Understanding microplastic presence in different wastewater treatment processes: Removal efficiency and source identification.

Municipal effluents discharged from wastewater treatment plants (WWTPs) are a considerable source of microplastics in the environment. The dynamic profiles of microplastics in treatment units in WWTPs with different treatment processes remain unclear. This study quantitatively analyzed microplastics in wastewater samples collected from different treatment units in two tertiary treatment plants with distinct processes. The influents contained an average of 15.5 ± 3.5 particles/L and 38.5 ± 2.5 particles/L in the two WWTPs with in the oxidation ditch process and the integrated fixed-film activated sludge process, respectively. Interestingly, microplastic concentrations in the influent were more influenced by the population density in the served area than sewage volume or served population equivalent. Throughout the treatment process, concentrations were reduced to 1.5 ± 0.5 particles/L and 1.0 ± 1.0 particles/L in the final effluents, representing an overall decrease of 90% and 97%, in WWTPs with the oxidation ditch process and integrated fixed-film activated sludge process, respectively. A significant proportion of the microplastics were removed during the primary treatment stage in both WWTPs, with better performance for foam, film, line-shaped and large-sized microplastics. Most microplastics were accumulated in activated sludge, indicating its key role as the primary sink in WWTPs. The multiple correspondence analysis identified laundry washing and daily necessities such as packaging and containers as the major contributors to microplastics in WWTPs. The study proposed recommendations for upgrading WWTPs, modifying designs, and implementing strategies to reduce microplastic sources, aiming to minimize the release of microplastics into the environment. These findings can shed lights on the sources of microplastics in WWTPs, and advance our understanding of the mechanisms for more effective microplastic removals in wastewater treatment technologies in future applications.

More resilient polyester membranes for high-performance reverse osmosis desalination.

Thin-film composite reverse osmosis membranes have remained the gold standard technology for desalination and water purification for nearly half a century. Polyamide films offer excellent water permeability and salt rejection but also suffer from poor chlorine resistance, high fouling propensity, and low boron rejection. We addressed these issues by molecularly designing a polyester thin-film composite reverse osmosis membrane using co-solvent-assisted interfacial polymerization to react 3,5-dihydroxy-4-methylbenzoic acid with trimesoyl chloride. This polyester membrane exhibits substantial water permeability, high rejection for sodium chloride and boron, and complete resistance toward chlorine. The ultrasmooth, low-energy surface of the membrane also prevents fouling and mineral scaling compared with polyamide membranes. These membranes could increasingly challenge polyamide membranes by further optimizing water-salt selectivity, offering a path to considerably reducing pretreatment steps in desalination.

Modulating electron density enable efficient cascade conversion from peroxymonosulfate to superoxide radical driven by electron-rich/poor dual sites.

The superoxide radical (•O2-)-mediated peroxymonosulfate (PMS)-based photo-Fenton-like reaction enables highly selective water decontamination. Nevertheless, the targeted construction of •O2--mediated photo-Fenton-like system has been challenging. Herein, we developed an electron-rich/-poor dual sites driven •O2--mediated cascade photo-Fenton-like system by modulating electron density. Experimental and theoretical results demonstrated that PMS was preferentially adsorbed on electron-poor Co site. This adsorption promoted O-O bond cleavage of PMS to generate hydrogen peroxide (H2O2), which then migrated to electron-rich O site to extract eg electrons for O-H bond cleavage, rather than competing with PMS for Co site. The developed versatile cascade reaction system could selectively eliminate contaminants with low n-octanol/water partition constants (KOW) and dissociation constants (pKa) and remarkably resist inorganics (Cl-, H2PO4- and NO3-), humic acid (HA) and even real water matrices (tap water and secondary effluent). This finding provided a novel and plausible strategy to accurately and efficiently generate •O2- for the selective water decontamination.

Efficient separation of impurities Fe/Al/Ca and recovery of Zn from electroplating sludge using glucose as reductant.

Electroplating sludge (ES), a hazardous waste containing heavy metals and Fe/Al/Ca impurities, is conventionally disposed of in landfills. In this study, a pilot-scale vessel with an effective capacity of 20 L was applied to recycle Zn from real ES. The sludge contained 6.3 wt% Fe, 6.9 wt% Al, 2.6 wt% Si, 6.1 wt% Ca, and 17.6 wt% Zn and was treated using a four-step method. First, ES was dissolved in nitric acid after washing in a water bath at 75 °C for 3 h to produce an acidic solution with Fe, Al, Ca, and Zn concentrations of 4527.2, 3116.1, 3357.7, and 21,275 mg/L, respectively. Second, the acidic solution was added with glucose at an Mglucose/Mnitrate ratio of 0.08 and hydrothermally treated at 160 °C for 4 h. During this step, nearly 100 % Fe and 100 % Al were simultaneously removed as a mixture containing 53.1 wt% Fe2O3 and 45.7 wt% Al2O3. This process was repeated five times, during which the Fe/Al removal and Ca/Zn loss rates remained unchanged. Third, the residual solution was adjusted with sulfuric acid, and over 99 % Ca was removed as gypsum. The residual Fe, Al, Ca, and Zn concentrations were 0.44, 0.88, 52.59, and 31,177.1 mg/L, respectively. Finally, Zn in the solution was precipitated as ZnO with a concentration of 94.3 %. Economic calculations showed that each 1 t of ES processed created revenue of about $122. This is the first study of high-value metal resource recovery using real electroplating sludge at the pilot scale. This work highlights the pilot-scale application of resource utilization of real ES and provides new insights into the recycling of heavy metals from hazardous waste.

Aquifer clogging caused by chlorine disinfection during the reclaimed water recharge.

Aquifer clogging plays a critical role in the efficiency of reclaimed water recharge. While chlorine disinfection is commonly used for reclaimed water, its impact on clogging has seldom been discussed. Thus, this study aimed to investigate the mechanism of chlorine disinfection on clogging by establishing a lab-scale reclaimed water recharge system that utilized chlorine-treated secondary effluent as feed water. The findings indicated that increasing the chlorine concentration led to a surge in the total amount of suspended particles, and the median particle size increased from 2.65 µm to 10.58 µm. Furthermore, the fluorescence intensity of dissolved organic matter decreased by 20%, with 80% of these compounds, including humic acid, becoming entrapped within the porous media. Additionally, the formation of biofilms was also found to be promoted. Microbial community structure analysis unveiled a consistent dominance of Proteobacteria consistently exceeded 50% in relative abundance. Moreover, the relative abundance of Firmicutes increased from 0.19% to 26.28%, thereby verifying their strong tolerance to chlorine disinfection. These results showed that higher chlorine concentrations could stimulate microorganisms to secrete an increased quantity of extracellular polymeric substance (EPS) and form a coexistence system with the trapped particles and natural organic matter (NOM) within the porous media. Consequently, this supported the formation of biofilms, thereby potentially elevating the risk of aquifer clogging.

Progress in Research and Application of Metal-Organic Gels: A Review.

In recent years, metal-organic gels (MOGs) have attracted much attention due to their hierarchical porous structure, large specific surface area, and good surface modifiability. Compared with MOFs, the synthesis conditions of MOGs are gentler and more stable. At present, MOGs are widely used in the fields of catalysis, adsorption, energy storage, electrochromic devices, sensing, analysis, and detection. In this paper, literature metrology and knowledge graph visualization analysis are adopted to analyze and summarize the literature data in the field of MOGs. The visualization maps of the temporal distribution, spatial distribution, authors and institutions' distribution, influence of highly cited literature and journals, keyword clustering, and research trends are helpful to clearly grasp the content and development trend of MOG materials research, point out the future research direction for scholars, and promote the practical application of MOGs. At the same time, the paper reviews the research and application progress of MOGs in recent years by combining keyword clustering, time lines, and emergence maps, and looks forward to their challenges, future development trend, and application prospects.

Enhanced degradation of emerging contaminants by percarbonate/Fe(II)-ZVI process: case study with nizatidine.

Pharmaceuticals have recently emerged as a significant environmental concern due to the growth of population, expansion of industry, and the shift in modern lifestyles. Herein, we present a Fe(II)/percarbonate (SPC) process with dramatically enhanced efficiency by the introduction of zerovalent iron (ZVI). After the addition of ZVI, the removal rate of nizatidine (NZTD) went up from 71.7 to 84.2%. The removal rate of NZTD decreases with rising pH and speeds up with increasing temperature. It was found that under the condition of pH = 7 and T = 25 °C, the molar ratio of the optimal concentration of NZTD degradation in the system was [NZTD]0:[SPC]0:[Fe(II)]0:[ZVI]0 = 1:8:24:16, with a degradation rate of 99.8%. At the same time, target pollutants can also be successfully eliminated from actual water bodies. Moreover, we test for toxicity using luminescent bacteria, and the results demonstrate that the system is capable of effectively decreasing the toxicity of NZTD. The research findings can contribute to the clarification of the migration and transformation law of NZTD in the oxidation process, thereby providing a scientific basis and technical support for the removal of NZTD in the tertiary water treatment for a water source.

Synergism in sequential inactivation of Cryptosporidium parvum with trypsin and UV irradiation.

Cryptosporidium, a protozoan parasite, in wastewater presents a major public health concern for water safety. However, bactericidal efficiencies of conventional disinfection methods towards Cryptosporidium oocysts are still hampered owing to the presence of their thick outer wall. In this study, we present a novel UV inactivation process where the efficiency has been significantly enhanced by addition of a trypsin pretreatment stage. Notably, inactivation (log-reduction) of oocysts was noted to be 73.75-294.72% higher than that obtained by UV irradiation alone, under identical conditions. Experimental observations and supporting mechanistic analyses suggest that trypsin led to cleavage of the protein layers on the oocyst wall, facilitating penetration of UV radiation into the oocysts leading to degradation of their genomic DNA (gDNA). The dissociative effect of trypsin on the oocyst wall was indicated by the fact that 64.50% of oocysts displayed early apoptosis after trypsinization. Imaging by scanning electron microscopy indicated that this combined treatment led to substantial disruption of the oocyst coat, deforming their shape. This resulted in the release of cellular proteins and gDNA, their concentrations in bulk solution increasing by 1.22-8.60 times. As UV irradiation time was prolonged, gDNA was degraded into smaller fragments with lower molecular masses. Both laddering and diffuse smear patterns in gel analysis indicated significantly detrimental effects on gDNA and viability of oocysts. Overall, this study demonstrated enhancement of UV inactivation of Cryptosporidium oocysts by trypsin and explored the underlying mechanisms for the process.

A modelling approach to explore the optimum bubble size for micro-nanobubble aeration.

Bubble aeration has been widely applied in water/wastewater treatment, however its low gas utilization rate results in high energy consumption. Application of micro-nanobubbles (MNB) has emerged as a process with the potential to significantly increase gas utilisation due to their high relative surface area and high gas-liquid mass transfer efficiency. In this study, we demonstrate through calibrated models that MNB of an optimum bubble size can shrink and burst at or below the water surface enabling (1) all encapsulated gas to thoroughly dissolve in water, and (2) the bursting of nanobubbles to potentially generate free radicals. Through the understanding of MNB dimensional characteristics and bubble behaviour in water, a dynamic model that integrated force balance (i.e. buoyancy force, gravity, drag force, Basset force and virtual mass force), and mass transfer was developed to describe the rising velocity and radius variation of MNB along its upward trajectory. Unlike for conventional millimetre-sized bubbles, intensive gas dissolution of MNBs led to radius reduction for small bubbles, while a large initial radius triggers bubble swelling. The initial water depth was also crucial, where greater depth could drive the potential for bubble shrinkage so that they were more liable to contract. For example, the optimum bubble size of air (42-194 µm) and oxygen (127-470 µm) MNB that could achieve complete gas transfer (100% gas utilisation) for a range of specific water depths (0.5-10 m) were calculated. The modelling results for microbubbles (10-530 µm) were well validated by the experimental data (R2>0.85). However, the validation of the modelling results for nanobubble (<1 µm) aeration requires further study due to a lack of available empirical data. In this study, the proposed model and analysis provided new insights into understanding bubble dynamics in water and offered fundamental guidance for practitioners looking to upgrade bubble aeration system.

Reclamation of ginseng residues using two-stage fermentation and evaluation of their beneficial effects as dietary feed supplements for piglets.

Environmental pollution caused by herbal residues, such as ginseng residue (GR), and the huge waste of medicinal ingredients in such residues hinder the development of the pharmaceutical industry. Few studies focused on the biotransformation of GRs and the practical utilization of their bioproducts. In this study, we developed a two-stage fermentation method to optimize GR bioconversion and used the fermented products as dietary supplements for piglets. The tested GR contained abundant lignocelluloses, protein, sugar, and amino acids. Approximately 43.10% of the total lignocelluloses were degraded into sugars by Inonotus obliquus in stage 1 of fermentation. Meanwhile, the sugar content increased by 36.20%, which became the feed for Bacillus subtilis and Saccharomyces cerevisiae in stage 2 of fermentation. These two strains boosted the production of bacterial proteins and other metabolites, including peptides, organic acids, and amino acids. At the end of fermentation, the contents of bioactive compounds significantly increased by 3.18%-21.79%. The dietary supplementation of fermented GR significantly improved the growth performance (6.47%-7.98%), intestinal microbiota, immune function, and healthy status and reduced the diarrhea incidence and noxious gas emission of the piglets. This study provides evidence-based results for the development and deployment of a circular economy between ginseng and livestock industries.

Mechanism comparisons of transport-deposition-reentrainment between microplastics and natural mineral particles in porous media: A theoretical and experimental study.

The migration and distribution of microplastic particles (MPs) in the natural environment has attracted global attention in recent years. However, little is known about the transport-deposition-reentrainment differences between MPs and natural mineral particles in porous media. In this study, polystyrene (PS) and silica (SiO2) particles, representing model MPs and natural mineral particles, respectively, were selected to study the responses of different particle types to changes in specific particle size and flow velocity. Three typical particle sizes and various flow velocities were chosen to compare and delineate the transport-deposition-reentrainment characteristics of PS and SiO2 in a packed-bed laboratory column. Collector efficiency was calculated using Tufenkji and Elimelech (TE) equation. The particle fractions released from the collector surfaces were predicted using DLVO theory and force analysis. Two types of particles were attached in the secondary minimum, which were either retained on the collector surface or reentrained to the fluid. The staged elution experiment wherein the flow velocity was increased experienced a period of flow shock, thus breaking the force balance of the particle. An increase in the flow velocity resulted in various degrees of particle elution. The breakthrough experiment at a specific flow velocity showed that the corresponding velocity alteration in staged elution experiment contributed to reentrainment to varying extents. When the effect of gravity on particle deposition was negligible, the particle size was larger, and the lower the velocity for releasing the particles. However, the opposite tendency was observed when considering the effect of gravity on particle deposition. Moreover, the deposition, mainly due to gravity, easily causes particle reentrainment as the flow velocity increases. This study further predicts and reveals the nature of transport and deposition differences between MPs and natural mineral particles, which helps to further assess the risk and potential of groundwater contamination with MPs of different sizes.

Deciphering the influence of multiple anthropogenic inputs on taxonomic and functional profiles of the microbial communities in Yitong River, Northeast China.

We conducted the analysis of physicochemical parameters, 16S rRNA amplicon sequencing and real-time quantitative polymerase chain reaction to explore the impact of human inputs on the bacterioplankton communities within a tributary of the largest river flowing through a megacity in northeast China. Agriculture largely accounted for the alteration of diversity and functions of the microbial communities. Furthermore, nitrate and total phosphorus declined at the reservoir outlet. The WWTP effluent discharge caused a decrease of the relative abundance of Actinobacteria and Cyanobacteria, while the impact on the variation of alpha diversity of river microbial community was slight. Carbon fixation and nitrogen cycle varied with the change of land use type. The rare taxa contributed with a predominant role in the response to environmental variables and NH3-N as well as NO3--N were the main environmental factors that drove the shift in the bacterial community. The occurrence of the human-specific fecal indicator was mostly derived from agriculture, and its increase in relative abundance was observed in the WWTP effluent. Thus, our study provides guidance for ecological assessment and management of rivers by revealing the response pattern of river bacterioplankton to multiple types of anthropogenic stressors.

Spatial distribution and potential sources of microplastics in the Songhua River flowing through urban centers in Northeast China.

Microplastics (MPs) have elicited increasing concerns in freshwater systems worldwide. However, little information is available on the MP pollution in the Songhua River, the third largest river in China. And the understanding of the sources and pathways of MPs is limited. In this study, MPs were sampled from river water and wastewater treatment plants in five cities along the Songhua River to investigate the occurrence, spatial distribution, characteristics, and potential sources of MPs. Polyethylene, polypropylene and polystyrene accounted for more than 95% of the total MPs. MP pollution was determined to be spatially heterogeneous. The concentration of MPs in the urban center was always considerably higher than that in the upper reach, and irregular variation was observed from the urban center to the lower reach for each city. Urbanization was one of the primary driving forces of spatial variability. Statistically significant positive correlations (p-value < 0.05) were noted between the average concentration of MPs in river water and population density (p = 0.0023) and number of industrial enterprises above designated size (p = 0.0042) of each city. Line and fiber were the major shapes, and white was the most dominant color. Large (1-5 mm) and small (≤ 1 mm) MP particles accounted for 50% each. Multiple correspondence analysis as a new methodological approach was conducted to elucidate the sources of MPs for the first time. The potential sources of MPs included daily use, fishing, agricultural, and industrial productions. This work provides information about MP contamination for future studies on freshwater systems and new insights into the source apportionment of MPs.

Oxidation of phthalate acid esters using hydrogen peroxide and polyoxometalate/graphene hybrids.

Phthalate acid esters (PAEs) have been adsorbed and oxidatively degraded into small molecules including lactic acid (LA), formic acid (FA), H2O and CO2 using polyoxometalates (POMs)/graphene hybrids. We demonstrated that super-lower concentrations of PAEs could be oxidized, which was due to their unique structure. POM molecules have been embedded onto graphene to form H5PMo10V2O40@surfactant(n)/Graphene(L wt%) (abbreviated as HPMoV@Surf(n)/GO(L wt%)) using surfactants with the carbon chain length n = 2, 4, 6 and 8 for the loading of HPMoV. The coexistence of the graphene and surfactant layer (on HPMoV@Surf(n)/GO(20 wt%)) adsorbed PAE molecules and transported them rapidly to HPMoV active sites. And n values determined the electron transfer ability between graphene and POMs that promoted PAEs oxidation. The loading of POMs on the surface of graphene permitted HPMoV@Surf(n)/GO(L wt%) act as interfacial catalyst which degraded various PAEs (i.e., diethyl phthalate (DEP), diallyl phthalate (DAP) and di (2-ethylhexyl) phthalate (DEHP)) while removed more than 70% of TOC and COD. The degradation of DEP achieved 93.0% with HPMoV@Surf(n)/GO(20 wt%) and H2O2, which followed first-order kinetics and the reaction activation energy (Ea) of 23.1 kJ/mol. Further, HPMoV@Surf(n)/GO(20 wt%) showed potential for the removal of PAEs in Wastewater Treatment Plant (WWTP), and the degradation efficiency for PAE (DEP) in secondary effluent achieved 55.0%. In addition, the loading method for POMs on graphene eliminated the leaching of POMs from graphene, and the degradation efficiency could still reach 88.1% after ten recycles.

Stepwise extraction of Fe, Al, Ca, and Zn: A green route to recycle raw electroplating sludge.

Electroplating sludge is a hazardous waste produced in large quantities in the electroplating industry during production. It is rich in heavy metal resources and can be recovered as value-added heavy metal products. To recover Zn in electroplating sludge, Fe/Al/Ca impurities were effectively removed as hematite, boehmite, and calcium sulfate, respectively, via a facile hydrothermal method with reduction of nitric acid by addition of glucose. After the sludge was dissolved in nitric acid, the generated solution contained 6.1 g/L of Zn, 2.2 g/L of Fe, 2.5 g/L of Al, and 2.9 g/L of Ca. First, approximately 100% Fe was extracted as hematite nanoparticles containing 94.6 wt% Fe2O3 after the solution was treated at 190 °C for 6 h. Second, when the temperature was elevated to 270 °C, nearly 99% Al was isolated as boehmite particles containing 95.2 wt% Al2O3. Third, more than 98% Ca was removed as anhydrite, which contained 95.9 wt% CaSO4, by adding sulfuric acid. During the steps, the total loss of Zn was less than 3%, and 5.75 g/L of residual Zn was recovered as zincite containing 92.2 wt% ZnO by adjusting the pH to 8. The dissolved Fe, Al, and Ca impurities were successfully removed as purified hematite, boehmite, and anhydrite, respectively, through the stepwise separation method by adjusting reaction temperatures and pH. The high content of Zn in the electroplating sludge was finally purified as zincite.

Bactericidal efficiency and photochemical mechanisms of micro/nano bubble-enhanced visible light photocatalytic water disinfection.

Microbial contamination of water in the form of highly-resistant bacterial spores can cause a long-term risk of waterborne disease. Advanced photocatalysis has become an effective approach to inactivate bacterial spores due to its potential for efficient solar energy conversion alongside reduced formation of disinfection by-products. However, the overall efficiency of the process still requires significant improvements. Here, we proposed and evaluated a novel visible light photocatalytic water disinfection technology by its close coupling with micro/nano bubbles (MNBs). The inactivation rate constant of Bacillus subtilis spores reached 1.28 h-1, which was 5.6 times higher than that observed for treatment without MNBs. The superior performance for the progressive destruction of spores' cells during the treatment was confirmed by transmission electron microscopy (TEM) and excitation-emission matrix (EEM) spectra determination. Experiments using scavengers of reactive oxygen species (ROSs) revealed that H2O2 and •OH were the primary active species responsible for the inactivation of spores. The effective supply of oxygen from air MNBs helped accelerate the hole oxidation of H2O2 on the photocatalyst (i.e. Ag/TiO2). In addition, the interfacial photoelectric effect from the MNBs was also confirmed to contribute to the spore inactivation. Specifically, MNBs induced strong light scattering, consequently increasing the optical path length in the photocatalysis medium by 54.8% at 700nm and enhancing light adsorption of the photocatalyst. The non-uniformities in dielectricity led to a high-degree of heterogeneity of the electric field, which triggered the formation of a region of enhanced light intensity which ultimately promoted the photocatalytic reaction. Overall, this study provided new insights on the mechanisms of photocatalysis coupled with MNB technology for advanced water treatment.

Cu transport and distribution in different cellular fractions of Klebsiella oxytoca strain CAV 1374.

This study elucidated copper (Cu) transport and trafficking mechanisms at the cellular interface using the Cu-resistant strain Klebsiella oxytoca CAV 1374. The optimum conditions for biosorption were determined by investigating uptake rates due to initial pH, initial Cu concentrations, and maximum tolerated concentrations (MTC) of Cu. Cellular fraction analysis and depth-profiling XPS were used to comprehensively evaluate the spatial-temporal distribution of Cu on cellular interfaces during biosorption. Potential uptake mechanisms were then further examined by biosorption kinetics analyses, ion exchange experiments, FTIR analysis, and K+ channel blocking experiments. The results indicated that Cu was primarily absorbed by extracellular polymeric substances through chemical interactions and little Cu penetrated inside cells under low Cu stress conditions (≤20 mg/L). In contrast, an intracellular rate-controlling physical interaction was predominant under high Cu stress conditions (≥30 mg/L). Further, Cu2+ could be bound by functional groups, followed first by replacement of Ca2+ at the cell surface. Subsequently, some of the Cu2+ in cell walls was reduced to Cu+, and only Cu+ could then penetrate into cell membranes. These results indicate that strain Klebsiella oxytoca CAV 1374 is a suitable biosorbent agent for Cu removal and can provide critical insights into Cu-uptake mechanisms of microorganisms.

Enhanced Photocatalytic Water Decontamination by Micro-Nano Bubbles: Measurements and Mechanisms.

Despite recent advancements in photocatalysis enabled by materials science innovations, the application of photocatalysts in water treatment is still hampered due to low overall efficiency. Herein, we present a TiO2 photocatalytic process with significantly enhanced efficiency by the introduction of micro-nano bubbles (MNBs). Notably, the removal rate of a model organic contaminant (methylene blue, MB) in an air MNB-assisted photocatalytic degradation (PCD) process was 41-141% higher than that obtained in conventional macrobubble (MaB)-assisted PCD under identical conditions. Experimental observations and supporting mechanistic modeling suggest that the enhanced photocatalytic degradation is attributed to the combined effects of increased dissolution of oxygen, improved colloidal stability and dispersion of the TiO2 nanocatalysts, and interfacial photoelectric effects of TiO2/MNB suspensions. The maximum dissolved oxygen (DO) concentration of the MNB suspension (i.e., 11.7 mg/L) was 32% higher than that of an MaB-aerated aqueous solution (i.e., 8.8 mg/L), thus accelerating the hole oxidation of H2O on TiO2. We further confirmed that the MNBs induced unique light-scattering effects, consequently increasing the optical path length in the TiO2/MNB suspension by 7.6%. A force balance model confirmed that a three-phase contact was formed on the surface of the bubble-TiO2 complex, which promoted high complex stability and PCD performance. Overall, this study demonstrates the enhanced photocatalytic water decontamination by MNBs and provides the underlying mechanisms for the process.

Resource Recycling of Mn-Rich Sludge: Effective Separation of Impure Fe/Al and Recovery of High-Purity Hausmannite.

Groundwater treatment sludge is a Fe/Mn-rich waste generated in mass production in a groundwater treatment plant for potable water production. The conventional disposal of sludge, such as direct discharge into river/lake, sea, and landfill, is not environmentally sustainable. Herein, a novel method was proposed to effectively separate Fe/Al and recover Mn via a combined hydrochloric acid leaching and hydrothermal route. The sludge contained 14.6% Fe, 6.3% Mn, and 11.5% Al and was first dissolved in 5 M HCl to prepare a leaching solution. Second, the leaching solution was hydrothermally treated, in which 97.1% Fe and 94.8% Al were precipitated as hematite and boehmite and more than 98% Mn was kept. Increasing the reaction temperature to 270 °C was beneficial for Fe/Al removal. With the consumption of abundant H+, the reaction of added glucose and nitrate accelerated as the temperature increased. An optimal pH was utilized for Fe/Al hydrolysis and crystallization, leading to extensive removal of Fe/Al. Third, the residual solution was adjusted to pH 8.3 with NaOH, and approximately, 99.2% Mn was removed as hausmannite with a Mn content of 63.6%. This method exhibited efficient separation of impure Fe/Al from Mn-rich groundwater treatment plant iron mud, and the recycled high-purity hausmannite was a marketable active pharmaceutical ingredient.

An integrated approach using ozone nanobubble and cyclodextrin inclusion complexation to enhance the removal of micropollutants.

Ozone (O3) has been widely used for the elimination of recalcitrant micropollutants in aqueous environments, due to its strong oxidation ability. However, the utilization efficiency of O3 is constrained by its low solubility and short half-life during the treatment process. Herein, an integrated approach, using nanobubble technology and micro-environmental chemistry within cyclodextrin inclusion cavities, was studied in order to enhance the reactivity of ozonisation. Compared with traditional macrobubble aeration with O3 in water, nanobubble aeration achieved 1.7 times higher solubility of O3, and increased the mass transfer coefficient 4.7 times. Moreover, the addition of hydroxypropyl-ß-cyclodextrin (HPßCD) further increased the stability of O3 through formation of an inclusion complex in its molecule-specific cavity. At a HPßCD:O3 molar ratio of 10:1, the lifespan of O3 reached 18 times longer than in a HPßCD-free O3 solution. Such approach accelerated the removal efficiency of the model micropollutant, 4-chlorophenol by 6.9 times, compared with conventional macrobubble ozonation. Examination of the HPßCD inclusion complex by UV-visible spectroscopy and Nuclear Magnetic Resonance analyses revealed that both O3 and 4-chlorophenol entered the HPßCD cavity, and Benesi-Hildebrand plots indicated a 1:1 stoichiometry of the host and guest compounds. Additionally, molecular docking simulations were conducted in order to confirm the formation of a ternary complex of HPßCD:4-chlorophenol:O3 and to determine the optimal inclusion mode. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of organic micropollutants.