Elemental sulfur reinforces storage-driven denitrification through complementary electron supply and mitigates N₂O in carbon-limited wastewater
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Published on: July 24, 2018
Hanbin Wang1, Yongzhen Peng1, Hongbin Weng1
1National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Engineering Research Center of Beijing, Beijing University of Technology, Beijing 100124, PR China.
Abstract:
Managing nitrogen removal while minimizing external organic-carbon addition remains a major challenge for carbon-limited wastewater treatment. Storage-driven endogenous denitrification improves carbon efficiency by storing influent organics as intracellular polymers, but the finite availability of these reserves constrains reducing-power supply during post-anoxic nitrogen removal. Here, we investigated whether elemental sulfur could complement intracellular-carbon-derived reducing power in a long-term anaerobic-aerobic-anoxic system treating real municipal wastewater with a low COD/TN ratio. S⁰ supplementation decreased effluent nitrate from 13.6 ± 2.7 to 3.4 ± 2.3 mg N L⁻¹, increased total nitrogen removal from 79.8 ± 2.5% to 94.1 ± 3.7%, and reduced total N₂O accumulation from 0.51 ± 0.04 to 0.09 ± 0.02 mg N L⁻¹. Direct cycle-resolved measurements showed that post-anoxic PHA/glycogen consumption decreased from 1.91 ± 0.17 to 1.28 ± 0.22 mM C L⁻¹ after S⁰ supplementation, demonstrating that sulfur-derived reducing equivalents partly substituted for intracellular-carbon oxidation while conserving the storage pool. Genome-resolved metagenomics and metatranscriptomics further identified putative carbon-storage sulfur-oxidizing denitrifying bacteria carrying linked functions for intracellular-carbon turnover, reduced-sulfur metabolism and stepwise denitrification. Dose-dependent respiratory inhibition, transcriptional responses and electrochemical characteristics were collectively consistent with reduced dependence on NADH/Complex I-mediated electron input and greater involvement of quinone- and cytochrome c-linked respiratory processes after sulfur amendment. These results demonstrate that coupling intracellular carbon storage with sulfur-derived reducing power can extend the electron-supply capacity of storage-driven denitrification and promote more complete nitrogen removal under carbon-limited conditions.
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