Efeito do pré-tratamento térmico-alcalino e da relação substrato/inóculo (S/I) no processo de digestão anaeróbia semisseca de dejeto suíno

Abstract

Pig farming is an important sector of Brazilian agribusiness, ranking as the fourth largest producer of pork worldwide. However, there is concern about the sector sustainability, due to the high-water demand in the process and the generation of wastewater with a high polluting power. A viable alternative for the destination of swine manure (SD) is anaerobic digestion (AD), a low-cost process that converts organic matter into biogas, a product that has great energy and economic potential. Such a product can even be used in the environment of the pig farms themselves, reducing greenhouse gas (GHG) emissions. It also has the possibility of using the digestate (final residue of digestion) to produce other value-added products, such as fertilizers and biochar. The objective of the study was to evaluate the effect of the thermal-alkaline pre-treatment and the substrate/inoculum ratio (S/I) in the process of semi-dry anaerobic digestion of swine manure. In addition, a kinetic modeling of biogas production was carried out, evaluating parameters and seeking to better understand the process. The experiment was carried out in batches, using a total solids (TS) content of 10%. After being characterized in physical-chemical analyses, the manure was inoculated with anaerobic brewery sludge at a mesophilic temperature of 37°C under orbital agitation at 150 rpm for 90 days, in three S/I ratios: 1, 3 and 5 g.VSsubstrate/g .VSinoculum, corresponding to treatments LDPt1, LDPt3 and LDPt5, respectively. The thermal-alkaline pre-treatment of swine manure was carried out with the addition of sodium hydroxide (NaOH 3%) in the proportion of 40% mass/volume and incubation in an autoclave at 121ºC for 30 minutes. The highest biogas yield was obtained at an S/I ratio of 3, producing about 366 mL/gVS. Biogas composition analysis revealed methane percentage in the biogas from 43 to 68%. The mathematical models applied to each experimental condition tested varied in relation to the best fit to the data, and it was not possible to observe the optimized predominance of a given model. Therefore, performing the pre-treatment increased the manure biodegradability, thus increasing the production of methane-rich biogas in semi-dry anaerobic digestion under mesophilic conditions with high total solids content (10%).