by Dr. Amandeep Singh
What we consider waste is ‘not actually a waste’. Rural households better understand the use of this waste for fertilizing their vegetables and crops but they are still unaware about most of the more potent and profitable uses of the waste. Whole world is suffering from the menace of global warming and we cannot neglect the contribution of greenhouse gases into it. The methane emission from the livestock industry along with agriculture is the second largest contributor to the greenhouse gases in the world. So, there is need to look for effective waste management protocols, so that the emissions can be reduced and we can reduce greenhouse emissions. Using livestock waste for energy generation can be a novel idea as it serves twin benefits, one reducing the greenhouse emissions from the waste and the second, a source of clean and green energy for the world.
Although all the livestock waste can be managed for one or the other purpose but in this blog we will be discussing about the generation of electricity from poultry litter. Poultry industry is almost well developed in every nook and corner of the world due to meager initial investment. Therefore, due to increase in the number of poultry farms, the amount of waste being generated is also on the rise. This waste can be harnessed for making biogas and then converting the gas into electricity.
A single chicken before slaughter produces about 2kg manure in its lifetime. Manure and droppings are the tremendous source of organic matter and a valuable feedstock for biogas production. Poultry waste is composed of manure/dropping (organic matter), blood & feather (proteins), offal (lipids) and head & feet (proteins & lipids). Manure contains 35%, 24% and 18% dry matter, protein and lipids, respectively. Biogas (methane) is produced from organic matter through anaerobic decomposition and this process is called methanogenesis. In slaughterhouse too, about 20% of a poultry bird of total weight converted into waste in the slaughtering process. The slaughtering waste is composed of organic matter and a valuable feed-stock for biogas production.
Biogas production from poultry waste
The poultry waste is organic in nature and is composed of biodegradable matter like carbohydrates, proteins and lipids. The organic matter is degraded into glucose, amino acid and fatty acid through a hydrolysis process. Overall, the biogas production process occurred in four phases, i.e., hydrolysis, acidogenesis, acetogenesis and methanogenesis. The acidogenic bacteria are able to produce biogas by converting the degradation products (in hydrolysis process) into H2, CO2, acetates and volatile fatty acids. The volatile fatty acids are decomposed into acetate and H2. Finally, by the help of methanogenic bacteria, methane is produced. This whole process is carried on in a silo where anaerobic digestion takes place called as biogas unit or biogas plant.
Anaerobic digestion is a viable technology for production of biogas from manure and an environment friendly management of waste, the residual of anaerobic digestion contains valuable nutrients and could be used as fertilizer, which is considered a good practice for conversion of manure to fertilizer. By the conversion of poultry waste into biogas, two objectives can be reached viz. production of biogas and valuable fertilizer for the crop production.
Composition of biogas
Biogas consists mostly of methane (CH4, around 65-70%) carbon dioxide (CO2, around 25-30%) and varying quantities of water (H2O) and hydrogen sulphide (H2S) and some trace amounts of other compounds, which can be found, especially in waste dump biogas (e.g. ammonia, NH3 hydrogen H2, nitrogen N2, and carbon monoxide, CO). The amount of each gas in the mixture depends on many factors such as the type of digester and the kind of organic matter. Diverse sludge composition requires diverse/specialised reactor designs to achieve a high conversion.
Methane is the valuable component under the aspect of using biogas fuel. The calorific value of biogas is about 6 kWh/m3, which corresponds to about half a liter of diesel oil and can be utilized directly as a heat source or to produce electricity. In all cases, the biogas must be dehumidified and purified before combustion; otherwise it can damage the gas engine.
Conversion of biogas into electricity
Various technologies to generate electricity from biogas on a household level are available. In principle, the chemical energy of the combustible gases is converted to mechanical energy in a controlled combustion system by a heat engine. This mechanical energy then activates a generator to produce electrical power. The most common heat engines used in for biogas energy conversion are gas turbines and combustion engines. Combustion engines can be either internal combustion engine (e.g. reciprocating engine) or external combustion engine (e.g. Stirling engine).
The biogas thus produced could be used for electricity generation locally. Based on the amount of biogas produced from poultry waste, there is a feasibility to generate 280 MWh/day of electricity. Additionally, this will reduce the environmental impact of poultry waste and digestion residue can be used as fertilizer. The generation of electricity could be a valuable addition of energy source in existing energy grid as a renewable energy.
Adapted from
Arshad M et al. 2018. Electricity generation from biogas of poultry waste: An assessment of potential and feasibility in Pakistan. Renewable and Sustainable Energy Reviews 81 (2018) 1241–1246
Sacher N et al. 2018. Biogas Electricity (Small-scale). Retrieved from www.sswm.info
