A Bench-Scale Study for the Treatment of Ultrafiltration Reject Generated at Perris Water Filtration Plant

Eastern Municipal Water District (EMWD) has evaluated candidate technologies for treatment and recovery of the reject (waste) stream from the ultrafiltration (UF) system at the Perris Water Filtration Plant (PWFP). The treated water from the reject recovery system will be returned to the head of the PWFP and processed into potable water. The treated reject flow should have characteristics that are similar to or better than raw water quality to minimize adverse impacts on UF system operation when the treated reject water is returned back to the PWFP (i.e., turbidity ≤2 NTU and TOC≤3 mg/L). In addition, the selected process should be relatively compact to meet approximately 3,000 sq-ft space dedicated for reject treatment and recovery system.Based on project objectives and constraints, three treatment technologies were short listed from a total of seven applicable technologies using non-monetary criteria and a quantitative scoring technique. The short-listed technologies (membrane filtration, inclined plate settling and ballasted flocculation) were further evaluated via multi-attribute analysis which identified membrane filtration as the best option. Ballasted flocculation received a higher benefit-to-cost ranking than plate settling, however the potential for sand and polymer carryover was deemed to represent a serious risk to the PWFP UF operation by the membrane supplier, negatively impacting their membrane warranty. Consequently, ballasted flocculation was eliminated as an implementable reject treatment alternative. To confirm the benefit of membrane filtration over plate settling, a bench testing was conducted such that final technology selection was based on empirical data, rather than assumptions. This paper describes the reject recovery treatment alternative selection and bench-testing findings.