Working of Modern Biogas Plants

An anaerobic digestion plant is a decentralized energy system, which can lead to self-sufficiency in heat and power needs, and at the same time reduces environmental pollution. The components of a modern anaerobic digestion plant include: manure collection system, anaerobic digester, effluent treatment plant, gas holder, and electricity generating equipment.

The fresh organic waste is stored in a collection tank before its processing to the homogenization tank which is equipped with a mixer to facilitate homogenization of the waste stream. The uniformly mixed waste is passed through a macerator to obtain uniform particle size of 5-10 mm and pumped into suitable capacity anaerobic digesters where stabilization of organic waste takes place.

In anaerobic digestion, organic material is converted to biogas by a series of bacteria groups into methane and carbon dioxide. The majority of commercially operating digesters are plug flow and complete-mix reactors operating at mesophilic temperatures. The type of digester used varies with the consistency and solids content of the feedstock, with capital investment factors and with the primary purpose of digestion.

Biogas contain significant amount of hydrogen sulfide (H2S) gas which needs to be stripped off due to its highly corrosive nature. The removal of H2S takes place in a biological desulphurization unit in which a limited quantity of air is added to biogas in the presence of specialized aerobic bacteria which oxidizes H2S into elemental sulfur.

Gas is dried and vented into a CHP unit to a generator to produce electricity and heat. The size of the CHP system depends on the amount of biogas produced daily. The digested substrate is passed through screw presses for dewatering and then subjected to solar drying and conditioning to give high-quality organic fertilizer.

The press water is treated in an effluent treatment plant based on activated sludge process which consists of an aeration tank and a secondary clarifier. The treated wastewater is recycled to meet in-house plant requirements. A chemical laboratory is necessary to continuously monitor important environmental parameters such as BOD, COD, VFA, pH, ammonia, C:N ratio at different locations for efficient and proper functioning of the process.

The continuous monitoring of the biogas plant is achieved by using a remote control system such as Supervisory Control and Data Acquisition (SCADA) system. This remote system facilitates immediate feedback and adjustment, which can result in energy savings.

Salman Zafar

Salman Zafar is the Founder of Cleantech Solutions, and an international consultant, advisor and trainer with expertise in waste management, biomass energy, waste-to-energy, environment protection and resource conservation. His geographical areas of focus include Asia, Africa and the Middle East.
Salman has successfully accomplished a wide range of projects in the areas of biogas technology, biomass energy, waste-to-energy, recycling and waste management.
Salman has participated in numerous national and international conferences all over the world.He is a prolific environmental journalist, and has authored more than 300 articles in reputed journals, magazines and websites. In addition, he is proactively engaged in creating mass awareness on renewable energy, waste management and environmental sustainability through his blogs and portals.
Salman can be reached at salman@bioenergyconsult.com or salman@cleantechloops.com.

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