Effect of turbidity on the efficiency of disinfection of waterborne bacteria

Abstract

The overall objectives were to identify the major types of turbidity which pass into the final stage of disinfection and to carry out laboratory studies to identify differences in shielding, disinfectant demand, and disinfection rate caused by the major types of turbidity. With increasing turbidity there was an increase in particle concentration for all of the turbidity causing materials (TCMs) tested (clay, chalk, humic acid, iron, manganese dioxide). There were, however, differences in the number of particles that caused the same turbidity signal, due to differences in how the materials scatter and interact with the light used to measure turbidity. For the particles under investigation, iron and chalk might cause a significant shielding effect for bacteria during disinfection as a result of aggregation and they should be reduced in water as much as possible prior to disinfection.

Humic acid was the only TCM investigated that had a chlorine demand and this decreased the efficiency of disinfection. For UV treatment both humic acid and iron had a significant detrimental impact on disinfection due to decreasing UV transmission. 

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