Concentration estimation of dissolved oxygen in Pearl River Basin using input variable selection and machine learning techniques.

Dissolved oxygen (DO) concentration is an essential index for water environment assessment. Here, we present a modeling approach to estimate DO concentrations using input variable selection and data-driven models. Specifically, the input variable selection technique, the maximal information coefficient (MIC), was used to identify and screen the primary environmental factors driving variation in DO. The data-driven model, support vector regression (SVR), was then used to construct a robust model to estimate DO concentration. The approach was illustrated through a case study of the Pearl River Basin in China. We show that the MIC technique can effectively screen major local environmental factors affecting DO concentrations. MIC value tended to stabilize when the sample size >3000 and EC had the highest score with an MIC >0.3 at both of the stations. The variable-reduced datasets improved the performance of the SVR model by a reduction of 28.65% in RMSE, and increase of 22.16%, 56.27% in R2, NSE, respectively, relative to complete candidate sets. The MIC-SVR model constructed at the tidal river network performed better than nontidal river network by a reduction of approximately 63.01% in RMSE, an increase of 62.36% in NSE, and R2 >0.9. Overall, the proposed technique was able to handle nonlinearity among environmental factors and accurately estimate DO concentrations in tidal river network regions.

3D MnO2 hollow microspheres ozone-catalysis coupled with flat-plate membrane filtration for continuous removal of organic pollutants: Efficient heterogeneous catalytic system and membrane fouling control.

A heterogeneous catalytic ozonation/membrane filtration (HCOMF) system was fabricated by integrating a flat-plate polyvinylidene fluoride (PVDF) membrane module along with a slurry catalytic ozonation reactor. The performance and catalytic activity of HCOMF was evaluated for degradation of model wastewater containing bisphenol A (BPA) and humid acid (HA) under different permeation flux in long-term continuous experiments. The membrane fouling was investigated by trans-membranous pressure (TMP), membrane filtration resistance, scanning electronic microscopy (SEM), and fluorescence spectra. The results showed that HCOMF system exhibited an excellent and stable catalytic activity in long-term continuous experiments owning to integration of 3D MnO2 hollow microsphere ozone-catalysis with flat-plate membrane filtration. The TMP of HCOMF system didn't increase significantly, and the membrane resistance Rp and Rc declined from 4% and 16% to 1% and 4%, respectively, thus, the membrane fouling of HCOMF system was mitigated compared to MF system. The mitigation of membrane fouling in HCOMF system was attributed to the increase of hydrophilicity of membrane surface and change of HA fractions.

Three-dimensional MnO2 porous hollow microspheres for enhanced activity as ozonation catalysts in degradation of bisphenol A.

Three-dimensional (3D) MnO2 porous hollow microspheres (δ- and α- MnO2 PHMSs), with high adsorption and catalytic ozonation performance, were synthesized by a self-template (MnCO3 microspheres) process at room temperature. The synthesized MnO2 PHMSs were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area. The results showed that PHMSs exhibit the excellent adsorption ability and catalytic activity owning to their hollow spherical structure, mesoporous shell and well-defined interior voids, leading to the strong adsorption for bisphenol A (BPA) and the retention of O3 molecules on catalyst. Moreover, the catalytic performance of α-MnO2 PHMSs was better than that of δ-MnO2 PHMSs which was attributed to the richer lattice oxygen of α-MnO2 PHMSs to accelerate O3 decomposition by producing more reactive oxidative species. The degradation efficiency of BPA using 3D α-MnO2 PHMSs was more than 90% in the presence of ozone within 30min reaction time. The probe tests for reactive oxidative species (ROSs) displayed that BPA degradation by catalytic ozonation is dominated by O2- and OH in our present study. Furthermore, the organic compounds as intermediates of the degradation process were identified by LC/MS.