Evaluation of Microbial Quality in Biosolids Generated from Municipal Wastewater Treatment Plants

Qualitative evaluation of sewage sludge before any kind of application is essential. The present study was aimed to investigate Total coliform, Fecal coliform and Salmonella in sewage sludge produced at wastewater treatment plants in Azerbaijan Province, Iran.
Nine wastewater treatment plants were chosen in East Azerbaijan Province, and their sludge from drying bed was studied. Total coliforms, thermo-tolerant coliforms, and Salmonella spp., were surveyed during winter time, 2015. Total and thermos-tolerant coliforms were enumerated by EPA method 1680 and salmonella was counted using EPA method 1682.
In the case of total coliform, sludge sample from Jolfa with 1.82×106 MPN/g showed the highest contamination, while Sarab showed lowest fecal coliform count with 2.02×103 MPN/g. As in the case for fecal coliform, the bacteria count for thermo-tolerant coliforms was higher in Jolfa than other cities; on the other hand, Ahar with no fecal coliform count or less than 2.2 showed the minimum contamination rate to fecal coliforms. In case of Salmonella spp., sludge samples from Ahar and Bostan Abad did not show any salmonella. While sludge sample from Tabriz wastewater treatment plant was determined as the most contaminant sludge with bacteria count equal to 84 per g. Moreover, sludge sample from Sarab wastewater treatment plant showed the least contamination rate, and bacteria count was 6 per g.
From the stand point of microbial quality, all sludge samples met class B standards set by USEPA, while none of them could provide class A standards. Thus, special precautions must be taken in case of soil amendments by the sludge produced from wastewater treatment plants.