Settling behaviors of microplastic disks in acceleration fall.

The settling of microplastics (MPs) in the initial acceleration fall stage, i.e., before reaching the terminal settling velocity, has not been investigated, which is however important for understanding MP transport and fate. MP disks sized 3-5 mm, of three shapes and made of three polymers (1.038-1.343 g/cm3) were examined. Five release ways and three release angles (0°, 45°, 90°) were used. MP disks with the release angle of 0° start to zigzag immediately after the release, while the MP disks with the release angles of 45° and 90° first adjust to a horizontal position and then zigzag. The adjustment distances in the vertical and horizontal directions, as well as the maximum vertical settling velocity, are influenced by MP density, size, release angle and release way. The detailed settling trajectory and velocity were also analyzed. Finally, the time-changing drag coefficient of MP disks was examined and discussed.

Photocatalytic degradation of norfloxacin by magnetic molecularly imprinted polymers: influencing factors and mechanisms.

Novel magnetic molecularly imprinted polymers (MMIP) were prepared for selective removal of norfloxacin by effectively utilizing photocatalytic degradation and magnetic separation techniques. The imprinted material with titanium layer and multihole surface showed an excellent photocatalytic property. In this paper, the kinetics of photocatalytic degradation of norfloxacin by MMIP was explored, and the influences of environmental factors, including solution pH, humic acid, common ions and water media on photocatalytic performance of MMIP were elucidated. The results showed that MMIP had good adaptability and could degrade norfloxacin within 60 min, but the degradation rate constant decreased in surface water. Based on the identification of intermediate products, the possible degradation pathways of norfloxacin were analysed, speculating that it might be degraded into small molecules in the form of de-piperazine ring, de-carboxyl group and de-fluorine. Moreover, the mineralization ratio of norfloxacin could reach 84.2% after ultraviolet irradiation for 150 min, and the low cobalt release of MMIP enhanced the security of the material. The results of adsorption and degradation cycle tests showed that MMIP obtained by molecular imprinting technology had excellent performance in sustainable use for micro organic pollutants removal.

Efficient removal of norfloxacin in water using magnetic molecularly imprinted polymer.

Effective and practical materials are important for the pollution control in the environment. A novel magnetic molecularly imprinted polymer (CoFe2O4@TiO2-MMIP) was prepared based on the surface molecular imprinting technology combined with photocatalytic degradation and magnetic separation. The adsorption rate constant and maximum adsorption capacity of CoFe2O4@TiO2-MMIP are 0.21 g mg-1 min-1 and 14.26 mg g-1, respectively. The effects of experimental factors on the adsorption properties of the magnetic molecularly imprinted polymer were investigated. CoFe2O4@TiO2-MMIP had selective adsorption ability towards fluoroquinolones. The adsorption efficiency was closely related to the molecular structure, molecular weight, polarity and functional groups of the target contaminant and the removal efficiency of norfloxacin was affected by another substance obviously in binary adsorption system. The adsorption-photocatalytic recycling experiment verified that CoFe2O4@TiO2-MMIP could simultaneously complete the degradation of pollutants and in-situ regeneration, indicating good reusability. This material with selective adsorption and photocatalytic regeneration would have substantial attraction for application in the removal of fluoroquinolones.

A comparative analysis for the development and recovery processes of different types of clogging in lab-scale vertical flow constructed wetlands.

Clogging is a major operational and maintenance issue associated with the use of constructed wetlands. In this study, four lab-scale vertical flow constructed wetlands (VFCW) were used to fully understand the development mechanisms of various types of clogging and their recovery characteristics. The VFCWs were fed with glucose solution, starch suspension with and without bacteriostat, glucose, and starch mixed solution, respectively, to simulate Bio-clogging, organic particle clogging (Op-clogging), inert particle clogging (Ip-clogging), and the combination of Bio-clogging and Op-clogging (C-clogging). Resting operations with water decline were applied to relieve the clogging in the VFCWs. The results indicate that Op-clogging occurred first, followed by C-clogging and Bio-clogging. Ip-clogging took the longest time to develop and did not occur by the end of this study. The microscope analysis found that the extracellular polymeric substances (EPS) bonded the starch particles together to form a dense membrane-like structure and promoted the clogging process. In addition, surface clogging was observed in all four experimental beds. Op-clogging occurred much closer to the surface than those caused by soluble organic matter and inert particles. Furthermore, the growth of biofilm caused significant decline in hydraulic conductivity, whereas its influence on porosity was relatively slight. Moreover, applying resting operation with water decline was effective for recovery from Bio-clogging, Op-clogging, and C-clogging in VFCWs except for Ip-clogging. The results also implied the recovery rates through applying resting operation with water decline were much higher than that with constant water level.