Hybrid Moving Bed Biofilm Reactor under different conditions for Increased Diclofenac Removal from Wastewater

Pharmaceutical micropollutants are a growing concern for aquatic ecosystems, with diclofenac (DCF) standing out due to its high use, persistence, and toxicity. Conventional wastewater treatment plants (WWTPs) cannot fully remove pharmaceuticals, causing continuous emissions into rivers and lakes. This has led to tighter regulations, such as Switzerland’s Water Protection Ordinance (limit 0.05 µg/L) and the EU Directive 2024/3019, which requires at least 80% removal of selected drugs. This study tested a pilot-scale Hybrid Moving Bed Biofilm Reactor (HMBBR) as a retrofittable biological option for DCF elimination under real wastewater conditions. Objectives were to assess biofilm growth on clean carriers and the effect of sludge retention time (SRT) on biofilm colonization and micropollutant removal. A three-line pilot plant operated for 112 days with SRTs of 2, 3, and 5 days. Batch tests compared biofilm carriers with suspended activated sludge from pilot- and full-scale WWTPs. Results showed successful biofilm development on clean carriers while maintaining stable removal of carbon, nitrogen, and phosphorus. Shorter SRTs promoted faster biofilm formation and better DCF removal: at influent concentrations of 10 µg/L, elimination reached 80% at 2 days SRT, versus 72% and 67% at 3 and 5 days. Batch experiments confirmed that biofilm-associated biomass degraded DCF more effectively than suspended sludge, emphasizing the central role of biofilms. Overall, findings indicate that reducing SRT shifts functional capacity from suspended to attached biomass, improving both nitrification and micropollutant elimination. HMBBRs therefore show promise as cost-effective and flexible technologies for advanced pharmaceutical treatment. Future work should examine long-term biofilm dynamics, links between nitrification and DCF degradation, microbial communities involved, and techno-economic feasibility to enable large-scale application.