INVESTIGATIONS ON THE EFFECT OF ULTRASONIC PRE-TREATMENT ON COW DUNG SLURRY WITH SLUDGE WATER AND FOOD WASTE FOR BIOGAS PRODUCTION

Abstract

In the present work, Ultrasonic pre-treatment was performed on cow dung slurry in anaerobic conditions to observe the methane quality and hydraulic retention time (HRT). There were four anaerobic digesters designated as B1, B2, B3, and B4 with the capacity of 10 litres each, had the ratio of cow dung:sludge water: food waste is 1:1.5:1 respectively with the additive of 10gm jaggery / kg-cow dung with organic loading rate (OLR) of 6 kg total solid (TS) m-3day-1. Initially, the HRT was 17 days at room temperatures varied between 28oC and 32oC respectively. B1 and B2 were treated by ultrasound for 35 minutes (230V, 18kHz, 1.5kW) at 50oC and 60oC (Thermophilic condition) respectively. It was observed that B1 had the maximum Methane (CH4) yield in the biogas which was 13.4% more than B2, 52% more than B3, and the least Methane yield in the biogas was observed in B4. At Mesophilic condition (30 oC - 40 oC) the methane yield was found 30% lower as compared to B1. Response Surface Methodology (RSM) was used to determine the most favourable ultrasonication time, temperature, and hydraulic retention time in this study for ultrasonic pre-treatment of cow dung for the production of biogas. This was accomplished with the help of a software programme (Design Expert 12.0.1.0). In order to analyse the result of the variables and their interlinkage to establish their optimal values, quadratic result datas for the responses were created, and a 3-Dimension response surface map was generated. The ultrasonication time, temperature, and retention period following HRT were determined by numerical optimisation to be 35 minutes, 60°C, and 8 days respectively.