%A Wenrui Guo, Yue Wen, Yi Chen, Qi Zhou %T Sulfur cycle as an electron mediator between carbon and nitrate in a constructed wetland microcosm %0 Journal Article %D 2020 %J Front. Environ. Sci. Eng. %J Frontiers of Environmental Science & Engineering %@ 2095-2201 %R 10.1007/s11783-020-1236-y %P 57- %V 14 %N 4 %U {https://journal.hep.com.cn/fese/EN/10.1007/s11783-020-1236-y %8 2020-08-15 %X

• Fe(III) accepted the most electrons from organics, followed by NO3, SO42‒, and O2.

• The electrons accepted by SO42‒ could be stored in the solid AVS, FeS2-S, and S0.

• The autotrophic denitrification driven by solid S had two-phase characteristics.

• A conceptual model involving electron acceptance, storage, and donation was built.

• S cycle transferred electrons between organics and NO3 with an efficiency of 15%.

A constructed wetland microcosm was employed to investigate the sulfur cycle-mediated electron transfer between carbon and nitrate. Sulfate accepted electrons from organics at the average rate of 0.84 mol/(m3·d) through sulfate reduction, which accounted for 20.0% of the electron input rate. The remainder of the electrons derived from organics were accepted by dissolved oxygen (2.6%), nitrate (26.8%), and iron(III) (39.9%). The sulfide produced from sulfate reduction was transformed into acid-volatile sulfide, pyrite, and elemental sulfur, which were deposited in the substratum, storing electrons in the microcosm at the average rate of 0.52 mol/(m3·d). In the presence of nitrate, the acid-volatile and elemental sulfur were oxidized to sulfate, donating electrons at the average rate of 0.14 mol/(m3·d) and driving autotrophic denitrification at the average rate of 0.30 g N/(m3·d). The overall electron transfer efficiency of the sulfur cycle for autotrophic denitrification was 15.3%. A mass balance assessment indicated that approximately 50% of the input sulfur was discharged from the microcosm, and the remainder was removed through deposition (49%) and plant uptake (1%). Dominant sulfate-reducing (i.e., Desulfovirga, Desulforhopalus, Desulfatitalea, and Desulfatirhabdium) and sulfur-oxidizing bacteria (i.e., Thiohalobacter, Thiobacillus, Sulfuritalea, and Sulfurisoma), which jointly fulfilled a sustainable sulfur cycle, were identified. These results improved understanding of electron transfers among carbon, nitrogen, and sulfur cycles in constructed wetlands, and are of engineering significance.