Enhancement of Nitrate-Removal Efficiency Using a Combination of Organic Substrates and Zero-Valent Iron as Electron Donors

Abstract

Agriculture is the most extensive source of nitrate to water resources. A high concentration of nitrate contamination in drinking water is a significant risk to human health. The aim of this study was to select the appropriate combination of organic substrates and zero-valent iron (ZVI) to use as an electron donor for denitrification in a permeable reactive barrier. From the results, a nitrate-removal efficiency of more than 85% was achieved for all the tested organic substrates at ambient temperature (25±5°C), neutral pH, and under anaerobic conditions. The initial nitrate concentration of 150 mg L−1 and the organic substrates (50 g L−1 concentration) were tested in this study. Different dosages for ZVI (10, 30, 50, and 70 g L−1) were also investigated. Using a mixture of rice husk and rice straw as an electron donor led to the highest nitrate-removal efficiency (93.3%). Using ZVI as an electron donor yielded a lower nitrate-removal efficiency than using the same amount of the organic substrate. However, the use of ZVI coupled with the organic mixture resulted in a higher nitrate-removal rate than when only the organic mixture was used. The nitrate-removal rate increased up to threefold when using ZVI wire, a type of waste from a lathe factory, mixed with the organic mixture as an electron donor.