M. Tech Seminar Presentation on

Pretreatment Process for Anaerobic Digestion of Municipal Solid Waste

by

Anil Kumar Jeph(153180018)

Under the guidance ofProf. Munish K. Chandel

Centre for Environmental Science and Engineering

Indian Institute of Technology Bombay5th November, 2015

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Presentation Outline

• Introduction• Objectives• Anaerobic Digestion• Pretreatment Processes • Case Study• Summary

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Introduction

• 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 disposal costs.

• 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.

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Objectives

• To study the role of Anaerobic digestion for Municipal solid waste.

• To study the technologies and processes of anaerobic digestion.

• 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 digestion.

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Anaerobic Digestion• 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 produce biogas.

• In anaerobic degradation process various groups of microorganisms are involved, which generates the two main products – energy-rich biogas and a nutritious digestate.

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Processes Involved in Anaerobic Digestion

• 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 follows:-

• Hydrolysis• Acidogenesis• Acetogenesis• Methanogenesis

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Flow diagram of Anaerobic Digestion Processes

(URL-1)

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Hydrolysis

• 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 this reaction.

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Acidogenesis• In this process products from hydrolysis stage are converted

into acids by microorganisms, called as acid formers.

• 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.

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Acetogenesis

• In Acetognesis breakdown of carbohydrates takes place to convert them into acetates, carbon dioxide and hydrogen.

• This reaction takes only in low concentrations of hydrogen.

• The presence of hydrogen consuming bacteria is critical for this reaction to take place.

• This reaction converts Ethanol, glucose and propionate to acetate.

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Methanogenesis

• 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 of biomass.

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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

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Optimum condition required for Anaerobes Metabolic Activities

(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 concentration

Varies upon substrate

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Pretreatment Processes

• Pretreatment processes are provided in order to reduce hydraulic retention time and amount of sludge produced.

• Pretreatment processes also improved biogas composition.

(Montgomery et al., 2014)

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Pretreatment Processes for MSW

• Mechanical Pretreatment• Thermal Pretreatment• Chemical Pretreatment• Combination of Various Pretreatments

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Mechanical Pretreatment• 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.

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Mechanical Pretreatment

Methods

(A) Screw Press (B) Disc Screen (C) Shredder (Ariunbaatar et al., 2014)

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Mechanical Pretreatment

Methods 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., 2014)

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Thermal Pretreatment• 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.).

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Chemical Pretreatment• 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 methanogens.

• Types of Chemical Pretreatment - 1. Alkali Pretreatment 2. Acid Pretreatment

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Alkali 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.

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Acid pretreatment

• 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 (HMF).

• 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.

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Combination of Various Pretreatments

• 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 1100C.

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Combination of Various Pretreatments (contd.)

• 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.

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Comparison of Pretreatment Methods to Enhance Anaerobic Digestion of MSW

(Montgomery et al., 2014)

Mechanical Pretreatments

Chemical and Thermochemical Pretreatments

Thermal pretreatment

The mechanical pretreatments result in 20–40% increased biogas yield as like to the untreated substrates.

Chemical and thermochemical methods 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% increased biogas production at 120ºC and 150ºC, separately for food waste.

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Case Study

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.

Features- • 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.

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Input Parameters-

• 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 manner digestibility.

Output Parameter-

• 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.

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(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

concentration

(C) Methane content of treated and untreated LMSW at 2.5% substrate

concentration (Yuan et al., 2014)

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Summary• 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 economic feasibility.

• Thermal pretreatment techniques at low (<110ºC) temperatures result in a more cost-effective process performance as compared to other pretreatment techniques.

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REFERENCES• Alvarez, J.M., Mace, S., and Llabres, P. (2000) Anaerobic digestion of organic solid

wastes. Bioresource Technology, 74, 3-16.

• Ariunbaatar, J., Panico, A., Esposito, G., Pirozzi, F., and Lens, P. N. L. (2014) Pretreatment methods to enhance anaerobic digestion of organic solid waste. Applied Energy, 123, 143– 156.

• Arshad, M., Anjum, M., Mahmood, T., and Dawson L.A. (2011) The anaerobic digestion of solid organic waste. Waste Management, 31, 1737–1744.

• Baere, L., and Mattheeuws, B. (2014) Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste in Europe – Status, Experience and Prospects, 517-526. 

• Braber, K., and Novem, B.V. (1995) Anaerobic digestion of municipal solid waste Part 2. A Modern Waste Disposal Option On The Verge of Breakthrough. Biomass and Bioenergy, 9, 365-376. 

• Cantrell, K.B., Ducey, T., Kyoung, S.R., and Hunt, P.G. (2008) Livestock waste to bio-energy generation opportunities. Bioresource Technology, 99, 7941–7953.

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• Jain, S., Jain, S., Wolf, I., Lee, J., and Tong. Y. (2015) A comprehensive review on operating parameters and different pretreatment methodologies for anaerobic digestion of municipal solid waste. Renewable and Sustainable Energy Reviews, 52, 142–154.

• 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 Municipal Solid Waste: A Critical Analysis. International Journal of Innovative Research Science, Engineering and Technology, 3(4), 224-234.

• Shahriari, H., Warith, M., Hamoda, M. and Kennedy, KJ. (2012) Anaerobic digestion of organic fraction of municipal solid waste combining two pretreatment modalities, high temperature microwave and hydrogen peroxide. Waste Manage, 32:41–52.

• Yuan, X., Wen, B., Ma, X., Zhu, W., Wang, X., Chen, S., and Cui, Z. (2014) Enhancing the anaerobic digestion of lignocellulose of municipal solid waste using a microbial pretreatment method. Bioresource Technology, 154, 1–9.

• Zhang, C., Su, H., Baeyens, J., and Tan, T. (2014) Reviewing the anaerobic digestion of food waste for biogas production. Renewable and Sustainable Energy Reviews, 38, 383–392.

• URL1:UnitedTech(2003)<http://www.wtert.eu/default.asp?Menue=13&ShowDok=12 (accessed on 30.10.2015)

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