Digestão anaeróbia em estado sólido de cama de aviário a diferentes razões de substrato/inóculo e intervalos de recirculação

Abstract

This study evaluated how the substrate/inoculum ratio and recirculation conditions of the digestate influence the yield of biogas, methane and the free ammonia concentration for poultry litter solid state anaerobic digestion. Experimental tests were conducted using a central composite design (2²), four trials at the factorial points and three at the central points, using avian bed as substrate, collected after 12 cycles of broiler production (TS = 76 % (w.w-1)). Three substrate/inoculums ratios (1:1; 1:1,66 and 1:3) and three daily recirculation intervals (2, 3 and 4) were tested for 15 min each. Three reactors were operated at mesophilic temperature (37øC) and seven experimental runs were performed with retention time of 30 days each. The highest yields of biogas and methane 182,77 LNbiogas.kgVSadd -1 e 74,06 LNCH4.kgVSadd -1 respectively) were obtained for the substrate/inoculum ratio of 1:3 with four-fold per day digestate recirculation. Recirculation of the digestate was the variable that influenced the concentration of free ammonia, the most frequently recirculated tests had lower concentrations (below 80 mg.L-1). The process presented high concentrations of hydrogen sulphide, between 1106 and 4000 mg.L-1. The concentrations found in this study were higher than those reported by other authors as inhibitory to the process, indicating that H2S was an inhibitory with the methane yield.