(Liquid and Solids Biological Treatment)
Liquid and solids biological treatment (LST) is a process that remediates soils and sludges contaminated with biodegradable organics (see figure below). The process is similar to activated sludge treatment of municipal and industrial wastewaters, but it treats suspended solids concentrations greater than 20 percent. First, an aqueous slurry of the waste material is prepared, and environmental conditions such as nutrient concentrations, temperature, and pH are optimized for biodegradation. The slurry is then mixed and aerated for a sufficient time to degrade the target waste constituents.
Several physical process configurations are possible, depending on site- and waste-specific conditions. Waste can be treated continuously or in batches in impoundment-based reactors. This configuration is sometimes the only practical option for projects greater than 10,000 cubic yards. Alternatively, tank-based systems may be constructed.
Constituent losses due to volatilization must be controlled during LST operations. The potential for emissions is greatest in batch treatment systems and lowest in continuously stirred tank reactor systems, particularly those with long residence times. Technologies such as carbon adsorption and biofiltration can control emissions.
LST may require pre- and posttreatment operations. However, in situ applications that store treated sludge residues do not require multiple unit operations.
Overall bioremediation in a hybrid system consisting of LST and land treatment systems can provide an alternative to landfilling treated solids. This combination rapidly degrades volatile constituents in a contained system, rendering the waste suitable for landfilling.
Remediation Technologies, Inc. (ReTeC), has constructed a mobile LST pilot system for field demonstrations. The system consists of two reactors, two 2,000-gallon holding tanks, and associated process equipment. The reactors are aerated using coarse bubble diffusers and mixed using axial flow turbine mixers. The reactors can operate separately, or as batch or continuous systems. Oxygen and pH are continuously monitored and recorded. Additional features include antifoaming and temperature control systems.
The technology treats sludges, sediments, and soils containing biodegradable organic materials. To date, the process has mainly treated sludges containing petroleum and wood preservative organics such as creosote and pentachlorophenol (PCP). LST has treated polynuclear aromatic hydrocarbons (PAH), PCP, and a broad range of petroleum hydrocarbons in the laboratory and the field.
This technology was accepted into the SITE Demonstration Program in 1987. The technology was demonstrated under SITE at the Niagara Mohawk Power Corporation facility at Harbor Point in Utica, New York from June through August 1995. The following equipment was used for the demonstration: (1) a 10,000-gallon cylindrical tank (12-foot diameter) with bottom-mounted air diffusers that provided aeration and assisted in suspending solids; (2) a tank cover outfitted with exhaust piping that contained and channeled air discharge; and (3) a spray system that recirculated liquid from within the tank to disperse foam buildup.
ReTeC has applied the technology in the field over a dozen times to treat wood preservative sludges with impoundment-type LST systems. In addition, LST has treated petroleum refinery impoundment sludges in two field-based pilot demonstrations and several laboratory treatability studies.
Analytical results from the SITE demonstration showed a reduction in oil and grease concentrations from 14,500 to 3,100 milligrams per kilogram (mg/kg), or 79 percent; total PAH concentrations were reduced from 137 to 51 mg/kg, or 63 percent; and total benzene, toluene, ethylbenzene, and xylene concentrations were reduced from 0.083 to 0.030 mg/kg, or 64 percent. PAH leachability in the solids was reduced to nondetect levels after treatment. Toxicity of the solids to earthworms was also decreased by the treatment. Only 24 percent of the earthworms survived when added to untreated contaminated soil, while earthworms placed in treated soil showed no toxic effects.
EPA PROJECT MANAGER:
Ronald Lewis
U.S. EPA
National Risk Management Research
Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7856
Fax: 513-569-7105
TECHNOLOGY DEVELOPER CONTACT:
Merv Cooper
Remediation Technologies, Inc.
1011 S.W. Klickitat Way, Suite 207
Seattle, WA 98134
206-624-9349
Fax: 206-624-2839