Transformation of sulfadiazine in humic acid and polystyrene microplastics solution by horseradish peroxidase coupled with 1-hydroxybenzotriazole.

Enzyme catalyzed coupling with redox mediators are considered as great interesting and viable technologies to transform antibiotics. This work demonstrated the horseradish peroxidase (HRP) was effective in transforming sulfadiazine (SDZ) transformation coupled with 1-hydroxybenzotriazole (HBT) at varying conditions. The removal of SDZ was independent of Na+ and its ionic strength, but Ca2+ could enhance transformation efficiency by increasing the enzyme activity of HRP. The presence of humic acid (HA) and polystyrene (PS) microplastics showed inhibition on the transformation of SDZ, and the transformation rate constants (k) decreased with the concentration of HA and PS particles increased. These primarily attributed to covalent coupling and electrostatic interaction between SDZ and HA, SDZ and PS, respectively, which reduced the concentration of free SDZ in the reaction solution. The presence of cation recovered the inhibition of SDZ transformation by HA and PS particles, which ascribed to compete between cation and SDZ. The divalent cations (Ca2+) showed more substantial competitiveness than mono (Na+) due to more carried charge. Eight possible transformation products were identified, and potential SDZ transformation pathways were proposed, which include δ-cleavage, γ-cleavage, carbonylation, hydroxylation, SO2 extrusion and SO3 extrusion. In addition, HA and PS particles couldn't affect the transformation pathways of SDZ. These findings provide novel understandings of the transformation and the fate of antibiotics in the natural environment by HRP coupled with redox mediators.

Nitrogen removal performance and microbial community structure in the start-up and substrate inhibition stages of an anammox reactor.

In this study, the nitrogen removal performance and microbial community structure were investigated during the start-up, instability, and recovery stages of an anaerobic ammonium oxidation (anammox) reactor loaded with compound carriers (shale ceramsite and suspended ball carrier). The results indicated that the anammox reactor successfully started up on 116th d when the nitrogen loading rate (NLR) reached 0.72 ± 0.05 kg N m-3 d-1. The anammox reactor ran well with free ammonia (FA) at 13.65 ± 2.69 mg/L and free nitrous acid (FNA) at 39.49 ± 10.95 µg/L, indicating that its tolerance for FA and FNA was higher than that of granular sludge anammox reactors. The anammox system was inhibited when FA and FNA reached 29.65 mg/L and 77.02 µg/L, respectively. The tolerance of anammox bacteria towards FA and FNA decreased after this inhibition. The nitrogen removal performance could be efficiently recovered by decreasing the influent substrate concentration and increasing the hydraulic retention time (HRT). Candidatus Brocadia and Candidatus Jettenia, two genus-level anammox bacteria, were detected in this reactor using a high-throughput sequencing technique. After high substrate shock, the abundance of Candidatus Brocadia decreased while that of Candidatus Jettenia increased, which might be due to the competition between Candidatus Jettenia and Candidatus Brocadia. The relationships between anammox communities and operational factors were investigated via redundancy analysis (RDA), which showed that FA was the principal factor affecting the microbial community structure during the operation stage.