Bioretention system mediated by different dry-wet alterations on nitrogen removal: Performance, fate, and microbial community.

In laboratory experiments, the nitrogen migration and transformation in the stormwater bioretention system under different dry-wet alterations were studied. The removal efficiency showed that nitrogen could be removed efficiently in bioretention system under all dry-wet alterations, and the shorter antecedent dry days (ADDs) (1-5 days) were beneficial to the removal of nitrogen before plants decay, compared to the longer ADDs (7-22 days). Using a new method combined with Hydrus-1D model, water transport was simulated and nitrogen migration in bioretention system was quantified, indicating that NH4+-N was mainly removed in the planting layer, and the removal of NO3--N was occurred in the submerged layer. Fate experiment showed the main fate of the nitrogen was microorganisms (1-5 ADDs) and soil immobilization (7-22 ADDs). Microbial analysis showed that shorter ADDs (1-5 days) were suitable for Firmicutes growth, while Proteobacteria and Actinobacteria accounted for greater abundance under longer ADDs (7-22 days). Canonical correlation analysis (CCA) revealed the relationships between microbial community and environmental factors. Soil moisture content, soil organic matter (SOM), TN (water), root length, and NO3--N (water) were significantly correlated with bacterial community. This work may give new insights into nitrogen migration and transformation, and can provide a reference for the further mechanism study and construction of stormwater bioretention systems.

Simultaneous regeneration of cathodic activated carbon fiber and mineralization of desorbed contaminations by electro-peroxydisulfate process: Advantages and limitations.

This study investigated the regeneration of phenol saturated activated carbon fiber (ACF) with a novel electro-peroxydisulfate (E-PDS) process. Compared with traditional electrochemical regeneration, E-PDS process could simultaneously regenerate the exhausted ACF and mineralize desorbed contaminants by activating PDS in water with a much lower energy consumption (1/6). According to the estimation of relative contributions involved in E-PDS process, reactive oxygen species (ROS), especially sulfate radical (SO4•-), played a dominant role in the degradation of phenol and its byproducts. It was worth noting that the accumulation of byproducts in solution increased significantly after SO4•- concentration decreased in aqueous solution. Further study proved that the regeneration efficiency of ACF could be improved by the application of multiple doses of PDS for the effective reduction of byproduct accumulation. However, application of multiple doses of PDS could not prevent ACF from being oxidized by ROS generated in the system, subsequently leading to loss of ACF adsorption capacity. This limitation is a significant concern in treatment technologies based on carbon materials activated by peroxides and such technologies should be studied further to obtain additional insights on their potential and applicability in industrial practice. Nevertheless, the adsorption capacity of ACF remained above 40% after three regeneration cycles in the E-PDS process. Therefore, E-PDS process showed promise for further evaluation as a potentially viable approach for the regeneration of carbons saturated with organic pollutants.

Adsorption behavior and mechanism of ibuprofen onto BiOCl microspheres with exposed {001} facets.

BiOCl microspheres with exposed {001} facets have been synthesized through a simple solvothermal method. The adsorption and photocatalytic activities of BiOCl microspheres were evaluated by removal of ibuprofen (IBP) as the model reaction. Parameters including IBP concentration, BiOCl dosage, and inorganic ions were investigated to reveal the role of adsorption in BiOCl-based photocatalysis. We found that the high IBP removal rate by BiOCl is not due to photocatalytic oxidation but to surface adsorption. The combination of ICP/MS, IC, XPS, and FT-IR results directly proved that anion exchange between dissociated IBP and Cl accompanied by the formation of surface complex (O-Bi-OOC-C12H17) onto the BiOCl surface is the main adsorption mechanism. In addition, we also demonstrated that organic compounds with carboxyl group (-COOH) such as diclofenac, benzoic acid, and p-phthalic acid can be adsorbed by BiOCl while organic compounds without carboxyl group such as carbamazepine, nitrobenzene, and p-chloronitrobenzene cannot be adsorbed. We believe that the BiOCl adsorption behavior and mechanism should be considered when discussing its photocatalytic mechanism.