Microbial Photoelectrotrophic Denitrification as a Sustainable and Efficient Way for Reducing Nitrate to Nitrogen

Abstract

Biological removal of nitrate, a highly concerning contaminant, is limited when the aqueous environment lacks bioavailable electron donors. In this study, we demonstrated, for the first time, that bacteria can directly use the electrons originated from the photoelectrochemical process to carry out the denitrification. In such photoelectrotrophic denitrification (PEDeN) systems (denitrification biocathode coupling with TiO photoanode), nitrogen removal was verified solely relying on the illumination dosing without consuming additional chemical reductant or electric power. Under the UV illumination (30 mW·cm, wavelength at 380 ± 20 nm), nitrate reduction in PEDeN apparently followed the first-order kinetics with a constant of 0.13 ± 0.023 h. Nitrate was found to be almost completely converted to nitrogen gas at the end of batch test. Compared to the electrotrophic denitrification systems driven by organics (OEDeN, biocathode/acetate consuming bioanode) or electricity (EEDeN, biocathode/abiotic anode), the denitrification rate in PEDeN equaled that in OEDeN with a COD/N ratio of 9.0 or that in EEDeN with an applied voltage at 2.0 V. This study provides a sustainable technical approach for eliminating nitrate from water. PEDeN as a novel microbial metabolism may shed further light onto the role of sunlight played in the nitrogen cycling in certain semiconductive and conductive minerals-enriched aqueous environment.

Impacts of enhanced microbial-photoreductive and suppressed dark microbial reductive dissolution on the mobility of As and Fe in flooded tailing soils with zinc sulfide

“…Understanding mechanisms resulting from the interactions between microbes, semiconducting minerals, and metal pollutants provide a comprehensive understanding to develop alternative bioremediation technologies. Considering the widespread prevalence of microbes, DOM, and minerals in soils, an alternative solarmicrobial extracellular electron transfer pathway is likely to occur in environments where bioavailable electron donors are limited [11,54]. Our work provides a rigorous understanding for the role of semiconducting minerals in the biogeochemical cycling of metals and carbon.…”

“…In natural environments, non-photosynthetic microorganisms, semiconducting minerals, DOM, and solar radiation serve as a notable quaternary reciprocal system [7,31,38]. With the presence of semiconducting minerals under illumination, conversion of solar to electrical energy will supply more electrons for As/Fe reduction [11,39]. However, an integrated bioelectro-photocatalytic system can be established when bioavailable electron donors are lacking.…”

“…Upon illumination, mineral photoelectrons are excited from their valence band to the conduction band of semiconducting minerals, forming photoelectron-hole pairs and triggering a series of redox reactions [10]. The separation of photoelectron-hole pairs and the released energy are desirable for non-photosynthetic microorganisms [11]. This suggests that possible synergetic interactions between mineral photoelectrons, semiconducting minerals, and microorganisms occur when there is a lack of bioavailable electron donors, and the excited photoelectrons are transferred to metal-reducing bacteria for metabolism [12,13].…”

Recent advances in the roles of minerals for enhanced microbial extracellular electron transfer

“…Previous studies have primarily focused on the behaviors of microbes that harbor EETs coupled with redox-active and/or electrically conductive minerals for mineralization of organic pollutants and methanogenesis [20,21]. In recent years, major advances in microbial EET processes include fixation of carbon dioxide to organic compounds and denitrification via photosynthesis in conjunction with (semi) conductive minerals [22][23][24]. Therefore, understanding the fundamental mechanisms underlying microbe EETs coupling with minerals is expected to have profound significance in revealing the environmental impact and practical application of minerals.…”

Bacteria-supported iron scraps for the removal of nitrate from low carbon-to-nitrogen ratio wastewater

“…Traditional nitrate removal methods include biological denitrication, [5][6][7] ion exchange, 8,9 osmosis, 10,11 electrodialysis, 12,13 etc. The chemical and physical methods of ion exchange, osmosis and electrodialysis have their drawbacks such as high cost and energy consumption, which limit the larger scale application.…”