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High sensitivity is essential for the application of bioelectrochemical system-based sensor (BES sensor) in water quality early-warning, where the electroactive biofilm is of vital importance as it delivers a responsive electric signal to toxic substances. This study artificially designed the morphology of a naturally formed biofilm by employing a serrated knife to scrape the biofilm and thus obtained a reduced thickness and roughness. Then it was further cut by half to halve the biomass. BES sensors equipped with control and processed biofilms were operated under constant anode potential (CAP) and tested at different Cu(II) concentrations to study their sensitivities. Results revealed that the scraped biofilms delivered much increased sensitivity towards Cu(II) shock, which was attributed to a reduced thickness as illustrated by macroscopic and microscopic morphology analysis. Another finding was that biomass per unit interfacial area, rather than the biomass, also affected the sensitivity. To further describe how the inner biofilm responded the toxicity after morphology design, a one-dimension mass transfer model was developed to simulate the mass transfer of Cu(II) in the biofilms with different thicknesses. The relative threshold value of inlet Cu(II) concentration was employed to fit the modeling and experimental results, indicating that decreased biofilm thickness was beneficial for improving the sensitivity. Unlabelled Image • Biofilm's morphology design leads to reduced thickness and roughness. • Scraping the biofilm raises the sensitivity by 34%. • Biofilm's thickness is recognized essential factor on sensitivity. • Biomass per unit interfacial area affects the sensitivity. • One-dimension model simulates the Cu(II) transfer in biofilm. [ABSTRACT FROM AUTHOR]

Sulfur autotrophic denitrification has been proved feasible for nitrate removal from aquatic environments and it utilizes elemental sulfur as the electron donor. A maximum denitrification rate of 194.57 mg N/L·d was achieved with biogenic sulfur as electron donor in a mixed culture collected from sulfur packed bed reactors; this rate was considerably higher than that delivered by α-S 8 or μ-S in the same mixed culture. The elemental sulfur was also tested in the pure culture of Thiobacillus denitrificans , while a lower denitrification rate was noted than in the mixed culture, bio-S (4.86 mg N/L·d) again outperformed other two elemental sulfur's. X-ray absorption near edge structure spectra were collected to examine possible metabolic intermediates during the sulfur autotrophic denitrification process. The analysis revealed the existence of two major intermediates: DL-cysteine and L-cystine. They were found to not only provide electrons but also play a critical role in promoting the elemental sulfur-mediated sulfur autotrophic denitrification process. In general, we investigated the formation and enhancement effects of sulfur intermediates in the sulfur autotrophic denitrification process. Unlabelled Image • Three forms of sulfurs were used for So-based denitrification process. • Bio-S could achieve the best nitrogen removal performance. • XANES analysis revealed the existence of DL-cysteine and L-cystine in bio-S. • DL-cysteine and L-cystine were able to improve So-based denitrification process. [ABSTRACT FROM AUTHOR]

Sulfur autotrophic denitrification utilizes elemental sulfur as the electron donor for nitrate removal from aquatic environments. Organic carbon could stimulate the conversion of sulfur and facilitates the S0-based denitrification process in the mix-trophic. In this study, the co-cultured system of sulfur reducer (Geobacter sulfurreducens) and Thiobacillus denitrificans was used to investigate that how organic carbon could boost the S0-based denitrification. The results showed that the rate of S0-based denitrification was improved with C/N ratio of 0.13 and this improvement continued even after the acetate was exhausted. Sulfur probe test and Raman analysis suggested that reduced sulfur species (S x 2−) were formed with the addition of organic carbon. The S x 2− could recombine with element sulfur and the bioavailability of S0 would be improved, as a result, the rate of S0-based denitrification increased as well. Nitrate reduction rate could further increase with the C/N ratio of 0.88, but it would decrease significantly when the C/N ratio increased to 1.50 as the high concentration of generated S2−. Our results provided explanations that why organic carbon addition would improve the bioavailability of S0 which could further promote the S0-dominant denitrification process. Unlabelled Image • Organic carbon can boost the S0-based denitrification of co-culture system. • Geobacter sulfurreducens could convert S0 to reduced sulfur species (S x 2−). • Sulfur bioavailability could be improved by the sulfur conversion process. [ABSTRACT FROM AUTHOR]

This study aims to explore the application of sulfur-based constructed wetlands (CWs) for effective nitrogen (N) removal from wastewater. Two solid sulfur sources namely elemental sulfur (S0) and pyrite (FeS 2) were used as substrates in two CWs, i.e. S-CW and P-CW, respectively. The CWs were vegetated with a common wetland plant Iris pseudacorus , and were operated to investigate the effects of hydraulic retention time (HRT) and temperature on N removal. The use of S0 resulted in the highest denitrification rate (19.0 ± 7.5 g m−2 d−1), whereas up to 20 times slower total inorganic nitrogen (TIN) removal was observed with FeS 2. Different sulfur sources had negligible effects on the growth of I. pseudacorus , but the element contents (e.g., N, S, and P) within the plant tissues were different. Iris roots in S-CW had higher S content compared with those in P-CW, which resulted in the difference in shoots colors. The characteristics of rhizospheric microbial communities were closely related to the sulfur and nitrogen sources. Briefly, denitrifying and sulfur-oxidizing genera (e.g., Denitratisoma , Sulfurimonas , Thiobacillus) were dominating in the S-CW, suggesting the occurrence of both autotrophic and heterotrophic denitrification processes in the wetland. On the other hand, nitrifying bacteria were more abundant (e.g. Nitrospira , Piscinibacter) in the P-CW. S0 layer and rhizosphere accounted for 99.3% of nitrogen removal and the former part most likely played important roles with a decrease in HRT. Low temperature strongly affected the rate and efficiency of denitrification but recovered to 49.2 ± 25.8% when added with 30 mg L−1 sodium acetate. This study broadens the applications of sulfur-based CWs and provides a promising management strategy for denitrification at low temperatures. Unlabelled Image • N removal was better in S-CW (3.4–19.0 g m−2 d−1) than P-CW (0–1.0 g m−2 d−1). • S0/FeS 2 affected element distributions in Iris pseudacorus and shaped rhizospheric microbes accordingly. • Short HRT (6–12 h) is recommended for S-CW operation in case of NH 4 +-N accumulation. • S0 layer and rhizosphere accounted for 99.3% of N removal in S-CW. • NaAC addition recovered N removal of S-CW which was restricted by low temperature. [ABSTRACT FROM AUTHOR]