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The Utilities Department of Chesterfield County, Va., has earned a reputation as a bellwether among public water and wastewater utilities. A seven-year capital improvement program, now underway, should continue that leadership.
Serving a largely suburban residential region around Richmond and the outlying southeastern county, the department has earned some of the industry’s most enviable recognition. The county’s wastewater operations serve more than 80,900 customers—77% residential and the rest industrial connections.
The collection and treatment infrastructure includes the Proctor’s Creek and Falling Water Wastewater Treatment Plants (WWTPs), 23 pump stations and 1,700 miles of sewer lines. The Proctor’s Creek WWTP accounts for 16 to 17 million gal per day (mgd) of the combined 25.5 mgd average flow for the two plants. The plant permits have a combined 37.10 mgd rating, so there is ample reserve capacity to serve the area well into the future.
Higher quality discharge
The department, which is known for innovations, must address the wide range of management challenges confronting the nation’s clean water community. Among the most recent of those innovations is a public/private collaboration with an electric power company to divert treated effluent from Proctor’s Creek WWTP to use as cooling and process water.
Long-range initiatives by the wastewater side of the utility’s operations are aimed at protecting the area’s historic James River and ultimately restoring the ecosystem of the downstream Chesapeake Bay. Future compliance with the nutrient reduction program for the Chesapeake Bay has been the basis for the utility’s investment in ongoing process upgrades to reduce the level of effluent nitrogen from the present range of 8 to 5 mg/L and phosphorous from 2 to 0.5 mg/L by 2011. The region’s rivers have, over the years, carried pollutants into the bay and compromised the estuary’s ecosystem.
To accomplish the objectives, the utility embarked on an ambitious upgrade program. Starting in 2006 and expected to extend into October 2012, higher quality biological and removal enhancements will be attained by headworks improvements, a new digester unit, fine screening and more efficient monomedia tertiary treatment. The utility’s staff insist on implementing these changes with only the highest quality technologies and process equipment.
“We have had a good operational record here and have become even more proactive with long-term planning than just five years ago,” said Scott Smedley, plant manager.
“The department expects to invest approximately $100 million worth of upgrades to support our enhanced nutrient reduction program.”
The utility’s award-winning Proctor’s Creek WWTP entered service in 1975 as a modest 1-mgd facility and underwent expansions in 1980, 1988 and 1995 that produced the present 27-mgd rated capacity. The facility operates with 20 personnel—three on each of four shifts and four assigned to maintenance. This is the larger of the two plants, and serves nearly 55,000 customers with a multistage biological nutrient removal process involving primary and secondary treatment, followed up until now by stratified tertiary filtration and chlorine contact disinfection. The utility disposes of dewatered sludge—consistently below the ceiling loadings of Class B biosolids—by land application.
“We are notably proud of the fact that neither plant has ever received a notice of violation from the Virginia Department of Environmental Quality,” Smedley said.
According to Smedley, reliability is the basis of specifications for any replacement equipment or upgraded technologies. A new system-wide SCADA, for example, has taken the utility’s monitoring and remote control onto system-wide radio-telemetry communications, with added features missing in the previous system.
The wastewater utility is equally conservative in specifying any equipment in the operational infrastructure and process chain. For example, shaft, bearing and U-joint failures became increasingly frequent with four of eight long-shaft influent pumps in a dry-pit configuration soon after they were installed in 1988 at one side of the two-cell headworks of the Proctor’s Creek WWTP. The failures increased to an unacceptably regular basis. This type of pump mounted the motors above the dry pit, with the shafts connected by a U-joint to their counterpart pump located at the base of the 26-ft deep dry pit.
When the pumps were installed in 1988, the flexible connections used for the original pumps had been replaced with rigid fittings.
An engineering study cited the likely problem—harmonic imbalance in the shafts—as inducing subtle but unrelenting vibration on the pumps along that one side of the split headworks, Smedley said.
Rather than continue the costly outsourcing of repairs and excessive maintenance, the utility replaced all eight long-shaft pumps on both sides of the headworks with ITT Flygt dry-pit submersible units at Proctor’s Creek WWTP. The pumps are sized to deliver 3,964 gal per minute at 83 ft total dynamic head, and each is fitted with variable speed drives that match speed and energy consumption with the variable flow rates.
“[However,] we could have replaced those problem-prone long-shaft pumps with submersibles at less cost than incurred with all the repairs and the engineering study,” Smedley said. “We decided to gain standardization by replacing all of the influent pumps with the same submersibles. The four on the trouble-prone side are now replaced and the other four purchased for installation later. The four now in service have eliminated the recurring failure problem associated with the long-shaft units.”
At the opposite link in the process chain, the reliability of the ITT Flygt pumps has earned them use in a planned lift station that will divert the high quality treated effluent from the plant’s discharge cascade to the neighboring power plant. It appears more than one industry can learn from the county’s experience.
The county currently regulates 39 significant industrial users (SIUs) monitored in the award-winning pretreatment program. The utilities surcharge 22 other industries for biochemical oxygen demand and total suspended solids treatment. Despite an increase of 106% in SIU operations since 1993, their aggregate pollutant loadings of arsenic, copper, cadmium, lead, nickel and zinc increased only moderately. Meanwhile, the loadings of chromium, mercury, cyanide and silver have decreased.
Some highlights of Chesterfield County’s SIU pretreatment program: