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TABLE 1 TYPICAL DESIGN CRITERIA PERFORMANCE FOR CLASS B ALKALINE STABILIZATION Alkaline stabilization is frequently selected by Parameter Design Criterion wastewater treatment facilities in regions where 0.25 pound per pound of soils have a tendency to be acidic and where low Alkaline dose wastewater solids at 20 cost alkaline materials are readily available. In areas percent solids where soils are acidic, the end product has greater Retention time in mixer 1 minute value. Table 2 shows location, size,and end use for Retention time in curing 30 minutes representative alkaline stabilization facilities. vessel Source: National Lime Association, undated. Alkaline stabilization systems are generally quite reliable and flexible. The same equipment can often The end use of the material is another important be used to produce either Class A or B biosolids factor when designing a biosolids management with minor process modifications, such as a larger program, including alkaline stabilization. The dosage of alkaline material or the addition of resulting material is suitable for many uses, supplemental heating (pasteurization.) including agricultural application,mine reclamation and landfill cover. The amount of land that must be With respect to pathogen reduction,Class B alkaline available differs with the use. Alkaline stabilized stabilization has been demonstrated to reduce total biosolids are generally lower in nitrogen than other coliform, fecal coliform, and fecal streptococci biosolids products because nitrogen is converted to bacterial concentrations by more than 99.9 percent. ammonia during processing. The material contains Concentrations of Salmonella and Pseudomonas approximately one to two percent nitrogen; one aeruginosa have been shown to be reduced below percent phosphorus; and negligible potassium, the level of detection. Pathogen concentrations in nutrients of primary importance for vegetative Class B alkaline stabilized biosolids range from 10 growth. In agricultural application, alkaline to 1,000 times less than those in anaerobically stabilized biosolids are often applied more for their digested sludge (U.S. EPA, 1979.) Alkaline pH adjusting characteristics at a typical application stabilization can result in an exceptional quality rate of two to five tons per acre. Nutrients supplied product when it meets Class A pathogen reduction, to the crop are a secondary benefit. In reclamation vector attraction reduction and the highest standards applications, the material is often applied only once for metal concentrations. This higher level of rather than annually or periodically as in agricultural processing can result in a more valuable product applications. Therefore, the material is usually because there are no restrictions on end use. The applied at a higher rate of between 60 to 100 dry high level of disinfection achieved in Class A tons per acre. In landfill cover applications, the products makes them easier to handle and apply. amount of material used is dictated more by For example, if a farmer purchases an exceptional regulatory requirements than nutrient content. quality product,he will not have to restrict access or Alkaline stabilized biosolids can be used as daily limit grazing and harvesting times. cover, or to amend the final cover, in accordance with federal regulations which require material to The appearance, odor causing potential, and enhance conditions for vegetative growth. For daily handling characteristics can vary greatly depending cover, a minimum of six inches of soil is required. on the type of alkaline stabilization process used. Equivalent thickness of alkaline stabilized material Processes that add larger amounts of alkaline must be approved on a case by case basis. Typical material or include added heat,drying,or curing will application rates for incorporation into final cover produce a drier product that resembles topsoil. material are similar to those at mine reclamation Other alkaline stabilization processes that simply sites.