Cold atmospheric plasma for bacterial inactivation in Nile water and wastewater

This study aims to evaluate the efficiency of cold atmospheric plasma (CAP) generated using a corona discharge system in inactivating Gram-positive (Bacillus species) and Gram-negative (Escherichia coli) bacteria in Nile River water and wastewater. CAP was characterized using voltage-current curves and optical emission spectra (OES), while scanning electron microscopy (SEM), growth curve methods, and viable plate counts were used to evaluate antibacterial activity. CAP treatment successfully reduced bacterial counts in both Nile water and wastewater samples, with a reduction of ≥ 6-log in bacterial population after 8 min of treatment in Nile water, and a reduction of ≥ 2.6-log after 6 min of treatment in wastewater samples. Plasma treatment significantly altered bacterial growth kinetics and caused extensive morphological damage. The treated water samples showed a notable change in their physicochemical characteristics, including a moderate rise in electrical conductivity and a reduction in pH. The OES showed strong emission from the second positive system of nitrogen, with minor emission from N₂⁺ and OH radicals, suggesting strong plasma-water interactions. CAP treatment was non-thermal, based on the temperature readings, thus suggesting that the CAP could be used to inactivate bacteria in the Nile River water and wastewater samples in an environmentally friendly way.