Challenge

The city of Rosemount, Minnesota, was seeking treatment for phosphorus in the effluent discharge from the city's wastewater treatment plant.  The customer's 0.75 MGD facility was permitted to discharge wastewater with a maximum average monthly total phosphorus level of 1.0 mg/l; however the effluent from the facility's newly installed disc filters was exceeding the NPDES permit limit.

Extremely cold winter temperatures was determined as the cause of the problem with total suspended solids (TSS).  New disc filters were installed to remove TSS and the associated phosphorus, but soon after the installation, it was determined that the phosphorus concentration had not been reduced.

Solution

A water sample was sent to Siemens Water Technologies, formerly USFilter, for testing where it was confirmed that soluble and insoluble phosphate was attaching itself to the suspended particles in the water.  The unusually cold temperatures were preventing the disc filters from effectively removing the suspended solids in the waste effluent which explained the presence of phosphorus.

The Siemens solution provided a high-rate mobile clarification unit for the removal of suspended solids and thus reducing phosphate levels.  The clarification system is a self-contained, trailer-mounted unit that treats water with high turbidity, high total organic carbon (TOC), algae or very cold water.

Results

Siemens Water Technologies enabled this customer to solve their phosphorus problem within a short timeframe to meet their monthly average discharge limits.

Four days after the clarification system began treating water, the total phosphorus level of the treated effluent was 0.75 mg/l, comfortably below the permitted 1.0 mg/l maximum provided by the NPDES.

No further capital investment was required to solve this temporary, weather-related condition.

City of Rosemount, Minnesota Case Study