EVALUATION OF BIOSOLID SAMPLE PROCESSING TECHNIQUES TO MAXIMIZE RECOVERY OF BACTERIA
Abstract:Current federal regulations (40 CFR 503) require enumeration of fecal coliform or Salmonella prior to land application of Class A biosolids. This regulation specifies use of enumeration methods included in “Standard Methods for the Examination of Water and Wastewater 18th Edition,” (SM). For “Class A” biosolids the regulation requires use of multiple-tube fermentation techniques for fecal coliform and multiple tube enrichment techniques for Salmonella followed by isolation and biochemical and serological confirmation. Enumeration of fecal coliform may also be used to determine if biosolids meet Class B criteria (<2 × 106 fecal coliform/g). SM, provides guidance on how to process “solid or semisolid samples,“ but does not specifically address processing biosolids samples for bacterial analysis. The procedure recommended in “Control of Pathogens and Vector Attraction Reduction in Sewage Sludge, EPA/625/R-92/013,” is to blend a specific mass of sample with a sterile buffered dilution water on low speed for two minutes. Other researchers have used low concentrations of surfactants or other chemical agents combined with blending for the purpose of enhancing the recovery of bacteria or other microorganisms from solid or semisolid samples. Results from such work suggests that application of the appropriate combination of mechanical and chemical treatments may effectively increase the recovery of bacteria from biosolids.
This study was designed to determine if modifications to pretreatment of biosolids samples could improve recovery of bacteria. The work was conducted in four phases: phase one compared recovery of bacteria based upon the effectiveness of blending biosolids samples at various blending speeds and specific times; phase two compared the effectiveness of adding various surfactants and chemical agents to the dilution water prior to mixing biosolid samples; phase three was developed based upon the results of phase one, and further examined a narrow range of sample blending times; finally, phase four compared the effectiveness of adding specific additives and combinations of additives to dilution water. Results showed that the highest recovery for indicator organisms was obtained when samples were blended at high speed for one minute with dilution water containing 0.1% peptone. No improvement in recovery of bacteria was observed following the addition of surfactants, chelating agents, or organic solvents.
Document Type: Research Article
Publication date: January 1, 2001
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