BioCycle March 2011, Vol. 52, No. 3, p. 58
The South Kern Compost Manufacturing Facility uses negative aeration of compost piles covered with a layer of finished compost, along with biofiltration, to comply with strict emissions limits.
THE South Kern Compost Manufacturing Facility (SKCMF), located on the outskirts of Taft, California, knew what was coming down the pike in terms of air emissions requirements when it embarked on its plant design. The cocomposting facility processes over 600 wet tons/day of biosolids with green and wood waste as amendment, and is situated in the San Joaquin Valley Air Pollution Control District (SJVAPCD). The SJVAPCD is designated as being in “extreme nonattainment” for ozone standards set by the U.S. Environmental Protection Agency.
The federal Clean Air Act requires San Joaquin Valley officials to reduce ozone-forming emissions from all known stationary sources of volatile organic compounds (VOCs). This led to the adoption of SJVAPCD Rule 4565 in March 2007, regulating air emissions from biosolids, animal manure and poultry litter operations, including composting and cocomposting facilities. The purpose of this rule is to reduce emissions of VOCs and ammonia by at least 80 percent by weight.
“Rule 4565 was not implemented at the time we built our composting facility in south Kern County, which is in the SJVAPCD air district,” says Lorrie Loder, senior communications manager with Synagro Technologies, Inc., the parent company of SKCMF. “Just prior to the adoption of Rule 4565, the South Coast Air Quality Management District (SCAQMD) had written Rule 1133 which set limits on VOC and ammonia emissions and required enclosure of composting facilities located in the Los Angeles air basin. By speaking with SJVAPCD during permitting of our South Kern facility, we understood that the District was developing their own rule. We learned that even though they were not considering enclosure as a requirement, they were establishing the same type of limits on VOCs and ammonia emissions as adopted by the SCAQMD due to their extreme nonattainment status at that time.”
Synagro had acquired 774 acres of industrially-zoned land for the cocomposting facility. When designing the facility, Synagro selected aerated static piles (ASP), under negative aeration, as its composting method, with the process air treated through a biofilter. The facility’s biofilter design set the Best Available Control Technology (BACT) standard for managing VOC emissions in the SJVAPCD. The venting of active and curing compost to the biofilter along with covering all active composting piles within three hours of their construction with at least 6-inches of finished compost is now included in the list of Class One Mitigation Measures in Rule 4565.
The composting site uses about 100 acres of the 774-acre parcel. The facility’s permitted capacity is 670,000 tons/year of biosolids and organic amendments. Operations began in 2007. “We have reached our design capacity, but not our permitted capacity,” says Loder. “We have the land area to expand if necessary.”
MAXIMUM AIR CAPTURE
The SKCMF has long-term management contracts with agencies from Los Angeles, Orange and Riverside counties to process a portion of the biosolids generated by their wastewater treatment plants. Most of the biosolids are digested, and range in solids content from 17 to 28 percent.
Trucks delivering biosolids drive directly to a mixing and receiving building. High-speed overhead doors close immediately after the trucks arrive in order to mitigate odors. After unloading, the trucks are washed down. Green waste and wood obtained from local Kern County municipalities are ground off-site (to about 3-inch minus particles) and are delivered to an outside receiving area. The amendment is loaded into a hopper that feeds the chips onto an enclosed conveyor belt that moves the material inside the building. “We were required by our air permit to install a misting system on the hopper to reduce emissions,” says Loder.
Biosolids and amendment are mixed in stationary, electric-powered Laird vertical auger mixers. The mixers off-load onto an enclosed conveyor belt that transports blended feedstocks outside to a pad. “Two draw fans provide 10 air changes per hour from within the building with the air treated in the biofilter adjacent to the building,” explains Ron Miesbauer, director of operations. “Air also is pulled off the enclosed conveyors and directed to the biofilter.” The five biofilters on site are each approximately 120-ft by 160-ft, and 7-ft tall. The media is composed of various types of wood chips.
Currently, the mixed biosolids and amendments are transported from the feedstock pad to the composting pad via dump trucks. Front-end loaders – the only other diesel-powered equipment on site – are used to build the piles. SKCMF is looking into a conveyor system to facilitate that part of the process and provide further GHG emission reductions. The static piles are built over aeration trenches covered with grates. The grates are lifted out and the trenches are flushed with water each time a pile is taken down. Before putting on the fresh feedstock, overs from compost screening are placed on top of the trenches to help with dispersion of air and prevent fines from getting into the pipes.
Both the composting and curing pads are lined and drain to a lined retention basin. The basin is aerated. Water is reused for cleaning the lateral pipes and for dust control on the lined surfaces.
The average retention time in the active composting piles is 20 to 22 days, followed by another 20 to 22 days in the aerated curing piles. Both the curing and composting pads are divided into five aeration zones, with large fans drawing air through the piles and into the biofilters. The facility utilizes a remote temperature probe system from Engineered Compost Systems to monitor temperatures throughout the composting process.
The SJVAPCD’s Rule 4565 includes requirements for the biofilter. The media temperature must be between 70°F and 110°F, with moisture content of the media between 40 and 70 percent by weight and a pH between 6.5 and 8.0. A visual inspection must show that the biofilter media is free of observable rodent burrows, cracks and channeling; weed coverage must be less than 10 percent of the exposed surface of the biofilter.
“We have cooling fans ahead of each biofilter to lower the temperature of the process air from the composting piles, followed by a humidification system to remove more heat,” explains Miesbauer. “This process achieves a temperature of approximately 95°F going into the biofilters.”
After curing, the compost is screened in mobile, electric-powered McCloskey trommels. “Right now, about 75 percent of the compost goes to agricultural land in neighboring counties,” says Miesbauer. “About 25 percent is going into the landscape market, and we are expanding sales in that sector.”
Kern County has been home to significant controversy related to land application of biosolids from urban generators outside of the County. Kern County Supervisors have adopted very restrictive rules that prohibit use of biosolids and bulk biosolids compost in the unincorporated areas of the county. Sensitive to the dynamics in the county related to biosolids, Synagro became involved in the westside Kern County cities of Taft and Maricopa three years before SKCMF opened. “We did presentations on the project throughout the community to provide education about the composting technology process and became actively involved in civic programs,” recalls Loder.
Synagro, along with Sempra Energy, Chevron and Wells Fargo, provide funding for the STEM (Science, Technology, Engineering and Mathematics) Program, a K-12 outreach initiative for schools in western Kern County, established by Taft College. STEM offers demonstrations and activities related to a wide range of topics, from the life sciences to physical science. “We are also helping to establish a community garden in Taft,” she adds.
Recently, Synagro received the U.S. Composting Council’s Composter of the Year award. Shortly thereafter, the company was recognized by the California Department of Resources Recycling and Recovery (CalRecycle) as the 2010 Waste Reduction Award Program (WRAP) winner for its environmentally sound business strategies and enhanced recycling initiatives. In 2010, Synagro recycled 400,000 tons of organic waste generated in California into soil amendments and compost. The company is also a Healthy Air Living Partner with the SJVAPCD.
The SKCMF has been successful in meeting SJVAPCD’S stringent air quality requirements. The rule requires that the biofilter be tested for VOC control efficiency within 90 days of installation and every two years thereafter. The baseline emissions and biofilter performance measurements for the site were conducted by air emissions consultants C.E. Schmidt and T.R. Card (authors of “Air Emissions Assessment Technologies” in this Global Conference Preview).
“The testing was conducted using strict agency protocols in order to ensure that the facility was in compliance with Rule 4565 requirements,” says Miesbauer. “The inbound air is measured to establish a baseline, and the outbound air from the biofilter is measured to determine the level of destruction of VOCs and ammonia. We don’t need to measure the top of the active composting piles, because the compost cover is a BACT under Rule 4565.” Although not required, SKCMF uses a hand-held analyzer to measure emissions from the compost piles on a quarterly basis.
Capital costs for the SKCMF were approximately $35 million. The utility costs to operate the fans and electric-powered equipment are significant. BioCycle asked Loder if the cost of compliance with the air district rules makes it challenging to succeed as a sustainable business enterprise. “What it really takes to operate as a business in this environment is air quality technology and long-term contracts,” she observes. “The public agencies involved with our facility are partnering with us for long-term sustainable solutions. We are helping them recycle two organic waste streams, which in turn assists municipalities in the region with AB 939 landfill diversion credits, sequesters carbon and improves the soils.”
March 23, 2011 | General
Cocomposting In A Restricted Air Quality Zone
BioCycle March 2011, Vol. 52, No. 3, p. 58