Treatment of dehydration wastewater from licorice residue via a novel microaerobic-aerobic combined process: Performance and microbial community

The initial step in the resource utilization of Chinese medicine residues (CMRs) involves dehydration pretreatment, which results in high concentrations of organic wastewater and leads to environmental pollution. Meanwhile, to address the issue of anaerobic systems failing due to acidification under shock loading, a microaerobic expanded granular sludge bed (EGSB) and moving bed sequencing batch reactor (MBSBR) combined process was proposed in this study. Microaeration facilitated hydrolysis, improved the removal of nitrogen and phosphorus pollutants, maintained a low concentration of volatile fatty acids (VFAs), and enhanced system stability. In addition, microaeration promoted microbial richness and diversity, enriching three phyla: Bacteroidota, Synergistota and Firmicutes associated with hydrolytic acidification. Furthermore, aeration intensity in MBSBR was optimized. Elevated levels of dissolved oxygen (DO) impacted biofilm structure, suppressed denitrifying bacteria activity, led to nitrate accumulation, and hindered simultaneous nitrification and denitrification (SND). Maintaining a DO concentration of 2 mg/L enhanced the removal of nitrogen and phosphorus while conserving energy. The combined process achieved removal efficiencies of 98.25 %, 90.49 %, and 98.55 % for chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP), respectively. Typical pollutants liquiritin (LQ) and glycyrrhizic acid (GA) were completely degraded. This study presents an innovative approach for the treatment of high-concentration organic wastewater and provides a reliable solution for the pollution control in utilization of CMRs resources.