Investigating the Interaction Effects of Inoculation and Temperature on Biogas Production from Dairy Industry Effluent in Anaerobic Digestion Process

In this study, batch series of laboratory-scale anaerobic digesters at 35 and 55 ° C were used to investigate the production of biogas from dairy effluents and reduce its pollution. Dairy effluent sludge with ratios of zero, 10, 20, 30, 40 and 100% was used for inoculation. The interaction effect of sludge percentage and temperature at the level of one percent on the volumetric indices of biogas production was significant for the amount of initial volatile solids, volatile solids removed and chemical oxygen demand removed at the level of one percent. With increasing sludge percentage, the amount of biogas produced per initial volume increased for the removed COD but decreased for the initial volatile solids. The highest biogas production efficiency was obtained based on the removed volatile solids at thermophilic temperature and 40% sludge ratio, with the removal of 47.7% volatile solids and 266.5 ml per gram of removed volatile solids. According to the results, the amount of biogas production at mesophilic temperature, in lower proportions of added sludge, is more than the amount of gas produced at thermophilic temperature, and due to the low volume of sludge production in the dairy industry and higher energy consumption under thermophilic conditions, anaerobic digestion and biogas production are more favorable at 35 ° C. The results also showed that by anaerobic digestion of each m3 of dairy effluent, 20.83 MJ of heat energy can be produced.