Effect of pH Fluctuations on Pathogenic Bacteria Removal in Domestic Wastewater

Fluctuations in pH may occur in waste stabilization ponds. This behaviour could be bactericidal. However, no studies have been conducted to confirm this. The present study addresses the issue by studying the die-off of Escherichia coli , coliforms, Salmonella and other enterobacteria in domestic wastewater. Fluctuating pH conditions were established in incubations with pH values ranging between 4-9, 7-8, 7-9, 7-10, and 7-11, while stable pH incubations were at pH 4, 5, 7, 8, 9, 10 and 11. A follow up on the experiment was done in sterilised domestic wastewater using E. coli (ATCC13706) and enterococci isolated from domestic wastewater. All experiments were done in replicates of three in 100ml plastic containers. Adjustment of pH was done twice a day at 08GMT and 16GMT with 0.2N HCl or 0.2N NaOH. Stable pH appeared more detrimental than fluctuating pH to E. coli and coliforms in domestic wastewater and E. coli (ATCC 13706), except fluctuating pH of 4-9, which had higher die-off rates than stable pH of 4, and 9 for E. coli. Fluctuations in pH had higher die-off rates than stable pH incubations for Salmonella and other enterobacteria. At pH 5, low die-off rates were recorded for E. coli and Salmonella . Increase in numbers was observed for E. coli (ATCC 13706), coliforms and other enterobacteria in at pH 5 and 8 incubations respectively. For enterococci, fluctuations in pH were more detrimental than stable pH incubations. Extreme pH treatment of 4, 10, and 11 were found to be most detrimental to all the faecal bacteria used in this study. Lower die-off rates were observed in sterilized wastewater incubations than non-sterilized wastewater incubations. This study shows that pH fluctuations, extremes of pH and presence of other microbes may all contribute to pathogen die-off in domestic wastewater.