Inline dosing of powdered activated carbon and coagulant prior to ultrafiltration at pilot-scale – Effects on trace organic chemical removal and operational stability

Hybrid membrane processes such as inline dosing of powdered activated carbon (PAC) prior to ultrafiltration membranes (UF) have already shown promising potential for the abatement of trace organic chemicals (TOrCs). However, questions regarding the optimization of the operational stability by the employment of coagulation and its interferences with inline dosed PAC, have not yet been comprehensively investigated. Within the scope of this pilot-scale study, inline dosing of different sized PAC types at different dosages was combined with or without the addition of polyaluminium chloride (PACl) coagulant prior to UF. As expected, when PAC was not employed, negligible TOrC removal was observed, whereas all the operational modes with the application of PAC inline dosing showed significant TOrC removal. Coagulation with PACl clearly reduced the build-up of transmembrane pressure, especially owing to maintaining hydraulic backwash efficiency. The operational mode of precoating the UF with PACl combined with continuous inline dosing of PAC exhibited particularly good TOrC removal results along with optimized membrane fouling mitigation. In contrast, the simultaneous and continuous dosing of PAC and PACl is not recommended, in particular owing to detrimental effects of the coagulant on TOrC removal efficiency by PAC.