Combine the European sense of sustainability with the American spirit of innovation and what do you get? In the clean-water profession, it’s the Kent County Wastewater Treatment Facility in Milford, Del.
Benefiting from the best of both cultures, the plant has made huge improvements from the old days when its performance was not always up to standard. Public works director Hans Medlarz and assistant director Reinhold Betschel are originally from Germany. Their leadership — supported by superintendent Keith Powell, environmental programs manager Jim Newton, and supervisors Billy Vincent and Mike Harrington and their staffs — has resulted in a plant that won the U.S. EPA O&M award for large advanced plants in 2007.
Additionally, the worldwide wastewater treatment community looks to the Kent County facility as a model of performance excellence (see sidebar). “It’s an innovative environment here,” says Newton. “Our management allows us to try new things and make improvements.”
Flexible process
The Kent County facility is Delaware’s second largest treatment plant, taking in about 11 mgd from a service area with a population of 130,000 in Kent County and parts of New Castle and Sussex Counties.
Influent passes through a headworks section containing fine filter bar screens and centrifugal grit removal before flowing into a Biolac biological wastewater treatment system supplied by the Parkson Corporation. There are no primary clarifiers.
The Biolac system employs fine-bubble diffusion and extended retention of biological solids to provide stable, efficient operation, as well as flexibility to meet various treatment requirements such as nitrification/denitrification and nutrient removal.
Instead of fixed aerators, the system’s aeration diffusers are suspended from moving aeration chains. This produces a controlled, back-and-forth motion of the diffusers and distributes the oxygen transfer and mixing energy evenly throughout the basin. As a result, the system efficiently and uniformly mixes aeration volumes associated with sludge ages of 30 to 70 days, while most extended aeration systems reach their maximum mixing capability at sludge ages of 15 to 25 days. The longer sludge age can lower effluent BOD and ammonia, and the large quantity of biomass treats widely fluctuating loads with very few operational changes.
At Kent County, the Biolac system is installed in two HDPE-lined 16-foot-deep earthen basins, each with a capacity of 10 million gallons. The solids retention time in the basins is 25 to 45 days. The system’s Wave Ox process enhances biological nutrient removal. The precise control of the air distribution to the aeration chains and the dissolved oxygen content provide moving waves of multiple oxic and anoxic environments in the two basins, promoting nitrification, denitrification and biological phosphorus removal.
“The system is very easy to operate,” says Newton. “The only significant change we’ve made is with the dissolved oxygen control system. The staff used to monitor DO at the end of the aeration process, but that was like driving a car while looking in the rear view mirror,” says Betschel.
At the suggestion of the supplier, Dresser Roots., the Kent County team moved the DO sensors to the front of the process and now controls the air supply based on what the process actually needs. Betschel says the modification has saved at least 10 percent in electrical costs, and diffuser upgrades have made the aeration system 25 percent more efficient.
Solids settle out in four peripheral-feed circular clarifiers, and a chlorination-dechlorination system disinfects the overflow before discharge to the Murderkill River, which flows to Delaware Bay and the ocean. High-quality effluent is the hallmark here; BOD and TSS average in single digits.
Holding tanks provide temporary storage of biosolids, and ferric chloride is added before dewatering on Ashbrook belt filter presses. A recently renovated pugmill mixes lime with the biosolids for stabilization. Indirect-heat dryers remove additional moisture, resulting in a granular, 50 percent solids final product called Kentorganite. The plant staff hauls and spreads the material on county lands and more than 100 area farms. The farmers pay the transportation and application costs. “We can’t make enough to meet demand,” says Newton.
New look
Plant operation wasn’t always this efficient and effective. Built in 1973, the original facility had some problems and violations, but things began improving with changes in management and operational philosophy about 10 years ago.
Betschel recalls some of the early progress. “Soon after Hans arrived, he suggested we start making improvements, beginning with the 550 miles of force mains we maintain,” he says. “We convinced our commissioners to allocate the necessary funds and made improvements to reduce overflows. After that, we went after the 85 pump stations, replacing the old pumps over time with machines from ITT-Flygt and EMU.”
More repairs and improvements followed, some bringing out the ingenuity of the staff. “We realized we needed to clean the aeration basins, but we couldn’t find any guidelines for doing so,” Betschel says. “Since they are HDPE-lined, we had to be careful. A metal bucket might have damaged the material, so we developed a wood and rubber modification that was more suitable.”
The team also improved the grit removal apparatus. On top of all this, Betschel adds: “We diligently practice our Environmental Health and Safety Management System (EHS-MS) Policy to continuously improve. That applies to our processes, our equipment and our people.”
Pushing sustainability
As well as the plant operates today, the Kent County team is not even close to completing the improvements. Next up: a more sustainable operation. “The Germans have a well-developed sustainability ethic,” explains Newton. “That is driving a number of things we plan to look at including renewable energy sources like wind and solar.”
Newton says they will try solar-generated heat on biosolids, with the idea that moisture can be driven from the material naturally in a passive solar greenhouse, instead of the current natural gas-fired processes.
“At night, we plan to use heat from our aeration blowers,” he says. Solar power will also be instrumental in a new disinfection configuration. Newton explains that Kent County will soon move to ultraviolet light instead of chlorine, and solar panels will power the UV system. Its UV lamps will be illuminated by microwaves, which do not buildup solids on the tubes, resulting in higher efficiency.
Over the last year, the plant has been gathering data from a wind anemo-meter mounted on one of the radio towers. “The Department of Energy says our area is marginal for wind, but we want to look at the data to see if wind power might be feasible,” says Newton.
In still another project, the plant has applied for a DOE grant under the 2009 economic stimulus program to use the water in the contact chambers as a heat pump. Buildings will obtain supplemental heating and cooling by heat exchange against geofluid (geothermal fluid) passing through the treatment basins.
These improvements correlate closely with the value Kent County places on certification. Newton explains that the plant is certified as ISO 14001 EMS (Environmental Management System), OSHA Assessment System 18001, and the National Biosolids Program EMS program. “We were the first to get all three,” he says.
Guiding principles
The impact on plant operations is clear. “Our goal is to reduce our environ-mental and health and safety footprint, especially as it affects our employees and neighbors,” Newton says. “That drives our efforts to move to sustainable energy sources, reduce power consumption, and eliminate handling chlorine.”
The model for these actions is the Natural Step framework for sustainability developed in Sweden (www.naturalstep.org). The framework has four principles:
• Eliminate our contribution to the progressive buildup of substances extracted from the earth.
• Eliminate our contribution to the progressive buildup of chemicals and compounds produced by our society.
• Eliminate our contribution to the progressive physical degra-dation and destruction of nature and natural processes.
• Eliminate our contribution to conditions that undermine people’s capacity to meet their basic human needs.
“We’ve adopted these principles as a fundamental part of our management philosophy,” Newton says. Betschel puts it another way: “When visitors see our effluent stream, they sometime question why we make water that is much cleaner than our permit requires. I simply tell them that we want to be the best that we can be.”
