BIOGAS PRODUCTION FROM

SEWAGE

Overview

•Biogas

•Composition of biogas

•Advantages and disadvantages

•Biochemical reaction and stages of anaerobic digestion

•Modes of operation

•Types of anaerobic digesters

•Paper presentation

What is biogas?

Biogas is a methane rich flammable gas that results from the decomposition of organic waste material

Biogas is produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, manure, sewage, municipal waste, green waste, plant material and energy crops.

Biogas also called as ‘Marsh gas’

Biogas is a type of biofuel.

This type of biogas comprises primarily methane and carbon dioxide

Composition of biogas

• Biogas is generated by the activity of anaerobic bacteria

• Composition depends on: the composition of raw material, organic loading to digesters, time and temperature of anaerobic digestion

Composition of biogasSubstances Symbol Percentage

Methane CH4 50 - 70

Carbon Dioxide CO2 30 - 40

Hydrogen H2 5 - 10

Nitrogen N2 1 - 2

Water vapour H2O 0.3

Hydrogen Sulphide H2S Traces

Advantages of biogas

• Production of large amount of methane gas (ambient temperature storage)

• Production of free flowing thick sludge• Odourless sludge• Sludge can be used as fertilizer and soil conditioner• Sanitary way for human and animal waste disposal• Conservation of scarce resources like wood

• Explosion chances• High capital lost• Incorrect handling of liquid sludge causes pollution• Requires control and maintenance• Needs proper condition

• Use as a fuel requires removal of CO2 and H2S

Disadvantages

Factors affecting yield and production of biogas

Many factors affecting the fermentation process of organic substances under anaerobic condition are,

The quantity and nature of organic matter

The temperature

Acidity and alkanity (PH value) of substrate

The flow and dilution of material

GENERAL FEATURES OF BIOGAS

Biochemical reactions

Organic matter

Stages of anaerobic digestion:1.Liquefaction by hydrolytic enzymes

2.Acid formation

3.Methane formation with methanogen production

CH4 + CO2 + H2 + NH3 + H2S

Liquefaction by hydrolytic enzymes

• Complex organic matter is degraded to basic structure by hydraulic bacteria.

Protein - Polypeptide and Amino Acid Fat -Glycerin and Fatty Acid Amylose - Monosacride and Polysacride

Acid Production

• Also called the acidogenesis

• Simple organic matters are converted into acetic acid, H2 and CO2

• Acting bacteria in this process are called hydrogen-producing bacteria and acid-producing bacteria.

Methane Production

• Methanogenesis

• In this process, acetic acid, H2, CO2, are converted into CH4.

• Methane-producing bacteria have strict PH requirement and low adaptability to temperature.

• Methanococcus jannaschii, Methanobacterium thermoautotrophicum

Flow chart of anaerobic digestion

Modes of operation

• Batch

• Semi-continuous – regular feeding of digester and decrease of organic matter at intervals

• Continuous – for liquid waste treatment

Continuous-fed System

• Suited for large-scale manure substrate bioreactor.

• Steady biogas production can be expected.

• May require auxiliary equipments.

• Requires high liquid content.

• Temperature, loading rate, and solid content need to be carefully monitored.

Batch-fed System

• The simplest design.

• Low cost.

• The feedstock is loaded one batch at time.

• Irregular biogas production.

• Can operate on high solid content.

• Requires manual labor.

Types of digesters

A typical biogas system consists of the following components:

• (1) Manure collection • (2) Anaerobic digester • (3) Effluent storage • (4) Gas handling • (5) Gas use.

TWO MAIN TYPES:1. Digesters utilizing dispersed growth of bacteria

2. Digesters utilizing attached growth of bacteria

DISPERSED GROWTH DIGESTERS

1. Fixed dome digester

2. Floating gas holder digester (Indian)

3. Plug flow digester (horizontal displacement)

4. Bag digester (Taiwan and Korea)

5. Separate gas holder digester

6. Conventional digester

Fixed dome digester

Drumless digester. Underground brick

masonry compartment (fermentation chamber) with a dome on the top for gas storage.

The fermentation chamber and gas holder are combined as one unit. Eliminates the use of costlier mild steel gas holder which is

susceptible to corrosion. 20 to 50 years.

Floating gas holder digester

In this design, the digester chamber is made of brick masonry in cement mortar.

A mild steel drum is placed on top of the digester to collect the biogas produced from the digester. Thus, there are two separate structures for gas production and collection.

Jashu Bhai J Patel developed a design of floating drum biogas plant

Popularly known as Gobar Gas plant.

Bag Biodigester• It consists of a long cylinder made of PVC or red mud plastic.

• The bag digester was developed to solve the problems experienced with brick and metal digesters.

Attached growth digesters

1. Anaerobic filter2. Up-flow anaerobic sludge

blanket (UABSR)

Anaerobic filter

The methane forming bacteria form a film on the large surface of the packing medium and are not carried out of the digester with the effluent.

For this reason, these reactors are also known as "fixed film" or "retained film" digesters.

It consists of a column filled with a packing medium.

A great variety of non-biodegradable materials have been used as packing media for anaerobic filter reactors such as stones, plastic, coral, mussel shells, reeds, and bamboo rings.

UASBR

The UASB reactors contain no packing medium, instead, the methane forming bacteria are concentrated in the dense granules of sludge blanket which covers the lower part of the reactor.

The feed liquid enters from the bottom of the reactor and biogas is produced while liquid flows up through the sludge blanket.

Gas Production potential of various types of dung

Types of Dung Gas Production Per Kg Dung

(m3)

Cattle (cows and buffaloes) 0.023 - 0.040

Pig 0.040 - 0.059

Poultry (Chickens) 0.065 - 0.116

Human 0.020 - 0.028

Source: www.fao.org.in

Material and methods

• The Sewage Treatment Plant has capacity to treat 18 mld sewage from main pumping station.

• After primary and secondary treatment, sludge is remain left that is being collected in thickener.

• Around 96X105 liters sludge is being drained from thickener to digester tank at each 12 hrs.

•

• The sludge was taken from thickener and digester tank and Temperature, pH, Total solids %, Volatile solids %, and Alkalinity parameters were analyzed

The present study was done in the months of winter and summer and the sampling were done seasonally from the sewage treatment plant.

Raw sewage consists of organic and inorganic solids in dissolved and suspended form with 90-99.9% of water

Results

Materials and methods

• In this study, experiments were conducted to investigate the production of biogas from municipal solid waste (MSW) and domestic sewage by using anaerobic digestion process.

• The MSW is collected from the Perungudi yard at the Chennai metropolitan city. The yard has an area of approximately 10 km2.

• Domestic sewage is collected from a college campus before disposal to the treatment plant. It is used in all digestion experiments for diluting the feedstock to achieve the required total concentration of TS.

• The domestic sewage is added to MSW, which is in the form of dry and shredded waste. Here both the wastes are mixed so that it forms slurry.

Experimental set up

Results

• The digester was operated at different organic feeding rates of 0.5, 1.0, 2.3, 2.9, 3.5 and 4.3 kg of volatile solids (VS)/m3 of digester slurry per day.

• Biogas generation was enhanced by the addition of domestic sewage to MSW.

• The maximum biogas production of 0.36m3/kg of VS added per day occurred at the optimum organic feeding rate of 2.9 kg of VS/m3/day.

ReferencesHenry, C., 2006." What is an Anaerobic biodigester?”

http://manure.unl.edu/adobe/v7n10_01.pdfhttp://www.fao.org.in (Biogas technology: a training manual

for extension" (FAO/CMS, 1996) http://www.habmigern2003.info/biogas/Baron-digester/

Baron-digester-Dateien/image006.jpghttp://www. en.wikipedia.org/wiki/Biogashttp://www.renewableoil.com/pages/applications.htmlhttp://www.omafra.gov.on.ca/english/engineer/facts/04-

097.htmlPolprasert, C., 1989. Biogas production. In: Organic waste

recycling. John Wiley Sons. Ltd., Great Britain. 105-144