Changing free residual chlorine, Hardness and Alkalinity during electrochemical denitrification process

The Electrochemical process has high performance efficiency in nitrate removal. And the process may change the values of the residual chlorine dosages, hardness and alkalinity alongside nitrate removal. In this study, the changes of these parameters during the electrochemical denitrification process were studied.
This experimental study was performed on synthetic wastewater in a reactor with an effective capacity of 3.5 L having carbon cloth and stainless steel mesh electrodes and powered by direct current (DC). The initial nitrate concentration was fixed in range of 50-150 mg/L in experiments. Moreover, the impacts of applied current density (5-60 mA), NaCL dosage (0.5-2 g/L) and initial pH (4, 7 and 9) on the changing free residual chlorine, hardness and alkalinity over the electrochemical denitrification process were studied.
A relative decline was observed in the levels of alkalinity and calcium hardness by the contact time of 60 min with increasing NaCl dosage. The amounts of all parameters leveled off with rising contact time. Free residual chlorine was detected at 2 g/L of NaCL dosage and initial PHS of 7 and 9. In pH of 9, residual chlorine decreased to zero by increasing contact time from 60 to 120 min, while, in pH of 4, residual chlorine was generated after 40 min of contact time. The residual chlorine at the end of the electrochemical denitrification was achieved only at the initial pH of 9 without NaCl addition.
According to the obtained results, the proposed electrochemical denitrification process can remove nitrates, while other water quality parameters such as hardness and alkalinity remain approximately unchanged. Therefore, by this process the selective removal of nitrate can be achieved.