Effect of Temperature Variation on Codigestion of Animal Waste and Agricultural Residue for Biogas Production

摘要

Anaerobic digestion and codigestion are processes that may aggregate economic value to the organic waste, not only through the production of biogas, as the main product, but also with a by-product, the digestate. The production of biogas (renewable and sustainable energy source) reduces GEE emissions, as well as the impact caused by waste disposal from the agribusiness sector. The present work aims at the potential optimization biogas production in rice residues (rice straw) in different proportions along with bovine residues (waste), under the effect of temperature increase (from 36 to 60 degrees C). Preliminary investigation consisted of sampling and drying the residues with analytical tests (TS, VS, COD, TOC, N, P, pH, moisture), which allowed the determination of the proportions to be used in experimental research. Then, anaerobic bench reactors (A, B, C, Control) in different proportions were monitored by means of BMP tests, in order to evaluate the potential of methane production in a period of 60 days. During this period, different temperatures were tested, varying from 36 to 60 degrees C, gradually increased by 2 to 2 degrees C, every three or 5 days, in order to adapt the anaerobic microorganisms, present in the waste mass. The three reactors presented different biogas production, which can be explained by the different temperatures proposed. Reactors A (ratio 1:1) and C (ratio 1:10) did not reach the proposed objective as their production level was below the production of the control reactor. The B reactor (3:1 ratio) was the one that presented the highest accumulated biogas production during the test period, with 76.95 NmL and the rice straw contribution of 7.55 NmL. As regarding to temperature, all reactors showed to adapt to the two conditions tested: mesophilic and thermophilic fact that demonstrates synergism among the residues tested. Despite the verified adaptability, the mesophilic condition was defined as the most favorable for biogas production because of its greater stability and lower energy cost. The BMP test has proven them to be a viable, easy-to-use, and inexpensive operational tool to monitor and determine biogas production potential for the waste used.