Nitrate removal from groundwater using a batch and continuous flow hybrid Fe-electrocoagulation and electrooxidation system

Abstract

During the last two decades nitrate contaminated groundwater has become an extensive worldwide problem with wide-reaching negative effects on human health and the environment. In this study, a combination of electrocoagulation (EC) and electrooxidation (EO) was studied as a denitrification process to efficiently remove nitrates and ammonium (a by-product produced during EC) from real polluted groundwater. Initially, EC experiments under batch operating mode were performed using iron electrodes at different applied current density values (20–40 mA cm−2). Nitrate percentage removal of 100 % was recorded, however high ammonium concentrations were performed (4.5–6.5 mg NH4+-Ν L−1). Therefore, a continuous flow system was examined for the complete removal of both nitrates and EC-generated ammonium cations. The system comprised an EC reactor, a settling tank and an EO reactor. The applied current densities to the EC process were the same as those in the batch experiments, while the volumetric flow rates were 4, 6 and 8 mL min−1. Regarding the current density of the EO process was kept constant at the value of 75 mA cm−2. The percentage nitrate removal recorded during the EC process ranged between 52.0 and 100 %, while the NH4+-N concentration at the outlet of the EO reduced significantly (53–100 %) depending on the applied current density and the volumetric flow rate. Also, the dissolved iron concentration in the treated water was always below the legislated limit of 0.2 mg L−1 (up to 0.027 mg L−1). These results indicate that the proposed hybrid system is capable of denitrifying real nitrate contaminated groundwater without generating toxic by-products, therefore making the water suitable for human consumption.