Our model with water jacket prevents escape of biogas and other obnoxious gas from the plant. Slurry obtained from the biogas plant is composted, does not have any stench and is complete organic manure.
Biogas plant is a unit which converts organic raw materials (living biomass) such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste into useful gaseous fuel. It is a renewable energy source and in many cases exerts a very small carbon footprint. Gaseous fuel consists of methane and a little amount of carbon di oxide which can be used as an alternative fuel for cooking gas (LPG). The byproduct is in a form of slurry which can be used as organic fertilizer.
The major components of the bio-gas plant are a digester tank, an inlet for feeding the kitchen waste, gas holder tank, an outlet for the digested slurry and the gas delivery system for taking out and utilizing the produced gas.
Biogas is generated through an anaerobic digestion process in which multiple kinds of naturally occurring bacteria, in the absence of air, breaks down organic, biodegradable material over time and converts it to biogas and an inorganic fertilizer (slurry).
Biogas is commonly made from animal manure, sludge settled from wastewater, and at landfills containing organic wastes. However, biogas can also be made from almost any feedstock containing organic compounds, both wastes and biomass (energy crops). Carbohydrates, proteins and lipids are all readily converted to biogas. Many wastewaters contain organic compounds that may be converted to biogas including municipal wastewater, food processing wastewater and many industrial wastewaters. However woody materials such as tree branches though organic in nature are not as easily digestible because of their strong fibre content. Hence these should be avoided in biogas plants.
Biogas is in fact a mixture of gases. It typically contains 60-65% methane (the energy source), 30-35% carbon dioxide and traces of other gases making up less than 1-2%.
Biogas contains traces amount (< 1%) of hydrogen sulphide (H 2 S) which has an odour similar to rotten eggs. Under normal operating conditions, this is not an issue given the insignificant quantity of this gas. However, as biogas is an outcome of a biological activity, the smell can become significant if the operating environment under which multiple kinds of bacteria thrive gets disrupted. E.g. If one feeds more quantity of food waste than what the plant is designed for, the pH of the digester will get disturbed which in turn will trigger a host of undesired reactions leading ultimately to higher concentration of H2S.
Biogas production can reduce the pollution potential in wastewater by converting oxygen demanding organic matter that could cause low oxygen levels in surface waters. Nutrients, like nitrogen and phosphorous are conserved in biogas effluents and can be used to displace fertilizers in crop production.
While combustion of biogas, like natural gas, produces carbon dioxide (CO2), a greenhouse gas, the carbon in biogas comes from plant matter that fixed this carbon from atmospheric CO2. Thus, biogas production is carbon-neutral and does not add to greenhouse gas emissions. Further, any consumption of fossil fuels replaced by biogas will lower CO2 emissions.
Biogas units can be divided into 2 major types:- Fixed dome and Floating dome. A fixed-dome plant consists of a digester with a fixed, non-movable gas holder, which sits on top of the digester. Floating-drum plants consist of an underground digester and a moving gas-holder. The gas-holder floats either directly on the fermentation slurry or in a water jacket of its own.
0.2-0.25 m 3 methane / kg dry waste.
Any content in the waste that lowers the pH, that is components that are Acidic in nature like Tamarind, Onion peel, Peels of citrus fruit (orange, lemon), bones etc. cannot be added into the biogas unit.
For one kg waste (per day) , a digester volume of 100 L is recommended. So in case you generate around 10 kg of solid waste per day, then the digester volume should be of 1000L capacity.
Biogas plants are now being preferred as excellent models in waste management for composting kitchen waste due to the fact that it helps in generating cooking gas, which directly reduces the consumption of LPG cylinders. For every 1 kg solid waste, an equivalent of around 0.1 kg of LPG is generated. So for a 0.5 m 3 capacity biogas plant which caters to one kg solid waste (per day), LPG gas for half an hour of cooking is obtained.
The slurry obtained from the biogas unit is an excellent fertilizer. It is always better to use it after diluting upto 2-3 times.