WPU looks at alternative to treat drinking water
A pilot study sought to determine if Worthington's water treatment plant could effectively use biological treatment to remove ammonia, iron and manganese from its drinking water supply. While further study is needed, it appears making the switch could save the city money.
WORTHINGTON — A 21-week pilot study evaluating the potential for the city’s drinking water supply to one day go through biological filtration rather than chemical treatment has shown promise, but further study is needed.
During a Monday meeting of the Worthington Public Utilities Water and Light Commission, general manager Scott Hain said the results of the study, conducted by WSB, show the city’s water treatment plant is a great candidate for biological treatment.
Biological treatment of water uses naturally occurring bacteria to remove specific nutrients from raw water. The pilot study in Worthington evaluated the removal of ammonia, iron and manganese. Those nutrients are currently removed from the city’s drinking water supply by running water through a green sand filter and then adding chlorine to neutralize ammonia in the water, Hain explained.
Using biological controls to treat water would result in a variety of cost savings for the city. For starters, with biological media, backwashing of filters would need to be done about every 800 hours using the utility’s existing filters, compared to the current process, which requires backwashing every 60 to 80 hours. If WPU was to invest in new media filters, backwashing would need to be done every 900 to 1,000 hours. The backwashing process uses a lot of water, Hain said, which is where he sees part of the cost savings.
The other savings would come from the reduced use of treatment chemicals — something Hain said could save between $45,000 and $50,000 per year.
While the study showed the city wouldn’t need to replace its existing filter media to make the switch to biological filtration, Hain said the media is nearly 30 years old and should be replaced anyway.
With the success of the pilot study, Hain said the next step is to conduct a feasibility study — to see how much it would cost to retrofit the water treatment plant to be able to incorporate biological filtration. He has requested an estimate from WSB to conduct a feasibility study in 2020.
In other business Monday, the commission:
Heard a brief report on the 2020 budget process. Hain said that, as directed, he is looking at succession planning for WPU. In the 2020 budget, he has included six months of salary and benefits for a new assistant manager or utility coordinator-type position. As general manager, Hain said it will be several more years before he looks to retire.
Received an update on Well 26 in the Lake Bella wellhead. The water level in the well is 9.5 feet above average and 20.6 feet higher than the same week in 2015, when the community was still considered to be in a drought.
“Back in mid-November 2015 we had an unprecedented fall recharge,” Hain recalled for commission members. “We went above the historic average on Dec. 11, 2015 and we haven’t come close to falling below average since.
“I like where we’re at — it’s a good place to be,” he said.
Since WPU began purchasing Lewis & Clark Regional Water System water this spring, less water is being used from the Lake Bella wellhead. Still, Hain said the city needs to maintain the capacity it has from the wellfield. He reported that the Minnesota Department of Health has some concerns about a couple of WPU’s wells and their proximity to surface water, and said he may need to come back and ask the commission to replace two of the city’s existing wells.
Learned that the line that carries water from the Lake Bella wellfield to Worthington has been successfully relocated at Hawkinson bridge along Nobles County 57 at Lake Ocheda. The water line needed to be relocated under the channel due to the planned removal of the bridge structure and replacement with precast concrete culverts.
The boring was completed and the first tie-in done a few weeks ago. The final tie-in was done on Sunday to complete the project. Hain said the contractor was asked to do the work on a Sunday because it had to be done when JBS wasn’t operating.