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M. Tech Seminar Presentation
Pretreatment Process for
Anaerobic Digestion of
Municipal Solid Waste
Anil Kumar Jeph
Under the guidance of
Prof. Munish K. Chandel
Centre for Environmental Science and
Indian Institute of Technology Bombay
5th November, 2015
• Anaerobic Digestion
• Pretreatment Processes
• Case Study
• Anaerobic digestion process is one of the suitable
method for its limited environmental impacts and
high potential for energy recovery.
• Anaerobic digestion process transforms organic
wastes into valuable resources with also reducing
the solid waste volumes and reducing waste
• To enhance biogas production, achieve faster
degradation rates and reduce the amount of final
residue to be disposed, there is need to enhance the
AD process performance by Pretreatment methods.
• To study the role of Anaerobic digestion for Municipal solid
• To study the technologies and processes of anaerobic
• To study the effects of various pretreatment process on
anaerobic digestion of municipal solid waste.
• To study the methods of pretreatment process for anaerobic
digestion and outputs of pretreatments for anaerobic
• Anaerobic digestion can be defined as breakdown of complex
organic matter into methane (CH4), carbon dioxide (CO2) and
compost by the help of some set of microorganisms in the
absence of oxygen.
• The AD process can applied to process organic
biodegradable matter in airproof reactor tanks (Digesters) for
• In anaerobic degradation process various groups of
microorganisms are involved, which generates the two main
products – energy-rich biogas and a nutritious digestate.
Processes Involved in Anaerobic
• In the process of anaerobic digestion feedstock is
collected, shredded coarsely and placed into anaerobic
digester with active inoculums of microorganism.
Processes involved in the anaerobic digestion are as
• Hydrolysis is enzymatic catalysed reaction process
which breakdowns the complex organic matter into
simpler soluble organic substances.
• Enzymes such as hydrolyses or lyses secreted by
hydrolytic and fermentative bacteria act as catalyst for
• In this process products from hydrolysis stage are
converted into acids by microorganisms, called as acid
• Products of this process are acetic acid, propionic acid,
butyric acid as well as alcohols, aldehydes, carbon
dioxide and hydrogen.
• Bacteria in this stage are typical Anaerobic bacteria.
• In Acidogenesis, hydrolysis products are converted into
ethanol, propionic acid, butyric acid; most of them are
volatile in nature.
• In Acetognesis breakdown of carbohydrates takes place
to convert them into acetates, carbon dioxide and
• This reaction takes only in low concentrations of
• The presence of hydrogen consuming bacteria is critical
for this reaction to take place.
• This reaction converts Ethanol, glucose and propionate
• Methanogenesis is the conversion of soluble organic
matter into methane and carbon dioxide with the help of
microorganisms called as methanogens.
• Methanogenesis is the final step in the decomposition
Parameters Affecting the Anaerobic
Digestion of Food Waste
• pH value
• Composition of organic waste
• Organic loading rates
• Hydraulic retention time
• Operating temperature
• Carbon-Nitrogen ratio
• Volatile fatty acids
Optimum condition required for Anaerobes
(Kondusamy and Kalamdhad, 2014)
Parameters Optimum condition
Temperature Mesophilic range (35ºC–40ºC)
Thermophilic range (50ºC–65ºC)
pH 6.5 -7.8
Carbon-nitrogen ratio 25-30:1
Volatile fatty acids 2000-3000 mg/l
Organic loading and inoculum
Varies upon substrate
• Pretreatment processes are provided in order to reduce
hydraulic retention time and amount of sludge produced.
• Pretreatment processes also improved biogas
(Montgomery et al., 2014)
Pretreatment Processes for MSW
• Mechanical Pretreatment
• Thermal Pretreatment
• Chemical Pretreatment
• Combination of Various Pretreatments
• Mechanical Pretreatment reducing the particle size of
substrate so as to increase the specific surface area.
• Increased surface area results in more contact
opportunities between microbes and substrate, so the
methane production increases and also reduces the
hydraulic retention time for anaerobic digestion.
• The advantages of Mechanical Pretreatment are odour
control, easy to implement, low energy consumption, and
better dewater ability.
Schematic diagram of a
hammer mill, biomass is
fed in above and
hammers rotate and
grind the substrate and
ground particles fall out
at the bottom
(Montgomery et al.,
• Thermal Pretreatment causes breakdown of cell
membrane which results in solubilization of organic
matter so it enhances the rate of hydrolysis process.
• Thermal pretreatment by microwave was found more
effective than steam and electric heating, because
microwave heating resulted in polarization of
macromolecules, which results in solubilization of more
biopolymers (proteins, lipids etc.).
• Chemical Pretreatment is provided to disintegrate
organic matter by strong acids, alkali, oxidants.
• Chemical Pretreatments are not suitable for substrate
with high biodegradability, because accelerated
degradation of carbohydrate results in accumulation of
volatile acids, which adversely affects the population of
• Types of Chemical Pretreatment -
1. Alkali Pretreatment
2. Acid Pretreatment
• In the Alkali Pretreatment Salvation and saphonication
reactions are take place, which utilizes an alkali to cleave an
ester into a carboxylic acid and alcohol.
• These reactions cause swelling of substrate which results in
increased specific surface area.
• As surface area is increased substrate becomes more
accessible to microbes.
• Chemical oxygen demands solubilization is enhanced through
various simultaneous reactions like saponification of uronic
acids and acetyl esters, as well as neutralization of various
acids formed by the degradation of the particulates.
• Acid pretreatment is more favourable for lignocellulosic
substrates due to it breaks down the lignin and hydrolytic
bacteria are capable of adapting into acidic conditions.
• Strong acidic pretreatment may cause production of
inhibitory by-products like furfural and hydroxymethylfurfural
• Some of the disadvantages in using acid pretreatment are
loss of fermentable sugar because of increased destruction
of complex substrate, high cost of acids, additional cost
incurred in stabilizing those acids with alkali.
Combination of Various
• Pretreatment techniques in combination studied to get a
further enhancement or up gradation of biogas production as
well as faster AD process kinetics.
• Thermo-chemical pretreatment - Shahriari et al. (2012)
investigated that the combination of microwaves with
chemical pretreatments and additionally the microwave
irradiation at temperatures higher than 145ºC output in a
larger segment of refractory material per g COD, causing
reduction of the biogas production.
• Thermo-mechanical pretreatment - Zhang et al. (2014)
obtained the highest enhancement of biogas production
(17%) by grinding (up to 10 mm) rice straw and heating it to
Combination of Various
• Alkaline pretreatment combined with thermal methods at
a lower temperature (70ºC) could bring about a higher
(78%) biogas production with a higher (60%) methane
content when contrasted with the best results (28%
expansion of biogas production with 50% methane
content) acquired by thermal pretreatment at higher
temperatures (>100ºC) because of the reduction of the
hemi cellulosic fraction.
• The combined pretreatment examined in increased
biogas production at consistent state, and the
dewatering characteristics of the sludge were
additionally enhanced, also disposal cost was reduced.
Comparison of Pretreatment Methods to
Enhance Anaerobic Digestion of MSW
(Montgomery et al., 2014)
pretreatments result in
biogas yield as like to the
could yield up to 11.5–
48% higher biogas yield.
In Thermal pretreatment,
Low temperature (70ºC)
of pretreatment can
result 2.69% higher
biogas and high
temperature results in
24% and 11.7%
production at 120ºC and
150ºC, separately for
Enhancing the Anaerobic Digestion of Lignocellulose of
Municipal Solid Waste using a Microbial Pretreatment Method
(Yuan et al., 2014)
Primary goal- To develop and demonstrate a novel microbial
pretreatment method to enhance biogas and methane production
yields for the effective anaerobic digestion of LMSW.
• LMSW was acquired by mixing waste office paper, newspaper, and
cardboard. Mass-mixing ratio of office paper, newspaper, and
cardboard was 1:1:1.
• The lignin, cellulose, and hemicellulose substance of this waste
were 14.2%, 70.1%, and 12.0%, separately and final LMSW
concentrations were 0.5%, 1.0%, 2.5% and 55.0% respectively.
• Prepared to do adequately corrupting different cellulosic
materials under aerobic static conditions.
• Pretreatment with the microbial consortium to expand
cellulose and hemicellulose accessibility and in this
• Pretreatment with the microbial consortium proved to be
effective in enhancing biodegradability and upgrading
methane production from LMSW.
• Methane production rate was faster in the treated LMSW
than in the untreated LMSW. 27
(A)Biogas yield of treated and
untreated LMSW at 2.5% and
5.0% substrate concentrations
(B) Methane yield of treated and
untreated LMSW at 2.5% substrate
(C) Methane content of treated
and untreated LMSW at 2.5%
(Yuan et al., 2014)
• Anaerobic Digestion is very suitable because of its limited environmental
impacts and high potential for energy recovery.
• To enhance biogas production, achieve faster degradation rates and
reduce the amount of final residue to be disposed, there is need to
enhance the AD process performance by pretreatment methods.
• Among the extensively reported pretreatment technologies, only limited
Mechanical, Thermal and Thermo-chemical methods were effectively
applied at the full scale to offer advantages to AD process.
• Pretreatment technologies offer advantages Such as Higher biogas yield,
Decisive effect on pathogen removal, Reduction of Digestate amount,
Reduction of the Retention time, Better energy balance and Better
• Thermal pretreatment techniques at low (<110ºC) temperatures result in
a more cost-effective process performance as compared to other
• Alvarez, J.M., Mace, S., and Llabres, P. (2000) Anaerobic digestion of organic
solid wastes. Bioresource Technology, 74, 3-16.
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Pretreatment methods to enhance anaerobic digestion of organic solid waste.
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Fraction of Municipal Solid Waste in Europe – Status, Experience and
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• Kondusamy, D., and Kalamdhad, A. S. (2014) Pretreatment and anaerobic
digestion of food waste for high rate methane production. Journal of
Environmental Chemical Engineering, 2(3), 1821–1830.
• Nalo, T., Tasing, K., Kumar, S., and Bharti, A. (2014) Anaerobic Digestion of
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pretreatment modalities, high temperature microwave and hydrogen peroxide.
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• Yuan, X., Wen, B., Ma, X., Zhu, W., Wang, X., Chen, S., and Cui, Z. (2014)
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