OPERATIONAL STRATEGIES AND TREATMENT TECHNOLOGIES FOR MEETING VERY LOW TOTAL PHOSPHORUS LIMITS

The Clark County Water Reclamation District (CCWRD), in Las Vegas, Nevada, operates a 100-mgd wastewater treatment plant that is one of largest biological phosphorus removal (BPR) activated sludge facilities in the world. The plant discharges into environmentally sensitive Las Vegas Wash and Lake Mead under a strict total phosphorus (TP) discharge limitation of 0.26 mg/L. This limit is currently met through a combination of BPR and conventional tertiary filtration. Recent concerns over the water quality of the Las Vegas Wash are expected to result in more stringent TP criteria in the future. Preliminary indications are that the TP limit at the planned plant buildout capacity of 130 mgd could be as low as 0.09 mg/L. Faced with the likelihood of having to meet these low limits, the District embarked on an evaluation to investigate operational strategies and new technologies capable of reliably meeting the projected low effluent limits. This evaluation investigated the following operational strategies / treatment technologies: (a) Operational strategies to improve BPR, (b) Coagulation / flocculation / sedimentation followed by conventional tertiary filtration, and (c) microfiltration. The paper presents the details of this evaluation, and should be of much interest given the proposed new stringent EPA nutrient criteria for TP.