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 Bio Gas plant  from Kitchen waste

Literature Study : Bio Gas from Kitchen waste

The Principle: Biomass in any form is ideal for the Biomethanation concept, which is the central idea of the Biogas plants. Based on thermophilic microorganisms and microbial processes develop the design of the biogas plant. The plant is completely gravity based. 

Brief process description: The segregated wet garbage (food waste) is brought to the plant site in bins and containers. It is loaded on a sorting platform and residual plastic, metal; glass and other non-biodegradable items are further segregated. The waste is loaded into a Waste Crusher along with water, which is mounted on the platform. The food waste slurry mixed with hot water is directly charged into the Primary digester.
This digester serves mainly as hydrolysis cum acidification tank for the treatment of suspended solids. For breaking slag compressed air is used for agitation of slurry. Compressed air will also help in increasing aeration since bacteria involved in this tank are aerobic in nature. The tank is designed in such a way that after the system reaches equilibrium in initial 4-5 days, the fresh slurry entering the tank will displace equal amount of digested matter from top into the main digester tank.
Main digester tank serves as a methane fermentation tank and BOD reduction takes place here. The treated overflow from this digester is connected to the manure pits. This manure can be supplied to farmers at the rate of 4-5 Rs. per Kg. Alternatively municipal gardens and local gardens can be assured of regular manure from this biogas plant.
The biogas is collected in a dome (Gas holder) is a drum like structure, fabricated either of mild steel sheets or fibreglass reinforced plastic (FRP). It fits like a cap on the mouth of digester where it is submerged in the water and rests in the ledge, constructed inside the digester for this purpose. The drum collects gas, which is produced from the slurry inside the digester as it gets decomposed and rises upward, being lighter than air. 1" GI piping will be provided up to a distance of 50 m from the Biogas plant. Biogas burners will be provided. The biogas can be used for cooking, heating and power generation purpose.

Cost details, saving and payback period from a biogas plant: The cost details and the savings envisaged from the plant are given in the following table. The life of the plant could be 20-30 years and payback period is 4-5 years.

Capacity (Tons / Day) Installation Cost (Rs In Lacks) Monthly Operation and Maintenance Charges (Rs) Methane Generation M3 Manure production (tons /day) Area Required M2 Power Manpower Fresh Water (KL /day) Hot water (Ltr / day of 50-60 C0) Cooking Fuel (Equivalent to LPG Cyl / day)
1 8-10 8,000/- 100-120 0.1 300 5hp(2hr) 2 2 200 2-3
2 10-12 12,000/- 200-240 0.2 500 5hp(3hr) 3 3 400 4-5
4 20-22 22,000/- 400-480 0.3 700 5hp(3hr) 4 5 400 8-10
5 28-30 30,000/- 500-600 0.5 800 10hp (4hr) 5 7 600 12-14 (25Kw)
10 65-70 50,000/- 1000-1200 2.5 1200 15hp (4hr) 10 15 1000 22-25 (50Kw)
* This is an approximate cost for biogas generation plant and may increase by 10%–20%, depending on location, site-specific parameters, cost of materials, labour cost, etc., in different states/cities. Cost of additional infrastructure like office space, toilets, security, Godown, Shades and power generation will be extra, if required.
Rs – rupees; m3 – cubic meters; m2 – square meters; h – hour; kL – kilolitre; LPG – liquefied petroleum gas; kW – kilowatt; cyl – cylinder
Suitable locations for installation of plant Hotel premises, army/big establishment canteens (private/ government), residential schools/colleges, housing colonies, religious places / temple trusts, hospitals, hotels, sewage treatment plants, villages, etc.


Bio Gas Generation from Dairy waste :
Ms Bhole Baba Milk food Industries Ltd. is coming up with a new plant at khair road, Aligarh
The Dairy will handle about 10-lac litre of milk every day. Depending on the season, major differences occur in the quantities of milk received from cooperative milk federation and in the use of butter, butter oil and milk powder. The value added products manufactured will be Casein,Milk Protien Concentrate,Lactose-Both Food &Pherma,Demineralised Whey Protien,Whole Milk Powder,Skimmed Milk Powder, & White Butter In Bricks Form, with future planning to produce processed Cheese/Mozerella.


The values of incoming wastewater at ETP is as under:

S.No. Parameter Unit Value
pH 6.0 – 10.5
Total Suspended Solids Mg/l 1500.0 – 2000.0
B.O.D. Mg/l 1500.0 – 1800.0
C.O.D. Mg/l 2500.0 – 3500.0
Oil & Grease Mg/l 150.0 – 250.0
Rated capacity of ETP KL/Day 1,000.0
Feeding of Effluent to USAB Reactor: Anaerobic digestion takes place here. Methane gas is generated because of anaerobic degradation. The top supernatant from the USAB reactor flows by gravity to the aeration tanks inlet. Three reactors are planned. When one reactor is out of operation, calamity flow is the designed flow. One distribution box will distribute the flow into the three reactors.

  1. Bio-gas collection & utilization or Flaring: The gas produced in the UASB reactors is led to the gas holder through a moisture trap and gas flow meter.The outlet of the gas holder is to be branched off in two directions, one going to the generator room for supply to the engines and the other to the gas flaring equipments. The primary purpose of a gas holder is to adjust the difference in the rate of gas production and consumption.The gas engines demand a constant supply of bio gas at a constant pressure. The bio gas holder is designed for a storage of 4 hours of bio gas production normally at a pressure of 40m bar. As bio gas enters or leaves, the holder rises or falls with the help of guide rails. Valves in the gas lines will be operated manually to maintain the gas dome at 90%(Gas flaring level), 80%(Engine level) and 20% (Low levels, where engine as well as flaring will be stopped and the dome will be allowed to rise.).
The gas flowing upward with the liquid will be prevented from escaping with the treated flow by GLSS and beam deflector, which will divert it to the gas collector domes. The gas produced shall be passed through 100 mm dia FRP pipe for individual domes and collected at a common point for each reactor by a common header of 200 mm dia pipe from where it will conveyed to the gas holder for constant flow to the gasomete generator or flaring in open atmosphere at about 6 meter above ground level.

Quantity of Gas Production:

BOD 1700 ppm 340 ppm 80%
COD 3300 ppm 1320 ppm 60%
TSS 1800 ppm 450 ppm 75%

FLOW IN UASB = 1500 KLD (Taking full future capacity into account)
Influent COD@ 3300 ppm = 4950 Kg
Effluent COD = 1980 Kg
COD removed in a day = 2970 kg
Bio gas produced @ 0.1 cu mtr per kg of COD removed = 297 cu mtr per day.
Capacity of gas holder: The primary purpose of a gas holder is to adjust the difference in the rate of gas production and consumption. As bio gas enters or leaves, the holder rises or falls by guide rails.
Provide a gas holder of 300 cu mtr capacity.
The bio gas produced in UASB process should be utilized for production of electric power. The amount of electric power generated shall be as under:
Bio Gas production = 297 cu mtr /day
Methane content (65.75%) = 195.28 cu mtr
Calorific value =28.9 MJ/N.cu mtr
Energy content 195.28x28.9x273/(273+30)=5048 MJ/Day
Generator efficiency--- 30%
Electricity generated =0.3x5048x1000000/3600x1000
= 420.66
Electric power generated = 420.66x0.04167=17.5289 kw say17 kw
= 1.25x 17= 21.25 kva.
We can go for a gas engine of capacity 10 KW . If any gas is left , it will be flared or supplied to staff quarters.

NOTE FOR COMPARISION : A 56 mld UASB plant having Inlet COD =400 ppm can safely run a 45 KW gas engine.


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