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United States Office of Water EPA 832-F-00-052 Environmental Protection Washington, D.C. September 2000 Agency ��EPA Biosolids Technology Fact Sheet Alkaline Stabilization of Biosolids DESCRIPTION Alkaline stabilization can achieve the minimum requirements for both Class A and Class B biosolids Biosolids are primarily organic materials produced with respect to pathogens,depending on the amount during wastewater treatment which may be put to beneficial use. Biosolids are used in home gardening, commercial agriculture, silviculture, greenways, recreational areas and reclamation of drastically disturbed sites such as those subjected to surface mining. Biosolids are often rich in nutrients such as nitrogen and phosphorus, and contain valuable micro nutrients. The Environmental Protection Agency's (EPA) 40 CFR Part 503, Standards for the Use and Disposal of Sewage Sludge, (the Part 503 Rule) requires that wastewater solids be processed before they can be ; beneficially used. The processing is described in this fact sheet as stabilization. Stabilization helps to minimize the potential for odor generation,destroys pathogens(disease causing organisms),and reduces Source: Parsons Engineering Science, Inc., 1999. the material's vector attraction potential. One method of stabilization is to add alkaline materials FIGURE 1 ALKALINE STABILIZED to raise the pH level to make conditions unfavorable BIOSOLIDS for the growth of organisms (such as pathogens). Figure 1 is a picture of alkaline stabilized biosolids of alkaline material added and other processes being dropped from an overhead conveyor into employed. Generally, alkaline stabilization meets windrow curing piles at Middlesex County Utility the Class B requirements when the pH of the Authority's facility in New Jersey. mixture of wastewater solids and alkaline material is at 12 or above after 2 hours of contact. The Part 503 Rule defines two types of biosolids with respect to pathogen reduction: Class A (no Class A requirements can be achieved when the pH detectable pathogens) and Class B (a reduced level of the mixture is maintained at or above 12 for at of pathogens). Both classes are safe,but additional least 72 hours, with a temperature of 52°C requirements are necessary with Class B materials. maintained for at least 12 hours during this time. In These requirements are detailed in the Part 503 Rule one process, the mixture is air dried to over 50 and include such things as limiting public access to percent solids after the 72-hour period of elevated the site of application, limiting livestock grazing, pH. Alternately,the process may be manipulated to and controlling crop harvesting schedules. Class A maintain temperatures at or above 70°C for 30 or biosolids are not subject to these use restrictions and more minutes,while maintaining the pH requirement can generally be used like any commercial fertilizer. of 12. This higher temperature can be achieved by