Commonly, organic matters with low molecular weight and large solubility cannot be removed effectively by the coagulation-sedimentation, which has high removal efficiencies for the hydrophobic organic matters of macromolecule in water. The pre-coagulation technologies applied before the microfiltration membrane can be mainly divided into two kinds, including standard coagulation and online coagulation. Coagulant dosing is traditionally based on jar-tests or operator experience, resulting in either overdosing or insufficient dosing. In this study, we assess the feasibility of a new coagulant dose control instrument, the online charge-based automatic titration system, charge analyzing system with titrator (CAST), to control membrane fouling in microfiltration (MF), following coagulation for the reclamation of municipal wastewater.

This paper presents a 100 m³/d pilot for effect of fouling control and organic matters (COD, DOC) removal using a coagulation/MF process with an online real-time charge analyzing system with titrator (CAST) system to control coagulant dosing. The online CAST coagulant dose control system allows the coupling of real-time colloid charge titration with on-line feed forward control. This system promises to measure coagulant or cationic demand (CD) volume over time in highly fluctuating wastewater quality conditions. The CAST system is a continuous sampling, on-line instrument that enables the treatment plant operator to know precisely and at all times the optimum coagulant dosage.

Initially, the MF membrane with In-line mixer with constant feed of coagulant (control) was operated at 60 LMH with a CIP interval of 16 days. The results of this research showed that microfiltration (MF) run time using In-line mixer with CAST system compared to the control unit can be extended 1.375 times of CIP interval due to the cake layer protection to the membrane, and cake layer characteristics were important for membrane performance. Over the three month study period, this equates to a reduction in the average coagulant dose of 2.1 mg/L (14%) and an over 10% and 20% increase in the average COD and UVA removal by the CAST unit compared to the control unit, respectively. Gao et al. considered that the pre-coagulation put emphasis on improving filtration efficiency of UF/MF membrane, so it was vital to choose proper coagulants and control coagulation conditions to produce flocs that had the best coagulation-UF/MF treatment efficiency based on raw water quality.