Removal performance, biotransformation pathways and products of sulfamethoxazole in vertical subsurface flow constructed wetlands with different substrates

The introduction of influent sulfamethoxazole loads induces changes in the removal pathways of sulfamethoxazole in vertical flow constructed wetlands featuring hematite substrate

High frequent detection of sulfamethoxazole (SMX) in wastewater cannot be effectively removed by constructed wetlands (CWs) with a traditional river sand substrate. The role of emerging substrate of hematite in promoting SMX removal and the effect of influent SMX loads remain unclear. The removal efficiency of SMX in hematite CWs was significantly higher than that in river sand CWs by 12.7-13.8% by improving substrate adsorption capacity, plant uptake and microbial degradation. With increasing influent SMX load, the removal efficiency of SMX in hematite CWs slightly increased, and the removal pathways varied significantly. The contribution of plant uptake was relatively small (< 0.1%) under different influent SMX loads. Substrate adsorption (37.8%) primarily contributed to SMX removal in hematite CWs treated with low-influent SMX. Higher influent SMX loads decreased the contribution of substrate adsorption, and microbial degradation (67.0%) became the main removal pathway. Metagenomic analyses revealed that the rising influent load increased the abundance of SMX-degrading relative bacteria and the activity of key enzymes. Moreover, the abundance of high-risk ARGs and sulfonamide resistance genes in hematite CWs did not increase with the increasing influent load. This study elucidates the potential improvements in CWs with hematite introduction under different influent SMX loads.

Bio-degraded of sulfamethoxazole by microbial consortia without addition nutrients: Mineralization, nitrogen removal, and proteomic characterization

Sulfamethoxazole (SMX) is widely employed as an antibiotic, while its residue in environment has become a common public concern. Using 100 mg/L SMX as the sole nutrient source, the acclimated sludge obtained by this study displayed an excellent SMX degradation performance. The addition of SMX resulted in significant microbiological differentiation within the acclimated sludge. Microbacterium (6.6%) was identified as the relatively dominant genera in metabolism group that used SMX as sole carbon source. Highly expressed proteins from this strain strongly suggested its essential role in SMX degradation, while the degradation of SMX by other strains (Thaurea 78%) in co-metabolism group appeared to also rely on this strain. The interactions of differentially expressed proteins were primarily involved in metabolic pathways including TCA cycle and nitrogen metabolism. It is concluded that the sulfonamides might serve not only as the carbon source but also as the nitrogen source in the reactor. A total of 24 intermediates were identified, 13 intermediates were newly reported. The constructed pathway suggested the mineralizing and nitrogen conversion ability towards SMX. Batch experiments also proved that the acclimated sludge displayed ability to biodegrade other sulfonamides, including SM2 and SDZ and SMX-N could be removed completely.

The environmental risk assessment of constructed wetlands filled with iron and manganese ores in typical antibiotic treatment

Constructed wetlands (CWs) is considered as an efficient and environmentally friendly technology for advanced wastewater treatment to eliminate organic pollutants such as sulfamethoxazole (SMX) and trimethoprim (TMP). Iron (Fe) and manganese (Mn) ores have attracted more and more attention as CWs substrates in treating SMX and TMP, but the potentially negative environmental effects of wetland effluents, ore contaminants leached from the substrates and the risk of transmission of antibiotic resistance genes (ARGs) are still not clear. Three CW groups with different substrates (river sand (C-CW), Fe ore (Fe-CW), and Mn ore (Mn-CW)) were set up to evaluate the average removal rates and environmental risk in treating wastewater containing SMX and TMP. The results showed that the average removal rates of SMX and TMP by Fe-CW and Mn-CW were significantly higher than that of C-CW by 12.46%, 6.59% and 38.93%,15.39% respectively (p < 0.05), suggesting that both Fe and Mn ores facilitated the removal of antibiotics. However, the least abundance of ARGs was found in the layer of Fe ore at the middle layer (ML) in Fe-CW among all CWs, which suggested that Fe ore could reduce the risk of ARGs transmission. Although the environmental risk of Fe-CW and Mn-CW effluent was low, Fe-CW effluent inhibited the growth of Chlorella in both 48h and 72h experiments, while Mn-CW effluent showed an inhibitory effect in 48h and then promoted the growth in 72h. Meanwhile, these findings offer valuable insights for wetland health assessment and substrate selection for CWs.

Biotransformation of sulfamethoxazole by newly isolated surfactant-producing strain Proteus mirabilis sp. ZXY4: Removal efficiency, pathways, and mechanisms

In this study, the SMX degrading strain Proteus mirabilis sp. ZXY4 with surfactant manufacturing potential was isolated from sludge utilizing blood agar and CTAB agar plate. FTIR analysis indicated that the biosurfactant generated by strain ZXY4 was glycolipid. 3D-EEM demonstrated that SMX biodegradation was strongly connected to biosurfactants, the synergistic effect of biodegradation and biosurfactant made strain ZXY4 have excellent SMX degradation performance. Under the optimal conditions of inoculation dosage of 15%, temperature of 30 ℃, pH of 7 and initial SMX concentration of 5 mg L^-1, strain ZXY4 could completely degrade SMX within 24 h. SMX biodegrades at low concentrations (less than5 mg L^-1) followed by the zero-order kinetic model, high concentration (>5 mg L^-1) is more consistent with the first-order kinetic model. LC-MS analysis revealed 14 SMX degradation intermediates, and five potential biodegradation mechanisms were postulated. The findings provide new insights into the biodegradation of SMX.