Assessment of a Natural Iron-Based Sand for the Removal of Nitrate from Water

This research investigated the efficiency of South African sands and a type of zero-valent iron (ZVI) to remove nitrate from contaminated water. Batch experiments were carried out using soils widely available in the region of Kwazulu-Natal in South Africa (Berea red Sand (BRS) and Umgeni Sand (US), a type of ZVI and two mixes of BRS-ZVI (75–25 and 50–50 % w/w). The experiments were conducted in semi-anoxic conditions to investigate the nitrate removal potentials of the substrates. Batch tests revealed 100 % of nitrate removal by ZVI at lower concentrations (10–25 mg/L), while at higher concentrations (up to 100 mg/L), the removal efficiency decreased. The BRS, as sole material, showed the highest removal (70 %) at 25-mg/L nitrate solution, while at higher concentrations (50 and 100 mg/L), the nitrate removal was 36.7 and 42.9 %, respectively. The ZVI-BRS 50 % mix showed the best performance in terms of both rates and percentage of removal for most of the nitrate concentrations investigated indicating that a higher amount of BRS in the mixes improves the adsorption capacity. Both Langmuir and Freundlich isotherm models were applied to experimental data, and Langmuir described better the nitrate removal process. According with our findings, the BRS could represent a viable alternative to the ZVI to reduce the cost of the treatment and to increase the nitrate removal capacity.