Effect of turbidity on chlorination efficiency and bacterial persistence in drinking water

Abstract

To define interrelationships between elevated turbidities and the efficiency of chlorination in drinking water, experiments were performed to measure bacterial survival, Cl demand and interference with microbiological determinations. Experiments were conducted on the surface water supplies for communities which practice chlorination as the only treatment. Therefore, the conclusions of this study apply only to such systems. Disinfection efficiency (log of the decrease in coliform numbers) was negatively correlated with turbidity and was influenced by season, Cl demand of the samples and the initial coliform level. Total organic C was associated with turbidity and interfered with maintenance of a free Cl residual by creating a Cl demand. Interference with coliform detection in turbid waters was demonstrated by the recovery of typical coliforms from apparently negative filters. The incidence of coliform masking in the membrane filter technique increased as the turbidity of the chlorinated samples increased. The magnitude of coliform masking in the membrane filter technique increased from < 1 coliform/100 ml in water samples of < 5 nephelometric turbidity U to > 1 coliform/100 ml in water samples of > 5 nephelometric turbidity U. Statistical models were developed to predict the impact of turbidity on drinking water quality. The results justify maximum contaminant levels for turbidity in water entering a distribution system as stated in the National Primary Drinking Water Regulations of the Safe Drinking Water Act [USA].