Impact of pretreatments on reverse osmosis treatment of secondary effluent

Impact of pretreatments on reverse osmosis (RO) membrane fouling was investigated in the City of Guelph Wastewater Treatment Plant (WWTP) Conventional treatment process and MBR pilot treatment system were selected as two pretreatment options of down stream RO pilot systems. It was shown that the MBR system provided better protection than conventional treatment process for down stream RO membrane from fouling. Two systems were operated at same constant permeate flow rate of 9.46 L/min (2.5 gpm) and constant recovery rate of 26%. The conventional-RO system reached the highest operating pressure within 23 days of operation due to the membrane fouling, while MBR-RO reached the highest operating pressure in 43 days of operation, which resulted in an overall 47% improvement of RO system performance by MBR-RO system. In addition, RO production water qualities were evaluated in terms of pH, turbidity, conductivity, TOC, COD, total/fecal coliforms, cations (sodium, ammonium, calcium and magnesium) and anions (chloride, nitrite, nitrate, sulfate and phosphate). High removal efficiencies were achieved by both RO pilot systems.