Study on feed pretreatment for membrane filtration of secondary effluent

Abstract

Abstract In this study, membrane filtration was used to treat a secondary effluent emanating from a sewage treatment works that treats a combined industrial and municipal wastewater. Three feed pretreatments for a spiral wound reverse osmosis (RO) membrane filtration were evaluated, including: (i) membrane ultrafiltration (System I); (ii) dual media filtration and granular activated carbon (GAC) adsorption (System II); (iii) dual media filtration with dosage of organic flocculant and GAC adsorption (System III). It is shown that System I yielded the best turbidity removal, with turbidity below 1.15 NTU. The combination of System I and RO showed the least flux decline between cleans. In addition, flux recovery was easily achieved with mechanical clean without chemicals. The overall total dissolved solids (TDS) rejection was well maintained at 81–89%. The dual media filter and GAC did not provide adequate pretreatment; this led to rapid fouling in the RO membrane. The impact on RO performance was a greater flux decline coupled with TDS rejection decrease from 78 to 66%. The addition of an organic flocculant (dosed at 15 mg/l to form filterable flocs) did not significantly improve the performance of the dual media filtration and the GAC. It was also observed that inadequate pretreatment had an adverse impact on the membrane flux recovery by cleaning. Simple mechanical cleaning was insufficient in recovering flux when Systems II and III were employed as pretreatment. Furthermore, longer chemical cleaning duration was required to recover membrane flux.