An award-winning wastewater treatment facility in Delaware is demonstrating
its commitment to ongoing operational excellence and innovative treatment
processes by selecting a microwave ultraviolet technology for its disinfection
needs.
The Kent County Regional Wastewater Treatment Facility is a 16-mgd advanced
wastewater treatment plant located in Kent County, Del. It received the
2007 Clean Water Act Recognition Award for Operations Excellence in the
large, advanced treatment category; the 2007 National Association of Counties
Achievement Award; and recently accepted one of the inaugural USEPA Region
III Environmental Achievement awards for its environmental health and safety
management system (EHS-MS). The plant also was the first wastewater facility
in the United States to be certified to the ISO 14001 EMS standard, the
OSHAS 18001 health and safety standard and the National Biosolids Partnership’s
EMS standard.
The plant receives wastewater from Kent County, southern portions of New
Castle County and northern portions of Sussex County, Del. The facility
treats an average of 12 mgd with a peak treatment capacity of 18 mgd, and
it is permitted for Enterococcus at 33.0 colonies/100 ml. Treated wastewater
is discharged to a tributary of the Murderkill River, part of the Delaware
River basin.
Switching from chlorine gas to microwave UV
Since the plant’s start-up in 1973, it has successfully used chlorine gas
as a disinfectant followed by dechlorination with sulfur dioxide. Recognizing
the safety and regulatory issues surrounding the use of chlorine gas, the facility’s
EHS-MS called for a goal of reducing or eliminating its use as the plant’s
disinfectant. The plant’s operator, the Kent County Levy Court Department
of Public Works, worked with the University of Maryland as part of a master’s
degree capstone project to evaluate disinfection alternatives that would meet
the goals of the EHS-MS. The result was a recommendation to switch to UV disinfection,
which would reduce chemical usage, simplify regulatory compliance issues and
improve employee and community safety.
Kershner Environmental Technologies LLC, an Owings Mills, Md.-based manufacturers’ representative
firm for advanced water treatment systems and other environmental technologies,
provided the facility with the MicroDynamics® microwave
UV disinfection system from Severn Trent Services. The MicroDynamics
UV technology is unique in that microwaves are used 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 bulb 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 system does not require the lamps to be submerged
in the channel – lamps can operate in air – thus reducing concerns
regarding precise water level control.
Pilot plant results
Before the Department of Public Works would commit to the MicroDynamics
system, Severn Trent Services was contracted to provide a pilot plant
to ensure that the unit could meet National Pollutant Discharge Elimination
System disinfection permit conditions. A 1-mgd pilot plant was installed
and tested during May 2008. The unit was installed near a secondary clarifier.
Water was drawn from the discharge side of the clarifier and pumped through
the pilot plant before being discharged back into the system prior to
the chlorine contact chambers. A water meter was used to measure flow
and an electric meter was installed on the unit to determine an approximate
electric load required by the plant. Once each shift, samples were drawn
from the pilot plant after exposure to the lamps.
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. The full scale UV system will be designed to handle the
plant’s normal and peak flows of 12 mgd and 18 mgd, respectively.
The Public Works Department recently received low interest State Revolving
Fund stimulus funding to cover the costs of the facility upgrades, which
now include adding 300 kW of photovoltaic solar panels to power the UV
system and portions of the biosolids operation. It is expected that the
project will be bid and under construction before the end of the year.
Hans Medlarz, director of public works, praised the microwave UV system. “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.”
Findings on the use of microwave
UV disinfection at the Kent County Regional Wastewater Treatment Facility
will be presented at the WEFTEC.09
Facility Operations session, "Disinfection
Utilizing an Innovative Microwave UV System," on Monday, October
12 at 4:00 p.m.
For more information, e-mail info@severntrentservices.com.