Membrane Fouling Reduction in a MBR Process by Combination of NaOCl Oxidation and FeCl3 Flocculation Agents

The combination of oxidation and flocculation has been used to alleviate the membrane fouling in MBR systems. As common and cheap additives, NaOCl and FeCl3 were employed to prolong the operation life of the membranes. To achieve the highest performance in terms of the SMPs and COD removal, the optimum dosages of FeCl3 and NaOCl additives were first evaluated. To do so, using the jar test, optimum dosages of 2 mg/L and 2 mg/L were respectively determined for the FeCl3 and NaOCl, leading to the highest possible SMPs and turbidity removals of 20.1% and 91%. Using such optimal dosages, different scenarios were examined and the MBR experiments were then conducted in three stages designed to have no chemical addition (stage 1), FeCl3 (stage 2), and a combination of FeCl3 and NaOCl (stage 3) to assess the effect of the additives on membrane performance under continuous flow condition. The results revealed that, although at such dosages, the additives were not able to affect the nitrifying and heterotrophic bacteria, when simultaneously employed (stage 3), they were able to significantly lower the cake layer resistance and the operating time by 4.3 and 2.6 times when compared to the conventional MBR systems (stage 1) and the ones flocculated by FeCl3 (stage 2).