Unsafe sewage sludge or beneficial biosolids?: Liability, planning, and management issues regarding the land application of sewage treatment residuals

Boston College Environmental Affairs Law Review, Summer 1999 by Goldfarb, William, Krogmann, Uta

3. Advanced Alkaline Stabilization

Advanced alkaline stabilization neutralizes harmful pathogens in the sewage sludge by adding liming agents to increase pH above twelve for at least seventy-two hours, with temperatures held above fifty-two degrees Celsius for at least twelve hours during this period.27 Quick lime, hydrated lime, or cement kiln dust are added to solidify the material, and the product has been used as a liming agent in agriculture or as daily cover and capping material at MSW landfills.28 Cases of public nuisances arising from the odor of this material have been reported.29 In addition, cement kiln dust itself may be contaminated because cement kilns sometimes burn hazardous wastes.30

4. Heat Drying

Another stabilization technique is the heat drying of sewage sludge. Heat drying technology can be used for sewage sludge stabilization in two ways. In the first method, dryers are sometimes used, after dewatering sewage sludge in presses or centrifuges, as a single process to reduce the weight and volume of the sludge so that it may be transported for disposal.31 In the second method, heat drying is also used as part of a process to create a usable end product that flows easily and can be used in fertilizer mixes.32 This pelletizing process uses heat to dry the sewage sludge to between ninety and ninety-five percent solids, thus reducing volume and killing pathogens before the sewage sludge is turned into pellets and sold as fertilizer.33 Heat drying is most often performed by private companies, which sometimes add nitrogen to increase the fertilizing value of the sewage sludge.34 One significant drawback to this process is that the drying uses a substantial amount of energy. For example, dryers employed to dry ten tons per day will use 10,000 to 20,000 cubic feet of gas per hour.35

B. Landfilling

In 1995, about twenty-five percent of sewage sludge in the United States was landfilled by co-disposal with MSW, by disposal in sludge monofills, or by use as landfill cover in MSW landfills.36 In a few states, this amount was much higher (e.g., Nevada-75%; New Mexico-73%; Rhode Island-60%; Louisiana-45%).37 In the 1980s and early 1990s, the number of available landfills decreased. Based on the tighter supply of landfill space and greater recognition of the beneficial properties of sewage sludge, a few states, including New Jersey, enacted legislation banning or limiting the amount of sewage sludge that could be disposed of in landfills.38 Currently, however, because of the increase in the number of so-called mega-landfills,39 landfill space is abundant. So for some communities, the landfilling of sewage sludge is the least expensive alternative? Additionally, the increased interest in bioreactor landfills contributes to this trend, since the addition of sewage sludge as inoculum in bioreactor landfills is a potential benefit.41 In bioreactor landfills, the decomposition of waste is controlled within the landfill environment, which lowers long-term risks to humans and the environment from the landfill gas and leachate.42 In contrast, central European countries have either already banned or soon will ban the landfill disposal of wastes with a high organic matter content, like sewage sludge and MSW. This is in order to minimize the long-term risks of landfills.43