APPLICATION OF REVERSE OSMOSIS MEMBRANES FOR WATER RECLAMATION WITH VARIOUS PRETREATMENT PROCESSES
Abstract:The City of San Diego is developing new water sources to serve its arid region. In addition, water reclamation is being seriously evaluated by the City to reduce the region's reliance on less dependable imported water. The City adopted the reverse osmosis (RO) process as the foundation of the advanced water treatment of many of their reclamation projects because RO has been shown to accomplish the best overall removal of organics, trace metals and total dissolved solids. In addition, RO has the potential for removal of all classes of pathogens. In order to operate the RO membranes reliably and minimize membrane fouling, a pretreatment step is required. A comparison of thin film composite (TFC) RO membrane operational performance from three different projects using the same municipal wastewater source but different RO pretreatment processes was performed. The treatment scenarios that were evaluated included (1) microfiltration (MF), (2) ultrafiltration (UF), (3) membrane bioreactor (MBR) and (4) lime clarification. The lime clarified effluent wastewater proved a possible pretreatment to thin TFC RO membranes. However, the variable effluent water quality resulted in cleaning intervals between 600 and 1400 hours. The MBR and MF/UF pretreatment scenarios produced a consistent effluent water quality. The MBR effluent did provide the RO membranes with a run time as long as 3200 hours, however the MF/UF gave a run time, as long as 10,000 hours with the MF effluent. There was no difference observed in quality of the MF or UF effluent as a pretreatment to RO. Although the MBR did produce a similar effluent water quality as the MF/UF system, the run time was significantly shorter. The exceptionally long run times experienced with the MF/UF after tertiary treatment by far makes it the best pretreatment to TFC RO membranes.
Document Type: Research Article
Publication date: 2000-01-01
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