Effects of coagulation and operational flux on the membrane performance of an inline coagulation/ultrafiltration process for water treatment

Abstract

The objective of the study was to investigate the effects of coagulation and operational flux on the membrane performance of an inline coagulation/ultrafiltration process for water treatment in the lab. A two-phase optimisation approach was adopted in order to achieve stepwise performance improvement using raw water (taken from one of Singapore’s reservoirs) as a case study. “Phase I” focused on the simulation of the inline coagulation/UF process composed of coagulation in jar test followed by immediate filtration with 0.05um paper filter, while “Phase II” consisted of the operation of a bench scale hybrid inline coagulation/UF system equipped with a pressurized membrane module in laboratory. The main focus area for “Phase I” was the identification of optimum alternative coagulant among aluminium chlorohydrate (ACH), polyaluminum chloride (PACl) and ferric chloride (FeCl3) compared to aluminium sulphate (alum). “Phase II” supplementary applied the previous findings of the selected coagulant and dosage in order to optimise the membrane performance during operation of a bench scale hybrid inline coagulation/ultrafiltration system. The experiments in “Phase II” included runs at different fluxes in the range of 72-146L/m2/h, for the determination of the fouling behaviour in terms of transmembrane pressure (TMP), fouling tendency and specific flux (K). The critical operational flux values were also estimated which might help in the determination of a “sustainable flux” under the operating conditions investigated. It was found that for “Phase I” the optimum coagulant would be ACH in a dosage of 1.7mg (Al)/L, with a TOC removal efficiency (40%) comparable to alum (35-45%), good effluent turbidity and acceptable dissolved aluminium concentration