Fenton-Anoxic–Oxic/MBR process as a promising process for avermectin fermentation wastewater reclamation

• Fenton-AO/MBR process was found efficient for AVM wastewater treatment.
• Under optimized operation conditions, the effluent can meet the discharge standard.
• The best membrane cleaning procedure for the MBR was HCl followed by NaClO.

Avermectin fermentation wastewater (AFW) is a highly toxic effluent generated in the pharmaceutical industry and is typically treated by using of an upflow anaerobic sludge blanket (UASB) reactor. This study aims to further optimize the overall treatment process to meet discharge standards and water quality for reuse. After the UASB reactor, the pretreated AFW undergoes Fenton oxidation, which improves the biodegradability of the UASB effluent and the removal of COD and ammonia in subsequent biotreatment processes. Optimal operating conditions for Fenton oxidation (pH = 3.5, H2O2 = 4 ml/l, FeSO4⋅7H2O = 1.1 g/l) and anoxic–oxic–membrane bioreactor (AO–MBR) system (HRT = 72 h, reflux ratio = 300%) show an average removal rate of 84.3%, 79.4%, and 72.3% for COD, ammonia, and TN, respectively, which could be further treated by nanofiltration or reverse osmosis (NF/RO). Toxicity of the effluent was also significantly reduced. For a high-flux MBR system, HCl + NaClO was found to provide the best treatment for increasing the acceptable transmembrane pressure (TMP) caused by cake layer accumulation and fouling by inorganic metal ions. Study results demonstrate the potential of Fenton-AO/MBR process as a post-UASB reactor treatment and a pre-treatment of NF/RO, improving biodegradability, pollutant removal, and toxicity reduction of AFW.