Introduction of an adsorption process into a surface water treatment system and its effect on disinfectant use

The study was conducted in a full-scale water treatment facility where surface water is treated. The analysis of required disinfectant dosage changes and disinfectant usage was conducted in a time period starting 6 months before introducing adsorption on granular activated carbon (GAC) into the treatment system, and continuing for 6 months after adsorption introduction. During the analyzed time period, both chlorine and chlorine dioxide were used. They were dosed separately and rapidly mixed into a pipeline before the clean water tank. Both short-term and long-term disinfectant consumption was studied. This is due to the different reaction rates of the disinfecting agents used. Introducing GAC adsorption contributed significantly to limiting organic substances in water undergoing disinfection, which resulted in average reductions of 51% for both disinfectants. During the first month after introducing adsorption only a small increase in disinfectant demand was found, connected with an increase in 22 °C cultivated bacteria count in water to be disinfected. The increase in organic substances removal achieved by the use of adsorption did not result in a reduction of analyzed trihalomethanes (THM), whose concentrations were low for both cases and amounted to 2.1–7.9 μg/dm³ and 1.6–5.2 μg/dm³ with and without adsorption respectively.