Researcher Seeks To Reduce Pathogens, Odor From Biosolids

A $400 million sludge handling system, slated to be built along the Potomac River by the Washington D.C. Water and Sewer Authority by 2010, may not be able to completely thwart odor problems if it uses current technology, states Virginia Tech environmental engineer John Novak.

Novak, the Nick Prillaman Professor of Civil and Environmental Engineering, is working with this and other facilities to identify better processes for the destruction of organic solids and the elimination of disease-causing organisms in biosolids, according to a Dec. 6 announcement.

Any time a treatment plant works with water or wastewater, sludge is generated. And twice a week, Novak's lab receives two shipments of the processed solids from the sewage.

"Biosolids management is one of the most-important aspects of wastewater treatment because of economic and health and safety issues," Novak said. "The cost of biosolid treatment and hauling is a major expenditure for wastewater treatment utilities. Pathogens and odor problems may restrict the biosolid disposal options and affect hauling costs."

Biosolids applied to land in the form of fertilizer also can impact groundwater quality, primarily through nitrogen contamination, Novak said.

His approach to reduce the volatility of waste and to remove nitrogen from the process differs from some of the previously tried techniques. His work is based in part on some successful treatments of wastewater where a sequential anaerobic and aerobic digestion, called a dual-digestion process, is used.

"Recent studies suggest that some solids in sludge are degraded only during the anaerobic digestion and some only during the aerobic digestion treatments," Novak explained. "Therefore, a dual digestion, using both anaerobic and aerobic treatments, would be expected to provide a reduction in the volatile solids beyond that achieved when using only one of the processes."

He said that his initial studies indicate that the theory is correct. The dual treatment achieved up to a 65 percent volatile solids reduction, compared to 46 percent and 52 percent when using one of the single anaerobic digestion processes. His studies also showed that more than 50 percent of the nitrogen and 80 percent of the ammonia can be removed from anaerobic effluent after digesting it aerobically.

He reported his findings at this year's Residuals and Biosolids Management Conference in Cincinnati.

Novak also has investigated the role that two specific metals, iron and aluminum, play in odor coming from sludge treated anaerobically. Working with researchers from Carollo Engineers and CH2M-Hill, Novak used a centrifuge-simulation method developed at Virginia Tech to anaerobically digest a blend of primary and waste activated sludge from 12 different wastewater treatment plants.

Their findings indicated that aluminum reduced the odor potential for sludges that were high in iron.

John Novak: http://www.cee.vt.edu

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