Efeito da relação substrato/inóculo na partida de reator anaeróbio para digestão de resíduos alimentares

Abstract

The energy recovery acquired through the anaerobic digestion is a viable alternative for treating food waste, though it requires an operational strict control. The choice of the best start up condition athwart the substratum /inoculum (S/I) ratios in terms of volatile solids (VS) may facilitate the process stabilization, resulting in increased production of biogas and methane content. The present study tested 5 different ratios of S/I in batch system at 35ºC, aiming the process stability and the optimization in the raised methane level biogas production. As the substrate, the residue collected at the university restaurant of Unisinos was used, and as inoculum the UASB reactor anaerobic sludge from the sewage wastewater treatment plant at the same university. The monitored parameters were pH, biogas amount, methane content, alkalinity and volatile fatty acids. All of the batches kept within the pH levels recommended by literature, between 6.5 and 7.5, exception to batch 5, which employed a relation of 1:1 substrate/inoculum and in which the pH level declined to 5.0. The biogas production in all of the studied conditions had its utmost production until the third day of inoculation and it was influenced by the S/I ration applied, since the increase of the substratum VS amount raised the yield and the methane content, exception to the condition 1:1 where there was an acidification of the system, and it was considered that the capacity of the commutation of substratum in methane was extrapolated. The biogas yields of the conditions 1:5, 1:4, 1:3, 1:2, 1:1 were, respectively, 0.69, 0.75, 0.67, 0.89 and 0.18 L/g VS of the substratum employed, and the average methane content in each batch were 69, 67, 65, 74 58%. The study shows that the best relation S/I to the process start-up was 1:2, to which it was obtained 0.89 L of biogas/g SV of the substratum with a methane content of 74% keeping the relation AGV/ALC under 0.5, demonstrating stability in the process.