Biomethanization: study of the influence of sludge and sawdust on the anaerobic treatment of an organic fraction of municipal solid waste (OFMSW)

The major evolution in the treatment of organic solid waste has been achieved by biomethanization, or simply Anaerobic Digestion. When treating the organic fraction, biomethanization produces a compound that can be used as a soil conditioner and provides energy recovery through the use of methane in the biogas produced. This dissertation reports on an analysis of the biomethanization technique and evaluates the influence of sludge and sawdust on the anaerobic treatment of OFMSW in 50 L and 5 L reactors operating under batch regime and mesophilic temperatures for 155 and 78 days, respectively. Slurry samples of biogas and digestato (solid material obtained after treatment with the opening of reactors) were analyzed. In the first stage, four 50 L reactors were operated with high solids content and under different conditions: Reactor 1 - control (filled only with OFMSW); Reactor 2 (filled with OFMSW, 5% sludge and sawdust); Reactor 3 (filled with OFMSW, 10% sludge and sawdust); Reactor 4 (filled with OFMSW and sawdust). The monitoring of the process enabled the maintenance of an acidic pH, even in reactors filled with sludge, and led to an acidic condition responsible for the inhibition of biomethanization in all treatments, which showed low organic matter removal and no production of methane. In the second stage of the study, three 5 L reactors were operated with low solids content for the testing of two types of sludge and increase in the percentage of inoculation, according to the following configurations: ETE 1 reactor - filled with OFMSW, sewage sludge and sawdust (3: 1: 1 ratio); ETE 2 - filled with OFMSW, sewage sludge and sawdust (2: 2: 1 ratio) and DACAR - filled with OFMSW, sludge from the anaerobic treatment of poultry effluent and sawdust (2: 2: 1 ratio). After 78 days of operation, higher proportions of inoculum and a higher temperature (30 to 35ºC) favored pH, alkalinity, degradation of organic matter and production of methane, observed in reactor ETE 2. However, the operating conditions adopted and environmental factors were not suitable for the success of biomethanization. No significant reduction in the organic matter was achieved and methane was produced only in one of the reactors of the second stage. (AU)