In Greenville, S.C., solid waste and wastewater management go hand-in-hand. Using biosolids generated by the Western Carolina Regional Sewer Authority (WCRSA) as an alternate daily landfill cover material, Greenville County's Enoree Landfill has created a long-term market that saves money and maximizes resources.
In 1989, WCRSA began producing Class A alkaline stabilized biosolids (ASB) at the wastewater treatment plant by mixing lime kiln dust with dewatered sludge. The end-product is a gray, dirt-like material with a pH of 11.0 standard units (s.u.) that, when combined with fill dirt at a ratio of approximately 1-to-1, creates topsoil. The material then can be used for city and county projects, such as restoring roadside construction sites.
In fact, because of its elevated pH level and lime content, which helps ASB material reduce landfill odor and metal concentrations in leachate, Greenville decided to use the material as an alternative daily landfill cover (ADC).
The relationship between the city of Greenville and WCRSA goes back to the early 90s, when WCRSA formed an agreement with the city's landfill to provide all of the ASB it produced for use as an ADC.
The city welcomed this idea because it lowered operating costs by reducing the need to locate and transport fill dirt as a landfill cover material. This option also benefited WCRSA because it provided a low-cost, long-term solution for sludge disposal.
However, in 1995, the agreement ceased because that landfill closed.
In June 1995, when Greenville County opened Enoree Landfill's Subtitle D portion, which handles approximately 850 tons of trash per day, six days per week and serves 350,000 county residents, it agreed to use ASB as an ADC material.
The new landfill was another opportunity to use the 35 tons of dry ASB per day that WCRSA produces.
Enoree landfill agreed to use the 210 cubic yards of ASB that WCRSA delivers five days per week at no charge, and accept "grit and screenings" from WCRSA for a reduced tipping fee of $30 per wet ton that saves WCRSA $3 per ton.
In turn, WCRSA provides a certified operator to inspect the landfill's leachate lagoon for $24 per hour. WCRSA also accepts all leachate from the landfill, five days per week, at a cost of $75 per tanker (approximately 7,000 gallons per tanker).
Once the agreement was final, they sought approval for using ASB as an ADC. Because WCRSA used biosolids at the Greenville City Landfill, a simple National Pollution Discharge Elimination System (NPDES) permit modification was submitted to the South Carolina Department of Health and Environmental Control (SCDHEC).
SCDHEC's approval took into account infiltration, odors, vectors and dust. WCRSA must renew its permit for biosolids every five years, while Enoree must renew its permit annually.
In the meantime, Enoree continues to make operational improvements in handling and applying the cover material.
The landfill recently developed a method of mixing mulch from yard waste with fill dirt and biosolids in a 1-to-1-to-1 ratio to produce cover material that is similar to topsoil. It also is friable - it crumbles easily and breaks up into small pieces - and is easier to handle during application at the landfill's working face.
This is an attractive option because the landfill has plenty of available mulch that now can be recycled. Additionally, Enoree recycles yard waste into mulch and provides it free to the community.
The community is pleased, although it initially was difficult to develop the intergovernmental agreement; persuade Greenville County to forgo a tipping fee for the ASB; educate landfill operators how to manage the biosolids as an alternate daily cover material; and develop a mixing process for biosolids, dirt and mulch that would result in a quality cover product.
Greenville County also maximizes its use of yard waste and is saving money by making its own cover material.
Furthermore, WCRSA has found a long-term market for the beneficial use of its biosolids that has been honored with a second place national U.S. Environmental Protection Agency (EPA) Award and a First Place Regional EPA Award in 1998.