An Indiana treatment plant looks into every area for ways to save energy and run a greener operation
From active solar biosolids dryers to an aggressive office-recycling program, the Noblesville (Ind.) Wastewater Treatment Plant has done its part to help the city become a state-certified CLEAN Community for its environmental policies.
Energy controllers, UV disinfection, a high-efficiency boiler, reuse of biogas, and even optimized travel routes for checking lift stations are all part of the plant’s approach.
Utility director Ray Thompson says the 10 mgd (design) activated sludge plant has improved its performance while using less energy even as its city of 50,000 has been adding 10,000 residents every five years (population in 2000 was 28,500).
Expansion and efficiency
Over the last three years, the plant has gone through several projects to double its capacity to meet demand. “It included installation of additional aeration tanks, two final clarifiers, and UV disinfection to replace chlorine,” says Thompson.
“In the past, our anaerobic digesters were heated by a boiler that was fueled separately by either methane or natural gas,” says Thompson. A U.S. Department of Energy grant provided $24,000 of the total $141,000 cost of a new Walker boiler that supports blending the two gases to take full advantage of available biogas. From May 2009 when it was installed through the end of 2010, the plant saved $28,400 and offset the use of just over 7,000 million Btu of natural gas.
“The next time we do major work on the digesters, we plan to install meters to better track methane and natural gas use,” says Thompson. “We hope that will help us determine what we may want to do in the future. We’ve considered going to turbines to generate electricity from biogas.”
He says UV has resulted in better disinfection, and while it’s difficult to measure if it has saved any money, it has eliminated the use of chlorine and sulfur dioxide and their inherent safety and storage concerns and regulatory inspections.
Another grant, from the Indiana Department of Energy, provided $26,690 toward the $53,000 cost of installing KVAR (kilovolt-ampere-reactance) energy controllers on 29 inductive motors and in nine lift stations. The controllers use capacitors to make the motors more efficient by improving the power factor. They also offer surge protection and reduce heat, thus decreasing wear and tear and maintenance needs.
Some of the expansion work, such as UV disinfection, was influenced by an environmental management system (EMS) developed in 2009 with the assistance of Purdue University’s Clean Manufacturing Institute, through a program funded by a U.S. EPA grant. An EMS is designed not only to reduce environmental impacts and prevent pollution, but to increase operating efficiency and, for businesses, to attract customers and increase market share. Regional EPA offices can provide more information about EMS and may even have a program to assist in developing an EMS plan.
“An EMS holds an organization accountable for its environmental actions,” says Thomas Watson, lab supervisor at Noblesville. “On a basic level, we have to follow the rules that apply to us through mandates and laws, plus anything we might want to place upon ourselves.” By following its EMS plan, the plant has become compliant with the international ISO standard 14001:2004 dealing with environmental performance.
While other wastewater plants have selected a limited EMS, Noblesville included its entire property, rather than just the treatment process. “We looked at all our procedures on how we do everyday work,” notes Karrie Hutson, chief operator. “That included looking at how we check our lift stations to make sure we took the most direct routes, and other simple things to conserve energy like limiting the idling of vehicles.”
The plant began buying flex-fuel vehicles that can use E-85 (85 percent ethanol), established rules for turning off lights and computers, added programmable thermostats, and installed more energy-efficient lighting in office buildings.
Gas heaters in garages were replaced with new radiant heaters that paid for themselves within five years from the gas savings alone. “It wasn’t all new,” adds Watson. “We could include things in the EMS that we were already doing. We just have to be accountable to do what we said we were going to do.”
A local company, Universal Blower Pac, selected the plant as a test site for a new efficient blower package design; an EE-Pacs screw-type blower with a high-efficiency variable-speed drive. The results are still pending, but the staff expects the design to use considerably less electricity.
Even garbage was included in the EMS work. “We’ve saved a lot of money with our trash containers,” says Watson. “The trash hauler used to come every week. Now they come when we call them, which works out to be about once a month.”
A key aspect of reducing refuse was a new recycling program. “We sent out 186 55-gallon containers of mixed recyclables last year, compared to none in years before,” says Watson. The plant also began recycling some potentially harmful materials, such as oil filters and fluorescent light bulbs. The waste management company picks up recyclables at no extra charge, so the plant saves money while sending less to landfills.
On the biosolids side, two THERMO-SYSTEM active solar dryers from Parkson Corporation began operation in September 2010 to help cut the cost of landfilling the material. Instead of just pressing to remove some water, the dryers can reduce total volume by up to 97 percent, according to the manufacturer.
“We put nine single-axle dump truck loads of biosolids in each one — that’s about 80 cubic yards,” says Thompson. After drying, the volume is reduced to 20 cubic yards. “We reduced our dump container cost by more than $12,000 in the first quarter. It is one of our biggest expenses.”
Long term, he expects the $1.2 million dryers to have a big impact on that part of the budget. “We should be able to reduce it by two-thirds,” he says. Direct solar provides 95 percent of the energy to dry the biosolids. Each 4,500-square-foot dryer has a 145 kW supplemental heating system with water-to-air heat exchangers that use excess hot water from the digester’s boiler.
A small, electric-powered wheeled “mole” from Parkson Corporation drives around the material to keep it mixed and aerated. Sensors and an automated PLC control the humidity through air inlets, ceiling fans and exhaust fans, so there’s no extra work for operators.
Parkson says the greenhouse-like structures can produce a Class A biosolids 75 to 90 percent dry. Noblesville didn’t use the dryers for a Class A biosolids at first. “We just did it for volume reduction during the colder months,” says Thompson, “so we found that 65 percent dry works just as well and doesn’t result in any difference in volume.”
He says drying to that level took about three weeks in fall and about five weeks in winter. He expected it to take about two weeks during warmer weather. “We don’t meet Class A consistently; we’re right at the line,” he says. “We hope to achieve a Class A product during the summer season.”
With give-away programs and other potential reuses of a Class A product, the plant could eliminate landfilling. Land application is no longer viable because growth has used up much of the farmland around the community, 30 miles north of Indianapolis.
Hutson says environmental awareness goes with a job in the wastewater field. “You go to school for the sciences and take environmental classes, so it naturally makes you a steward of the environment,” he says. “We have always been very well supported by our city administration, Board of Works and council, as well as the citizens of our community. Our job is environmental protection.”