Meeting Stringent Standards

Aug. 16, 2018
Waterbury, Vt., faced tighter phosphorus limits under a wide range of seasonal fluctuations, including algal blooms

The Village of Waterbury (Vt.) Wastewater Treatment Plant (WWTP) is located on the Winooski River floodplain, which poses challenges from significant flooding during the spring runoff and storm seasons to strong algal blooms in late spring. During algal blooms, the plant encounters bright green lagoon effluent that is high in total suspended solids (TSS), resulting in treatment upsets and inconsistent permit compliance. The system is part of a sensitive mountain watershed that discharges into Lake Champlain.

The Waterbury facility was designed in the 1980s for an average daily flow of 0.51 mgd and a peak hourly flow of 1.02 mgd. It uses three lagoons for biological treatment, followed by a chlorine contact chamber before discharging into the Winooski River.

Tertiary Treatment Needed

In 2010, the village and its engineer, Stantec, evaluated tertiary treatment systems to polish its lagoon effluent with the flexibility to meet the current total phosphorus (TP) limit of 0.8 mg/L, as well as the foreseen ultra-low limit of 0.2 mg/L.

The village selected the CoMag System because it meets stringent TP limits in a small footprint and can handle wide fluctuations in feed TP and TSS concentrations, as well as wide swings in flow rates and treatment demands.

The CoMag System is a high-rate ballasted clarification technology that settles chemical floc up to 30 times faster than conventional clarification. It infuses magnetite (a readily available iron ore) as a weighting agent into the floc.

Plant investment costs are reduced because rapid and reliable settling, which increases treatment capacity, can be achieved with existing tanks. Additionally, because 99% of the magnetite ballast is easily recovered, the CoMag System is sustainable and cost-effective to operate.

The CoMag System dramatically reduced algae in the Waterbury WWTP lagoon effluent.

A Successful Pilot

The village’s 2012 CoMag System pilot demonstration proved that it could meet TSS and TP targets under all conditions, including high-flow and high-solids stress tests. In addition, the system reduced biochemical oxygen demand (BOD), turbidity and E. coli levels.

Full-Scale Operating Results

Based on the pilot results, the village proceeded with a full-scale CoMag System installation in September 2014, which immediately met the plant’s current effluent TP limit of 0.8 mg /L. The village conducted a process performance test to:

  • demonstrate the ability to meet the future 0.2 mg/L TP limit;
  • test the system at design and maximum flow rates; and
  • adjust the system (increasing and decreasing the coagulant dose) to provide operating setpoints and conditions for the plant to meet the current 0.8 mg/L TP limit.

For more information, contact Sergio Pino-Jelcic, senior technical sales manager for Evoqua Water Technologies, at [email protected] or 262.521.8253.

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