Effect of gentamicin mycelial residues disintegration by microwave-alkaline pretreatment on methane production and gentamicin degradation during anaerobic digestion

Abstract

Gentamicin mycelial residues (GMRs) are microbial fermentation residues of the pharmaceutical industry. In this study, anaerobic digestion of GMRs in combination with microwave-alkaline pretreatment (MAPT) was first employed to enhance methane production and the efficiency of gentamicin degradation. The anaerobic digestion batch tests were conducted to optimize the MAPT conditions, and semi-continuous tests of three-month duration were carried out to investigate the anaerobic digestion performance and fate of gentamicin. The results indicated that the GMRs flocs were substantially disintegrated after MAPT, and the average particle size was significantly related to methane production (p < 0.05). Meanwhile, the solubilization of proteins after MAPT demonstrated a prominently positive effect on the anaerobic digestion performance of GMRs (p < 0.05), including biochemical methane potential, lag phase and maximum methane production rate fitted by modified Gompertz model. The results of the batch tests of MAPT pretreated GMRs (pH > 12) suggested that the excessive alkali dosage in the pretreatment process adversely affected the anaerobic digestion performance due to the solubilization or generation of the refractory compounds (e.g. melanoidin). An increase of 58.05% in methane production (323.33 ± 11.88 mL gVS−1) was accomplished by MAPT in the sable running stage of the semi-continuous stirring tank reactor. The analysis of gentamicin mass balance in anaerobic digestion process demonstrated that the degradation was a preponderant mechanism for gentamicin removal. Simultaneously, MAPT facilitated the release of gentamicin trapped in flocs, thus, effectively improving the average degradation efficiency of gentamicin in anaerobic digestion process (degradation efficiency: 97.70 ± 0.63%).