Reverse osmosis within water reclamation -- An evaluation of low-pressure membrane pretreatment options

Pretreatment with low-pressure membranes has been shown to improve reverse osmosis (RO) performance dramatically in water reclamation applications and is the focus of this work. There are two options for membrane pretreatment of wastewater for RO: Treatment of conventional activated sludge (CAS) effluent with tertiary membrane filtration (TMF) and treatment of wastewater with a membrane bioreactor (MBR). The focus of this research was to compare these two pretreatments in terms of their ability to minimize RO fouling.;In addition, two pilot-scale RO systems were operated, one with each pretreatment. Side-by-side experimental runs demonstrated higher RO fouling given pretreatment with the TMF system. The MBR pretreatment resulted in RO fouling rates that were less than half of the fouling rates found given TMF pretreatment, on average. Further analyses demonstrated that the foulants were organic in nature. In addition, the average fouling rates for the different experimental runs were shown to depend on the average TOC concentration.;Bench-scale RO fouling studies were conducted in parallel with the RO pilot testing to allow surface analyses to be conducted as a function cumulative filtration volume within a series of RO cross-flow cells. These tests included an analysis of fouling trends and surface analyses with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). As with the pilot experiments the RO membranes with MBR pretreatment were found to encounter less fouling which was demonstrated in this testing through a lower accumulation of surface foulants.;The results indicated that MBR pretreatment provided effluent with a lower fouling propensity and that organic/biofouling was the governing fouling mechanism for RO filtration with both pretreatments.;A comparison of permeate water quality is presented to elucidate the removal capabilities of these two technologies. The MBR pretreatment system was found to provide lower organics concentrations with average differences of approximately 25% for both TOC and COD.