October 2007, Vol. 19, No.10
Coffee Creek Wastewater Treatment Plant Location: Edmond, Okla.
Startup date: 1972
Service population: 75,000
Number of employees: 5
Design flow: 9 mgd (34,000 m3/d)
Average flow: 7 mgd (26,500 m3/d)
Peak flow: 13.5 mgd (51,100 m3/d)
Annual operating cost: $1.1 million
This year, Mother Nature has conspired against the Coffee Creek Wastewater Treatment Plant (WWTP) in Edmond, Okla. During the first 6 months of the year, the service area exceeded its normal annual rainfall total of 35 in. (889 mm), and the first half of July brought another 6.5 in. (165 mm).
The plant, which uses a continuous flow activated sludge treatment model, averages 7 mgd (26,500 m3/d) — serving about 75,000 people — under normal conditions; however, the average flow for May was 8.1 mgd (30,700 m3/d). June averaged 9 mgd (34,000 m3/d). The plant’s highest single-day flow, 12.7 mgd (48,000 m3/d), was recorded five times in June.
The plant’s main limiting factor for flow is the sludge blanket depth in the two secondary clarifiers, which are 15-ft (4.6-m) deep. When the sludge blankets reach 12 ft (3.7 m), the flow must be reduced to sustain the blanket and ensure that the solids do not wash out of the clarifiers.
To prevent washouts this year, staff members used the plant’s wet weather operations procedures to stay in compliance. Operators can control the flows to the plant by shutting off pumps at the two main lift stations. The lift stations have large stormwater holding ponds to hold the excess flow. A few times this year, it has taken a week or more to process through the plant the water temporarily stored in the holding ponds.
Flows entering the plant pass through a mechanical bar screen and fine screening on their way to one of three treatment trains. The first train, called Phase 1, was the original treatment train for the plant when it opened in 1972. It is a two-stage nitrification system composed of two primary aeration basins, each followed by a clarifier and two secondary aeration basins, each also followed by a clarifier. Phases 2 and 3, which were added in 1987 and 1994, respectively, are identical an each include two oxidation
During extended periods of extremely high flows this year, the staff of the Coffee Creek Wastewater Treatment Plant (Edmond, Okla.) maintained effective treatment and protected the activated sludge system from washouts. Pictured are (left to right) Tony Henderson, operations and maintenance; Bryan Mitchell, operations and maintenance; Brian Green, laboratory technician; Gary Langley, mechanic; and Kris Neifing, chief plant operator. (Photo by James Montgomery, instrumentation and controls technician.)
ditches and two clarifiers.
Effluent from all of the phases is polished. The effluent passes through one of eight sand–anthracite filters. The filtered water is disinfected with chlorine gas and dechlorinated with sulfur dioxide gas. Per Oklahoma Pollutant Discharge Elimination System permit requirements, the plant only chlorinates and dechlorinates from May through September, as these are the months when recreational use of the receiving stream — Coffee Creek — is most likely.
Biosolids wasted from the wastewater treatment process are treated in three facultative lagoons. After the sludge has spent an average of 1 to 2 years in a lagoon, it is tested for compliance with regulatory requirements, and then land-applied via injection 6 to 10 in. (150 to 250 mm) underground to local farmland to fertilize crops, such as hay for stock feed.
The staff strives to be fiscally conservative while attuned to the necessity of maintaining the plant’s facility and wastewater infrastructures. The City of Edmond routinely invests the money necessary to keep the plant and lift stations in good working order and sized properly to efficiently handle community needs for growth and business.
The Coffee Creek Wastewater Treatment Plant (Edmond, Okla.)uses one set of primary and secondary aeration basins and two sets of oxidation ditches, like those pictured above, to treat the 7 million gal (26,500 m3) of wastewater that its 75,000 customers generate on an average day. (Photo by Kris Neifing, chief plant operator.) To that end, in 2005 and 2006, EMA Inc. (St. Paul, Minn.), a technology and process consulting company, conducted a competitiveness assessment for the Coffee Creek plant and utility line maintenance functions. The difference between the plant’s current practices and industry standards for best practices in publicly operated and privatized facilities was less than 2%. The company noted
this was the lowest gap they had measured in more than 400 assessments to date.
Coffee Creek is equally serious about protecting its staff through safety training. Staff members receive safety training on all topics required by the U.S. Occupational Health and Safety Administration, such as bloodborne pathogens, sight and hearing protection, confined-space permitting and entry, lockout–tagout procedures, personal protective equipment, respiratory protection, and process safety management.
Employees also receive and are required to use uniforms, safety boots, safety glasses, and any other personal protective equipment deemed necessary. The plant’s diligence has paid off: Coffee Creek has not had a recordable incident or lost-time injury in more than 10 years.