What a difference some clarifiers make ... and some bacteria.
The two glass containers both held water, but the liquid in the left was opaque and gray, while the liquid in the container on the right was see-through, and appeared indistinguishable from drinking water. It was a before-and-after example arranged by the staff of Moline's newly upgraded North Slope Wastewater Treatment Plant, showing off the difference the plant has on the city's sanitary sewer water.
The water on the right would still need further purification before it was potable, but not much, Rob Barnard, treatment operations manager, said.
The plant was officially marked complete Tuesday with a ribbon cutting. Dozens were present, including Moline's elected officials, staff and representatives of the contractors and others who contributed to the project.
"This is not only good for our residents," Mayor Stephanie Acri said during opening comments. "It's good for the environment which we are part of."
The years-long project, planning for which began in 2012, cost about $43 million and the upgrades included the ability to better clean the sewer water, updated equipment, increased storage capacity for excess water and removed waste, and better energy efficiency, according to a city news release. The old plant could process a similar amount of water, but had about half the storage.
The overhaul of the 50-year-old plant was designed to improve efficiency using automation and up-to-date equipment. The also is designed to prevent or minimize overflows on River Drive during heavy rains.
In 2009, the Illinois Environmental Protection Agency notified Moline that the overflows had to be addressed. River Drive manholes would overflow because the North Slope facility could not handle the influx from the rains.
The plant serves Moline properties from Avenue of the Cities north to the Mississppi River, Barnard said.
North Slope itself is just west of Sylvan Island, near Moline's border with Rock Island.
Tina Sebold, project manager with Strand Associates Inc., the engineering firm working with the city on the plant, gave a tour of North Slope, showing how it cleans the waste water, which, at the end of the process, is mostly released into the Mississippi River.
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Untreated water from the service area is fed into North Slope via a 60-inch pipe, she said. From there, the first step removes solid inorganic matter from the flow, separating it mechanically, drying it out and placing it bins for disposal in a landfill.
The water is then pumped up into a squat tower, then allowed to flow down and into the rest of the system, letting gravity work for Moline.
The next step is the primary clarification tanks, Sebold said. There are two, and while the water sits in them, further solids settle to the bottom or float to the surface and also are removed.
From there, the water is sent to new tanks where it is exposed to bacteria, she said. This bacteria further breaks down contaminants in the water. Then the water is sent to a second set of clarification tanks so further contaminants can settle or skimmed from the water's surface.
The final step is exposure to chlorine in a tank on the edge of the Sylvan Slough, Sebold said. This scrubs the water of any remaining bacteria or other unwanted material before it is released into the slough.
On average, the plant treats about 5.5 million gallons a day, but it can handle as much as 13.75 million, she said. Should more than that come in, the excess can be diverted into storage tanks. Those tanks in total have about a 20-million-gallon capacity.
Much of the old plant was reused in the new design, she said. Buildings and tanks were upgraded and repurposed.
Barnard said the project was funded partially with Moline money, but the city also made use of a loan through the Illinois Environmental Protection Agency.
Acri, Moline Public Works Director J.D. Schulte and other officials credited the close cooperation of the city, the engineers, contractors and others in getting the project done.
Schulte complimented the city's employees for the extra work performed on the project, including some of the final engineering work, and preparing the landscaping.
"They closed this project out strong," he said.