Methodology

Methods and Techniques Used

This study used a mixed method approach. According to creswell and plano clark (2011), a
mixed methods research design is a procedure for collecting, analyzing, and “mixing” both
quantitative and qualitative research and methods in a single study to understand a research
problem. And, since this study aims to identify and examine how biogas coming from organic
waste will be an alternative solution to the high price of fuel gas, it is best to use an explanatory
research method to integrates all of the findings for a broader and deeper understanding about
biogas. That’s why Explanatory Sequential Design was choose, so we can start with collecting
first the data and analyzing it through descriptive context. From this we will know how it works
the biogas turns into renewable energy as fuel and what chemical reaction and composition of
biogas to become an alternative fuel.

Population and Sample of the Study

The researchers use probability sampling specifically, Stratified sampling. According to Hayes
(2020), stratified random sampling involves the random selection of data from an entire
population, so each possible sample is equally likely to occur. The plant considered in this study
is located in Nord Trøndelag County in central Norway. It’s actual “waste-zone” covers an area
of 98200 km2, with a population of 230000 inhabitants. Three organic substrates are treated in
the plant: organic household waste, sludge from waste water and a minor part of ensilage waste
from fish farms.
The plant has a total capacity of 30000 to 45000 tons of organic waste. Due to high demand on
waste flexibility, the original plan was based on 50 % of BDMSW and 50 % Waste Water
Sludge(WWS). In addition, the plant was prepared to treat additional ABP category 2 waste
(Category 2 ABP material includes high risk material), as well as Biological Degradable
Industrial Solid Waste (BDISW).
Based on the research study of Banks et.al. it monitored the bio-cycle anaerobic digester in South
Shropshire, UK over a period of 14 months just to create biogas to fuel.

Instrument of the Study

Data Gathering Procedure

The researchers submitted a letter-request to get a sample of organic waste that located to Nord
Trøndelag County in central Norway a “waste-zone” area. Also letter of approval in in South
Shropshire, UK to conduct a study, and perform the bio-cycle anaerobic digester. After the
permit was approved, the researchers start the ideal percentage of organic waste which is 50 % of
BDMSW and 50 % Waste Water Sludge(WWS). To gather the data needed, first perform
Anaerobic Digestion and a Conversion of Biogas to Fuel.
Anaerobic digestion, which is also known as biomethanation, or methane fermentation can be
divided into four stages:
Hydrolysis or fermentation: where complex organic molecules (cellulose, proteins and fats) are
broken down into simple sugars, amino acids, and fatty acids by hydrolase, an exoenzyme.
Hydrolysis of carbohydrates takes place within a few hours while proteins and lipids take a few
days to break down.

What can be noted from the reaction in Equation:

Is the hydrolysis of cellulose (C6H10O5) via addition of water (H2O) to form glucose
(C6H12O6) as the primary product and giving off H2.

Acidogenesisor formation of organic acids: This is the fermentation stage, where soluble
compounds formed in the hydrolysis stage are degraded and converted into CO2 and H2 through
the bacteria known as acidogenic bacteria (fermentative microorganisms); the important acid in
this stage is the CH3COOH, and it is the most significant organic acid used as a substrate by
CH4- forming microorganisms. Whereas, the production of volatile fatty acids (VFAs) is
increased when process pH is > 5, the production of ethanol (C2H5OH) is characterized by lower
pH < 5 with reaction process coming to a halt at a pH < 4. Equations: presents the reaction
sequence that summarizes the acidogenic stage of AD.

Acetogenesis: The waste product of acetogenesis is the H2 gas formed in the acidogenic stage of
the AD process hence this stage is also known as the dehydrogenation stage. This is true because
the metabolism of acetogenic bacteria is inhibited by the H2 gas produced. However, the H2 gas
can be consumed by CH4-producing bacteria to function as hydrogen-scavenging bacteria that
can convert some of the bacteria to CH4.
The reaction series associated with this stage of AD are represented by
Equations:

the reactions are two-way reactions showing the release of H2. The first Equation, indicates that
acid phase products are converted to acetate (CH3COO−) and hydrogen (H2), which may be
used by methanogenic bacteria in the next stage of the AD process; bacteria such as
Methanobacterium suboxydans and Methanobacterium propionicum actually account for the
decomposition of the acid phase products into acetate (CH3COO−) and, the H2 released in the
reaction exhibits toxic effects on the microorganisms that carry out the process of acetogenesis
[43,44]. This makes a symbiosis necessary for the acetogenic and methanogenic bacteria to use
the H2 released in the process. The acetogenesis stage of AD is equally vital because it reflects
the efficiency of biogas production since approximately 70% of CH4 is formed through
reduction of CH3COO−, which is the key intermediary product of the digestion process;
approximately 25% of CH3COO− and about 11% of H2 are formed in the acetogenesis stage of
AD [43]. However, it is vital to clearly state that the VFAs produced in the previous stage are
further broken down in this stage by obligate hydrogen-producing acetogenic microorganisms
for the production of CH3COOH, CO2 and H2. This is because some amount of H2O from the
previous stages is still available and acts as an electron source to facilitate the conversion of the
VFAs.

Methanogenesis: In this final stage of the AD process, bacteria convert CH3COOH and H2 into
CO2 and CH4; the bacteria responsible for this conversion are called methanogens and they are
strictly anaerobes that are highly vulnerable to small amounts of oxygen. The methanogens are
very important to AD processes because they grow slowly and are extremely sensitive to changes
in environment. They can absorb and digest the simplest of substrates. Some of the notable
species of the methanogens are Methanobrevibacter ruminantium, M. bryantic and M.
thermoautotrophicum, Methanogenium cariaci and M. marinsnigri, etc. Since the stages which
precede the methanogenic stage merely convert organic matter from one form to another, organic
pollution load in terms of chemical oxygen demand (COD) or biochemical oxygen demand
(BOD) is reduced considerably by the anaerobic process in the methanogenic stage hence
efficient methanogenesis is usually construed to mean efficient elimination of carbonaceous
pollution. The reaction equation representing the condition taking place in the methanogenic
stage of AD processes is represented by the following:
The first Equation, shows the conversion of CH3COOH into CH4 and CO2. The CO2 formed is
reduced to CH4 through H2 gas in the second Equation and, lastly Equation, shows the
production of CH4 by decarboxylation of CH3CH2OH. Methane-producing bacteria can be
divided into two groups namely acetophilic and hydrogenophilic; the former depicts CH4
production by decarboxylation of acetate while the latter reflects CH4 production by reduction of
H2/CO2 [40,48,49]. There are six major pathways in the methanogenesis stage. Each pathway
converts a different substrate into CH4 gas and, the major substrates used in this stage are acetic
acid (CH3COOH), methanoic acid (HCOOH), carbon dioxide (CO2), dimethyl sulfate
((CH3)2SO4)), methanol (CH3OH), and methylamine (CH3NH2).

Biogas to Fuel
As Biogas created this is the time it will convert into Fuel
Chemical and biological pathways can be used to convert cleaned biogas (primarily
containing CH 4 and CO 2) into methanol, ethanol, diesel, liquefied petroleum gas (LPG) and
gasoline. For methanol production, partial oxidation of methane (Eq. 1) is a method that
has been developed and widely used since first reported in 1923. This chemical conversion
process is usually carried out at high pressures of 0.5–15 MPa.
CH4+0.5O 2→CH3OH ∆H0= -128 kJ/mol (Eq. 1)
Biological conversion of methane to methanol, in which methanotrophic bacteria are often
employed for methanol production, is currently at the research stage. Methanotrophic
bacteria contain a special enzyme, named methane monooxygenase (MMO), which enables
them to use methane as their only carbon source for metabolism under ambient conditions.

Methanol can also be produced after reforming methane to syngas followed by catalytically
converting syngas to methanol as shown in Eqs. 2 and 3.

2H2+CO→CH3OH ∆H0= -91 kJ/mol (Eq. 2)

0
3H2+CO2→CH3OH+H2O ∆H = -49 kJ/mol (Eq. 3)

Produced methanol can be further converted to gasoline via an MTG (methanol-to-

gasoline) process.
Syngas, which is an important starting material for creating other fuels, can be generated
from biogas/biomethane via three main reforming processes. Dry reforming and steam
reforming can use cleaned biogas to produce syngas (Eqs. 4–6), while POR oxidizes
methane to syngas (Eq. 7). Dry reforming and steam reforming are highly endothermic
reactions and typically take place at 700–900°C. Steam reforming is often followed by a
water shift reaction to enhance H 2 production (Eq. 6). POR is an exothermic reaction;
therefore, it can be combined with either dry reforming or stream reforming to reduce
energy inputs (Eq. 7). The combination of steam reforming and POR is recognized as
autothermal reforming (ATR).
Besides being converted to methanol, syngas can be used for the production of a variety of
other products (e.g., LPG, diesel, jet fuels) via the Fischer-Tropsch (FT) process (Eqs. 8–
9). Syngas can also be converted to ethanol via chemical methods such as the FT process,
while related biological methods are currently being researched, with extensive interest in
genetically engineered microorganisms.

Dry reforming:
CH4+CO2→2CO+2H 2 ∆H0= 247 kJ/mol (Eq. 4)

Steam reforming and water shift reaction:

CH4+H2O→CO+3H2 ∆H0= 206 kJ/mol (Eq. 5)
CO+H2O→CO2+H2 ∆H0= -41 kJ/mol (Eq. 6)

Partial oxidative reforming (POR):

CH4+0.5O 2→CO+2H2 ∆H0= -25.2 kJ/mol (Eq. 7)

Fischer-Tropsch:
(2n+1)H 2+nCO→CnH 2n+2+nH2O (Eq. 8)
2nH2+nCO→C nH2n+nH2O (Eq. 9)