Insights into the influence and mechanism of biomass substrate and thermal conversion conditions on FeN doped biochar as a persulfate activator for sulfamethoxazole removal

Fe-N-doped biochar is a promising material for advanced-oxidation heterogeneous catalysis, but its adsorption-catalytic performance is significantly affected by biomass feedstock compositions and thermal conversion conditions and is not yet conclusive. In this paper, four lignocellulosic biomasses (rice straw, bamboo, poplar wood, and corn stover) were selected as raw materials to prepare Fe-N-biochar as persulfate activators by hydrothermal-thermolysis composite. Their lignocellulosic fractions and elemental contents were detected, and a variety of thermal conversion conditions were investigated for the rice straw-based Fe-N-biochar with the best activation performance among them. It was found that the holocellulose and lignin contents of the biomass affected the catalytic activity of the prepared catalysts with correlation coefficients of 0.57 and -0.93, respectively. Increasing the pyrolysis temperature from 500 °C to 800 °C could increase the ratio of Fe2+/Fe3+ and the relative amounts of CC, graphitized N, and oxidized N in the catalyst by 0.17 %, 7 %, 12 %, and 18 %, respectively. Extending the pyrolysis time from 0.5 to 2 h was able to increase the relative content of CC, graphitized N, and oxidized N by 0.18 %, 3 %, 9 %, and 4 %, respectively. The most catalytically active rice straw-derived Fe-NRBC was able to remove 91.7 % of sulfamethoxazole (SMX) and 93.07 % of TOC mainly via ·SO4- and ·OH in an adsorption-catalytic reaction of 60 min with a k of 0.047 min-1 and the main active sites are FeN, Fe0, pyridine N, oxidized N and CO. Finally, degradation intermediates and pathways were also characterized. This paper is expected to provide a basis for the future targeted regulation of Fe-N biochar for water pollution treatment.

Biological conversion of sulfamethoxazole in an autotrophic denitrification system

Sulfamethoxazole (SMX) is a common antibiotic prescribed for treating infections, which is frequently detected in the effluent of conventional wastewater treatment plants (WWTPs). Its degradation and conversion in a laboratory-scale sulfur-based autotrophic denitrification reactor were for the first time investigated through long-term reactor operation and short-term batch experiments. Co-metabolism of SMX and nitrate by autotrophic denitrifiers was observed in this study. The specific SMX removal rate was 3.7 ± 1.4 μg/g SS-d, which was higher than those reported in conventional wastewater treatment processes. The removal of SMX by the enriched denitrifying sludge was mainly attributed to biodegradation. Four transformation products (three known with structures and one with unknown structure) were identified, of which the structures of the two transformation products (TPs) were altered in the isoxazole ring. Additionally, the presence of SMX significantly shaped the microbial community structures, leading to the dominant denitrifier shifting from Sulfuritalea to Sulfurimonas to maintain the stability of system. Collectively, the sulfur-based autotrophic denitrification process could effectively remove SMX in addition to efficient nitrate removal, and further polish the effluent from conventional WWTPs.