Improvement in methane concentration in the biogas produced through the co-digestion of waste from the seafood restaurant industry and mezcal vinasses.

Abstract

Abstract The release of waste by the mezcal and seafood restaurant industries, due to their characteristics, generates adverse effects on soils, bodies of water, and air. An important aspect of anaerobic digestion is having an inoculum whose microbial consortium is in suitable conditions for carrying out the anaerobic process in its four stages. Applying the combined pretreatments (chemical, thermal, and volumetric ratio of waste) modifies its bioavailability and, consequently, its consumption rate by the microorganisms in the anaerobic inoculum. This research focused on evaluating the strategy of having an enriched inoculum, co-digestion of waste, and applying pretreatments to methane production in the biogas produced through the BMP test. The development of the tests was carried out considering a Taguchi L4 orthogonal experimental design for the variables in two levels of pretreatment: by temperature, volumetric ratio of waste from the restaurant industry of seafood waste and mezcal vinasses, and chemical by pH adjustment, for an initial concentration of residue mixture of 18 g VS L-1; the monitoring variables were biogas production, methane concentration, volatile solid, pH, conductivity, and alkalinity. The results show that the enriched inoculum used in the test had a pH of 8.18, a conductivity of 19.24 mS cm-1, an alkalinity of 31 g CaCO3 L-1, and an alpha (α) ratio of 0.75; the time in which the BMP test was carried out was of the order of 29 days. At the best test, with pretreatment at a temperature of 50°C, a residue ratio of 1 VSW/ 2 VMV, and a pH of 6.5, a production of 1420.51 ± 0.038 N mL CH4 and an 82.3 % CH4 concentration in the biogas were reached, with a yield of 175.37 N mL CH4 g-1 VS and a degradation constant of 0.14 d-1.