A Study of Faecal Coliform Die-Off in Sewage Sludge Drying Bed
The aim of this study was to assess the interacting characteristics of sewage sludge such as temperature, pH, and moisture content of sludge at defined time intervals as to how they affect Coliform die-off in a drying bed. Samples were collected at 0.0mm depth (i.e. surface of sludge), 60mm, 120mm, 180mm and 240mm, and colony count tests were performed on the samples. Results indicate that the number of Coliforms was minimum at the surface, maximum at 60mm depth, and decreased consistently to another minimum value at 240mm depth. This trend could be as a result of the organisms being in their exponential phase with adequate nutrients and growth conditions at 60mm depth, which later experienced decrease in available nutrients, oxygen and unfavorable growth conditions such as unfavorable temperatures, reduced moisture content, acidic pH and water activity. Range of the maxima and minima values of CFU/100ml for the five horizons considered over a period of 76 days were This finding does not conform with the work of Al Malack and others  because from their results, the various pathogenic organisms studied were found to survive longer as the sludge initial depth was increased. Short-term and long-term effect of drying indicate that low moisture content favours microbial decay because pathogen removal rate was consistently increasing from 21/01/2013 to 08/02/3013, a condition which started prevailing when the moisture content of sludge in the drying bed had decreased from 88.99 per cent on 29/11/2012 to 65.48 per cent on 21/01/2013. It was recommended that conditioners should be used to dewater sludge faster in order to speed-up pathogen die-off rate in drying beds.