Codigestão anaeróbia de lixiviado de aterro sanitário e água residuária de fecularia visando à produção de biogás

Abstract

The search for sustainability, based on environmental goals such as Sustainable Development Goals, established by The United Nations, has been a challenge for both public and corporate sectors that aim at associating those goals with financial stability of an enterprise. Among those goals, clean energy generation has a spotlight, which can be achieved by several ways, such as by biogas generation. Anaerobic digestion, a biological process to decompose organic matter, which is carried out by microorganisms, can be used to achieve liquid effluent treatment as well as to produce biogas and methane. This last one can be applied as biofuel, which can generate clean energy. It can also cover the operating costs of the treatment, generate profits and meet environmental goals. Most of organic wastewaters can be applied as substrates for anaerobic digestion; however, sometimes the appropriate conditions are not achieved to carry out an efficient anaerobic digestion process. For example, cassava wastewater (CW) is rich in biodegradable organic matter, whose pH and alkalinity are both low. These features make microorganisms’ stabilization difficult, and can inhibit anaerobic digestion. Applying co-digestion with other wastewaters allows overcoming those difficulties, as the application of landfill leachate, with low organic matter concentration, but high alkalinity and nutrients concentrations, such as iron and nickel, and can enhance the process. Thus, this trial aimed at applying anaerobic co-digestion of landfill leachate and cassava wastewater to produce biogas, since there are landfills and cassava industries in Cascavel Intermediate Region, Paraná state. The first phase was to elaborate a simplex design with five mixtures between leachate:CW (100:0, 67:33, 50:50, 33:67, 0:100) in batch reactors with 1 L volume and 50% of useful volume. The reactors were inoculated with UASB sludge in an S/I ratio of 0.4 gDQO.gSV-1, and kept at mesophilic temperature without controlling pH of mixture for 50 days. The mixture with 67% leachate allowed for maximum CH4 yield, 331.2 mL.gVS-1, while mixture 50:50 allowed for maximum COD removal, 80%. The desirability analysis suggested the substrate ratio of 53:47 as the most favourable. The second phase of this research applied the ideal ratio in a fixed bed reactor with continuous upflow feeding, with a 3.6-L useful volume, kept at mesophilic temperature range. Four experimental conditions were developed, with hydraulic retention time variation in descending order: 25, 20, 15 and 10 hours; each condition was monitored for 30 days. Maximum COD removal and maximum CH4 concentration in biogas were obtained under condition 1 (25 h of HRT), which were 86.2 and 64.7%, respectively. The maximum CH4 productivity was obtained in conditions 3 and 4 (15 and 10 h of HRT), which were, respectively, 3.3 and 3.4 L.Lreactor-1.d-1. Mean comparison test was carried out to evaluate if there were significant differences among the studied conditions. Then, condition 3 was defined, with 15 hours of HRT, as the best condition to reach these researched goals, with a CH4 yield of 3.3 L.Lreactor-1.d-1, COD removal of 75.4% and CH4 concentration on biogas of 62.5%. Thus, it was possible to apply an anaerobic co-digestion for the chosen substrates, and obtain satisfactory results for the evaluated variable responses. Therefore, this research showed the possibility of applying these substrates to generate methane, as a sustainable treatment alternative.