Avaliação do efeito da carga orgânica volumétrica na digestão de resíduo de frutas e verduras em reator de agitação contínua em um e dois estágios

Abstract

Fruit and vegetable waste (FVW) has a composition rich in carbohydrates and a high concentration of total solids. These characteristic favors excessive acidification in the reactor, affecting the anaerobic digestion process and harming stability and methane production. One of the alternatives used to mitigate this problem is the adoption of a two-stage process. Therefore, the work in question aims to evaluate the anaerobic digestion of FVW in a single stage and in two stages, using a complete mixing reactor (CSTR) and to compare the performance of the two-stage process with the single-stage process. In this sense, the performance of the single-stage process was evaluated using a methanogenic CSTR (CSTR U) with organic loading rates (OLR) 1.0, 1.5 and 2.0 kgCOD.m-3.d-1 in conjunction with the reduction of hydraulic detention time (HRT) from 34 to 22 and 16 days, respectively. In the two-stage process, two CSTRs were used, a first-stage acidogenic (CSTR-1) and a second stage methanogenic (CSTR-2). CSTR-1 was inoculated with a OLR of 15 kgCOD.m-3.d-1. The effluent produced by CSTR-1 fed CSTR-2, which was operated with a OLR of 1.5 and 2.5 kgCOD.m-3.d-1 with a reduction in HRT from 20 to 12 days, respectively. The best performance was observed in the two-stage process, in which CSTR-2 achieved an organic matter removal efficiency of 84% and presented a methane yield (MY) of 428 mL CH4.gSV 1 and volumetric methane production (VMP) of 0.459 L CH4.Lreactor-1.d-1. Comparing the performance of the two-stage process with the single-stage process, the two-stage process provided a 35% reduction in the total reactor volume, as the best performance of the CSTR-U was recorded at a OLR of 1.0 kgCOD.m-3.d-1 with HRT of 34 days, an MY of 312 mL CH4.gVS-1 and VMP of 0.339 L CH4.Lreactor-1.d-1. Therefore, the two-stage process presented better operational performance and greater stability compared to the single-stage process, with a 50% gain in OLR applied to the reactor.