Water Portfolio

As part of a plant upgrade to increase treatment capacity, the Siloam Springs wastewater treatment plant has incorporated a custom-designed biological nutrient removal (BNR) process without filtration. Now operational, the new bioreactor is producing a discharge phosphorus of less than 0.4 mg/L and nitrate less than 10 mg/L.

To achieve this level of performance, the city partnered with Garver to develop, design and implement the enhanced nutrient removal program, which reduces the phosphorus levels in three process phases. The project’s first two phases are now online and improve the liquid process treatment train through BNR and chemical nutrient removal (CNR).

The BNR treatment process involves a combination of anaerobic/anoxic/aerobic zones to target effluent phosphorus and nitrate concentrations. Although the new BNR technology has achieved phosphorus nutrient removal as low as 0.4 mg/L at the treatment plant, its marriage to the CNR process will help the plant achieve phosphorus levels another magnitude lower.

To ensure compliance with a potential future 0.037 mg/L phosphorus mandate, the treatment plant is designed to integrate membrane biological reactor (MBR) technology, which provides a physical barrier against phosphorus by using membrane media. Prior to full-scale design, Garver performed a pilot study to verify MBR performance at the plant. Two parallel pilot-scale MBR process trains were demonstrated over a six-week period. The data revealed that MBR technology, in combination with BNR and CNR, can consistently produce effluent with phosphorus levels at 0.025 mg/L, well below any reported ultimate final discharge limits.

Together, the custom-designed nutrient reduction program and biosolids improvements have increased treatment performance, reliability and operational flexibility for the city.

• Pilot study
• Design
• Implementation