Thursday, July 15, 2010

Effective wastewater treatment benefits wildlife, human health

Effective wastewater treatment benefits wildlife, human health

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In recent years my morning run has often included a pause to observe the wildlife of the Copper Slough, where it runs under Rising Road in southwest Champaign. Great blue herons and mallards are regulars there, as is a pair of belted kingfishers, which nest in the bank nearby and noisily patrol the stream corridor. In the pool below the bridge live masses of some fish that tolerate fairly degraded waters, especially common carp and suckers. But there are fish with higher standards there, too, among them some decent sized largemouth bass, as well as an occasional snapping turtle.

What makes the variety of life at this site remarkable is that less than a hundred feet upstream from my vantage point, the Urbana-Champaign Sanitary District’s southwest treatment plant, which serves roughly 40,000 people, discharges some 6 million gallons per day of treated wastewater into the stream. [Photo: Discharge from the UCSD plant entering the Copper Slough from the left, just upstream from where Rising Road crosses the stream.]

I recently had the opportunity see for myself what happens to wastewater at the plant that renders the effluent capable of supporting life, thanks to a tour with Mike Guthrie. In his current life, Guthrie is an East Central Illinois Master Naturalist, but before his retirement in 2006 he had been supervisor of operations for the Sanitary District.

Guthrie emphasized that contrary to whate many people expect, most of the processes that take place at the plant do not rely on chemicals. Rather, they replicate processes that occur in nature, only they are managed to occur very efficiently.

In the first stage of wastewater treatment re the sewage that comes into the plant is screened to remove paper. This process takes place inside a building, the only place on the tour where we really had to hold our noses. The material removed in this process is the only byproduct of the plant that goes to a landfill, and the quantity of that is surprisingly small, on the order of one dumpster a week.

In the next stage of treatment, wastewater is channeled through a series of open-air basins where bacteria and other microorganisms are introduced to remove phosphorous and other pollutants. [Photo: Secondary treatment basins, left, and clarifiers, right, seen from the top of the nitrification tower.]

From this secondary treatment, water flows into clarifying tanks where the microorganisms introduced before settle out, to be cycled back into the previous process. From this point the water is pumped to the top of nitrification towers, the tallest structures at the plant. Here it is sprayed over stacked layers of honeycomb-like plastic that fill the inside of the tower. As it runs down through them, another group of microorganisms converts toxic ammonia into nontoxic nitrates.

After passing through a filter that removes any solids that might have been introduced in the nitrification process, the water from the Southwest Plant is released into the Copper Slough.

We have effective federal law—the Clean Water Act—to thank for the current high standard of wastewater treatment in the United States. And when I spoke with Glynnis Collins, executive director of Champaign-based Prairie Rivers Network, which seeks to ensure the consistent application of that law in Illinois, she shared my enthusiasm about how far we’ve come in the past 50 years.

But Collins also noted there is still work to be done. She pointed out, for example, that the Illinois EPA, which administers permits for discharge into streams, sometimes exempts wastewater plants from the final step of disinfection, making them unsuitable for human contact for some distance downstream. In addition, she explained, we’re still just beginning to understand how pollutants that are not treated by current systems, especially some of the human medications that are showing up in water all over the world, impact people and wildlife.