Commissioning-phase hydraulic loading and influent quality of a market-fed wastewater plant in Parakou, Bénin: baseline data for adaptive management.

Abstract

Wastewater plants (WWPs) are widely recognised as nature-based solutions for wastewater management in West Africa, yet empirical data from their commissioning phase remain limited. This study investigates the rehabilitated Arzêké WWP in Parakou, Bénin, which treats wastewater from a large urban market through a three-stage anaerobic, facultative, and maturation pond system. A two-phase monitoring protocol compliant with ISO 5667-10 was applied, yielding 293 flow observations and 70 concurrent flow -quality pairs. Eleven physicochemical parameters were analysed: pH, electrical conductivity, total suspended solids (TSS), chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD₅), total nitrogen, total phosphorus, iron, copper, lead, and zinc. Phase 1 yielded a mean daily flow of 6.14 m³/d (27.4% of design); Phase 2 confirmed underloading at 5.47 m³/d (24.4%). This resulted in a nominal hydraulic retention time of 549 days, 4.1 × the design value, with implications for sludge accumulation and greenhouse gas emissions. The influent was concentrated but biodegradable (median BOD₅ 983 mg/L; COD/BOD₅ 1.85). Trace metals were strongly associated with TSS (rs = 0.68-0.81), with inter-week increases exceeding 100% for Pb and Zn. This study provides the first commissioning-phase reference dataset for a market-fed WWP in West Africa.