Persistency of Bacterial Indicators in Biosolids Stabilization with Coal Fly Ash and Lime
Abstract:Alkaline coal fly ash and lime were tested for their effectiveness in pathogen removal from biosolids at different time intervals and temperatures. Coal fly ash at 10 and 35% w/w was mixed with dewatered biosolids and then the ash–biosolids mixture was mixed separately with 0, 1.1, 2.2, 4.4, 8.5, 11, and 18% calcium oxide (w/w on a dry weight basis) with and without heating to 55 °C. Total bacteria, salmonella, and total coliforms were monitored at various time intervals. Both ash–biosolids mixtures with or without lime amendment had a significantly lower total bacterial population than the biosolids control, but the residual indigenous bacterial flora in the ash and lime stabilized biosolids still maintained a population of greater than 104 g−1 dry biosolids. Alkaline-stabilized biosolids with a lime amendment rate greater than 8.5% could maintain pH greater than or equal to 12 for more than 2 hours, which effectively removed total coliforms and salmonella in the mixture. Heat treatment to 55 °C and a storage time of 14 days provided an added advantage resulting in a further reduction in pathogens for all treatments. It is recommended that 10% ash–biosolids mixture should be amended with a minimum of 8.5% lime on a dry weight basis for at least 2 hours to achieve acceptable levels of salmonella and total coliforms to ensure no pathogenic risk following land application.
Document Type: Research Article
Publication date: September 1, 2001
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