DBPs control in European drinking water treatment plants using chlorine dioxide: two case studies

The paper reports results of the experiments carried out at Fortore (Foggia, South Italy) and Mosina (Poznan, Poland) drinking water treatment plants aimed at DBPs control. Pilot scale GAC filters were installed in both plants in order to assess the efficacy of different kind of GAC for chlorites, NOM and THMs removal. Both pilot plants operated with and without chlorine dioxide pre-disinfection. In Fortore plant, because of free chlorine was added in ClO(2) pre-disinfection solution, THMs formation was evaluated. Results showed an high efficacy of chlorites removal on GAC filters up to 5500 and 10000 bed volumes for mineral and vegetal GAC in Fortore and up to 11000 bed volumes in Mosina. A preliminary characterization of natural organic matter (NOM) dissolved in Fortore raw water was performed as well, in order to confirm its reactivity towards chlorine dioxide. The presence of small molecules (< 500 Da) in Fortore pre-disinfected water, has resulted in THMs and carboxylic acids formation due a fast reaction with Cl(2)-ClO(2). GAC columns have shown percentages of removal ranging from 60 to 72% for THMs and ranging from 14.6 to 43% for TOC, so that adsorption represents an essential step for DBPs control.