Balancing Nutrients in a Reuse World

The Western Corridor Recycled Water Project (WCRWP) in Queensland will reclaim water from municipal effluent for reuse to reduce demand by industrial users of current sources and possibly also to replenish source water. A total of three AWTPs will be constructed to treat secondary effluent from six wastewater treatment plants to provide an ultimate reuse water supply of 310 MLD. The first project, Bundamba-A, went into service in September 2007 with an initial capacity of 20 MLD. The second phase, Bundamba-B will go into service in mid 2008 to provide an additional 40 MLD. The liquid stream process will consist of microfiltration, reverse osmosis and advanced oxidation using UV- peroxide. Unique to this project is treatment of the reverse osmosis waste stream to remove nitrogen and phosphorus prior to discharge to a brackish river. In addition, high levels of ortho phosphorus can adversely impact the RO operation due to scaling. Several nutrient reduction alternatives were considered to determine the preferred location for nutrient reduction. The recommended plan included pre-treatment of the AWTP feed water to reduce ortho phosphates to a concentration that would not result in scaling of the RO units and would minimize the quantity of phosphorus removal required in the ROC to meet the discharge permit. A storage basin will provide equalization of the ROC prior to chemical/physical treatment for phosphorus removal in a high rate solids contact clarification process. Chemical feed to the solids contact clarifiers will include bisulfite for dechlorination, caustic for alkalinity and pH control, and ferric chloride and polymer for coagulation and chemical precipitation of phosphorus. Deep bed denitrification filters will provide nitrate removal using methanol as a carbon source.