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Phosphorus Reduction Evaluation

Client: City of Beloit

Location: Beloit, Wisconsin

The City of Beloit owns and operates an advanced 11-mgd regional water pollution control facility (WPCF) that serves the City and several townships. The WPCF has historically complied with an NR 217-imposed 2 mg/L effluent phosphorus limit through enhanced biological phosphorus removal, coupled with partial chemical treatment of sidestreams from sludge thickening/dewatering. However, with recent revisions to NR 217, the City will be facing more stringent effluent phosphorus limits, as low as 0.2 mg/L.

The City hired Donohue to assist with evaluating phosphorus compliance in the near and long term and to develop a planned phasing of improvements. Several workshops were held with the City to review findings from the historical performance evaluation and to brainstorm and screen potential alternatives that could become elements of a phased compliance implementation plan.

Donohue used Biowin modeling to assess/confirm historical performance and to evaluate the effectiveness of four alternatives to optimize the existing plant’s performance. The evaluation resulted in a roadmap to compliance that involved three major phases: 1) optimize existing plant performance using filtrate equalization faciltiies, enhanced chemical treatment, and modified EBPR, 2) add effluent chemical polishing facilities, and 3) add high-rate effluent disc filters for effluent TSS control.

The plan also noted that a fourth phase, involving either ballasted flocculation, high efficiency clarification or membrane filtration, may be required in the future should the plant’s effluent phosphorus limits be lowered below the TMDL based 0.2 mg/L limit.