A simple method to evaluate the short-term biogas yield in anaerobic codigestion of WAS and organic wastes

The present study was aimed at setting and applying a procedure to measure the anaerobic degradability of different organic substrates by short-term tests (2-7 days) carried out at lab-scale with a low food to biomass (F/M) ratio. All tests were carried out using an acclimated sludge taken from a pilot-plant anaerobic digester ( 200 L). Trials were performed with a manometric system. The experimental reliability of the device in measuring the anaerobic degradability was assessed by several preliminary tests carried out using acetate and glucose as reference substrates. The average conversion to methane was 99% for acetate and of 83% for glucose. The results of tests in triplicate showed the high repeatability of the method with an average coefficient of variation lower than 2%. Then, the lab-scale procedure was applied to study the short-term anaerobic degradability of complex organic substrates: thickened waste activated sludge, two kinds of organic fraction of municipal solid waste ( a kitchen waste and a fruit and vegetable waste collected at the wholesale market of Florence), olive mill wastewater and freshly harvested grass. Results indicated that organic fraction of municipal solid waste, olive mill wastewater and grass were characterized by a much higher anaerobic degradability if compared to the thickened activated sludge, well in agreement with literature data.