The removal of organic pollutants presents a major challenge for drinking water treatment
plants. The chemical oxygen demand (COD) is essentially the measure of oxidizable
organic matter in source waters. In this study, we report that COD can efficiently
be decreased by adding Fe(II)/Fe(III) and sulfite ion to the source water while purging
it with air. In this process, oxygen is activated to oxidize the main constituents
of COD, i.e. organic substrates, via the generation of reactive inorganic oxysulfur
radical ions. In the end, the total amount of sulfur(IV) is converted to the non-toxic
sulfate ion. It has been explored how the COD removal efficiency depends on the concentration
of S(IV), the total concentration of iron species, the concentration ratio of Fe(II)
and Fe(III), the purging rate and the contact time by using source water from a specific
location (Királyhegyes, Hungary). The process has been optimized by applying the Response
Surface Methodology (RSM). Under optimum conditions, the predicted and experimentally
found COD removal efficiencies are in excellent agreement: 85.4% and 87.5%, respectively.
The robustness of the process was tested by varying the optimum values of the parameters
by ± 20%. It was demonstrated that the method is universally applicable because a
remarkable decrease was achieved in COD, 62.0–88.5%, with source waters of various
compositions acquired from 9 wells at other locations using the same conditions as
in the case of Királyhegyes.
