Digestão anaeróbia da fração orgânica de resíduos sólidos urbanos (FORSU) em reator de mistura completa

Abstract

Organic waste generated in restaurants, supermarkets and small agro-industries is destined, in most Brazilian municipalities, to the system of sanitary or irregular landfills. Due to the fact that they present a high concentration of organic matter, expressed in SV/ST (volatile solids/total solids), around 90%, food residues are promising substrates for methane production. Aiming to value this by-product, this study aimed to evaluate the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). The FORSU samples were made available by the biogas thermal plant in the municipality of Ponta Grossa, Paraná. To evaluate the performance of the process against different organic loads, 0.5 g SV L-1 d -1 (Phase I - Start), 1.0

g SV L-1 d -1 (Phase II) and 1.5 g SV L-1 d -1 (Phase III), the parameters of FOS/TAC (Volatile Organic Acids/Total Inorganic Carbon), biogas production, methane production, concentration of volatile organic acids and solids removal efficiency were evaluated . Three batches of OFMSW collected on different dates were used, which presented 132, 85 and 63 g SV kg-1 , with digestible potential (SV/ST) of 92, 94 and 87%, respectively. After inoculation, the reactor took 12 days to stabilize, showing FOS/TAC values of 0.2 and methane concentration in the gas of 40%. After stabilization, the reactor was started up, Phase I, with a VOL of 0.5 g SV L -

1 d -1 , duration of 4 days, mean SV removal of 95±0.01% and generation of 0.083± 60 LBiogás LReactor d -1 with 40% methane. Phase II, with a VOL of 1.0 g SV L-1 d -1 , lasted 10 days, showed

SV removal of up to 95% and production of 0.2±0.1 LBiogás LReactor d

-1 with 50% methane average. During Phase I, the predominant organic acid produced was propionic, with concentrations of 60 to 78% of the total. In Phase II, the percentage of propionic acid dropped to 12% and the acetic acid content increased to 30%. Phase III, which lasted 126 days, showed SV removal from 68% to 91%, methane content in biogas from 50 to 75% and acid accumulation, resulting in a FOS/TAC ratio between 0.5 and 2.0. In this phase, the acetic and propionic acid contents were 7,422 and 4,596 mg L-1

, respectively. The anaerobic digestion process was interrupted when the biogas contents and methane concentration stabilized at 0.06 LBiogás LReactor d -1 and 50%. Analyzing the results obtained, the anaerobic digestion of FORSU can be considered an important treatment both for the stabilization of organic matter and to produce methane.