Laboratory investigation of the discharge method and production biogas pressure effect on anaerobic digestion process.

The anaerobic digestion process is associated with biogas production, so pressure will be an important parameter affecting process. How the produced biogas discharge will be affected on system type as well as operating pressure, both of which affect the anaerobic digestion process, quality and quantity of produced biogas. In this research, effect of how produced biogas discharge by the laboratory scale anaerobic digestion system on the biogas production process with an industrial approach has been investigated in three methods.  In all methods, after injecting feed into the digester, system was subjected to a relative vacuum about   -0.1 barg per feed mass unit. First method system was batch, for second and third methods with respect biogas output were considered semi batch and continues, respectively. Other operating conditions such as temperature, mixing, type and amount of feed were same for all three methods.  For feed and digested, moisture, dry and organic matter and ash were measured and elements analysis were done. Production biogas analysis was also performed to measure the average relative composition of biogas.The results of products analysis and measurements show that volume of produced biogas in the third method compared to the second and first methods increased by 9.64% and 15.53%, respectively. These characters were shown increasing of methane volume share in compare of total biogas production 2120.22% and 21.31%, respectively. The four steps in the anaerobic digestion process are performed continuously in balance with each other uniformly. The gradual release of biogas produced and low pressure of system make the process conditions uniform and susceptible to the activities of microorganisms, especially methanogenic. Therefore, the gradual discharge method of produced biogas and its low pressure due to  lack of accumulation in the digestion tank during anaerobic digestion process has best results in terms of produced biogas and  methane  volume.