MICROFILTRATION OF PRIMARY EFFLUENT FOR OCEAN DISCHARGE

During more than one year of successful pilot testing of a new integrated membrane-anaerobic stabilization (IMANS) system for wastewater treatment and water reclamation, microfiltration of primary effluent was demonstrated to produce a high quality effluent suitable for ocean discharge. The success of the pilot work prompted the Orange County Sanitation District (OCSD) to embark on a second phase project to investigate the performance of microfiltration of primary effluent at a larger scale.A major concern for the OCSD is management of peak flows. While the District has two ocean outfalls to discharge treated wastewater, the shorter of the two is not currently in regular use because it discharges closer to the shoreline and requires a significantly higher quality effluent. Regular use of the “short” ocean outfall could save the District millions of dollars by delaying the need to build another deep-water outfall. In addition to the flow management issues, the District is also facing the need to renew its discharge permit. Permit renewal is coupled with public pressure for the District to implement full secondary treatment prior to ocean discharge, instead of the current approach of discharging a 50:50 blend of primary and secondary treated effluent. To meet the needs for higher quality effluent, microfiltration of primary effluent is one alternative that the District is now considering.Four months of continuous operation of the larger scale (200 gpm) microfiltration plant treating enhanced primary treated wastewater has confirmed the positive results observed during the pilot plant work. Excellent solids and bacterial removals were achieved, with negligible evidence of long-term (irreversible) fouling of the membranes. Operation of the plant continues.