Assessing the Effect of Temperature on Performance of the High Altitude Anaerobic Digesters

Abstract

Biomass is the main source of energy in Nepal as the majority of the population uses biomass as the energy source. Firewood serves as a primary source of fuel for cooking and heating that has led to depletion of forest resources. Renewable energy technologies account for 0.53% of total energy consumption in Nepal. Due to the high performance in volume reduction and stabilization, an anaerobic digestion is a solution for the treatment of agricultural waste, industrial waste, which leads to efficient energy production. Of many factors affecting anaerobic digester process, temperature is one of the major factors. Organic waste can be easily digested to produce methane gas and this process also generates good manure as a by-product. The main aim of the paper is to assess the effect of temperature on the performance of the high altitude anaerobic digesters. A continuous lab-scale anaerobic digester was fabricated. The different substrates, i.e., cow dung, horse dung, sheep dung, human faces, and greenhouse residue were used as feed. The tests were performed at different temperatures, i.e., 10, 17, 30, and 40 °C. Biogas production was studied every day for 45 days by the water displacement method. The Biochemical Methane Potentials (BMPs) for the substrate was conducted in the sample bottle of 125 ml and gas produced was measured by syringe. The cow dung was found to have highest biogas production potential under mesophilic condition than that of psychrophilic. Among all types of feed mix used, mix with cow dung, horse dung, sheep dung, and human feces were found to be efficient. The amount of gas produced from this mix at psychrophilic temperature was 4120 ml from 2.2 kg substrate used in 22 days. Initially, 8.5 ml of inoculum was used. For the production of sufficient amount of biogas, heating is required at higher altitude due to the cold climatic condition.