AWWA MTC69743

The Orange County Water District (OCWD) recently commissioned the Groundwater Replenishment (GWR) System, an advanced wastewater treatment facility consisting of microfiltration (MF), followed by reverse osmosis and advanced oxidation (ultraviolet treatment with hydrogen peroxide). Developed as an indirect potable reuse facility, the GWR system provides 70mgd of purified wastewater for groundwater recharge and maintenance of an intrusion barrier to protect the local groundwater basin from seawater infiltration. Source water to the GWR system consists of secondary municipal effluent provided by the Orange County Sanitation District (OCSD). Secondary wastewater is produced by operating two processes, activated sludge (AS) treatment and trickling filter (TF) treatment. The GWR System design specifies a blended feed of AS effluent and TF effluent from OCSD. During GWR System MF feasibility testing, however, only AS effluent was evaluated. Infrastructure limitations at the time prohibited blending at the OCWD test facility. While the AS and TF processes produce acceptable secondary effluent, there are disparities in water quality between the two, differences that could impact MF performance. The concentration of dissolved organic constituents and particulate material are generally higher in TF effluent, when compared to AS effluent. Trickling filters also provide a favorable environment for snails, which graze on the zoogenic biological slime present on the TF media. Snails are problematic since they add to the organic and suspended solid load when sloughed off and carried to the secondary clarifiers. The snails (and snail shells) could also physically damage the MF membrane fibers if conveyed to the GWR system. MF membrane integrity would be compromised, resulting in a host of deleterious affects that reduce effective plant operations. Given these concerns, TF effluent was not treated during the first 8- months of operation until further studies were performed. This decision resulted in the treatment plant being unable to operate at the design capacity, therefore expediting the need to resolve this issue in a timely manner. This paper documents the streamlined and innovative pilot testing efforts undertaken to verify the impact TF effluent would have on the MF treatment process (and operations of the GWR system). In addition, a variety of water quality analyses were performed to examine the differences in effluent water quality between the two secondary treatment processes. Includes figures.