Biogas from Energy Crops: Evaluation of a MultiStage Procedure

Abstract del Poster presentato al Simposio "14th International Biotechnology Symposium and Exhibition, IBS 2010", Rimini, 14-18 settembre 2010. - An experimental method for the evaluation of a multi stage anaerobic digestion (AD) has been studied. In literature, in absence of international standards, potential errors in the laboratory-scale quantitative evaluation of AD bioconversions, can be introduced: amongst the others, the quantification of biogas produced and the substrate total COD analysis, making difficult the COD balance from the incoming and outgoing COD flows. To reduce the problem a laboratory-scale apparatus was assembled for the two-stage AD of two different energy crops, apples and potatoes. Two coupled 5 l batch-fed completely stirred reactors, one for the hydrolyticacidogenic step and one for the acetogenic-methanogenic step, kept at mesophilic temperature (35 ◦C), were adopted. In the first acidogenic reactor, the influence of fermentative bacteria (Saccharomyces cerevisiae) on the degree of idrolization and on the acidification rate of the vegetable substrates was measured taking into account the carbon dioxide production, the total and soluble CODratio and the pH variations. Using fermentative bacteria, a high idrolization degree and a stable low pH was reached with apple and potato substrates: all runs were performed without the addition of chemicals. Samples of idrolized substrates were sent to the second methanogenic bioreactor to evaluate the specific gas production (SGP), the methane yield in the biogas produced and the specific methanogenic activity (SMA).The whole process was repeated for simulating an anaerobic sequencing batch reactor (ASBR) process and final COD balances were carried on to verify experiments reliability.