuel and chemicals.

17
PEF may contribute to delignification of lignocellulosic biomass (Janositz et al., 2011), and

depending on the PEF parameters, cell wall structure may be variably affected (Cholet et al.,

2014). Future work is needed to explain the effects of pulsed electric fields on lignocellulosic

structures (Golberg et al., 2016).

5.6 High hydrostatic pressure (HHP)

High hydrostatic pressure (HHP) has been used for decades as a tool in the food industry for

“non-thermal” Pasteurization that involves subjecting products to a high hydrostatic pressure

(100–600 MPa) without a deterioration in product quality or compromising safety. The

industrial application of HPP is currently successful in the United States, Europe and Japan

for Pasteurization of food products. Initial capital and operating costs have been reduced due

to innovative concepts introduced by different equipment manufacturers. HPP tolling is

another option for manufacturers who otherwise would never have access to the technology

because of equipment costs which are still relatively high.

HPP treatment is based on two fundamental principles: (a) pressure is distributed

proportionally in all parts of a biomass, irrespective of its shape and size; and (b) pressure

favours all structural reactions and changes that involve a decrease in volume. Although

researchers do not often have to take changes in pressure into account, like temperature it is a

thermodynamic parameter of any enzyme-catalyzed reaction. Pressure treatment has the

advantage over thermal treatment in not being time/mass-dependent. Additionally, pressure

also only affects hydrogen bonds, leaving covalent bonds untouched and thus reducing the

processing time. In addition, pressure affects the activity of some enzymes by direct changes

in enzyme structure, changes in the reaction mechanism and modifications to the physical

properties of substrate (Eisenmenger and Reyes-De-Corcuera, 2009).

18
Oliveira et al. (2012) reported that high hydrostatic pressure is a promising tool for the

engineering of enzymatic reactions within lignocellulosic biomass to obtain products with

tailored properties, as changing the pressure and the exposure time of high hydrostatic

pressure during the pretreatment step can control the rate and the extent of enzymatic

hydrolysis. The authors investigated the effect of hydrostatic pressures of 300–400 MPa for

15–45 min on Eucalyptus globulus kraft pulp, and found a 5–10-fold increase in the initial

hydrolysis rate of xylan by xylanase after this pretreatment. In 2013, Castañón-Rodríguez et

al. used increasing HPP up to 400–800 MPa to pre-treat sugarcane bagasse, in combination

with different concentrations of chemical compounds, and reported significant increases in

the susceptibility of biomass to enzymatic hydrolysis and a rise in glucose concentrations.

Results showed few cracks, tiny holes and some fragments flaked off from the compacted

lignocellulosic structure by the HPP treatments at an optimally efficient pressure of 250 MPa.

It is reported also that hydrolytic performance of fungal cellulases on coconut husk biomass

increased by a factor of 2 under pressurised conditions (Albuquerque et al., 2016). Results

showed porous areas and rupturing on coconut fibres treated by pressure values of 300 MPa

for 30 minutes. HPP is a promising choice, not only for biomass pretreatment, but also for

inducing hydrolytic enzymes stability and activation (Murao et al., 1992).

5.7 High-pressure homogenization (HPH)

HPH is a well-known mechanical method for cell disruption and recovery of intracellular bio-

products. The homogenizer is geared towards producing a homogenous size distribution of

particles suspended in a liquid, by using a pressure pump to force the liquid through a

specific valve to achieve homogenization. Depending on the operating pressure, the process

19
is called high-pressure homogenization (HPH, up to 150-200 MPa), or ultra-high pressure

homogenization (UHPH, up to 350-400 MPa).

Jin et al. (2015a) pre-treated four different lignocellulosic materials (corn straw, grass

clipping, pine sawdust, and catalpa sawdust) with HPH under 10 MPa working pressure. The

authors reported a decrease of biomass particle size and an increase in the accessible surface

area for enzyme hydrolysis, which led to high reducing sugars yield. Compared with alkaline-

heat pretreatment of grass clippings, HPH pretreatment is a promising eco-friendly method

for biogas production from lignocellulosic biomass, which can destroy the microstructure of

lignocellulosic biomass to an “empty-inside” structure, accessible for enzyme attack without

loss in hemicellulose (Jin et al., 2015b). Chen et al. (2010) found that sugarcane bagasse

treated with HPH (100 MPa) resulted in a significant decrease in particle size and a

disturbance in the microstructure of the biomass that increased accessible surface area by 3-

fold. This highly efficient, yet simple and green, mechanical homogenization has been used

recently to isolate nano-fibrillated cellulose from lignocellulosic biomass (Saelee et al.,

2016).

6 Techno-economic feasibility

Equipment based on emerging technologies are available in the market, and are used mainly

in food processing industry. Example of these equipment includes: continuous flow

microwaves (Advanced Microwave Technologies, United Kingdom), ultrasonic processors

(Industrial Sonomechanics, United States), pulsed electric field systems (Pulsemaster,

Netherlands), electron beam system (Pro-beam, Germany), and high pressure systems

(Multivac, France).

Microwave use in chemical processing has been shown to be a technically and economically

feasible alternative to conventional heating. Hasna (2011) evaluated the cost-benefit of using

20
microwave drying in corrugated paperboard manufacturing as an alternative to conventional

steam platens. It was concluded that the microwave capital cost ($7000 per kW) could be off-

set against utilities and power savings (from $128.00 to $38.00 per hour), compared with

conventional steam platens. Such savings were achievable in less than one year with an

assumption that operation hours are 6000 per year. The author also reported additional

benefits from using microwave drying in corrugated paperboard manufacturing, such as

improved quality, reduced wastage, and minimum starch consumption. In a recent feasibility

study on ginger processing to oleoresin, an ultrasound pretreatment step was introduced as a

novel method to enhance extraction of chemical constituents from plant materials (Romis

Consultants Ltd, 2017); however, the study did not focus on economics related to ultrasound

specifically. A feasibility study in Egypt on using gamma rays for food preservation indicated

that the cost of irradiation for one ton of frozen poultry was US $130.4, smoked fish US

$78.2, spices $ 260.1 and dried vegetable $ 26. Economic analysis evaluation indicated that

the average rate-of-return would be about 16.9% annually, with a payback period of about 6

years (Eldin et al., 2002). The feasibility and the economic impact of electron beam

processing in chestnut fruits was evaluated by Lopes (2014), who reported a strong

dependence on processed quantity per unit time and product costing. Puértolas et al. (2010)

calculated the economic cost of the treatment of grape mass to improve the phenolic

extraction for red wine fermentation using PEF, and reported that cost could be around 0.01

and 0.2 €/ton. However, the author reported that inactivation of wine spoilage

microorganisms by PEF is not feasible and can increase production costs by 4.2-8.4 €/ton due

to energy inputs needed. The cost of high pressure processing (HPP) in comparison with

thermal pasteurization was estimated to be 10.7 ¢/l for processing 16,500,000 l/year (3,000

l/h), which corresponds to 7-fold higher than thermal pasteurization (Sampedro et al., 2014).

Generally, the economic feasibility of emerging technologies is limited by the high cost of

21
capital investment for new equipment. For commercial application of the emerging

technologies in pretreatment of lignocellulosic biomass further feasibility studies will be

needed considering the complexities of biorefining process, inter-dependence of pretreatment

processes and the economics related to the market of the finished product.

7 Conclusion

To date, sustainability, energy saving, capital cost minimization and downstream process

efficiency are still challenges toward commercial scale pretreatment of lignocellulosic

biomass. The tendency is thus to use energy efficient green technologies. Interestingly, green

commercial innovations from food technology present promising opportunities. Different

emerging technologies have been investigated for pretreatment of lignocellulosic biomass;

however, capital cost is generally high, and comparative efficiency of these techniques on

different lignocellulosic biomass is not available. Hence, further studies are needed to

identify the most efficient emerging technology, as well as feasibility studies to evaluate the

viability of using these technologies in a commercial biorefinery.

8 Acknowledgement

Authors would like to acknowledge the funding from Dublin Institute of Technology (DIT)

under the Fiosraigh Scholarship programme, 2017.

References

1. Albuquerque, E.D., Torres, F.A.G., Fernandes, A.A.R., Fernandes, P.M.B., 2016.

Combined effects of high hydrostatic pressure and specific fungal cellulase improve

coconut husk hydrolysis. Process Biochem. 51, 1767–1775.

2. Álvarez, A., Cachero, S., González-Sánchez, C., Montejo-Bernardo, J., Pizarro, C.,

22
 Bueno, J.L., 2018. Novel method for holocellulose analysis of non-woody biomass

wastes. Carbohydrate Polymers. 189, 250-256.

3. Aylin Alagöz, B., Yenigün, O., Erdinçler, A., 2016. Ultrasound assisted biogas

production from co-digestion of wastewater sludges and agricultural wastes:

Comparison with microwave pre-treatment. Ultrason. Sonochem. 40, 193–200.

4. Augustin, M.A., Dumsday, G.J., Mawson, R., Melton, L.D., Oliver, C.M., 2012.

Treatment of plant biomass. WO2012000035A1.

5. Barba, F.J., Parniakov, O., Pereira, S.A., Wiktor, A., Grimi, N., Boussetta, N.,

Saraiva, J.A., Raso, J., Martin-Belloso, O., Witrowa-Rajchert, D., Lebovka, N.,

Vorobiev, E., 2015. Current applications and new opportunities for the use of pulsed

electric fields in food science and industry. Food Res. Int. 77, 773–798.

6. Bajpai, P., 2016. Pretreatment of lignocellulosic biomass for biofuel production.

Springer Nature.

7. Bu, Q., Lei H., Ren S., Wang L., Holladay J., Zhang Q., Tang J., Ruan R., 2011.

Phenol and phenolics from lignocellulosic biomass by catalytic microwave pyrolysis.

Bioresour. Technol. 102, 7004–7007.

8. Capolupo, L., Faraco, V., 2016. Green methods of lignocellulose pretreatment for

biorefinery development. Appl. Microbiol. Biotechnol. 100, 9451–9467.

9. Castañón-Rodríguez, J.F., Torrestiana-Sánchez, B., Montero-Lagunes, M., Portilla-

Arias, J., De León, J.A.R., Aguilar-Uscanga, M.G., 2013. Using high pressure

processing (HPP) to pretreat sugarcane bagasse. Carbohydr. Polym. 98, 1018–1024.

10. Chandel A., da Silva, S., 2013. Sustainable Degradation of Lignocellulosic Biomass -

Techniques, Applications and Commercialization. InTech. Rijeka.

11. Chen, W., Chen, Y., Yang, H., Xia, M., Li, K., Chen, X., Chen, H., 2017. Co-

pyrolysis of lignocellulosic biomass and microalgae: Products characteristics and

23
 interaction effect. Bioresource Technology. 245A, 860-868.

12. Chen, D., Guo, Y., Huang, R., Lu, Q., Huang, J., 2010. Pretreatment by ultra-high

pressure explosion with homogenizer facilitates cellulase digestion of sugarcane

bagasses. Bioresour. Technol. 101, 5592–5600.

13. Chen, H., Liu, J., Chang, X., Chen, D., Xue, Y., Liu, P., Lin, H., Han, S., 2017. A

review on the pretreatment of lignocellulose for high-value chemicals. Fuel Process.

Technol. 160, 196–206.

14. Cholet, C., Delsart, C., Petrel, M., Gontier, E., Grimi, N., L’Hyvernay, A., Ghidossi,

R., Vorobiev, E., Mietton-Peuchot, M., Gény, L., 2014. Structural and Biochemical

Changes Induced by Pulsed Electric Field Treatments on Cabernet Sauvignon Grape

Berry Skins: Impact on Cell Wall Total Tannins and Polysaccharides. J. Agric. Food

Chem. 62, 2925–2934.

15. Choudhary, R., Umagiliyage, A.L., Liang, Y., Siddaramu, T., Haddock, J.,

Markevicius, G., 2012. Microwave pretreatment for enzymatic saccharification of

sweet sorghum bagasse. Biomass and Bioenergy 39, 218–226.

16. Dai, L., He, C., Wang, Y., Liu, Y., Yu, Z., Zhou, Y., Fan, L., Duan, D., Ruan, R.,

2017. Comparative study on microwave and conventional hydrothermal pretreatment

of bamboo sawdust: Hydrochar properties and its pyrolysis behaviors. Energy

Convers. Manag. 146, 1–7.

17. Daza Serna, L. V, Orrego Alzate, C.E., Alzate, C.A.C., 2016. Supercritical fluids as a

green technology for the pretreatment of lignocellulosic biomass. Bioresource

Technology. 199, 113-120.

18. De Caprariis, B., De Filippis, P., Petrullo, A., Scarsella, M., 2017. Hydrothermal

liquefaction of biomass: Influence of temperature and biomass composition on the

bio-oil production. Fuel. 208, 618-625.

24
19. Devendra, P., Maurya, Ankit, S., Negi, S., 2015. An overview of key pretreatment

processes for biological conversion of lignocellulosic biomass to bioethanol. Biotech.

6, 597–609.

20. Diaz, A.B., Moretti, M.M. de S., Bezerra-Bussoli, C., Carreira Nunes, C. da C.,

Blandino, A., da Silva, R., Gomes, E., 2015. Evaluation of microwave-assisted

pretreatment of lignocellulosic biomass immersed in alkaline glycerol for fermentable

sugars production. Bioresour. Technol. 185, 316–323. Dunson, J., Tucker, M.,

Elander, R., Hennessey, S., 2006. Treatment of biomass to obtain a target chemical.

US20070031919 A1.

21. Duque, A., Manzanares, P., Ballesteros, M., 2017. Extrusion as a pretreatment for

lignocellulosic biomass: Fundamentals and applications. Renewable Energy.. 114B,

1427-1441.

22. Eisenmenger, M.J., Reyes-De-Corcuera, J.I., 2009. High pressure enhancement of

enzymes: A review. Enzyme Microb. Technol. 45, 331–347.

23. Eldin, M., El-Fouly, Z., Karem, H.A., 2002. Commercial feasibility and evaluation of

consumer acceptance for certain irradiated food products in Egypt, in: Study of the

Impact of Food Irradiation on Preventing Losses: Experience in Africa. International

Atomic Energy Agency, Austria.

24. Gedye, R., Smith, F., Westaway, K., Ali, H., Baldisera, L., Laberge, L., Rousell, J.,

1986. The use of microwave ovens for rapid organic synthesis. Tetrahedron Lett. 27,

279–282.

25. Golberg, A., Sack, M., Teissie, J., Pataro, G., Pliquett, U., Saulis, G., Stefan, T.,

Miklavcic, D., Vorobiev, E., Frey, W., 2016. Energy-efficient biomass processing

with pulsed electric fields for bioeconomy and sustainable development. Biotechnol.

Biofuels 9, 94.

25
26. Grabowski, C., 2015. The Impact of Electron Beam Pretreatment on the Fermentation

of Wood-based Sugars. SUNY College of Environmental Science and Forestry.

Honors Theses. Paper 63.

27. Hall, C.A.S., Balogh, S., Murphy, D.J.R., 2009. What is the minimum EROI that a

sustainable society must have? Energies 2, 25–47.

28. Hall, C.A.S., Lambert, J.G., Balogh, S.B., 2013. EROI of different fuels and the

implications for society. Energy Policy 64, 141–152.

29. Hans Sejr Olsen, 2011. Biogas production process with enzymatic pre-treatment.

WO2011092136A1.

30. Hasna, A.M., 2011. Microwave Processing Applications in Chemical Engineering:

Cost Analysis. J. Appl. Sci. 11, 3613–3618.

31. Huang, Y.-F., Chiueh, P.-T., Kuan, W.-H., Lo, S.-L., 2016a. Microwave pyrolysis of

lignocellulosic biomass: Heating performance and reaction kinetics. Energy. 100,

137-144.

32. Huang, Y.-F., Chiueh, P.-T., Kuan, W.-H., Lo, S.-L., 2015. Effects of lignocellulosic

composition and microwave power level on the gaseous product of microwave

pyrolysis. Energy 89, 974–981.

33. Huang, Y.-F., Chiueh, P.-T., Lo, S.-L., 2016b. A review on microwave pyrolysis of

lignocellulosic biomass. Sustainable Environment Research. 26, 103-109.

34. Hyun Hong, S., Taek Lee, J., Lee, S., Gon Wi, S., Ju Cho, E., Singh, S., Sik Lee, S.,

Yeoup Chung, B., 2014. Improved enzymatic hydrolysis of wheat straw by combined

use of gamma ray and dilute acid for bioethanol production. Radiat. Phys. Chem. 94,

231–235.

35. Janositz, A., Semrau, J., Knorr, D., 2011. Impact of Pulsed Electric Fields (PEF) on

post- permeabilization processes in plant cells. Innov Food Sci Emerg Technol. 12,

26
 269–274.

36. Jönsson, L.J., Martín, C., 2016. Pretreatment of lignocellulose: Formation of

inhibitory by-products and strategies for minimizing their effects. Bioresource

Technology. 199, 103-112.

37. Jin, S., Zhang, G., Zhang, P., Fan, S., Li, F., 2015a. High-pressure homogenization

pretreatment of four different lignocellulosic biomass for enhancing enzymatic

digestibility. Bioresour. Technol. 181, 270–274.

38. Jin, S., Zhang, G., Zhang, P., Jin, L., Fan, S., Li, F., 2015b. Comparative study of

high-pressure homogenization and alkaline-heat pretreatments for enhancing

enzymatic hydrolysis and biogas production of grass clipping. Int. Biodeterior.

Biodegradation 104, 477–481.

39. Junli, R., Huan, Y.Y., Runcang, S., Xuan, L.Q., Fu, L.C., 2016. Method for preparing

xylose hydrolysis fluid through hydrothermal pretreatment of corncobs under control

of trace alkali. CN106222312A.

40. Kim, H., Ahn, Y., Kwak, S.-Y., 2016. Comparing the influence of acetate and

chloride anions on the structure of ionic liquid pretreated lignocellulosic biomass.

Biomass and Bioenergy. 93, 243-253.

41. Khan, A.S., Man, Z., Bustam, M.A., Nasrullah, A., Ullah, Z., Sarwono, A., Shah,

F.U., Muhammad, N., 2018. Efficient conversion of lignocellulosic biomass to

levulinic acid using acidic ionic liquids. Carbohydrate Polymers. 181, 208-214.

42. Kumar, A.K., Sharma, S., 2017. Recent updates on different methods of pretreatment

of lignocellulosic feedstocks: a review. Bioresources and Bioprocessing. 4:7.

43. Kumar, P., Barrett, D.M., Delwiche, M.J., Stroeve, P., 2011. Pulsed Electric Field

Pretreatment of Switchgrass and Wood Chip Species for Biofuel Production. Ind.

Eng. Chem. Res 50, 10996–11001.

27
44. Kunaver, M., Jasiukaityte ˙, E., Uk, N.Č., Jasiukaityte, E., Čuk, N., 2012.

Ultrasonically assisted liquefaction of lignocellulosic materials. Bioresour. Technol.

103, 360–366.

45. Leskinen, T., Kelley, S.S., Argyropoulos, D.S., 2017. E-beam irradiation &amp;

steam explosion as biomass pretreatment, and the complex role of lignin in substrate

recalcitrance. Biomass and Bioenergy 103, 21–28.

46. Li, H., Qu, Y., Yang, Y., Chang, S., Xu, J., 2016a. Microwave irradiation - A green

and efficient way to pretreat biomass. Bioresour. Technol. 199, 34–41.

https://doi.org/10.1016/j.biortech.2015.08.099

47. Li, J., Dai, J., Liu, G., Zhang, H., Gao, Z., Fu, J., He, Y., Huang, Y., 2016b. Biochar

from microwave pyrolysis of biomass: A review. Biomass and Bioenergy 94, 228–

244.

48. Li, Q., Li, X., Jiang, Y., Xiong, X., Hu, Q., Tan, X., Wang, K., Su, X., 2016c.

Analysis of degradation products and structural characterization of giant reed and

Chinese silvergrass pretreated by 60Co-γ irradiation. Ind. Crops Prod. 83, 307–315.

49. Liu, X., Hiligsmann, S., Gourdon, R., Bayard, R., 2017. Anaerobic digestion of

lignocellulosic biomasses pretreated with Ceriporiopsis subvermispora. Journal of

Environmental Management. 193, 154-162.

50. Liu, Y., Guo, L., Wang, L., Zhan, W., Zhou, H., 2017. Irradiation pretreatment

facilitates the achievement of high total sugars concentration from lignocellulose

biomass. Bioresour. Technol. 232, 270–277.

51. Liu, Y., Zhou, H., Wang, L., Wang, S., Fan, L., 2016. Improving Saccharomyces

cerevisiae growth against lignocellulose- derived inhibitors as well as maximizing

ethanol production by a combination proposal of c-irradiation pretreatment with in

situ detoxification. Chem. Eng. J. 287, 302–312.

28
52. Liu, Y., Zhou, H., Wang, S., Wang, K., Su, X., 2015. Comparison of γ-irradiation

with other pretreatments followed with simultaneous saccharification and

fermentation on bioconversion of microcrystalline cellulose for bioethanol

production. Bioresour. Technol. 182, 289–295.

53. Lo, S.-L., Huang, Y.-F., Chiueh, P.-T., Kuan, W.-H., 2017. Microwave pyrolysis of

lignocellulosic biomass. Energy Procedia 105, 41–46.

54. Lopes, A.M., 2014. Ionizing radiation applications for food preservation: effects of

gamma and e-beam irradiation on physical and chemical parameters of chestnut fruits.

University of Salamanca. PhD thesis.

55. Luo, J., Fang, Z., Smith, R.L., 2013. Ultrasound-enhanced conversion of biomass to

biofuels. Prog. Energy Combust. Sci. 41, 56-93.

56. Madison, M.J., Coward-Kelly, G., Liang, C., Karim, M.N., Falls, M., Holtzapple,

M.T., 2017. Mechanical pretreatment of biomass Part I: Acoustic and hydrodynamic

cavitation. Biomass and Bioenergy. 98, 135-141.

57. Mante, O.D., Amidon, T.E., Stipanovic, A., Babu, S.P., 2014. Integration of biomass

pretreatment with fast pyrolysis: An evaluation of electron beam (EB) irradiation and

hot-water extraction (HWE). J. Anal. Appl. Pyrolysis 110, 44–54.

58. Morten Gjermansen, 2014. Biogas From Enzyme-Treated Bagasse.

US20140106427A1.

59. Murao, S., Nomura, Y., Yoshikawa, M., Shin, T., Oyama, H., Arai, M., 1992. NII-

Electronic Library Service Enhancement of Activities of Cellulases under High

Hydrostatic Pressure. Biosci. Biotech. Biochem 56, 1366–1367.

60. Muranaka, Y., Nakagawa, H., Hasegawa, I., Maki, T., Hosokawa, J., Ikuta, J., Mae,

K., 2017. Lignin-based resin production from lignocellulosic biomass combining

acidic saccharification and acetone-water treatment. Chemical Engineering Journal.

29
 308, 754-759.

61. North, P.H., 2016. Method and system for fractionation of lignocellulosic biomass.

US20160068920 A1.

62. Noparat, P., Prasertsan, P., O-Thong, S., Pang, X., 2017. Sulfite Pretreatment to

Overcome Recalcitrance of Lignocellulose for Enzymatic Hydrolysis of Oil Palm

trunk. Energy Procedia 138, 1122–1127.

63. Nitsos, C., Rova, U., 2017. Organosolv Fractionation of Softwood Biomass for

Biofuel and Biorefinery Applications. Energies 11, 50.

64. Oliveira, S.C.T., Figueiredo, A.B., Evtuguin, D. V, Saraiva, J.A., 2012. High pressure

treatment as a tool for engineering of enzymatic reactions in cellulosic fibres.

Bioresour. Technol. 107, 530–534.

65. Östergren, K., Gustavsson, J., Hansen, J., Møller, H., Anderson, G., O’Connor, C.,

Soethoudt, H., Quested, T., Easteal, S., Politano, A., Bellettato, C., Canali, M.,

Falasconi, L., Gaiani, S., Vittuari, M., Schneider, F., Moates, G., Waldron, K.,

Redlingshöfer, B., 2014. FUSIONS Definitional Framework for Food Waste.

Göteborg.

66. Pielhop, T., Amgarten, J., Von Rohr, R., Studer, M.H., 2016. Steam explosion

pretreatment of softwood: the effect of the explosive decompression on enzymatic

digestibility. Biotechnol. Biofuels 9: 152.

67. Puértolas, E., Ló Pez, N., Condó, S., Alvarez, I., Raso, J., 2010. Potential applications

of PEF to improve red wine quality. Trends Food Sci. Technol. 21, 247–255.

68. Rajendran Velmurugan, K.M., 2012. Ultrasound-assisted alkaline pretreatment of

sugarcane bagasse for fermentable sugar production: Optimization through response

surface methodology. Bioresour. Technol. 112, 293–299.

69. Ramadoss, G., Muthukumar, K., 2014. Ultrasound assisted ammonia pretreatment of

30
 sugarcane bagasse for fermentable sugar production. Biochem. Eng. J. 83, 33–41.

70. Ravindran, R., Jaiswal, A., 2016. A Comprehensive Review on Pre-treatment Strategy

for Lignocellulosic Food Industry Waste: Challenges and Opportunities. Bioresour.

Technol. 199: 92-102.

71. Ravindran, R., Jaiswal, S., Abu-Ghannam, N., Jaiswal, A.K., 2017. Evaluation of

Ultrasound Assisted Potassium Permanganate Pre-Treatment of Spent Coffee Waste.

Bioresour. Technol. 224, 680–687.

72. Ravindran, R., Jaiswal, S., Abu-Ghannam, N., Jaiswal, A.K., 2018. A comparative

analysis of pretreatment strategies on the properties and hydrolysis of brewers’ spent

grain. Bioresour. Technol. 248, 272–279.

73. Raud, M., Tutt, M., Olt, J., Kikas, T., 2016. Dependence of the hydrolysis efficiency

on the lignin content in lignocellulosic material. International Journal of Hydrogen

Energy. 41(37), 16338-16343.

74. Romis Consultants Ltd, 2017. Model feasibility study and business plan for ginger

processing to oleoresin-an industry wide study report.

75. Saelee, K., Yingkamhaeng, N., Nimchua, T., Sukyai, P., 2016. An environmentally

friendly xylanase-assisted pretreatment for cellulose nanofibrils isolation from

sugarcane bagasse by high-pressure homogenization. Ind. Crops Prod. 82, 149–160.

76. Saha, B.C., Qureshi, N., Kennedy, G.J., Cotta, M.A., 2016. Biological pretreatment of

corn stover with white-rot fungus for improved enzymatic hydrolysis. Int. Biodeterior.

Biodegrad. 109, 29–35.

77. Salema, A.A., Ani, F.N., Mouris, J., Hutcheon, R., 2017. Microwave dielectric

properties of Malaysian palm oil and agricultural industrial biomass and biochar

during pyrolysis Fuel Processing Technology. 166, 164-173.

78. Sampedro, F., Mcaloon, A., Yee, W., Fan, X., Geveke, D.J., 2014. Cost Analysis and

31
 Environmental Impact of Pulsed Electric Fields and High Pressure Processing in

Comparison with Thermal Pasteurization. Food Bioprocess Technol 7, 1928–1937.

79. Sharma, A., Pareek, V., Zhang, D., 2015. Biomass pyrolysis - A review of modelling,

process parameters and catalytic studies. Renew. Sustain. Energy Rev. 50, 1081–

1096.

80. Shirkavand, E., Baroutian, S., Gapes, D.J., Young, B.R., 2016. Combination of fungal

and physicochemical processes for lignocellulosic biomass pretreatment - A review.

Renew. Sustain. Energy Rev. 54, 217–234.

81. Sindhu, R., Binod, P., Pandey, A., 2016. Biological pretreatment of lignocellulosic

biomass - An overview. Bioresour. Technol. 199, 76–82.

82. Singh, R., Krishna, B.B., Kumar, J., Bhaskar, T., 2016. Opportunities for utilization of

non-conventional energy sources for biomass pretreatment. Bioresour. Technol. 199,

398–407.

83. Stenmarck, Å., Jensen, C., Quested, T., Moates, G., 2016. Estimates of European food

waste levels, 2016th ed. FUSIONS.

84. Subhedar, P.B., Babu, N.R., Gogate, P.R., 2015. Intensification of enzymatic

hydrolysis of waste newspaper using ultrasound for fermentable sugar production.

Ultrason. Sonochem. 22, 326–332.

85. Subhedar, P.B., Ray, P., Gogate, P.R., 2017. Intensification of delignification and

subsequent hydrolysis for the fermentable sugar production from lignocellulosic

biomass using ultrasonic irradiation. Ultrason. Sonochem. 40, 140–150.

86. Sun, J.-X., Sun, R., Sun, X.-F., Su, Y., 2004. Fractional and physico-chemical

characterization of hemicelluloses from ultrasonic irradiated sugarcane bagasse.

Carbohydr. Res. 339, 291–300.

87. Sun, S., Sun, S., Cao, X., Sun, R., 2016. The role of pretreatment in improving the

32
 enzymatic hydrolysis of lignocellulosic materials. Bioresour. Technol. 199, 49–58.

88. Wood, R.W., Loomis, A.L., 1927. The physical and biological effects of high-

frequency sound-waves of great intensity. Philos. Mag. 4, 417–436.

89. Xiang, Y., Xiang, Y., Wang, L., 2017. Electron beam irradiation to enhance

enzymatic saccharification of alkali soaked Artemisia ordosica used for production of

biofuels. J. Environ. Chem. Eng. 5, 4093–4100.

90. Xing, X., Wenhua, G., Jiming, X., Shouyong, Z., Yijiang, Z., Jun, X., Xiaoyan, L.,

2017. Method for improving lignocellulose enzymolysis efficiency by lignocellulose

pretreatment through ultrasonic-microwave synchronously-assisted ionic liquid

system. CN106591395A.

91. Xu, Q.Q., Zhao, M.J., Yu, Z.Z., Yin, J.Z., Li, G.M., Zhen, M.Y., Zhang, Q.Z., 2017.

Enhancing enzymatic hydrolysis of corn cob, corn stover and sorghum stalk by dilute

aqueous ammonia combined with ultrasonic pretreatment. Ind. Crops Prod. 109, 220–

226.

92. Yang, S.J., Yoo, H.Y., Choi, H.S., Lee, J.H., Park, C., Kim, S.W., 2015. Enhancement

of enzymatic digestibility of Miscanthus by electron beam irradiation and chemical

combined treatments for bioethanol production. Chem. Eng. J. 275, 227–234.

93. Yoo, C.G., Pu, Y., Ragauskas, A.J., Turner, C., Wang, J., 2017. Ionic liquids:

Promising green solvents for lignocellulosic biomass utilization. Curr. Opin. Green

Sustain. Chem. 5, 5–11.

94. Yu, J., Paterson, N., Blamey, J., Millan, M., 2017. Cellulose, xylan and lignin

interactions during pyrolysis of lignocellulosic biomass. Fuel 191, 140–149.

95. Zhang, C., Su, X., Xiong, X., Hu, Q., Amartey, S., Tan, X., Qin, W., 2016a. 60Co-γ

radiation-induced changes in the physical and chemical properties of rapeseed straw.

Biomass and Bioenergy 85, 207–214.

33
96. Zhang, C.-W., Xia, S.-Q., Ma, P.-S., 2016b. Facile pretreatment of lignocellulosic

biomass using deep eutectic solvents. Bioresource Technology. 219, 1-5.

97. Zhang, Z., Xie, Y., He, X., Li, X., Hu, J., Ruan, Z., Zhao, S., Peng, N., Liang, Y.,

2016c. Comparison of high-titer lactic acid fermentation from NaOH- and NH 3 -H 2

O 2 -pretreated corncob by Bacillus coagulans using simultaneous saccharification

and fermentation. Scientific Reports. 6, 37245.

98. Zhang, Y.Q., Fu, E.H., Liang, J.H., 2008. Effect of Ultrasonic Waves on the

Saccharification Processes of Lignocellulose. Chem. Eng. Technol. 31, 1510–1515.

99. Zhou, H., Zhang, R., Zhan, W., Wang, L., Guo, L., Liu, Y., 2016. High biomass

loadings of 40 wt% for efficient fractionation in biorefineries with an aqueous solvent

system without adding adscititious catalyst. Green Chem. 18, 6108–6114.

100. Zhuang, X., Wang, W., Yu, Q., Qi, W., Wang, Q., Tan, X., Zhou, G., Yuan,

Z., 2016. Liquid hot water pretreatment of lignocellulosic biomass for bioethanol

production accompanying with high valuable products. Bioresource Technology. 199,

68-75.

34
Table 1. Chemical composition of different lignocellulosic feedstocks (% dry basis)

Source Cellulose Hemicellulose Lignin References

Hardwood
Eucalyptus 44.9 28.9 26.2 (Muranaka et al., 2017)
Oak 43.2 21.9 35.4 (Yu , 2017)
Rubber wood 39.56 28.42 27.58 (Khan et al., 2018)
Softwood
Spruce 47.1 22.3 29.2 (Yu , 2017)
Pine 45.6 24.0 26.8 (Yu , 2017)
Japanese cedar 52.7 13.8 33.5 (Muranaka et al., 2017)
Grasses
Bamboo 46.5 18.8 25.7 (Chen et al., 2017)
Amur silver-grass 42.00 30.15 7.00 (Raud et al., 2016)
Natural hay 44.9 31.4 12.0 (De Caprariis et al.,
2017)
Hemp 53.86 10.60 8.76 (Raud et al., 2016)
Rye 42.83 27.86 6.51 (Raud et al., 2016)
Reed 49.40 31.50 8.74 (Raud et al., 2016)
Sunflower 34.06 5.18 7.72 (Raud et al., 2016)
Silage 39.27 25.96 9.02 (Raud et al., 2016)
Szarvasi-1 37.85 27.33 9.65 (Raud et al., 2016)
Agroindustrial
waste
Walnut shell 23.3 20.4 53.5 (De Caprariis et al.,
2017)
Groundnut shell 37 18.7 28 (Subhedar et al, 2017)
Pistachio shell 15.2 38.2 29.4 (Subhedar et al, 2017)
Almond shell 27  30  36  (Álvarez et al., 2018)
Pine nut shell 31  25  38.0  (Álvarez et al., 2018)
Hazelnut shell 30  23  38.0  (Álvarez et al., 2018)
Coconut coir 44.2 22.1 32.8 (Subhedar et al, 2017)
Cotton stalk 67 16 13 (Kim et al., 2016)
Hemp stalk 52 25 17 (Kim et al., 2016)
Acacia pruning 49 13 32 (Kim et al., 2016)
Sugarcane peel 41.11 26.40 24.31 (Huang et al., 2016b)
Rice husk 40 16 26 (Daza Serna et al., 2016)
Rice straw 38.14 31.12 26.35 (Huang et al., 2016b)
Barley straw 35.4 28.7 13.1 (Liu et al., 2017)
Coffee grounds 33.10 30.03 24.52 (Huang et al., 2016b)
Extracted olive 19  22  40.0  (Álvarez et al., 2018)
pomace
Palm oil frond 37.32 31.89 26.05 (Khan et al., 2018)
Corn stover 43.97 28.94 21.82 (Huang et al., 2016b)
Bamboo leaves 34.14 25.55 35.03 (Huang et al., 2016b)
Hazel branches 30.8 15.9 19.9 (Liu et al., 2017)

35
Table 2. Major advantages and disadvantages of each of the common pretreatment methods

Pretreatment Method Effects Advantage Disadvantage References

Mechanical Milling Reduce the particle size Control of final High energy (Devendra et al.,
and crystallinity of particle size, Make consumption 2015)
lignocellulosic materials handling of material
easy

Extrusion Shortening of fiber and operate at high High energy (Duque et al.,
defibrillation solids loadings, low consumption, effect is 2017)
production of limited when no
inhibitory chemical agents are
compounds, short used, mostly effective
time on herbaceous type
biomass
Acid Hemicellulose and lignin Enzymatic High cost of the (Jönsson and
fractionation hydrolysis is reactors, chemicals are Martín, 2016)
sometimes not corrosive and toxic,
required as the acid and formation of
itself may inhibitory by-products
hydrolyses the
biomass to yield
fermentable sugars
Alkaline Lignin and hemicelluloses Cause less sugar Generation of (Zhang et al.,
removal degradation than inhibitors 2016c)
acid pretreatment
Organosolv Lignin removal and Produce low residual High capital (Nitsos and
hemicellulose lignin substrates that investment, Handling Rova, 2017)
fractionation reduce unwanted of harsh organic
adsorption of solvents, formation of
enzymes and allows inhibitors
their recycling and
reuse.
Oxidation Removal of lignin and Lower production of Cellulose is partly (Chandel and da
hemicelluloses by products degraded, High cost Silva, 2013)

Ionic liquid Cellulose crystallinity low vapor pressure Costly, complexity of (Yoo et al.,
reduction and partial designer solvent, synthesis and 2017)
hemicellulose and lignin working under mild purification, toxicity,
removal reaction conditions poor biodegrability
and inhibitory effects
on enzyme activity
Liquid Hot Water Removal of soluble lignin The residual lignin High water (Zhuang et al.,
and Hemicellulose put a negative effect consumption and 2016)
on the subsequent energy input
enzymatic
hydrolysis
AFEX Lignin removal High efficiency and It is much less (Bajpai, 2016)
selectivity for effective for softwood,
reaction with lignin Cost of ammonia and
its environmental
concerns
SPORL Lignin removal Effective against Pretreatment is (Noparat et al.,
hardwood and preceded by biomass 2017)
softwood, and size-reduction
energy efficient

36
Table 3. Major advantages and disadvantages of selected green chemistry pretreatment methods.

Pretreatment Methods Effects Advantage Disadvantage References

Deep eutectic solvents lignin removal Green solvent, Poor Stability (Zhang et al.,
and biodegradable under higher 2016b)
hemicellulose and pretreatment
fractionation biocompatible temperatures,
Steam Explosion lignin low capital It is much less (Pielhop et
softening, investment, effective for al., 2016)
particle size moderate energy softwood
reduction requirements
and low
environmental
impacts
Supercritical fluids Cellulose Green solvent is Total utilities (Daza Serna
crystallinity used, it does not costs are high et al., 2016)
reduction and cause
lignin removal degradation of
sugars, method
is suitable for
mobile biomass
processor
Microbes Lignin and Environment Very long (Sun et al.,
hemicellulose friendly, pretreatment time 2016)
degradation selective (several weeks)
degradation of due to slow yield
lignin and
hemicelluloses

37
38
 Highlights

 Conventional pretreatment methods of lignocellulose suffer significant disadvantages.

 Non-thermal food processing technologies investigated as emerging pretreatments.

 Emerging technologies are promising candidates as sustainable green pretreatments.

 Comparative and feasibility studies are required for the emerging pretreatments.

39