Classification of Ultrafine Particles Using a Novel 3D-Printed Hydrocyclone with an Arc Inlet: Experiment and CFD Modeling.

Ultrafine particle classification can be realized using hydrocyclones with novel structures to overcome the limitations of conventional hydrocyclones with tangential inlets or cone structures. Herein, the hydrocyclones with different inlet structures and cone angles were investigated for classifying ultrafine particles. Computational fluid dynamics (CFD) simulations were performed using the Eulerian-Eulerian method, and ultrafine MnO2 powder was used as a case study. The simulation results show a fine particle (≤5 µm) removal efficiency of 0.89 and coarse particle (>5 µm) recovery efficiency of 0.99 for a hydrocyclone design combining an arc inlet and a 30° cone angle under a solid concentration of 2.5 wt %. Dynamic analysis indicated that the novel arc inlet provided a preclassification effect to reduce the misplacement of fine/coarse particles, which cannot be provided by conventional tangential or involute inlets. Furthermore, the proposed design afforded comprehensive improvement in the flow field by regulating the residence time and radial acceleration. Subsequently, a novel hydrocyclone with an arc inlet and 30° cone angle was manufactured using the three-dimensional (3D) printing technology. Experiments were conducted for classifying ultrafine MnO2 particles using the novel 3D-printed hydrocyclone and conventional hydrocyclone. The results demonstrate that the classification performance of the 3D-printed hydrocyclone was superior to that of the conventional one, in particular, the removal efficiency of fine particles from 0.719 to 0.930 using a 10 wt % feed slurry.

Enhancement of perchloroethene dechlorination by a mixed dechlorinating culture via magnetic nanoparticle-mediated isolation method.

Highly enriched active dechlorinating cultures are important in advancing microbial remediation technology. This study attempted to enrich a rapid perchloroethene (PCE) dechlorinating culture via magnetic nanoparticle-mediated isolation (MMI). MMI is a novel method that can separate the fast-growing and slow-growing population in a microbial community without labelling. In the MMI process, PCE dechlorination was enhanced but the subsequent trichloroethene (TCE) dechlorination was inhibited, with TCE cumulative rate reached up to 80.6% within 70 days. Meanwhile, the microbial community was also changed, with fast-growing genera like Dehalobacterium and Petrimonas enriched, and slow-growing Methanosarcina almost ruled out. Relative abundances of several major genera including Petrimonas and Methanosarcina were positively related to TCE dechlorination rate and the relative abundance of Dehalococcoides. On the other hand, Dehalobacterium was negatively related to TCE dechlorination rate and Dehalococcoides abundance, suggesting potential competition between Dehalobacterium and Dehalococcoides. The regrowth of Methanosarcina coupled well with the recovery of TCE dechlorination capacity, which implied the important role of methanogens in TCE dechlorination. Via MMI method, a simpler but more active microbial consortium could be established to enhance PCE remediation efficiency. Methanogens may act as the indicators or biomarkers for TCE dechlorination, suggesting that methanogenic activity should also be monitored when enriching dechlorination cultures and remediating PCE contaminated sites. CAPSULE: A rapid perchloroethene dechlorinator was gotten via magnetic nanoparticles and dechlorination of trichloroethene coupled well with growth of Methanosarcina.

Acceleration of perchloroethylene dechlorination by extracellular secretions from Microbacterium in a mixed culture containing Desulfitobacterium.

The study was conducted to demonstrate the influence of extracellular secretions from Microbacterium on the reductive dechlorination of tetrachloroethene (PCE). A series of mixed cultures were established from a paddy soil sample. In the mixed cultures amended with extracellular secretions from Microbacterium, PCE was rapidly and completely converted into cis-1,2-dichloroethene (cis-DCE) and trans-1,2-dichloroethene (trans-DCE) within 40 days. The unamended mixed cultures showed weak signs of dechlorination after a pronounced lag phase, and trichloroethene (TCE) was accumulated as a major end product. This result means that amendment with extracellular secretions from Microbacterium shortened the lag phase, increased the dechlorination velocity and promoted the production of less-chlorinated chloroethene. The results were corroborated by defined subculture experiments, which proved that microorganisms from unamended mixed cultures could also be stimulated by extracellular secretions from Microbacterium. Desulfitobacterium was identified as the main dechlorinating population in all mixed cultures by direct PCR. Additionally, the 16S rRNA gene copies of Desulfitobacterium increased by one or two orders of magnitude with PCE dechlorination, which provided corroborative evidence for the identification result. The volatile fatty acids were monitored, and most interestingly, a close association between propionate oxidation and dechlorination was found, which has rarely been mentioned before. It was assumed that the oxidation of propionate provided hydrogen for dechlorination, while dechlorination facilitated the shift of the reaction toward propionate oxidation by reducing the partial pressure of hydrogen.