Messenger - Vol. 1, No. 3, Page 10 Spring 1992 A safer sludge Seeking to maintain the environment as we know it, Steven Dentel boldly goes where few researchers dare to tread. An environmental engineer working in the oft hidden world of wastewater management, Dentel, an associate professor of civil engineering, is exploring the uncertain fate of chemical additives in sludge. Under a $300,000 grant from the Water Environment Research Foundation, Dentel and his four graduate students are investigating the use and overuse of polymers intended to remove water from sludge. The goal of all sewage treatment plants is to separate and purify the water contained in municipal sewage. Polymers, long repeating chains of carbon compounds, are routinely added to "de-water" the precipitated, semi-solid sludge, which even in its final stage is still 70-80 percent water. Because they have a positive charge, the polymers bind tightly to negatively charged particles in the sludge, pulling the particles together and "squeezing out" the water. Although this treatment has been in use for some 20 or 30 years, Dentel says no one has determined how the optimum polymer dose should be found, and studies also are needed to establish the ultimate fate of polymers that make up 1 percent of the total solids in the de-watered sludge. "Polymer overdosing is fairly typical in a variety of de-watering operations in the Delaware Valley," he says, and overdosing allows some unattached polymers to slip into the water that will be recycled into local rivers and bays. "We know some polymers are toxic to fish at very low levels (less than one milligram per liter)," he says, "and some monomers remaining after the polymerization reaction are highly carcinogenic." And no one knows what happens to the polymers when the sludge is dumped into a landfill or spread out as a soil supplement on the landscape, he says. Dentel's research will result in a manual to help sewage treatment plant personnel evaluate and select the appropriate polymer products and the second phase will develop a technology to monitor proper doses of polymers for optimum effect. "Polymers can represent up to 25 percent of the cost of sewage treatment," Dentel says, "so by carefully monitoring the dose, cost savings are expected, as well as the decreased release of polymers into the environment." How polymers interact with other solids in the sludge and how they can be separated or extracted from these solids is the most challenging aspect of this research project, Dentel says. He expects some analogies with another on-going project in which he and Herbert E. Allen, professor of civil engineering, are trying to assess the impact of surfactants on sludge. "We've always assumed that surfactants, which are frequently used in laundry detergents to remove oil, were harmless," he says, "but researchers have reported that surfactants lift pollutants off the soil and transport them into the water." Testing on artifically produced sludge will take place in the laboratory. The researchers will study the "real stuff" on site at sewage treatment plants in Wilmington; Elkton, Md.; Warminster, Pa.; and Hatfield, Pa. -Cornelia Weil