Antagonistic effect of the anaerobic co-digestion of thermoalkaline pretreated press mud fractions with vinasse

Abstract

As a result of their activities, the sugar and ethanol industries generate large quantities of waste with high levels of organic matter. Two good examples are sugarcane press mud and vinasse (V), both with a great potential for biogas production. The geographical proximity of the aforementioned industries offers an opportunity to evaluate their anaerobic co-digestion behaviour. In this study, liquid fractions (LF) and solid fractions (SF) from lime (Ca(OH)₂) pretreated press mud (at 100°C), were mixed with V following a three factor mixture design, in order to evaluate synergistic and antagonistic effects on methane yield. The methane yield was determined in batch assays under mesophilic conditions (37 ± 1 °C). The Hill model was used to determine the maximum methane yield, and the specific methane production rate. Synergistic, antagonistic or unclear effects were included in a parameter phi (∅), for evaluation of the co-digestion. Experimental results showed antagonistic effects for nearly all mixture combinations (∅ < 1). However, for the mixture SF-V when SF>V, the effect was synergistic (∅ > 1). Thus far in terms of methane yield and process kinetics, anaerobic co-digestion of the mixtures has not been found to be a better option than the digestion of the separate components.