Disinfection/disinfectant by-product optimisation with ozone, biological filtration and chloramines

The upcoming Disinfection/Disinfectant By-product and Enhanced Surface Water Treatment Rules will require utilities in the USA to increase their current level of disinfection and, at the same time, reduce the concentration of disinfection by-products formed during the disinfection process. To address these complex issues, the Jefferson Parish Water Department conducted a detailed pilot column evaluation on clarified lower Mississippi River water using ozone, biological filtration and chloramines, which achieved calculated removals of 5.5 logs for Giardia and 8 logs for virus, while limiting annual average disinfection by-product formation to less than 10 μg/L for trihalomethanes and haloacetic acids. While elevated concentrations of biologically degradable organic carbon (BDOC) and aldehydes were produced by ozonation, biological filtration with empty bed contact times of 5 and 9 min was effective in preventing any significant increase in BDOC or total aldehyde concentrations above those normally produced by chloramine disinfection. Total organic carbon removal as required by enhanced coagulation under the proposed Disinfection/Disinfectant By-product Rule were also achieved by ozonation and biological filtration.