Performance of the municipal wastewater treatment plant for removal of Listeria monocytogenes

Abstract

Aims: The aim of present study was determination of occurrence of Listeria Listeria spp. in various point of a municipal wastewater treatment plant. Materials and Methods: The samples were collected of influent, effluent, raw sludge, stabilized sludge and dried sludge from north wastewater treatment plant Isfahan, Iran. The presence of Listeria spp. was determined using USDA procedure and enumerated by a three-tube most probable number assay using Fraser enrichment broth. Then, biochemically identified Listeria monocytogenes was further confirmed by PCR amplification. Results: L. monocytogenes, L. innocua and L. seeligeri were isolated from 76.9%, 23.1% and 23.1% of influent, 38.5%, 46.2% and 7.7% of effluent, 84.6%, 69.2% and 46.2% of raw sludge, 69.2%, 76.9% and 0% of stabilized sludge and 46.2%, 7.7% and 0% of dried sludge samples, respectively. The efficiency of wastewater treatment processes, digester tank and drying bed in removal of L. monocytogenes were 69.6%, 64.7% and 73.4%, respectively. All phenotypically identified L. monocytogenes were further confirmed by PCR method. Conclusion: Application of sewage sludge in agricultural farms as fertilizer may result in bacteria spreading in agriculture fields and contaminated foods with plant origin. This may cause a risk of spreading disease to human and animals. Using parameters such as BOD 5 is not sufficient standard for the elimination of pathogenic microorganisms.