Colfax approves using alum to remove phosphorus; annual cost estimated at $15,000

By LeAnn R. Ralph

COLFAX  —  A new system using aluminum sulfate to remove phosphorus will soon be in operation at the Colfax wastewater treatment lagoons.

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

The annual cost for the alum system will be approximately $15,000, said Jeremiah Wendt, the village’s wastewater treatment engineer from Short Elliot Hendrickson Inc. (SEH) out of Chippewa Falls.

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, Wendt said.

Colfax must comply and will have a limit of one milligram of phosphorus per liter when the new wastewater treatment permit goes into effect January 1, he said.

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

Initially, Colfax was considered as a candidate for pollutant trading, Wendt noted.

Under a pollutant trading program, the village would have worked with farmers upstream to help fund methods for reducing phosphorus run-off, such as no-till planting, at a ratio of two to one: two pounds from farm fields for every pound discharged by the village.

The new phosphorus rules are more stringent and are based on the stream to which the municipality is discharging. The new rules also removed pollutant trading as an option, Wendt said.

Phosphorus study

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 around $3 million, while other methods were estimated to cost between $100,000 and $500,000.

The state Department of Natural Resources asked Colfax to perform pilot testing in 2013 to find out what level of phosphorus removal could be achieved in the existing lagoon system without constructing major upgrades.

The DNR will use the report from the pilot testing to help write the village’s wastewater treatment permit.

Aluminum sulfate

Wendt said he had visited the Village of Granton, which operates a lagoon system similar to Colfax’s lagoon system.

Granton uses ferric chloride for phosphorus removal, which works well for Granton but probably would not work well for Colfax because of the size of the lagoons and the solar mixers used at Colfax, Wendt said.

Wendt contacted a chemical supplier, Hawkins, Inc., to perform “jar testing” on the village’s wastewater to determine which chemical would be the most effective.

Jar testing revealed that aluminum sulfate (alum) was the most effective and that an application of 200 parts per million would remove phosphorus down to .76 milligrams per liter, he said.

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

A total of 4,300 gallons of alum would be needed each year, at a cost of $3.40 per gallon, or about $15,000 annually, Wendt said.

To confirm the assumptions from the jar testing, Wendt recommended the village proceed will full-scale pilot testing of the alum as soon as possible.

Colfax’s wastewater treatment lagoons discharge to the Red Cedar River from May until November but not during the winter or early spring.

During the pilot testing, Wendt recommended additional monitoring of the phosphorus.

Phosphorus tests from Commercial Testing in Colfax cost $15 each, so the additional testing for 2013 will cost about $2,000, Wendt said.

 

Using alum does not require spending money on upgrades to the system, Wendt noted.

The cost per year of using alum would be “in the ballpark” of using pollutant trading, he said.

Alum would be fed into the lagoons from April or May until November, from the time the village begins discharging into the river until the village stops discharging into the river, Wendt said.

Within the first month of treatment, Colfax will have a good idea of how well the alum is working, he said.

The village’s existing lagoon system does a good job, and maintenance costs are minimal, Wendt said.

The village should keep the lagoon system running as long as possible, although sludge will have to be removed from the bottom of the lagoons at some point, he said.

The village board also will have to consider how to address the erosion in the river bank that could eventually end up washing out the lagoons, Wendt said.

If the lagoons wash out, the cost to replace them would be more than the cost of fixing the gullies, he said.

The gullies appeared during the August of 2010 thunderstorm that produced about seven inches of rain in two hours.

In July of 2011, the village board received an estimate of $400,000 to riprap the river bank to keep the lagoons from washing out.

The Colfax Village Board unanimously approved a motion to move forward with the pilot testing.

Wendt said that Hawkins would have the alum system set up within the next week or two.