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Denitrification in Simulated Groundwater Using Lignite as a Solid-Phase Organic Carbon Source

To ensure safety standards of drinking water, it is essential to perform NO3 remediation in groundwater. Owing to the lack of organic carbon in groundwater, heterotrophic denitrification is not quite effective in groundwater. Few studies have reported about how Chinese lignite can be used as an organic carbon source for denitrification. In simulated conditions of groundwater, we determined whether the four lignite types (Lignite was obtained from Sanjitun, Lingshi, Wangniutan, and Zhaotong in China.) could be used as a solid-phase organic carbon source for denitrification; the analyses were performed in a test water column. For denitrification, the most effective carbon source was the lignite obtained from Wangniutan. It showed the highest efficacy of 34% in nitrate (NO3) removal for an influent NO3-N concentration of 30 mg• L−1. The effluent NO3-N concentrations below 20 mg L−1 and the water samples showed no acute toxicity when they were subjected to luminescent bacteria test. We performed static carbon release test and infrared spectral analysis on all the four lignite types, and we found that there was a direct relation between NO3 removal and the lignite’s ability for static carbon release. When NO3 concentrations were high and the rate of static carbon release was low, the efficacy of denitrification was greater. This effect was achieved when the molecular structure of lignite contained small molecular organic compounds in free states; these compounds primarily included the following functional groups: alcohols, phenols, and organic acids. These compounds were primarily used by the denitrifying bacteria.