Anaerobic Digestion
Anaerobic digestion is a process which involves the breakdown of almost all kinds of organic matter by concerted action of a wide range of microorganisms in the absence of oxygen or other strong oxidizing chemicals. It is recognized as one of the most efficient biological processes for the treatment of strong organic wastes such as Palm Oil Mill Effluent (POME).
Anaerobic process is divided into three (3) stages: Hydrolysis, Acidogenesis andMethanogenesis.
Hydrolysis is a process whereby complex organic materials such as protein, carbohydrates and lipids are converted into simpler molecules like amino acids, sugar and fatty acids by the actions of extra-cellular enzymes from hydrolytic microorganisms.
During Acidogenesis, the hydrolyzed products are fermented, forming simpler organic compounds predominantly volatile acid (VA).
VA is converted into methane (CH4) and carbon dioxide (CO2) duringMethanogenesis.
Closed Anaerobic Tank Digestor
“High rate conventional” digester is a closed tank of mild steel construction with integrated gas storage and all safety and functional devices.
Anaerobic Digester Tanks
Biogas Burner c/w Igniter
The contents of the digesters must be well-mixed and complete, thus preventing scum formation, solids settlements and stratification.
The contents and its temperature are homogeneous whereby excellent contact between the substrates and microorganisms can be achieved. The solids retention time is the same as the hydraulic retention time and the effective capacity is normally well-maintained.
The high rate of digestion means it is possible to operate at low hydraulic retention time (about 10 days – HRT) with high organic loadings (up to 4.8 kg volatile solids per cubic metre of digester capacity/day). With closed tank, the characteristic foul odor is minimized as the biogas is not released to the atmosphere.
The initial high capital costs of this digester are offset with the increasing land value. The main advantage is that it requires about 20% of anaerobic pond area.
Biogas Production
Biogas produced is harnessed and utilized in the combined heat and power plants to generate green electricity and heat. It is a clean renewable energy source and has good economic value.
In Malaysia, this source of renewable energy is the largest and easily trapped for immediate use.
The biogas after purification can also be fed into the natural gas grid or used as bio-fuel in vehicles which use natural gas. An additional product of biogas production is fertilizer, which can be used as a substitute for cost intensive mineral fertilizer.
From the point of view of climate protection; the use of biogas reduces CO2 emissions and savings of fossil energy sources.
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