S. Thakral, G. McPherson, G. Lai 1
A revised National Pollution Discharge Elimination System (NPDES) permit issued for the City of Riverside Regional Water Quality Control Plant (RWQCP) in May 1992 requires the plant to meet a new discharge requirement for total inorganic nitrogen (TIN). A "partial nitrogen control at the RWQCP and partial control in the wetlands system followed by wetlands polishing" alternative was selected for its many advantages over the other nitrogen management strategies. In lieu of making major capital improvements at the plant, the City has a unique opportunity of using an existing constructed wetlands system in the Hidden Valley Wildlife Area to provide the additional nitrogen removal at a much lower cost with the added benefits of environmental enhancement. The City decided to restore the existing wetlands in two phases. Site-specific design parameters are being developed through a pilot testing program with the implementation of Phase I and prior to a larger scale of wetlands restoration for denitrification for the entire effluent. Phase I is a 70 to 80 acre project treating 0.44 m3/s (10 mgd) of nitrified RWQCP effluent and Phase II is the expansion of Phase I to a full-scale system, treating the entire RWQCP effluent. The construction of Phase I project was completed in March, 1995. Currently the project is in the process stabilization period and a pilot testing program is being implemented. Initial indications for nitrogen removal are encouraging. By the end of 1995, more data will be available to determine the effectiveness of nitrogen removal through the constructed wetlands at Hidden Valley.
