A study of biogas generation from poultry litter and its impurity removal

Abstract

This study is focused on the anaerobic digestion of poultry waste to produce biogas. Waste was collected from three different poultry farms (Sekela farm, Emarldene and Parkside poultry industry) in Kwazulu-Natal, South Africa. The aim is to assess energy from poultry waste in Kwazulu-Natal and to enhance the process of biogas production by treating the impurities of sulphur content, moisture and carbon dioxide in the biogas. The objectives are: to determine the energy potential of poultry waste in Kwazulu-Natal region, to increase the energy density of the biogas by the removal of moisture content, incombustible and corrosive gas and to assess techno-economic feasibility of biogas generation from poultry waste. 1 kg of each waste was thoroughly mixed with 3 L of water and loaded into ten digesters with each water bath (thermal conductor) bearing two digesters. The slurry was investigated using water displacement method to determine biogas produced for a period of 21 days and at an average temperature of 30 0C, 31 0C, and 32 0C respectively. Production started on the 3rd day for each digester at different temperatures (30 0C, 31 0C, and 32 0C), and attained maximum value on the 14th and 15th days. The maximum amount of biogas produced was 265.6 ml at a temperature of 32 0C from waste A (Sekela farm). At 32 0C, an optimal biogas yield of 421.6 ml/g VS was observed from Sekela farm (poultry waste A) compared to Emarldene (370.10 ml/g) and Parkside poultry industry (349.10 ml/g) in KwaZulu-Natal. Biogas was collected from the digester with the maximum volume of biogas produced using 100 µʟ gas syringe and was taking to Gas chromatography for characterization. The result showed that it was composed of about 57.71 % methane (CH4), 26.8 % carbon dioxide (CO2), 0.8 % nitrogen (N2), traces of hydrogen sulfide (H2S), fractions of water vapor, and other impurities which the detector was unable to quantify with an energy potential of 0.028 MJ/ml. Purification and Upgrade system was comprised of one column charged with steel wool (iron sponge), and two cylinders charged with pressurized water and silica gel to treat H2S, CO2, and water vapor in the biogas for improvement of its energy density. Biogas was collected from the purified system using gas syringe to the Gas chromatography for characterization and result showed that it is composed of about 84.56 % CH4 and energy potential of 0.046 MJ/ml. The result confirmed that the biogas heating value/energy density was improved/increased using steel wool, pressurized water and silica gel as biogas contaminants removal. Techno-economic studies were carried out to assess the techno-economic feasibility of a small-scale biogas plant using poultry waste in KwaZulu-Natal. A fixed dome digester was selected as the most convenient technology for the community. Result showed that 2,160 kWh per year of energy could be produced from about 4,000 kg of poultry waste and the payback time was eleven years and nine months. It showed that it is techno-economically feasible to use a fixed dome digester for energy generation for domestic usage and is cost-effective. In conclusion, poultry waste as a feedstock is suitable for anaerobic digestion, producing methane which can be used as an energy source and which can be purified to improve its energy potential. Biogas optimization is dependable on: temperature, physio-chemical characteristics of waste, pH and retention time e.g. at same temperature (either 30 0C, 31 0C or 32 0C) and time, waste A production is higher than waste B and C because of its favorable physio-chemical characteristics and pH-value. It is deduced that the energy potential in poultry waste could be determine by treating the waste via anaerobic digestion and the increase in the energy density of the waste is dependable on temperature, pH, retention time and physio-chemical characteristics of the waste.