Thermal pretreatment of swine waste to improve biodegradability in the anaerobic digestion process. Effect on the physicochemical characteristics of the substrate

Abstract

In anaerobic digestion (AD) processes, hydrolysis is considered the limiting stage in the degradation of solid wastes. Such is the case of swine manure digestion, which due to the complex physical and chemical structure of the lignocellulosic material that composes it, an energy wastage has been observed in terms of methane production. Among the strategies used to improve the hydrolysis stage, it is possible to mention the thermal pretreatment of the substrate, which can significantly improve the biodegradability of the material used as raw material in AD. In this study, the effect of temperature (60–177 °C) and exposure time (30–60 min) on the physicochemical properties of the substrate such as pH, volatile organic acids (VOAs), total inorganic carbonates (TIC), volatile solids (SV), total solids (ST), soluble chemical oxygen demand (CODs) and biochemical methane potential (BMP) were determined. The temperature factor had a higher level of significance compared to the exposure time on the parameters of pH, VOAs, and TIC before and after the biogas generation process. However, the effect was different for CODs, where time was more significant than treatment temperature. As for the parameters of total and volatile solids content (ST and SV), the factors evaluated (temperature and exposure time) did not show significant effect. Also, the pretreatments showed an increase in biochemical methane potential, outperforming the untreated substrate by up to 70.4 % (121.74vs.71.44 mLCH4 gVS-1). The best combination of heating temperature and operating time was 120 °C and 45 min, which promoted the hydrolysis step that was reflected in an increase in CODs and improvement in methane production by 42 % over the untreated substrate