It was a classic case of understatement.
The headline in an October 2010 edition of the Clinton (Okla.) Daily News proclaimed, "City sewer, water plants doing well."
During the summer of 2010, a public-private partner had begun operation of the City of Clinton's 4-mgd sewer plant and its 5.5-mgd Clinton Lake water treatment plant. The wastewater plant was experiencing chronic sludge overloading when receiving only a quarter of the design flow. At the water treatment plant, turbidity rates were high, resulting in poor drinking water taste and odor. And energy consumption by the two plants was much higher than expected.
The first-year cost of the contract with the new public-private partner was approximately $160,000 less than it was costing the City to operate and maintain the plants itself. Three months after the partnership commenced, water and wastewater quality and compliance had improved. The city manager reported that the plants were running at "much improved levels of efficiency." And the plant's energy usage has been significantly reduced.
Doing well, indeed!
Clinton is in western Oklahoma, about 85 miles west of Oklahoma City and 70 miles east of the Texas border. Located at the crossroads of I-40 and Highway 183, with U.S. Route 66 running right through the downtown business district, Clinton has earned the nickname, the Hub City of Western Oklahoma. In recent years, Clinton could rightfully claim another nickname: City of Champions, as its Clinton High School "Red Tornadoes" football team has won six state championships since 2000.
When Clinton officials decided to initiate a search for a public-private partner to operate its water and wastewater systems, they turned to another champion: The Chickasha (Okla.) Wastewater Treatment Plant, which was named Plant of the Year by the Oklahoma Water Pollution Control Association in 2007. Located 45 miles southeast of Oklahoma City, the Chickasha plant has been operated by Severn Trent Services since 1979. After talking with Chickasha representatives, the City of Clinton chose Severn Trent Services to operate its plants.
Addressing excessive sludge inventory
According to Rusty Whisenhunt, project manager, for Severn Trent Services, "The wastewater plant is an activated sludge, extended aeration plant. The plant was overloaded and was barely able to handle the incoming flow. The plant staff was not using any process controls for sludge wasting. Instead, they were estimating when wasting needed to be done — and land application of the plant's waste wasn't being done. This resulted in sludge levels in the clarifier that were at least five times what was optimal. The mixed liquor suspended solids (MLSS) count was about 10,000 mg/l compared to a normal count of 2,500 mg/l. And the plant was processing only about 1 mgd of wastewater."
Prior to the partnership, compliance with Oklahoma Department of Environmental Quality (ODEQ) wastewater quality standards also was an issue, as the plant did not pass two consecutive quarterly whole effluent toxicity (WET) tests, requiring that the plant perform toxicity reduction evaluations.
Within three months of commencing operation of the plant, Severn Trent Services staff instituted proper controls and increased the plant's operating capacity back to the plant's design capacity. The filamentous bacteria (Nocardia amarae) that had formed on the surface of the wastewater basins were no longer present, and the MLSS count was being maintained at 2,500 mg/l. As a result, two of the plant's three clarifiers were no longer needed and were taken offline.
Plant personnel also are replacing the air diffusers in the aeration basin. The existing diffusers are 15 years old — past their life expectancy by several years — and some of the diffusers were clogged and were not properly distributing air.
Improving drinking water quality
The quality of the City's drinking water, processed by the Clinton Lake treatment facility, also needed to be addressed. Turbidity rates were typically .2 to .25 NTU. Plant personnel determined that the automatic chlorine dioxide pre-oxidant system was not operating properly, enabling algae growth. Once the problem was identified, plant personnel restarted the system and adjusted the dosage rate. Working with various vendors, they were able to determine a better alum and cationic polymer blend. Once the proper blend was implemented, the turbidities from the effluent filters were reduced to .05 NTU. Severn Trent Services personnel continue to work with these vendors and the company's technical services group to fine tune the chemical dosages, ensuring optimum operations of the Clinton Lake plant. The plant staff also implemented a filter backwash schedule and changed the coagulant in the clarifiers.
To solve the problem of long detention times in the water treatment system as well as low total chlorine residuals that the system had experienced, Severn Trent Services personnel have identified a location for automatic flushing equipment, a SCADA system and supplemental chloramines injection locations. These actions will help the City remain in compliance with ODEQ regulations and with the USEPA's Stage 2 Disinfection Byproducts Rule.
"As with the wastewater plant, the key to improving the water quality at Clinton Lake was implementing an ongoing process of testing and evaluation," said Whisenhunt. "Severn Trent Services has many years of experience in the operation and maintenance of water and wastewater plants, so we usually know the causes of water and wastewater facility problems and the best remedies, too."
Significant energy savings
The wastewater plant and the Clinton Lake water treatment plant, combined, are the City of Clinton's largest user of electricity, so any reductions in energy usage at the plants would be most welcomed. Once Severn Trent Services had implemented efficiencies throughout the two plants — including, importantly, shutting down the two small clarifiers — energy use was reduced by 45 to 50 percent.
In recent months, the City has approved additional maintenance expenditures to ensure the two plants' ongoing efficient operation. These expenditures will reduce the City's cost savings in the first year to about $100,000. That seems to be fine with the city's mayor, Allen Bryson, who notes that it is "exciting" to have the plants' performance live up to Severn Trent Services' promises.
According to city manager, Grayson Bottom, regulatory compliance was the number one priority in bringing in a public-private partner. After nearly three months of working with Severn Trent Services, Bottom said an ODEQ representative visited the plants and was "absolutely radiant." The government official told Clinton representatives that the plants "had exceeded every expectation they had," Bottom said.
For more information, e-mail info@severntrentservices.com.
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