Economical approach to nitrate removal via membrane capacitive deionization

Abstract

Groundwater is the most widely used water resource worldwide. In addition to natural underground pollutants, it is also affected by anthropogenic pollution sources. Highly soluble nitrate can easily leak into groundwater via precipitation. Nitrate has the potential to produce nitrosamines and thus can cause blue baby syndrome as well as several types of cancer, including that of the digestive system. Moreover, nitrates lead to eutrophication in bodies of water such as rivers and lakes. Therefore, organizations such as the World Health Organization (WHO) and the US Environmental Protection Agency (EPA) have limited the maximum acceptable nitrate concentration in drinking water to 10 mg/L. These adverse effects make it necessary to remove nitrates from water. The membrane capacitive deionization (MCDI) process can successfully remove nitrate. In this study, solutions with different concentrations of nitrate were treated via MCDI at different removal efficiencies, resulting in nitrate reductions below the limit values. Thus, the MCDI process proved to be an economical treatment approach, and during the treatment phase no significant effect of nitrate concentration levels was observed on the recovery efficiency. During the MCDI treatment, the electrodes accepted the SO42− and NO3− ions approximately equally, while Cl− removal rate was lower. Groundwater obtained from the Meric district of Edirne (Turkey) containing 233 mg/L nitrate was successfully purified via the MCDI process, with a nitrate removal efficiency of 98%. The energy expenditure calculated for the nitrate removal treatment of the groundwater was 0.4 kWh/m3.