Post‐treatment of up‐flow anaerobic sludge blanket reactor effluents in activated sludge process‐based system for anionic surfactants

This paper presents the performance of two full‐scale up‐flow anaerobic sludge blanket–activated sludge process ( UASB‐ASP )‐based sewage treatment plants ( STPs ) (surface and diffused aeration‐based activated sludge processes as post‐treatment units). Performance of this combination is compared with UASB –polishing ponds and UASB –ozonation‐based STPs. Post‐treatment units removed 89 and 92% of anionic surfactants ( AS ) by surface and diffused aeration, respectively. Finally, 0.61 and 0.23 mg/ L of AS were discharged from post‐treatment steps after overall reduction of 90–92%. Final concentrations from UASB‐ASP ‐based STPs were low compared with UASB –polishing ponds (3.60–4.91 mg/ L ) and UASB –ozonation (1.52 and 0.53 mg/ L ). Overall, UASB‐ASP ‐based STPs were working efficiently for the removal of organics in terms of chemical oxygen demand ( COD ) (84%) and biochemical oxygen demand ( BOD ) (93%), but they need further modifications for the removal of AS up to the level of risk quotient [risk quotient ( RQ )] ≤ 1 for no risk to aquatic environment.