Assessment of pathogenic microorganisms inactivation by electron beam irradiation and physico-chemical characteristics evaluation in sewage sludge

Abstract

This study mainly focused on detection and quantification of the Salmonella Enterica (S1), Salmonella Bongori (S2), enterococci, and E. coli in domestic sewage sludge samples (SSS) from two different sampling locations which are denominated as point A and B. The aim of this study was to validate the efficiency of electron beam irradiation (EBI) treatment on the inactivation of S1, S2, enterococci, and E. coli. The inactivation was measured in terms of different dose rates by varying irradiation current. Meantime, the absorbed dose and energy were fixed for each experimental portfolio. The dose rate was determined by correlation with the conveyor speed. Irradiation was performed in batch mode and the irradiated samples were then accessed for the detection of S1, S2 enterococci, and E. coli. Detection of S1, S2, and enterococci was conducted based on APHA 9620 and APHA 9260 standard methods. Meanwhile, E. coli were detected by using APHA 9221 standard method. The results attained clearly indicated that EBI treatment is effective on the inactivation of theS1, S2, enterococci and E. coli. The higher inactivation efficiency was observed at a lower dose rate with higher energy. The higher inactivation kinetics constant, k were attained at higher irradiation energy. Thus, this outcome proofs that irradiation energy effectively plays a crucial role in the inactivation of the targeted microorganisms. The physico-chemical properties of the SSS remain intact with variable dose rates. This outcome suggested that the EBI treatment is able to inactivate the microorganisms present onto the SSS without imparting many changes to the properties of the sludge samples. The bacterial re-growth onto the irradiated samples was monitored over a prolonged storage of 60 days. The survival of bacteria was detected for up to 7 days at a very low level. However, the re-growth of the bacteria was not detected at 60 days of storage.