Addition of powdered activated carbon to anaerobic membrane bioreactor for fouling control

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Membrane fouling remains a challenging issue which is the main obstacle of wider applications of anaerobic membrane bioreactors (AnMBRs). This is because the cake layer in AnMBRs is thicker and less removable than that in aerobic membrane bioreactors due to the different sludge characteristics. Pretreatment of feed wastewater can efficiently control membrane fouling by altering the feed water properties with the addition of fouling reduction enhancers, such as adsorbents and flocculants. Activated carbon, such as powdered activated carbon (PAC), which is comparatively simple and effective adsorbent, has been largely applied as an adsorbent to aerobic membrane bioreactors for membrane fouling mitigation. However, only a limited amount of research has focused on the application of PAC to AnMBRs. Although some studies have reported the effects of PAC addition on pollutants removal performance and fouling control of AnMBR system, few studies discussed the overall nutrient and organics removal performance as well as detailed membrane fouling behaviour regarding PAC addition at an ambient temperature. In addition, no study has been carried out on the effect of PAC on microbial community in AnMBR. The long-term effects of the optimal PAC dosage, which was found to be 5 g/L from the short-term experiments, on conventional AnMBR performance with a hollow fiber membrane were investigated in this study. The optimal one-off PAC dosing could increase average COD and total organic carbon (TOC) removal rates up to 15.71% and 15.69%, respectively. The PAC addition exhibited not only lower transmembrane pressure (TMP) increase rate, but also reduction of soluble microbial product (SMP) and extracellular polymeric substances (EPS). High protein fraction of SMP as well as increased zeta potential in AnMBR with PAC addition could enhance hydrophobicity, which improved the flocculation ability of sludge. In addition, lower total membrane resistance and pore blocking resistance indicated that PAC addition could prevent both severe pore blocking and irreversible fouling, due to the lower amount of polysaccharide of SMP in cake layer. PAC addition could reduce the abundance of fouling-related bacteria such as Cloacibacterium and Smithella, which contribute to the biofouling development due to the high affinity to attach on membrane surface. This is because the high adsorption capacity of PAC could enabled 1.7-4.7 times lower abundance of those bacteria by inhibiting proliferation of them. These results demonstrated that PAC addition to AnMBR could effectively mitigate membrane pore blocking and irreversible membrane fouling as well as improve microbial community.
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