BioCycle July 2007, Vol. 48, No. 7, p. 50
Solution comes from investing $3.1 million in a facility that produces up to 18,000 cubic yards of compost each year and handles up to 9,600 pounds of dewatered sludge per day.
Thomas Mansur and Richard Nicoletti
SEVERAL YEARS AGO, the City of Ardmore, Oklahoma realized that they needed to improve disposal methods for the biosolids produced at its wastewater treatment plant (WWTP). All their biosolids were delivered then to local farmers for land application. The volume of liquid sludge, required manpower, and aging transport vehicles meant Ardmore had to invest more or develop a more efficient method.
One option was to haul sludge to a local landfill about eight miles from its treatment plant. Current tipping fees are about $24/ton, and Oklahoma law requires that the sludge be stabilized before it is landfilled. Therefore, the City would have had to develop a system to do this, while also purchasing and installing needed equipment at the WWTP.
As a two-time winner of the National Municipal League’s All American City award, Ardmore prides itself on being innovative and conscious of its agrarian roots. For these reasons, it chose to pursue a state-of-the-art composting facility to produce Class A, pathogen-free compost from its biosolids and green waste streams, which could then be used to improve the soil for area residents and farmers. With a fixed and limited budget, the City focused on getting the best technology for this composting facility.
The compost facility would be built at the WWTP, located among farms and heavy industry. As such, the City determined that odors produced during the compost process would not be a nuisance as they might be in a residential area. They decided, however, to design the facility to allow for future installation of a biofilter to scrub odors, should the area become more residential. Including the requisite building ventilation system and biofilter at this time would have added a significant cost to the facility and made it impossible for the City to afford the desired compost system. They also decided on a technology that was automated, thereby minimizing labor and operations costs.
FROM BELT PRESS TO MIXER
The compost facility is housed in a 24,000 square-foot building, which includes a single 2-meter Komline-Sanderson sludge dewatering belt press. From the belt press, dewatered sludge (biosolids) is then conveyed onto the mix floor, dumped into a large Kuhn Knight mixer machine and mixed with ground yard waste provided by the City’s Operation Pride Program. Next, it is placed into one of five 195-foot long bays where the sludge-yard waste mixture is allowed to compost.
An IPS Compost System from Siemens Water Technologies, complete with automated bed mix and transport aerator-mixer, moves the individual compost charges down the bay. Each charge is advanced along the bay and allowed to compost for approximately 21 days. Temperatures in the bay reach as high as 150°F for 10 or more days. The high temperatures eliminate pathogens and produce a mulch mixture that can be used for landscaping, soil amendments and erosion control.
The facility is designed to produce up to 18,000 cubic yards of compost each year and handle as much as 9,600 pounds of dewatered sludge per day. This eliminates the need to transport as much as 40,000 gallons of sludge each day to a land-application site or landfill.
“By processing sludge on-site, we greatly reduce the manpower, equipment costs and hassle associated with the old way of handling sludge,” says Carol Anderson, Wastewater Treatment Plant Manager. “Our folks are excited about the challenge and opportunity to operate a facility such as this.”
Total compost facility capital cost was approximately $3.1 million, including ancillary equipment such as loaders, finished compost screen and laboratory equipment. There are three full-time personnel assigned to the facility – a superintendent or chief operator and two operators. They are supervised by the WWTP Manager. All lab work is performed by a laboratory technician whose main duties are lab work for the WWTP. Maintenance is performed by the WWTP chief mechanic and assistant mechanic.
Thomas Mansur, P.E., is a Civil Engineer specializing in water and wastewater systems in the Tulsa office of the Benham Companies LLC. He can be reached at (918) 492-1600 or by e-mail at firstname.lastname@example.org. Richard M. Nicoletti, P.E., is Technical Sales Manager for IPS Composting Systems at Siemens Water Technologies based in Shrewsbury, Massachusetts. He can be reached at (508) 849-4747 or by e-mail at email@example.com.
July 25, 2007 | General
Agitated Bay Composting In Ardmore, Oklahoma
BioCycle July 2007, Vol. 48, No. 7, p. 50