October 22, 2008 | General

Anaerobic Digestion Solution At Dairy Complex (India)

BioCycle October 2008, Vol. 49, No. 10, p. 53
Anaerobic digester installation processes 235 tons/day of animal waste for generation of 1 MW of electricity and high quality fertilizer.
Salman Zafar

ESTABLISHMENT of anaerobic digestion systems for livestock manure stabilization and energy production has accelerated substantially in the past several years. In India, the biogas facility at Haebowal Dairy Complex in Ludhiana utilizes animal manure for generation of 1 MW electricity and production of high quality organic fertilizer. It has been operating for five years.
This project was set up as a demonstration project with UNDP/GEF (United Nations Development Program/Global Environmental Facility) assistance under the direct supervision of the Ministry of New and Renewable Energy, Government of India. There are more than 500 dairies in Haebowal Dairy Complex, producing more than 2,500 tons/day of animal manure. The capacity of the plant is 235 tons/day of animal waste, which produces approximately 9,000 m3 of biogas and 37 tons of organic fertilizer on a daily basis.
System components include manure collection, anaerobic digester, effluent treatment, gas storage, and gas use/electricity generating equipment. The layout of the biogas facility using livestock manure as raw material is shown in Figure 1.
Digester Operations
Fresh manure is stored in a collection tank before going to a homogenization tank where it is passed through a macerator to obtain uniform particle size of 5 to 10 mm. The Haebowal Dairy Complex has two digesters, each 5,000 m3. Material from the homogenization tank is pumped into the digesters. The plant uses an emerging concept of anaerobic digestion called Biogas Induced Mixing Arrangement (BIMA) patented by Entec in Austria. The two-chamber system uses the gas being produced to build a level difference between the two chambers – yielding a mixing pressure of up to 500 mbar. Depending on the gas production, the digester is turbulently mixed 4 to 10 times a day by releasing this pressure. The main advantages of BIMA digesters are its mixing system without mechanical moving parts, and the ability to control scum/sediments and handle high solids concentration.
Removal of H2S takes place in a biological desulphurization unit. A limited quantity of air is added to the biogas in the presence of specialized aerobic bacteria, like Thiotrix or Thiobacillus, which oxidizes H2S into elemental sulfur.
Biogas coming out of the desulphurization unit is stored in a gas holder made of polyester. A concrete silo is used to contain the polyester bag (insulation would be required if the gas holder were made of stainless steel). The gas holder buffers the difference between gas production and gas consumption. Its capacity is based on daily gas consumption and production rates.
Biogas And Digestate Utilization
Gas is dried and vented into a generator with combined heat and power (CHP) to produce electricity and heat. Heat transfer is required in the plant to raise the temperature of the feed to the mesophilic or thermophilic range, to compensate for heat losses through walls, floors and roof and to make up the losses that might occur in the piping network.
The digested slurry leaving the reactor is dewatered in a series of screw presses to remove moisture. Solar drying is employed to enhance the market value of the fertilizer by increasing the solids concentration to around 70 percent.
The concentration of BOD and COD in the press water is too high to be disposed of directly. It passes through an effluent treatment plant to meet the regulatory discharge limits. The plant consists of an aeration tank and a secondary clarifier. The effluent from the secondary clarifier can be utilized to meet the plant water requirements and/or discharged into the drain. A portion of the sludge is recycled to the aeration tank to maintain the required biomass concentration; remaining sludge is sent to the drying yard.
Continuous monitoring of the biogas plant is achieved by using a remote control system known as Supervisory Control and Data Acquisition (SCADA). This system facilitates immediate feedback and adjustment, resulting in energy savings. Numerous sensor signals and all important engines, valves, armatures etc. are connected to the controller. SCADA systems have a modern fault message system (i.e. a message is sent to the operator in case of malfunctioning). The remote terminal unit also makes it possible to control the plant from a distance via wired or wireless telecommunication networks.
Contributing To Sustainable Development
The Haebowal Dairy Complex biogas facility is addressing many issues related to global warming by reducing greenhouse gas emission by captive utilization of methane for power generation. Moreover, soil and water pollution due to the seepage of leachate into the soil and water bodies is minimized to a great extent. The project is also advantageous in replacing power generation from limited reserves of polluting conventional energy resources. In addition, the production of organic manure aids in replacing chemical fertilizers and hence makes a positive contribution to the environment and public health. The project also provides employment to many people who supply the fresh manure to the plant in carts and trolleys.
Salman Zafar is an independent renewable energy advisor. His areas of expertise include biomass utilization, biogas production, waste-to-energy conversion and sustainable development. He can be reached at salman.alg@gmail.com.

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