From the Boulder Daily Camera (Heath Urie):
The Colorado Water Quality Control Commission in 2007 approved new standards for wastewater discharge lines that require municipalities to better control the temperature of the water that’s treated and then dumped into creeks and rivers. The rules were put in place to protect fish and other wildlife that are sensitive to water temperature.
Now, Boulder is finding itself to be something of a guinea pig for the state, as it’s the first municipality to renew its wastewater-discharge permit since the rules went into effect last year for streams within the South Platte River Basin. When city utility officials received a proposed draft of the new discharge permit earlier this year, they found out that Boulder’s 75th Street Wastewater Treatment Plant — which discharges about 20 million gallons a day into Boulder Creek — is not meeting the new standards during the coldest months of the year. According to the Water Quality Control Division of the Colorado Department of Public Health and Environment — which is tasked with enforcing the standards and issuing permits — the new rules limit the maximum average temperature of discharged water to 59 degrees during the winter. But Boulder’s water ranges from 53.24 to 61.34 degrees from December through February…
“They’re pretty close to meeting the standards,” Steve Gunderson, director of the state Water Quality Control Division, said of the Boulder utility. “They are not quite there for the winter months.” Gunderson said the state has proposed giving Boulder until October 2013 to comply with all of the standards. “This is a challenge for a domestic wastewater treatment plant,” he said. “It can be pretty expensive to upgrade a wastewater treatment center.”[…]
Williams said it’s not yet clear how the city will meet the new temperature requirements. “We’re trying to sort it out, better understand it, talk to the state about it and see what might happen in our final permit,” Williams said. He told the City Council earlier this week that a worst-case scenario is that the utility will be forced to “chill our wastewater.” That could force the city to make some “very unusual” capital improvements, such as purchasing a giant chiller that would cool the water, or creating detention ponds where water can naturally cool off, Williams said. It is possible that the city could ask the state for an exemption from the temperature rules, but that would have to be approved through both the water commission and the U.S. Environmental Protection Agency. The city has until late September to file a response about the state’s offer for a three-year grace period.
More wastewater coverage here.
Once option is to subject the warm effluent to a specialized cross-flow (air) cooling towers (6 or more) arranged in a circle, which could reduce the water temperature by 5-10 *F. The enthalpy is transferred to air which exits tangentially into an circular arena, from where it rises high into the atmosphere in the form of a buoyant vortex.
The power required to pump the water through the cooling cells can be extracted from the in-rushing air by passing it through and extraction turbine.
In some cases, depending on design, the power extracted could be great enough to power the entire waste treatment facility.
Any residual odors would be raised to a level high enough in the atmosphere where they would be oxidized (UV) before returning to ground level.
Depending on location with respect to the prevailing wind, such a scheme could also take care of any additional odors emanating from the balance of the plant.