The layout of Rigby’s Wastewater Treatment Plant located at 3939 E. 500 N.

Rigby's Wastewater Treatment Operator Scott Humphries (right) details how the treatment plant processes wastewater to Councilman Richard Datwyler (left) and the rest of the City Council during its special meeting May 29. 

The layout of Rigby’s Wastewater Treatment Plant located at 3939 E. 500 N.

Rigby's Wastewater Treatment Operator Scott Humphries (right) details how the treatment plant processes wastewater to Councilman Richard Datwyler (left) and the rest of the City Council during its special meeting May 29. 

The Rigby City Council held a special meeting May 29 to tour the city’s wastewater treatment plant facility with Wastewater Treatment Operator Scott Humphries, Keller Associates Project Manager Marvin Fielding and Keller Associates Vice President Jim Mullen to understand which areas of the treatment plant that are under discussion for replacing or modifying.

Humphries explained that the wastewater is first processed though the headworks, and then is sent to the plant’s oxidation ditches where biodegradable organics are removed. After the waste is sent through the oxidation ditches it then travels to clarifiers where remaining solids are mechanically removed. By the time the wastewater leaves the clarifier, the liquid is much clearer.

The wastewater is then sent through another disinfectant treatment through ultraviolet technology. This is where the disease-causing organisms in the wastewater effluent are destroyed. Lastly, the sludge is compressed to remove the remaining liquids and is then deposited in a pile that is taken to the landfill twice a year.

The city is currently looking at $17 million in additions and modifications to the wastewater treatment plant to accommodate upcoming Environmental Protection Agency requirements and the city’s ongoing population growth.

To help meet the future requirements, Keller Associates looked at four different options; build additional oxidization ditches like the city currently has, a new oxidization ditch configuration (only change the type of aeration and mixing), enhanced oxidization ditches using Integrated Fixed Film Activated Sludge (IFAS) and enhanced oxidization ditches utilizing Nuvoda Mobile Organic Biofilm.

During the tour, Fielding indicated that the IFAS system would also help with phosphorous levels if the Department of Environmental Quality decides to regulate it in the future, which Fielding indicated they are not planning to enforce.

Keller Associates also looked at disinfection alternatives.

According to the existing ultra violet disinfection system manufacturer, the city’s current system is obsolete and spare parts will likely be unavailable in the next five to seven years. Therefore the first alternative would be to look at a similar horizontal ultra violet system. The second option discussed was an inclined vertical ultra violet system.

Lastly, the study looked at solids thickening and dewatering alternatives. The existing gravity belt thickener and belt filter press combination unit will be unable keep up with the additional solids associated with ammonia removal and planned growth.

Three alternatives were chosen for evaluation; continue to utilize the gravity belt section of the belt filter press for thickening and hen purchase a screw press for dewatering; purchase a second combination unit for redundancy; or purchase a new rotary drum thickener for dewatering and a screw press for dewatering.

If the city decides to proceed with each of the recommended alternatives, city residents would likely see an increase to their monthly utility bill by at least $70.

Near the end of the tour, Mayor Jason Richardson indicated a need for the city to pursue grants to help cover the cost and limit the increase to resident’s utility bills.

Fielding said they are currently looking into a grant from the United States Department of Agriculture in the amount of $1.5 million. He said they will also research grants at the state level that could be more substantial such as a block grant.

Richardson also suggested they draft a letter to Senator Mike Crapo and Congressman Mike Simpson requesting financial aid.

Humphries stressed with the council that ammonia treatments need to be installed by 2023 or else the city would face hefty fines. He said such fines could equate to $35,000 per fine, per day.

“Everything is timing because we’ve got that 2023 looming over your head,” he said.

For the time being, Fielding said they will present a draft study to the council in the first part of July.

The council was presented with a list of alternatives May 16.

During the presentation, Fielding said they calculated what the growth would be between now and 2040 with a 3.25 percent growth which equaled more than 8,000 people. He indicated that the city currently produces 1,200 pounds of biochemical oxygen demand each day. With the projected growth, the study figured 3,165 pounds would be produced each day.

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