Electro-Fenton, hydrogenotrophic and Fe2+ ions mediated TOC and nitrate removal from aquaculture system: Different experimental strategies

A number of methods for denitrification were studied including Electro-Fenton method, hydrogenotrophic as well as innovative Fe2+ mediated denitrification and their technical feasibility in terms of changes in TOC and nitrate concentrations, effect of different Fenton’s reagent dosage, current and the effect of the pH was investigated. This study was carried out using tailor made electrodialytic reactor. It was found that the highest TOC removal was achieved at pH 2.2 and 2.4 (77.1% and 97.8%, respectively) at the anode and the lowest accumulation of 33% at pH of 6.2 at the cathode. The highest TOC removal in terms of using different H2O2 concentrations was achieved at 40 mM reaching as high as 97.3%. Regardless experimental strategy, initially nitrates migrated towards the cathode due to the strong hydraulic gradient under the applied electric current. During the course of experiments, nitrates were transported towards the anode where their concentration decreased. The highest nitrate removal was achieved at 0.12 mA cm−2 electric current density (94.8%) at the anode and a complete removal at the cathode. Hydrogenotrophic denitrification was the highest reaching 92.5%, however, when Fe2+ ions as electron donor was used for the destruction of nitrates, only 66.6% removal was achieved. Denitrification using only Fe2+ ions was a factor 1.4 less than using electrically generated hydrogen or a Fenton’s reagent.