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<p>Nitrate pollution in groundwater has become a serious global environmental problem. Biological denitrification has been considered a promising nitrate removing process from groundwater, but its application was generally constrained by low temperatures. The mixotrophic system showed a stronger capacity to resist environmental shock, however, an in-depth understanding of the process feasibility and the microbial dynamics at low temperatures need to be further studied. Herein, mixed electron donors (glucose and sodium thiosulfate) were selected to explore the impact on the denitrification process at low temperature (5&#xa0;°C), and a conventional single electron donor (glucose) was set as a control. Results showed that the minimum HRT of both the mixed electron donors (R1) system and single electron donor system (R2) was 4.5&#xa0;h at 5&#xa0;°C when nitrate concentration in the effluent was below 10&#xa0;mg/L. However, a relatively high denitrification efficiency of 88.10% was obtained in R1, and a high nitrite accumulation (2.64&#xa0;mg-N/L) was observed in R2 during the process. Microbial dynamics revealed that electron donors had a great impact on EPS content and microbial communities. The mixed electron donors can promote the production of EPS, thereby benefiting microorganisms to resist low temperature. The low-temperature resistant denitrifiers in R1 were identified as <i>Thauera</i> and <i>Trichococcus</i>, while in R2 they were <i>Trichococcus</i> and <i>Acidovorax</i>. The functional genes encoding key enzymes (ATP production, and electrons production, transportation, and consumption) associated with carbon, sulfur and nitrate metabolism were enriched in R1 at low temperature. Furthermore, the S<sub>4</sub>I and branched oxidation pathways were inhibited at low temperature, and electrons and energy from thiosulfate oxidation in R1 were primarily from the Sox pathway, which does not release free intermediates. These results will benefit further exploration of the denitrification bioprocess driven by mixed electron donors in low-temperature environments and guide its future applications in groundwater treatment.</p>

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Insights into the Superior Performance of Mixotrophic Denitrification at Low Temperature

  • 期刊论文

  • 发表日期：

    2026年3月25日

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  • Na Yu,
  • Yufeng Lv,
  • Tingting Li,
  • Sheng Zhai,
  • Shuchen Sun,
  • Xiaofei Tian,
  • Jinjia Wu

摘要

Nitrate pollution in groundwater has become a serious global environmental problem. Biological denitrification has been considered a promising nitrate removing process from groundwater, but its application was generally constrained by low temperatures. The mixotrophic system showed a stronger capacity to resist environmental shock, however, an in-depth understanding of the process feasibility and the microbial dynamics at low temperatures need to be further studied. Herein, mixed electron donors (glucose and sodium thiosulfate) were selected to explore the impact on the denitrification process at low temperature (5 °C), and a conventional single electron donor (glucose) was set as a control. Results showed that the minimum HRT of both the mixed electron donors (R1) system and single electron donor system (R2) was 4.5 h at 5 °C when nitrate concentration in the effluent was below 10 mg/L. However, a relatively high denitrification efficiency of 88.10% was obtained in R1, and a high nitrite accumulation (2.64 mg-N/L) was observed in R2 during the process. Microbial dynamics revealed that electron donors had a great impact on EPS content and microbial communities. The mixed electron donors can promote the production of EPS, thereby benefiting microorganisms to resist low temperature. The low-temperature resistant denitrifiers in R1 were identified as Thauera and Trichococcus, while in R2 they were Trichococcus and Acidovorax. The functional genes encoding key enzymes (ATP production, and electrons production, transportation, and consumption) associated with carbon, sulfur and nitrate metabolism were enriched in R1 at low temperature. Furthermore, the S4I and branched oxidation pathways were inhibited at low temperature, and electrons and energy from thiosulfate oxidation in R1 were primarily from the Sox pathway, which does not release free intermediates. These results will benefit further exploration of the denitrification bioprocess driven by mixed electron donors in low-temperature environments and guide its future applications in groundwater treatment.