Working of a Modern Biogas Plant

Biogas plants are decentralized energy system that can lead to self-sufficiency in heat and power requirements, and at the same time reduces environmental pollution. A biogas plant stabilizes organic waste through natural biological process in the absence of air and transforms waste into biogas and biofertilizer.

Such facilities are well-suited to wet organic material and are commonly used for treating biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage and animal waste. The components of a modern biogas plant includes manure collection, anaerobic digester, effluent treatment plant, gas storage, and CHP or electricity generating equipment.

Working of a Biogas Plant

The fresh animal manure 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. Currently, biogas is also being used as a fuel in boilers.

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 monitoring system such as Supervisory Control and Data Acquisition (SCADA) system. This remote system facilitates immediate feedback and adjustment, which can result in energy savings.