Preliminary results: alum has cut Colfax phosphorus in half

By LeAnn R. Ralph

COLFAX — Although the results are preliminary, using aluminum sulfate to remove phosphorus at the Colfax wastewater treatment lagoons has cut the phosphorus discharge in half.

Rand Bates, director of public works, talked about the aluminum sulfate delivery system and the need for electricity at the lagoons at the Colfax Village Board’s public works committee meeting October 3.

Installing electricity at the lagoons would allow the level of aluminum sulfate to be adjusted automatically instead of Bates going out to the lagoons several times a day and recalibrating the delivery system to mix in the proper amount of alum.

Discharge rates from the lagoons vary, which means that the amount of aluminum sulfate needed is going to vary, Bates said.

For example, before the rain that fell October 2, the discharge rate was about 40 gallons per minute. After the rain, the discharge rate was around 60 gallons per minute, he said.

Alum works by binding with phosphorus, causing it to settle to the bottom of the lagoon.

Although Colfax has been granted variances in the past to allow a higher discharge of phosphorus than allowed by state law, the new Total Daily Maximum Load (TMDL) established by the federal Environmental Protection Agency for the Red Cedar River will not allow another variance.

Colfax is expected to have a phosphorus limit of one milligram per liter when the village receives a new wastewater treatment permit.

The village’s existing permit expires on December 31.

The current discharge limit for Colfax is 9.9 milligrams of phosphorus per liter.

Using aluminum sulfate to see if the discharge of phosphorus can be reduced to one milligram is an experiment for Colfax.

Initially, village officials had been working with Jeremiah Wendt of Short Elliott Hendrickson (SEH) and Dunn County officials to set up a pollutant-trading program for phosphorus.

Pollutant trading was close to being a “done deal” when state Department of Natural Resources officials changed their minds and said pollutant trading was no longer an option for Colfax and that the village should try using aluminum sulfate.

The Colfax Village Board approved moving forward with the pilot-testing program using alum at the June 24 meeting.

One year

DNR officials say they need a full year’s worth of phosphorus testing results before they will decide if aluminum sulfate is effective as a treatment program for Colfax, Bates told the public works committee October 3.

Just because preliminary results indicate that the phosphorus discharge has been cut in half from eight down to four does not mean that Colfax can actually get down to one, he said.

Earlier jar tests indicated that when the wastewater is put into jars and treated with alum, the phosphorus level can be brought down to .76.

Collecting phosphorus data this year has been especially difficult because of the drought, Bates said.

Without any rain, the lagoons stopped discharging, he said.

Colfax typically discharges from the lagoons into the Red Cedar River from May until November.

Although Colfax’s wastewater treatment permit technically expires on December 31, the DNR will extend the current permit to allow the village to collect more data in an effort to find out how effective the alum treatments will be, Bates said.

If Colfax can get down to 1.5 milligrams of phosphorus per liter, it’s possible the DNR may allow 1.5 as a limit, he said.

Electricity

Electricity to the lagoons and a pump would cost about $11,000, Bates said.

A small building would also need to be constructed over the pump, he said.

According to a cost estimate from Dunn Energy Cooperative, bringing electricity to the lagoons would cost $6,500.

Although having electricity at the lagoons would be very helpful, Bates said he would not recommend installing electricity and buying a pump and building a pump house until the village knows whether the DNR is going to accept the phosphorus level that Colfax can achieve — especially if that level is somewhat higher than one milligram per liter.

The TMDL establishes a limit of 320 pounds of phosphorus a year from Colfax. The village currently discharges between 1,100 and 1,200 pounds of phosphorus annually.

Phosphorus is the nutrient that feeds toxic algae blooms during the summer in Tainter Lake and Lake Menomin.

The TMDL for the 1,700 square-mile Red Cedar River Basin is intended to help control the amount of phosphorus being discharged into the watershed, which in turn is expected to reduce the duration of algae blooms in the two lakes.

Because phosphorus is a commonly-occurring soil nutrient in this area and throughout the watershed, millions of pounds of phosphorus are discharged into the watershed each year.

Water coming out of the tap in Colfax is at the legal limit for phosphorus.

The EPA has listed Tainter Lake and Lake Menomin as impaired waters.

The annual cost of aluminum sulfate for Colfax is expected to be around $15,000.

Several years ago, the Colfax Village Board approved a contract with SEH to assess the village’s lagoon system and to suggest options for controlling phosphorus.

Wendt completed the phosphorus removal report in 2010.

A new mechanical wastewater treatment plant would cost about $3 million, while other methods were estimated to cost between $100,000 and $500,000.

At the October 3 meeting, the public works committee also reviewed a proposed water expense budget for 2014 of a little over $231,000, and a proposed sewer expense budget for 2014 of nearly $232,000.