The Kent County Regional Wastewater Treatment Plant (WWTP) in Delaware is internationally recognized as a model of excellence. Representatives from utilities in many countries — including Brazil, South Africa, Germany and Russia — have visited the plant to observe its innovative practices. So it is no surprise that the Milford, Del. plant recently claimed another distinction when it incorporated the world's largest microwave UV system into its plant operation.
The Kent County facility is Delaware's second largest treatment plant, taking in 12 mgd from a service area with a population of 130,000 in Kent County and parts of New Castle and Sussex counties. The treated wastewater is then discharged to a tributary of the Murderkill River. The original plant was built in 1973 and has since won several high-profile awards for innovation and operational excellence, including the inaugural USEPA Region II Environmental Achievement Award. The plant also was the first wastewater facility in the United States to be certified to the ISO 14001 EMS (Environmental Management System) standard, the OSHA Assessment System 18001 standard and the National Biosolids Program EMS program.
Selection of microwave UV technology reflects culture of innovation and continuous improvement
According to Jim Newton, environmental program manager, improving plant performance is an ongoing process, and personnel are encouraged to explore innovative alternative technologies to achieve continuous improvement. Newton also noted that safety and the environmental impact of plant operations are ongoing focuses of Kent County management. "Our goal is to reduce our environmental and health and safety footprint, especially as it affects our employees and neighbors. That has driven our efforts to move to sustainable energy sources, reduce power consumption and eliminate the handling of chlorine."
The Kent County WWTP successfully used gaseous chlorine to disinfect the wastewater for almost 40 years. However, the utility's Environmental, Health, Safety and Sustainability Management System (EHSS-MS) set as an objective the replacement of this process with UV disinfection because of the health, safety and regulatory burdens the chlorine process required. UV disinfection provides a number of advantages for wastewater treatment plants compared to the use of gaseous chlorine. Its employment reduces chemical usage, simplifies regulatory compliance issues and improves employee and community safety.
True to its reputation as an innovator, Kent County decided to explore the possible use of microwave UV technology based upon a study comparing all disinfection processes conducted by master's degree students in the Environmental Management Department of the University of Maryland. The groundbreaking technology, Severn Trent Services' MicroDynamics® microwave UV system, uses microwaves to generate monochromatic UV light from electrodeless lamps. With electrodeless lamps, there are no electrical connections to fail, corrode or leak, which dramatically increases system efficiency and lamp life when compared to traditional UV lamps. The MicroDynamics system is modular and can operate at ambient water temperatures, making it less susceptible to rising temperatures during periods of low flow. And the lamps can operate in air, so the system does not require lamps to be submerged in the channel, thus reducing concerns regarding precise water level control.
Successful pilot plant leads to full scale microwave UV system
Before the Kent County Department of Public Works would commit to the MicroDynamics system, Severn Trent Services was contracted to provide a 1-mgd pilot plant to ensure that the unit could meet National Pollutant Discharge Elimination System disinfection permit conditions. Over a 35 day period in 2008, the system was found to meet the permit limits of 33.0 colonies/100 ml of Enterococcus. The unit was operated at 150 percent of its 1-mgd design flow capacity and was able to produce an effluent with a geometric mean of 3.5 colonies/100 ml.
According to Newton, "With a three-year lamp life guarantee, the MicroDynamics system offered the lowest overall operational costs and maintenance requirements of any UV technology we evaluated. The further appeal of this innovative technology was the improved reliability it offered compared to traditional UV systems and lamps. The system's unlimited on/off capability was perfect for our peak treatment capacity needs. And the safety of the MicroDynamics electrodeless lamps, which have no electrical connections in the water, just couldn't be matched."
The full scale system, which was placed into operation on 7 October 2010, is designed to handle the plant's normal and peak flows of 12 mgd and 18 mgd, respectively. Twenty-four microwave UV modules are configured in six trains of four each. Until a control panel is installed, which will enable automatic operation based upon flow, the system is being operated manually.
Microwave UV technology demonstrates many benefits over chlorine disinfection
In the short period of time that the full-scale microwave UV system has been in operation, Newton said its efficacy has been verified. "With permit limits of 33.0 colonies/100 ml of Enterococcus, we're consistently achieving 2.0 to 10.0/100 ml of Enterococcus."
In addition, Kent County now saves $100,000 per year that was being spent on chlorine and sulfur dioxide when gaseous chlorine disinfection was used. Risk planning training and paperwork has been eliminated, too. "We donated HAZMAT suits to the local HAZMAT team," Newton said. "And since we no longer had to maintain a 1/2-mile evacuation route in the event of possible chlorine gas releases, we were able to completely decertify the USEPA risk management program."
One benefit of the microwave UV system that doesn't show up on the balance sheet is its safety. Because the electrodeless lamps have no wires under water, safety concerns inherent with the repair of possibly corroded electrodes or wiring are eliminated.
But the electrodeless lamps also offer benefits that are reflected in bottom line calculations. "Because electrodeless lamps operate at lower temperatures than traditional UV lamps, you don't get the build-up of solids as with traditional lamps. And the lamps take less time to generate full power compared to traditional UV lamps."
The County is already planning to propose eight more microwave UV systems, as the current system is operating at 85 percent of capacity, and a state Department of Natural Resources and Environmental Control rule requires an increase in system capacity when that rate of usage is reached.
To cover the costs of the facility upgrades, the Public Works Department received low interest State Revolving Fund stimulus funding, which included adding a 1.2 megawatt solar farm to power the UV system and portions of the biosolids operation. The solar power system is due to go online in March 2011.
"The initial plan for the solar farm was to offset electric costs. When the solar power system comes online in February, it's anticipated that all the Kent County WWTP's power will be provided by the 6,000 solar panels."
The new solar farm and microwave UV disinfection system are just the latest examples of how the Kent County WWTP uses innovation to improve health, safety and environmental sustainability and satisfy customers. And it is likely that one of the country's most highly praised wastewater plants will need to make room in its trophy case for the additional awards that are surely coming its way.
For more information, e-mail info@severntrentservices.com.
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