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Golden, Colo., February 13, 1998 A new pretreatment process may give cities better options in dealing with a persistent environmental problem: disposing the tons of sludge biosolids generated every day by sewage treatment plants.
The pretreatment process was developed at the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL), which recently issued a license to commercialize the technology to Peak Treatment Systems, Inc. of Golden, Colo.
Conventional disposal methods include landfilling and tilling treated waste into soil. But tougher environmental regulations have imposed more restrictions on the disposal of sewage sludge and sent many municipalities looking for new solutions.
The average city needs to treat and dispose of an estimated 3.8 million tons of sludge per year, at an average cost of $40 a ton. Alternatives could reduce disposal costs and help generate revenue through new products.
The NREL-developed pretreatment process destroys all pathogens in municipal sewage sludge, allowing the biosolids to be considered for beneficial uses beyond immediate disposal. The sanitized waste could be converted to a high protein feedstock and used in high-efficiency waste-to-energy digesters producing methane-rich gas, which could be used for heat or to run a turbine to generate electricity.
The pretreatment process involves heating sewage sludge to high temperatures with steam under pressure and then rapidly decompressing the material. The process begins to break down and weaken the sludge's cellular structure. The softened material is then fed into a mill where the cellular structure is completely broken down.
Peak Treatment Systems is using the equipment at a pilot-scale high solids anaerobic digester in Stanton, Calif., to validate the technology in cooperation with the University of Puerto Rico. The company is also interested in developing additional testing sites in the United States.
Licensing agreements are one tool used to commercialize technology developed at NREL. The laboratory also enters into cooperative research and development agreements (CRADAs) with industry to help transfer promising technologies to the marketplace.