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USA’S PRACTICES FOR CONTROLLING PATHOGENS IN BIOSOLIDS
Citation:
SMITH, J. E. AND R. S. REIMERS. USA’S PRACTICES FOR CONTROLLING PATHOGENS IN BIOSOLIDS. In Proceedings, Australian Water Association's Biosolids Specialty III Conference, Melbourne, AUSTRALIA, June 07 - 08, 2006. Australian Water Association, Artarmon, Australia, 43-44, (2006).
Impact/Purpose:
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Description:
The U.S.A. initially established regulations for the management of sewage sludge in 1979 and updated them in 1993. They are briefly discussed with emphasis on the rationale for the procedures chosen to disinfect sludge and control its vector attractiveness. By controlling pathogenic microorganisms humans are protected from coming into contact with them via biosolids exposure pathways that include inhalation and ingestion of aerosols, ingestion of contaminated soil or water, and consumption of contaminated crops or crops grown in contaminated soil. Issues with the present Class A disinfection alternatives such as their only being concerned with the presence or absence of three microorganisms, one or two of which are typically not present are discussed and remedies suggested. Similarly Class B’s Alternative 1 requires monitoring the fecal coliform concentration in the sludge to determine if it is Class B. Many untreated sludges today have concentrations lower than the Class B requirement. Limitations with several of the current options for measuring vector attractiveness are also noted. For example anaerobically digesting a sludge and achieving a volatile solids reduction of 38% does not necessarily mean that it will not putrefy and attract vectors, since some sludges require much more time to digest and can achieve greater than 65% volatile solids reduction. Innovative and alternative methods for disinfection are frequently proposed and it is important that the science behind each process’ operation be understood. Further the process’ performance must be demonstrated. Developers of new technologies need to identify the stressors working with their process and how they contribute to the reduction of pathogenic bacteria, viruses, protozoa and helminths. For example with alkaline disinfection processes like that of Bioset it is possible to show the beneficial effects of time, temperature, pH, chemical agents like ammonia, and pressure. Data from treating raw, anaerobically digested, and aerobically treated sludges were presented. An acid-oxidative process that employs chlorine dioxide, low pH, and nitrous acid for disinfection was also studied and data is presented for several sludges showing effective kill of all Ascaris eggs, Poliovirus and fecal coliforms. An anaerobic digestion system with a thermophilic acid phase and mesophilic methane phase was studied at Indianapolis, IN and data for its successful Class A disinfection of sludge is presented. The relatively high level of volatile solids in the raw sludge was likely responsible for the higher levels of volatile fatty acids and free ammonia in both reactors. These chemicals together with the high temperature in the acidogenic-thermophilic digester contributed to a large reduction of pathogens. Vermicomposting and a process that uses a fumigant are currently under evaluation by the PEC and briefly discussed. Work is underway to identify improved methods for measuring a sludge’s vector attractiveness and possibly stability. It includes the use bacterial enzymatic activity and biochemical oxygen demand.