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In this study, the effect of arsenic on the sulfamethoxazole (SMX) removal efficiency and microbial community structure was investigated over 60 days using the SBR process. The results showed that the presence of arsenic had no significant impact on the system performance, the removal efficiencies of two reactors, R1 (the control test) and R2 (with the addition of arsenic), were 13.36 ± 5.71 and 14.20 ± 5.27%, which were attributed to the adsorption of SMX by fulvic acid-like substances and tryptophan-like proteins of extracellular polymeric substances. Compared to the seed sludge, the species number indicated that R2 possessed the richer diversity, while R1 possessed the lower diversity on day 60, which might be relative to the transferring of antibiotic resistance genes (ARGs) in sludge bacterial communities; the minute amounts of arsenic could make the relative levels of Sul1 and Sul2 genes which encode ARGs of sulfonamides in R2 (2.07 and 2.47%) be higher than that in R1 (1.65 and 1.27%), which made the bacterial community of the R2 system more adaptable to SMX stress. Therefore, the minute amounts of arsenic weakened the effect of SMX on the system and enhanced the stability of the microbial community structure.

High-risk arsenic contamination found in aqueous system is reported across the world and causing severe environmental issues. In this study, the Mg-Al Layered Double Hydroxide (LDH) modified by sulphur species (LDH-S) was found exhibiting high effectivity and selectivity in As(V) removal owing to the strong interaction between embedded HS - and AsO 4 3- . The LDH-S with Mg to Al ratio 2-1 give the best performance with As(V) adsorption capacity 40.8 mg/g, which is 715% higher than that of pristine LDH (2-1). The adsorbent exhibits a high tolerance to concentrated competitive anions. In the continuous flow test, the adsorbent can reduce the As(V) concentration from 20 ppm to below-ppb-level indicating the potential in industry application. The adsorption mechanism is experimentally investigated and examined by Density Function Theory (DFT) calculation. The result illustrates that, differ from the traditional ion exchange mechanism of LDH, the enhanced removal capacity and selectivity of LDH-S for As(V) is attributed to the strong affinity between H atom from HS- ion (in the interlayer region of LDH) and the O atom from AsO 4 3- ., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Inc.)

In this study, the effect of ball milling on pyrite (FeS 2 ) promoting arsenic (As) removal by zero-valent iron (Fe 0 ) was investigated. The influences of different mass ratios of ball-milled FeS 2 /Fe 0 , the dosage of ball-milled FeS 2 /Fe 0 used and initial pH value were evaluated by batch experiments. The results showed that the ball-milled FeS 2 /Fe 0 system had a higher total As removal efficiency than the mixed FeS 2 -Fe 0 system, ball-milled FeS 2 and ball-milled Fe 0 systems in equal mass. Higher As removal efficiency in ball-milled FeS 2 /Fe 0 system was primarily related to the accelerated corrosion of Fe 0 , which was supported by the determination of total Fe 2+ release and electrochemical experiments. SEM-EDS and XPS characterizations revealed that there were iron sulfides (Fe(II)-S and Fe(III)-S) produced on the surface of Fe 0 in ball-milled FeS 2 /Fe 0 , which could facilitate the electron transfer of Fe 0 and enhanced the corrosion of it. BET test also indicated that ball-milled FeS 2 /Fe 0 possessed a higher specific surface area than ball-milled Fe 0 . In addition, the results also showed the optimum mass ratio of FeS 2 and Fe 0 in ball-milled FeS 2 /Fe 0 to remove As ([As(III)] = 2 mg/L) was 1:1, and the optimum dosage was 0.5 g/L, thereby indicating the optimal As:Fe 0 molar ratio was about 1:168. And the removal rate of As by ball-milled FeS 2 /Fe 0 was faster in acidic condition than that in alkaline condition. These findings suggest that Fe 0 -based arsenic removal efficiency can be enhanced by ball-milling with FeS 2 , making it more feasible for remediation of arsenic-polluted water., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, the enhanced effect of pyrite (FeS 2 ) on zero-valent iron (Fe 0 ) corrosion for arsenic (As) removal was investigated in a combined-Fe 0 /FeS 2 system. The effects of different Fe 0 /FeS 2 composition, dosage and initial pH were evaluated by batch experiments. Results showed that the best combination ratio of Fe 0 :FeS 2 (w/w) was 1:1 and the optimal dosage of mixture was 2.0 g/L. The combination of Fe 0 and FeS 2 in a system significantly enhanced the reactivity of Fe 0 for effective As removal within a broad pH range (3.0-9.0). The effective As removal in the combined-Fe 0 /FeS 2 system was primarily ascribed to being enhanced corrosion of Fe 0 by addition of FeS 2 . SEM and XRD characterizations strongly verified this point. Specifically, the mechanism study (the releases of Fe 2+ and total Fe ion, variations of pH values as well as XPS characterization) suggested that FeS 2 in the combined-Fe 0 /FeS 2 system could alleviate the passivation of Fe 0 (pH ini 3.0-5.0) and accelerate the dissolution of pristine oxide film that coated on Fe 0 surface (pH ini 6.8-9.0). Besides, FeS 2 in combined-Fe 0 /FeS 2 system could also accelerate the reactions between Fe 0 to O 2 at pH ini 3.0-9.0. These phenomena were well explained by a galvanic couple between Fe 0 and FeS 2 , where FeS 2 was a cathode and Fe 0 was an anode. Consequently, electrons released from Fe 0 that mediated by FeS 2 to oxide film, passivation layer and O 2 were accelerated in combined-Fe 0 /FeS 2 system and thereby enhanced the corrosion of Fe 0 for efficient As removal. Our findings suggest that utilizing FeS 2 to enhance the corrosion of Fe 0 would be a promising technology for remediation of As-contaminated water., (Copyright © 2019 Elsevier Ltd. All rights reserved.)