Enhanced biodiesel wastewater treatment using moving bed biofilm reactor (MBBR) and improved applicability to subsequent coagulation process

Biodiesel wastewater (BDW) is a high-strength industrial effluent rich in organic matter, oils, and suspended solids, posing significant challenges for conventional treatment processes. In this study, a pilot-scale moving bed biofilm reactor (MBBR) was operated continuously for three months to evaluate its performance in treating biodiesel wastewater (BDW) and its impact on the efficiency of subsequent coagulation. The MBBR achieved sustained chemical oxygen demand (COD) and total organic carbon (TOC) removal under fluctuating influent conditions, with average removal rates of 74.79% and 81.37%, respectively. Microbial community analysis based on 16 S rRNA gene sequencing revealed a diverse biofilm community in the MBBR carriers, with Bacteroidetes, Saccharibacteria_TM7, Proteobacteria, and Firmicutes as major phyla. At the genus level, Saccharimonas, Chryseobacterium, and Proteiniphilum were the predominant taxa. In addition, MBBR pre-treatment substantially enhanced the performance of downstream coagulation using ferrous sulfate. The COD removal efficiency by coagulation increased more than 2.5-fold after MBBR treatment (from 13.35% to 34.29%), along with notable enhancements in TOC and SS removal. These enhancements may be associated with biological modification of wastewater characteristics during MBBR pretreatment, which improved the conditions for particle aggregation during subsequent coagulation. By linking continuous pilot-scale MBBR operation, carrier-associated biofilm characterization, and downstream FeSO₄ coagulation response, this study provides practical insight into the integration of biofilm-based pretreatment with existing physicochemical treatment processes for high-strength industrial wastewater.