Bioconversion of Lemna sp and Nejayote into Biogas as a starting point for agrowaste

Abstract

Agrowaste has some issues such as management or disposal in the transformation industry of corn and pig farms. Sub-products obtention from waste of both industries can represent an opportunity if processes are technically and economically feasible. In this study, bioconversion of Lemna sp and Nejayote in biogas via anaerobic digestion was evaluated at short term as function of biogas production, as well as chemical oxygen demand (COD) and total solid (TS) removal. Lemna sp was collected from a pond system applied for wastewater treatment of pig farms, while Nejayote, the wastewater generated in the nixtamalization process of corn, was collected in a local corn processing store. Results indicated that the digesters with Lemna sp generated up to 32% higher biogas than that for Nejayote. This is also reflected in the biogas yield obtained, 0.31 L of biogas/ g COD and 0.46 L of biogas/ g COD for Nejayote and Lemna sp, respectively. Regarding biochemical oxygen demand (BOD) removal, the evaluation of the substrates indicated a greater removal of BOD present in the reactors with Lemna sp, reaching an average of 79% of BOD removed in 120 h, for a 37% removal in the reactors with Nejayote. On the other hand, an increase in the concentration of total COD was observed in both substrates, demonstrating the potential solubilization of the particulate material present in both substrates. Although the Lemna sp reactors increased the concentration of TS, a fraction may be attributable to the development of microorganisms typical of anaerobic digestion. On the contrary, in the case of digesters with Nejayote, a decrease in TVS and an increase in COD are observed simultaneously. This could be due to increase is closely related to the hydrolysis of the organic material present in the anaerobic digesters. In general, methanogenic viability were more suitable for the Lemna sp conversion at the conditions applied and the same COD load of both substrates.