Comparative performance of activated sludge and waste stabilization ponds for the removal of pollutants and pathogens in full-scale wastewater treatment plants in Egypt

The discharge of inadequately treated wastewater poses serious public health and environmental risks worldwide. In this study, the performance of two wastewater treatment plants (WWTPs) was evaluated for their ability to remove pathogenic viruses and bacteria, organic and nitrogen compounds, bacteriophages, and bacterial indicators. WWTP-A employs activated sludge treatment technology, whereas WWTP-B utilizes waste stabilization ponds (WSP). The removal rates of chemical oxygen demand (COD) and biological oxygen demand (BOD) were higher in WWTP-A than in WWTP-B, indicating the limited efficiency of the WSP system in treating heavily contaminated sewage. In WWTP-A, bacterial removal rates ranged between 3.9log10 for Listeria spp. and 6.2 log10 for Escherichia coli (E. coli), while in WWTP-B, removal ranged from 3.2 log10 for Pseudomonas aeruginosa to 5.3 log10 Fecal Streptococci. The viral reduction rate by WWTP-A ranged from 0.9 log10 for crAssphage to 3 log10 for human adenovirus (HAdV), whereas in WWTP-B, viral removal ranged between 0.8 log10 for somatic coliphages (SOMCPH) and 3 log10 for crAssphage. CrAssphage exhibited significant influent–effluent reduction in both WWTP-A and WWTP-B (Wilcoxon test, p < 0.05). In contrast, significant HAdV reduction was observed only in WWTP-A, SOMCPH only in WWTP-B, while RoV showed no significant reduction in either system. These findings highlight limitations in the ability of conventional treatment processes to consistently remove viral contaminants from treated effluent and underscore the need for improved management strategies to enhance effluent quality.