Improving natural organic matter and turbidity removal from surface water by pre-coagulation combined with ozone/ultrasound

Abstract

Recently, we showed that pre-treatment with ultrasound/ozone (US/O3) could remarkably enhance the performance of coagulation in removing natural organic matter (NOM) and turbidity from surface waters. In the present study another of our aims was to investigate whether pretreatment with coagulation combined with post-oxidation (US/O3) can also remove NOM, turbidity and coliform from the same water resources. NOM and turbidity removal were measured by UV absorbance at 254 nm (UV254) and a turbidimeter, respectively. Aluminum sulfate (alum), ferric chloride (FC), and poly aluminum chloride (PACl) were tested as coagulants. The disinfection potential of the US/O3 process was evaluated by measuring coliform counts. The effects of different input variables including ozone dose, power intensity, ultrasound frequency, reaction time, coagulant type, dose of coagulant and coagulant aid were examined on the process performance. Design of experiments (DoE) and surface response methodology (RSM) techniques were employed to optimize the operating parameters. Individual coagulation process with ferric chloride decreased NOM and turbidity up to 33% and 15%, however pre-coagulation with ferric chloride combined with US/O3 decreased NOM and turbidity 75% and 32%, respectively. PACL was the best coagulant in the sole coagulation, but in pre-coagulation combined with US/O3 process, FC exhibited the best performance. Treatment with US/O3 following pre-coagulation decreased the amount of coagulant and coagulant aid needed for the treatment. Pre-coagulation followed by US/O3 improves the NOM, turbidity and coliform removal, and so could be considered as a potential method for removing NOM, turbidity and coliform.