Nitrate reduction using hybrid system consisting of zero valent magnesium powder/activated carbon (Mg0/AC) from water

In this study, the hybrid system of zero-valent magnesium powder and activated carbon has been introduced to reduce nitrate from water in the laboratory scale under ambient temperature and open conditions. The effect of pH, dosage of zero-valent magnesium powder and the mass ratio of magnesium to activated carbon during reaction time have been studied as operational parameters. The ratio of the remained nitrate concentration to its initial concentration has been considered as the response of the removal process. The assessments for determining the effect of pH value on the nitrate removal process have carried out in two different conditions, with keeping pH value constant during the process and adjusting the initial pH on a specific value without trying to keep it constant. Also, in order to approach a better understanding of the system's performance, the changes of the oxidation-reduction potential (OCP) and dissolved oxygen (DO) have been evaluated. According to the tests results, for the conditions that the pH values have not been kept constant, despite the significant removal of nitrate in the early times of the reaction, the pH value of the process increased to more than 11, shortly after the start of the reaction and the nitrate reduction reactions were stopped. While, for the conditions that the pH values have been kept constant, in addition to high nitrate ions removal efficiency in the first few minutes of reaction, the reduction process continued until the end of the reaction. Also, entire removal of nitrate ions has been achieved in the pH values equal to 3, the initial NO3−−N concentration of 90 mg/l, Mg0 dose equal to 0.65 g/l and the mass ratio of Mg0 to activated carbon powder 4:1 in less than 20 min. According to the results, the hybrid systems demonstrated better performance in lower pH values. The system nitrate removal ability modified by increasing the Mg0 dose as well as the activated carbon particles in the hybrid system. The outputs of the OPR and DO concentrations evaluations confirmed the results of the experiments and observations. Comparing the results of this study with the literature showed that the nitrate removal efficiency of the Mg0/activated carbon hybrid system is noticeably better than Mg0 system as well as Fe0/activated carbon hybrid systems, in the similar operational conditions.