Performance of surfactant supplementation on alleviating membrane fouling in treatment of waste activated sludge: Experimental and modeling analyses

In this research, surfactant supplementation was investigated as a novel strategy for alleviation of membrane fouling in waste activated sludge (WAS) membrane filtration process. The effect of WAS pre-treatment with different surfactants on membrane performance were investigated in terms of flux variation, membrane rejection and fouling mechanisms. A generalization form of blocking law was developed to determine membrane fouling mechanism. According to the results, cationic surfactant below critical micelle concentration (CMC) values improved membrane performance, while anionic and non-ionic surfactant showed a negative impact at all dosages. It was observed that WAS pretreatment with 300 mg/L Cetyltrimethylammonium bromide (CTAB) could increase the water flux from 195 to 611 L/m²/h (LMH) and decrease the rejection rate from 93% to 85%, respectively. Although CTAB addition increased the total extracellular polymeric substances (EPSs) amount from 56.16 to 119.6 mg/L which was due to the surfactant solubilization property, the total resistance decreased from 0.33×10¹⁰ to 0.11×10¹⁰ m^-1. This was attributed to the flock formation induced by CTAB through charge neutralization and bridging mechanism. Modeling simulation of the results indicated that CTAB addition transformed fouling mechanism from cake to intermediate-blocking model. The environmental risk assessment revealed that only 0.3 mg/L surfactant penetrated in permeate which was low ecological risk (risk quotients (RQ) < 0.5) to the aquatic environment. Our finding suggested CTAB treatment at low dosage (0.1 g/L) as a promising and efficient approach for fouling mitigation and improving membrane process for wastewater treatment.