Effect of reduced gas pressure on yield of biogas and other physicochemical parameters

Abstract

The internal gas pressure is one of the major parameters affecting the microclimate of the anaerobic digester. The effect can be described by Henry’s Law and Ideal Gas law. In this experiment, the effect of reduced gas pressure on the yield of biogas and its composition was observed. The pressure of gas was reduced by displacement of a piston connected to the balancing weight, to maintain constant reduced pressure. As the piston is displaced to its maximum point due to gas generation, then the gas is transferred to the gas storage tank for further analysis. The gauge pressure applied was 0, - 100 , and - 200 mmHg for systems A, B, and C, respectively. The specific gas yield of systems A, B and C was 26.09, 70.41, and 246.5 L/kg (on dry basis). The production of methane was increased with a decrease in internal gas pressure. The corresponding average methane content of systems A, B and C was 38.33, 44 and 63.97%. The BOD 5 removal efficiencies were 6.25, 33.33 and 70.83% for systems A, B, and C, respectively. The pH of the substrate was stable in the system C. The rate of Total Solid (TS) reduction was high in System C. The TS reduction efficiency of systems A, B, and C was 14.7, 16.64, and 22.19%, respectively. The reduction in internal gas pressure can be a new effective and efficient process control strategy. The reduced-pressure system reduces the chemical cost incurred by the addition of alkalinity to maintain the pH.