A series of experiments has provided data which indicate that treatment of municipal wastewater sludge cakes with 35 % kiln dust (cement, CKD or lime, LKD), alone or with a small amount of quicklime, will reduce the pathogenic microbial population in the sludge to below the U.S. Environmental Protection Agency's (USEPA) Process to Further Reduce Pathogens (PFRP) standard (USEPA, 1989). Both laboratory and large-scale field tests show that maintaining treated sludge at 52°C for 12 h, while the pH exceeds 12.0, kills viable indigenous and seeded populations of salmonella, poliovirus, and ascaris ova.
The addition of the cement or lime kiln dust results in a granular, easy-to-handle, soil-like material that is then treated in one of two methods. In one alternative no heating is necessary, while in the other, sludge cake is heated to 52°C for 12 h. In both, the pH must exceed 12.0 for a defined period. After this, the alkaline treated sludge is air dried through intermittent turning of windrows.
These patented (N-Viro) and USEPA's PFRP-approved pasteurization processes leave approximately 106 indigenous microorganisms per 5 g dry weight sludge, which help maintain the treated sludge in a nearly odor-free, stable, soil-like form. The specific chemical and physical effects of cement and lime kiln dust on municipal sludge cakes are presented to explain the mechanisms of the pasteurization process. Sludges from over twenty cities have been processed to make N-Viro Soil and all of them have achieved the PFRP criteria.
This process helps to prevent metal release in leachate by fixing the heavy metals present in the product and converting them to insoluble metal hydroxides. Data will show the degree to which alkaline treatment renders insoluble the heavy metals present in sludge. The modified EP Tox test was used to quantify the metal fixation accomplished by the mixing of kiln dust and sludge.