Anaerobic Digester for Biogas Production

A process, which involves breakdown of organic sludge in an airtight reactor under anaerobic condition, is known as anaerobic digestion. It is widely used and practiced in wastewater treatment plant because the byproduct in the form of methane can be used as good energy source for heating and electricity generation. The whole system involves collected sludge being continuously introduced and is left in the reactor for a specific period of time in order for the process to take place. In fact, the long retention period is one of the primary disadvantages associated with using the system compared to other aerobic biological unit processes such diffused aeration and RBC system.

There are basically two different types of anaerobic digesters, one is a standard-rate and another is a high-rate. In a standard-rate digester, the sludge breakdown process is usually left on its own to take place without using heat or mixer and the retention period can be anywhere between 30 to 60 days. For high-rate digester, the slurry is well mixed and then heated up and the whole process will require less than 15 days. Today, advancement in technologies for wastewater treatment plants manipulate both processes combined together to form a single two-stage process for better conversion.

In a typical anaerobic digester, there is usually presence of three different groups of bacteria working cooperatively to breakdown the sludge compound. The first group of bacteria is responsible to hydrolyze large compounds such as protein and fats to basic smaller molecules like amino acids and fatty acids. A second group known as the fermenter, further breaks down the smaller molecules under anaerobic condition mainly into acetic acid and lastly, the final group of bacteria will utilize these acetic acids to form methane and carbon dioxide. In an efficient organic waste anaerobic digester system, all these bacteria must exist in a state of dynamic equilibrium.

To get a wider picture and understand the whole working principle, refer to anaerobic reactor suspended growth system for detailed explanation about the whole process. Also, you might want to read up on odor generation problem resulting from waste breakdown, the effects and how to control it.

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