A novel insight of degradation ibuprofen in aqueous by catalytic ozonation with supported catalyst: Supports effect on ozone mass transfer.

Catalytic ozonation is an effective wastewater purification process. However, the low ozone mass transfer in packed bubble columns leads to low ozone utilization efficiency (OUE), poor organic degradation performance, and high energy consumption. Therefore, there is an urgent need to develop efficient supported catalysts that can enhance mass transfer and performance. However, the reaction mechanism of the support on ozone mass transfer remains unclear, which hinders the development of catalytic ozonation applications. In this study, lava rocks (LR)-supported catalysts, specifically CuMn2O4@LR and MnO2Co3O4@LR, were proposed for catalytic ozonation of IBP degradation due to their superior catalytic activity, stability, and high OUE. Addition of CuMn2O4@LR or MnO2Co3O4@LR increased IBP removal efficiency from 85% to 91% or 88%, and reduced energy consumption from 2.86 to 2.14 kWh/m3 or 2.60 kWh/m3, respectively. This improvement was attributed to LR-supported catalysts enhancing mass transfer and promoting O3 decomposition to generate •OH and •O2-, leading to IBP degradation. Furthermore, this study investigated the effects of ozone dose, supporter sizes, and catalyst components on ozone-liquid mass transfer. The results revealed that the size of the supporter influenced stacked porosity and consequently affected ozone mass transfer. Larger-sized LR (kLa= 0.172 min-1) exhibited better mass transfer compared to smaller-sized supports. Based on these findings, it was concluded that both CuMn2O4@LR and MnO2Co3O4@LR are potential catalysts for catalytic ozonation in residual IBP degradation of pharmaceutical wastewater, and LR showed good credibility as a catalyst supporter. Understanding the effects of supporters and active components on ozone mass transfer provides a fundamental principle for designing supported catalysts in catalytic ozonation applications.

Review: The application of source analysis methods in tracing urban non-point source pollution: categorization, hotspots, and future prospects.

The contribution of urban non-point source (NPS) pollution to surface water pollution has gradually increased, analyzing the sources of urban NPS pollution is of great significance for precisely controlling surface water pollution. A bibliometric analysis of relevant research literature from 2000 to 2021 reveals that the main methods used in the source analysis research of urban NPS pollution include the emission inventory approach, entry-exit mass balance approach, principal component analysis (PCA), positive matrix factorization (PMF) model, etc. These methods are primarily applied in three aspects: source analysis of rainfall-runoff pollution, source analysis of wet weather flow (WWF) pollution in combined sewers, and analysis of the contribution of urban NPS to the surface water pollution load. The application of source analysis methods in urban NPS pollution research has demonstrated an evolution from qualitative to quantitative, and further towards precise quantification. This progression has transitioned from predominantly relying on on-site monitoring to incorporating model simulations and employing mathematical statistical analyses for traceability. This paper reviews the principles, advantages, disadvantages, and the scope of application of these methods. It also aims to address existing problems and analyze potential future development directions, providing valuable references for subsequent related research.

Contribution of filtration and photocatalysis to DOM removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane process.

The use of ceramic membranes and ultraviolet light-emitting diodes (UV-LEDs) has advanced the application of photocatalytic membrane for water treatment. We systematically evaluated the contribution of filtration and photocatalysis to dissolved organic matter (DOM) removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane filtration. The results showed that physical rejection primarily led to removal of 4-15 kDa molecules and photocatalysis further increased the removal of 1-4 kDa molecules, causing small sized microbial humic-like or protein-like materials in the permeate. In-situ UV-LED photocatalysis had an excellent effect on membrane fouling mitigation regardless of DOM sources. The dominant fouling mechanism changed from partial blockage to gel layer formation with increasing Ca2+ concentration but did not change with UV treatment. Correlation analysis revealed that the removal of 1-4 kDa molecules contributed to the mitigation of both reversible and irreversible fouling resistance, and the small molecules were the major cause of irreversible fouling resistance. Removal of 1-4 kDa terrestrial humic acid-like contributed to the pore blockage mechanism for synthetic water. Removal of 4-15 kDa protein-like materials was closely correlated to the pore blockage mechanism for real water. Trihalomethanes (THMs) and haloacetic acids (HAAs) formation potential (FP) were both significantly reduced after photocatalytic ceramic membrane process, but precursors of nitrogenous disinfection by-products (N-DBPs) with high toxicity were not removed by filtration or by photocatalysis, which deserves attention. Membrane rejection made higher contribution to better DBPFP control than photocatalysis. This study provides novel insights into the impact of UV-LED on DOM removal, DBPFP control and fouling mitigation, promoting the development of photocatalytic ceramic membrane filtration.

Interfacial reactions of catalytic ozone membranes resulting in the release and degradation of irreversible foulants.

An efficient in-situ self-cleaning catalytic ceramic-membrane tailored with MnO2-Co3O4 nanoparticles (Mn-Co-CM) was fabricated. Density functional theory calculations result substantiated that molecular ozone could be effectively adsorbed by oxygen vacancies (OV) on the Mn-Co-CM surface and then direct activated into a surface-bound atomic oxygen (*Oad) and a peroxide (*O2, ad), ultimately producing ·OH. Mn-Co-CM coupling with ozone efficiently removed foulants from the permeate and the membrane surface simultaneously and leading to in-situ formation of ·OH that changed the nature of the irreversible foulants and ultimately resulted in the rapid release and degradation of humic acid-like substances causing irreversible fouling. However, the commercial CM with ozone mainly removed cake layer fouling including protein-like and fulvic acid-like substances, followed by the slow release and degradation of irreversible foulant, resulting in many humic acid-like substances remain on the membrane surface as irreversible fouling. Based on these, the flux growth rate of Mn-Co-CM was 3.5 times higher than that of CM with ozone. This study provides new insights into the mechanism of in-situ membrane fouling mitigation, when using an efficient catalytic ceramic-membrane. This will facilitate the development of membrane antifouling strategies.

Novel insights into the interaction reactive components and synergistic fouling mechanisms of ultrafiltration by natural organic matter fractions and kaolin.

The mechanisms governing interactions among various natural organic matter (NOM) fractions and the subsequently impact on ultrafiltration process have not been systematically studied. In this work, bovine serum albumin (BSA), humic acid (HA), sodium alginate (SA) were applied as model NOM to explore the influence of the interactions among NOM on ultrafiltration process. Results indicated that tryptophan-like fluorescence fraction was the dominant reaction fraction of HA to react with SA and BSA. Different interactions among model NOM not only changed the interception order of fluorescence fractions by ultrafiltration from fulvic acid-like, humic-like and tryptophan-like in BSA/HA mixture to tryptophan-like, humic-like and fulvic acid-like in BSA/HA/SA/kaolin mixture, but also remarkably influence the membrane fouling behavior. In BSA/HA mixture, new-generated aggregates with molecular weight (MW) of 10 kDa could not pass though ultrafiltration membrane and mainly contributed to chemical reversible fouling. In BSA/HA/SA mixture, SA simultaneously reacted with BSA and HA to generate aggregates with larger MW which could be washed down by physical cleaning. In BSA/HA/SA/kaolin mixture, the aggregates with MW of 10 kDa and chemical reversible fouling were disappeared due to the adsorption role of kaolin. These findings could further improve our understanding regarding membrane fouling mechanisms of raw water with different components.

Two-dimensional layered carbon-based catalytic ozonation for water purification: Rational design of catalysts and an in-depth understanding of the interfacial reaction mechanism.

This review renewed insight into the existing complex and contradictory mechanisms of catalytic ozonation by two-dimensional layered carbon-based materials (2D-LCMs) for degradation toxic refractory organics in aqueous solution. Migration and capture of active electrons are central to catalytic ozonation reactions, which was not studied or reviewed more clearly. Based on this perspective, the catalytic ozonation potential of 2D-LCMs synthesized by numerous methods is firstly contrasted to guide the design of subsequent carbon based-catalysts, and not limited to 2D-LCMs. Matching ROS to active sites is a key step in understanding the catalytic mechanism. The structure-activity relationships between reported numerous active sites and ROS evolution is then constructed. Result showed that OH could be produced by -OH, -C=O, -COOH groups, defective sites, immobilized metal atoms, doped heteroatoms and photo-induced electrons; and O2- could be produced by -OH groups and sp2-bonded carbon. The normalized model further be used to visually compare the contribution degree of various regulatory methods to performance improvement. More importantly, this review calls for 2D-LCMs-based catalytic ozonation to be studied without circumventing the issue of structural stability, which would lead to many proposals of catalysts and its involved catalytic reaction mechanism being meaningless.

Energy-efficient removal of carbamazepine in solution by electrocoagulation-electrofenton using a novel P-rGO cathode.

In this study, carbamazepine (CBZ) decay in solution has been studied by coupling electrocoagulation with electro-Fenton (EC-EF) with a novel P-rGO/carbon felt (CF) cathode, aiming to accelerate the in-situ generation of •OH, instead of adding Fe2+ and H2O2. Firstly, the fabricated P-rGO and its derived cathode were characterized by XRD, SEM, AFM, XPS and electrochemical test (EIS, CV and LSV). Secondly, it was confirmed that the performance in removal efficiency and electric energy consumption (EEC) by EC-EF (kobs=0.124 min-1, EEC=43.98 kWh/kg CBZ) was better than EF (kobs=0.069 min-1, EEC=61.04 kWh/kg CBZ). Then, P-rGO/CF (kobs=0.248 min-1, EEC=29.47 kWh/kg CBZ, CE=61.04%) showed the best performance in EC-EF, among all studied heteroatom-doped graphene/CF. This superior performance may be associated with its largest layer spacing and richest C=C, which can promote the electron transfer rate and conductivity of the cathode. Thus, more H2O2 and •OH could be produced to degrade CBZ, and almost 100% CBZ was removed with kobs being 0.337 min-1 and the EEC was only 24.18 kWh/kg CBZ, under the optimal conditions (P-rGO loading was 6.0 mg/cm2, the current density was 10.0 mA/cm2, the gap between electrode was 2.0 cm). Additionally, no matter the influent is acidic, neutral or alkaline, no additional pH adjustment is required for the effluent of EC-EF. At last, an inconsecutive empirical kinetic model was firstly established to predict the effect of operating parameters on CBZ removal.

How do urban rainfall-runoff pollution control technologies develop in China? A systematic review based on bibliometric analysis and literature summary.

Rapid urbanization in China is driving the need of urban rainfall-runoff pollution control technologies due to adverse impacts on water environment. In this study, literature from China National Knowledge Infrastructure, Web of Science and Scopus in 1995/1/1-2019/5/15 are used to review research hotspots, development process and future directions of urban rainfall-runoff pollution control technologies in China and global world. Temporal evolution of publications showed that source reduction played better growing trend in urban rainfall-runoff pollution control field for both China and global world. Furthermore, with bibliometric tool, density visualization maps and co-occurrence network maps were created to identify research hotspots in China and global world. By comprehensively analyzing research hotspots above and development process from extracted literature, future directions of urban rainfall-runoff pollution control technologies were predicted. For model and strategy, both China and global world would concern on the accuracy of models to evaluate combination technologies. For source reduction, China would explore rainwater purification in sponge city, while global world would investigate match characteristics between specific regions and control technologies, combination between model and technologies, and improvement of pollutants removal. For process control, China would enhance ecological gutter inlet performance, whereas global world would concentrate on optimization of rainwater harvesting system. For post treatment, China would estimate modified hydrocylone and coagulation technology, and improve performance of filtration systems, riparian buffers and constructed wetlands, while global world would explore ecological and landscape function of constructed wetlands. Since China ranked first in producing Western publications and was the second most cited country for Western publications recently, China would significantly influence future development of urban rainfall-runoff pollution control technologies around the world. Meanwhile, some directions including infiltration basin and rainwater harvesting system were still shortcomings for China due to a late start of urban rainfall-runoff pollution control technologies in China.

Effects of side-stream operation on the mainstream biological phosphorus metabolic pathway for phosphorus recovery: Simulation by an extended ASM2d model.

An extended activated sludge model (E-ASM2d) was established by including the metabolic processes of double-layer extracellular polymeric substances (EPS) and glycogen-accumulating organisms (GAOs) into the existing ASM2d model for describing and predicting the metabolic processes of the side-stream phosphorus (P) recovery reactor. A sensitivity analysis of model parameters on SPO4(soluble phosphate), XLEPS (loosely-bound EPS), XTEPS (tightly-bound EPS), COD, and SNH4 (soluble ammonia nitrogen) outputs was conducted for identifying influential parameters. The predicted effluent values of COD, ammonia nitrogen (NH4), and P corresponded well with actual measured values and all the model performance coefficient values for COD, NH4, and P were higher than 0.65, implying the E-ASM2d model could accurately simulate the metabolic processes of the side-stream P recovery process under different COD:P ratio conditions. The variations in the mainstream biological P metabolic pathway under different COD:P conditions were investigated by the E-ASM2d model. At COD:P ratios of 30, 20, and 10, the values of fPP,TEPS (fraction of XTEPS in polyphosphate metabolic process) increased from 0.092, 0.094, and 0.096 in the initial phase to 0.107, 0.124, and 0.187 in the side-stream phase, respectively, demonstrating that the fraction of P removal by tightly-bound EPS was improved by the side-stream operation.

FeS2/carbon felt as an efficient electro-Fenton cathode for carbamazepine degradation and detoxification: In-depth discussion of reaction contribution and empirical kinetic model.

Carbamazepine (CBZ) decay by electro-Fenton (EF) oxidation using a novel FeS2/carbon felt (CF) cathode, instead of a soluble iron salt, was studied with the aim to accelerate the reaction between H2O2 and ferrous ions, which helps to produce more hydroxyl radicals (•OH) and eliminate iron sludge. First, fabricated FeS2 and its derived cathode were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Anodes were then screened, with DSA (Ti/IrO2-RuO2) showing the best performance under EF oxidation regarding CBZ degradation and electrochemical characterization. Several operating parameters of this EF process, such as FeS2 loading, current density, gap between electrodes (GBE), initial [CBZ], and electrolyte type, were also investigated. Accordingly, a nonconsecutive empirical kinetic model was established to predict changes in CBZ concentration under the given operational parameters. The contribution of different oxidation types to the EF process was calculated using kinetic analysis and quenching experiments to verify the role of the FeS2-modified cathode. The reaction contributions of anodic oxidation (AO), H2O2 electrolysis (EP), and EF oxidation to CBZ removal were 12.81%, 7.41%, and 79.77%, respectively. The •OH exposure of EP and EF oxidation was calculated, confirming that •OH exposure was approximately 22.45-fold higher using FeS2-modified CF. Finally, the 19 intermediates formed by CBZ degradation were identified by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Accordingly, four CBZ degradation pathways were proposed. ECOSAR software was used to assess the ecotoxicity of intermediates toward fish, daphnia, and green algae, showing that this novel EF oxidation process showed good toxicity reduction performance. A prolonged EF retention time was proposed to be necessary to obtain clean and safe water, even if the targeted compound was removed at an earlier time.

Occurrence and risk assessment of volatile halogenated disinfection by-products in an urban river supplied by reclaimed wastewater.

The reuse of the sewage is an effective way to solve the shortage of water resources, but disinfection by-products (DBPs) caused by chlorination may bring potential ecological and health risks to the supplied water. In this study, the occurrence and potential ecological risk of DBPs in SH River in Beijing were evaluated. Four kinds of DBPs were detected in 84 samples by GC-MS, including THM, CH, CTC and TCAN, whose detection rates were 100%, 100%, 100% and 2.38%, respectively. Combining with the relevant standard limitation and corresponding threshold values in China, and the reported concentration in domestic and foreign literatures, the results showed that the number of samples which [THM], [CTC] and [CH] exceeded the threshold values in relevant standard for 23.81%, 100.00% and 89.29%, respectively. CTC showed the highest excess times than the threshold value with [CTC]max was 356.46 µg/L. In addition, the temporal and spatial characteristics of identified DBPs were studied. [THM], [CTC] and [CH] all exhibited the highest concentration in Aug., which was as the same as the variation trend of air and water temperature. With the increase of sampling distance, [THM] and [CTC] fluctuated greatly, and the background values in SH River were higher due to the supplement of the reclaimed water. [CH] and [TCAN] gradually decreased, which may be due to that they were more prone to volatilize in the channel and be degraded by aquatic microorganisms. In addition, the occurrence situation in S2 and S7, were in the order of CTC > CH > THM. Hence, the rank of the occurrence situation of identified DBPs was CTC > CH > THM > TCAN. Multivariate analysis showed that THM was significantly positively correlated with CTC and their sources were similar. Moreover, they were all affected by solution pH and DO. Potential ecological risk assessment indicated that the rank of identified DBPs ecological risk was CTC > THM > CH > TCAN. Among them, the risk level of CTC and THM were high in both daily and extreme situations. Therefore, the potential ecological risk caused by DBPs should be fully considered in the process of reclaimed water supplying landscape water, such as urban river. If a higher level of the ecological risk management is needed, THM, CTC and CH, especially CTC, should be considered firstly.

Synchronous degradation of aqueous benzotriazole and bromate reduction in catalytic ozonation: Effect of matrix factor, degradation mechanism and application strategy in water treatment.

Ozone-based technologies are used for micro-pollutants removal in wastewater treatment. However, the generation of the toxic by-product bromate (BrO3-) is of a great concern. LaCoO3 (LCO) catalytic ozonation has been used to overcome this significant drawback in the sole ozonation, achieving better BrO3- elimination efficiency. However, a key challenge is how to enhance micro-pollutant (benzotriazole, BZA) degradation efficiency and to eliminate formed BrO3- synchronously under various water qualities in drinking water or wastewater treatment. Therefore, the objective of this study is to propose a practical strategy of BZA removal and BrO3- reduction synchronously in water or wastewater treatment. In this study, important factors influencing BZA removal and BrO3- reduction were investigated, including [catalyst], [BZA], initial pH solution, [NH4+-N] and [(bi)carbonate alkalinity]. Based on the performance and mechanism of these effects, a practical strategy for BZA degradation and BrO3- elimination with and without Br- in the influent was developed. Additionally, the density functional theory (DFT) calculation successfully predicted the attack site on BZA by molecular ozone and formed hydroxyl radical (HO·) during LCO catalytic ozonation. Fukui indexes of f+ and f0 were calculated to forecast direct ozone molecule and HO· attack, respectively. Combination of DFT calculation with intermediates that identified through liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS), BZA degradation pathway was established more accurately. Additionally, four new intermediates were identified in this study. Overall, this study proposes a useful strategy for synchronous micro-pollutants degradation and BrO3- elimination, while also suggesting the feasibility of LCO catalytic ozonation for water or wastewater purification.

Effect of Al species of polyaluminum chlorides on floc breakage and re-growth process: Dynamic evolution of floc properties, dissolved organic matter and dissolved Al.

Influence of floc breakage and re-growth on the release of natural dissolved organic matter (DOM) and dissolved Al was explored. Results indicated that Al species including monomeric species (Ala), medium polymer species (Alb), and colloidal or solid species (Alc) in polyaluminum chlorides (PACls) played significant role. At lower doses ranged from 5 to 20 mg/L, floc breakage damaged Ala-NOM bonds for AlCl3, causing obvious release of DOM and dissolved Al. After re-growth, dissolved Al mainly connected with broken flocs, rather than released DOM. Thus, after re-growth, DOM release was still remarkable, but additional removal of dissolved Al was observed. At higher doses above 20 mg/L, more Ala transformed to Alb and Alc. Due to the enmeshment effect induced by Alc coagulation, fewer DOM and dissolved Al were released after breakage, and additional removal of DOM and dissolved Al were attained after re-growth. For PAClAl13 which mainly contained Alb, at optimal dose, floc breakage generated the most severe release of DOM and dissolved Al, while the result after re-growth was just reverse. This was ascribed to stronger charge neutralization ability of Alb. Furthermore, the influence of floc breakage and re-growth on DOM and dissolved Al for PAClC was similar to that for AlCl3. The reason was fully analyzed in this research. This study may give further indication regarding reaction mechanisms of floc breakage and re-growth for PACls.

Quantitative analysis of cake characteristics based on SEM imaging during coagulation-ultrafiltration process.

Cake formed by flocs is a crucial factor to affect membrane fouling during coagulation-ultrafiltration process. To investigate the role of floc properties on cake, cake characteristics under various coagulant dosage conditions were calculated by scanning electron microscope (SEM) imaging. Results found that one SEM image with × 5000 magnification could accurately estimate cake porosity with relative error lower than 5.00% for all conditions, whereas more SEM images with × 10,000 magnification or × 20,000 magnification should be applied to calculate cake porosity precisely. This could be explained by different pore information of SEM images with various magnifications. Compared to single SEM image with × 10,000 magnification and × 20,000 magnification, single SEM image with × 5000 magnification contained the most comprehensive pore information and slightly overestimated pore area for pore smaller than 0.4 µm2 due to lower resolution. To verify feasibility by SEM image evaluating cake characteristics, cake porosity calculated by SEM image and Carman-Kozeny equation were analyzed. The results showed that cake porosity estimated by these two methods were nearly the same, proving the feasibility of this method. Moreover, with the increase of coagulant dosage, cake porosity presented similar variation with floc average size, indicating that floc average size was likely to dominate cake porosity in this study. For pore characteristics, pore average characteristic length and pore average area were in accordance with floc fractal dimension, whereas pore fractal dimension and pore amount were consistent with floc average size. This gives specific information about the relation between floc properties and cake characteristics.

Study on the efficiency of ultrafiltration technology in dealing with sudden cadmium pollution in surface water and ultrafiltration membrane fouling.

In this paper, the application of ultrafiltration (UF) technology to treat cadmium (Cd) pollution in surface waters is investigated. The effect of the UF membrane molecular weight cut-off (MWCO), Cd ion (Cd2+) concentration, solution pH and ionic strength on the removal, and mass balance of Cd were explored. In addition, the effect of the solution pH on UF membrane fouling was analyzed. The results indicated that UF membranes with a low MWCO resulted in an improved Cd removal rate. In addition, as the Cd2+ concentration in feedwater increased, the Cd removal rate decreased, while the Cd concentration in the permeate increased. Since the solution pH and ionic strength had a notable impact on the Cd removal rate, a high pH value and low ionic strength led to a higher removal rate of Cd. Under optimal Cd removal conditions, UF reduced the influent Cd concentration from 1.0 to 0.019 mg/L. For membrane fouling, increasing the solution pH led to more serious membrane fouling. This phenomenon was the result of Cd2+ reacting with OH- and forming a Cd (OH)2 precipitate. The precipitate and humic acid formed compact cakes on the membrane surface and blocked membrane pores. These results provided adequate evidence for the higher removal of Cd with increasing solution pH. In addition, SEM images under different pH conditions were in agreement with the conclusion mentioned above, which provided further support for the effect of the solution pH on Cd removal and membrane fouling.

Effect of the micro-flocculation stage on the flocculation/sedimentation process: The role of shear rate.

Dynamic analysis on the variation of particle size distribution (PSD) and the fractal characteristics of PSD (Df) were investigated to better understand the continuous procedure of the floc growth and optimize the control of flocculation process. It was found that the flocculation process could be divided into three stages, i.e., the micro-flocculation stage, the growth stage and the steady (or breakage) stage. As the stage which is crucial to the morphology of micro-flocs (the building blocks of large flocs), the micro-flocculation stage plays an important role on flocculation/sedimentation process. The results showed that an increase in shear rate (11s-1

Characterization of re-grown floc size and structure: effect of mixing conditions during floc growth, breakage and re-growth process.

The impact of mixing speed in three stages-before breakage, during breakage, and after breakage-on re-grown floc properties was investigated by using a non-intrusive optical sampling and digital image analysis technique, respectively. And then, on the basis of different influence extent of mixing speed during each stage on size and structure of re-grown flocs, coagulation performance with varying mixing speed was analyzed. The results indicated that the broken flocs could not re-grow to the size before breakage in all cases. Furthermore, increasing mixing intensity contributed to the re-formation of smaller flocs with higher degree of compactness. For slow mixing before breakage, an increase in mixing speed had less influence on re-grown floc properties due to the same breakage strength during breakage, resulting in inconspicuous variation of coagulation efficiency. For rapid mixing during breakage, larger mixing speed markedly decreased the coagulation efficiency. This could be attributed that mixing speed during breakage generated greater influence on re-grown floc size. However, as slow mixing after breakage was elevated, the coagulation efficiency presented significant rise, indicating that slow mixing after breakage had more influence on re-grown floc structure upon re-structuring and re-arrangement mechanism.

Breakage and regrowth of flocs formed by sweep coagulation using additional coagulant of poly aluminium chloride and non-ionic polyacrylamide.

The breakage and regrowth of flocs formed by sweep flocculation were investigated on different flocculation mechanisms using additional dosage coagulant of poly aluminium chloride (PACl) and non-ionic polyacrylamide (PAM) to explore the reversibility after floc breakage. The optimal dosage of PACl was 0.15 mM (as alum), and zeta potential exceeding 1 mV meant that sweep flocculation was dominant in the pre-flocculated process. Re-coagulation efficiency increased with additional coagulants dosing, and sedimentation rates of flocs re-formed by small additional dosage of non-ionic PAM are faster than that of flocs re-formed by additional PACl. For additional inorganic coagulant (PACl) during regrowth processes, few negatively charged particles that existed in water sample restricted the effect of charge neutralization. An amorphous aluminum hydroxide precipitation could re-activate the weaker points on the broken floc surface, but regrown flocs have loose structure indicating worse settleability. For additional non-ionic PAM dosing, lower dosage showed large values of fractal dimension and average size, probably due to that unfolded curly molecular chain and exposed amide groups of non-ionic PAM which provide superb conditions for amide group interacting with particles. The use of non-ionic PAM in flocculation has advantage of being more effective than the cationic PACl, probably because it may avoid the re-stabilization of broken flocs by polymer adsorption driven by electrostatic attraction. Hence, appropriate dosing of PAM after breakage could improve the flocs characteristics with large size and compact structure.

Experimental and numerical characterization of floc morphology: role of changing hydraulic retention time under flocculation mechanisms.

The formation, breakage, and re-growth of flocs were investigated by using modified flocculation tests and numerical simulation to explore the evolution of floc morphology for different hydraulic retention times. The shorter the aggregation time was, the smaller the flocs produced for the same hydraulic conditions were. Another interesting discovery was that broken flocs that formed in shorter aggregation time had the capacity to completely recover, whereas those formed in a longer amount of time had rather worse reversibility of broken flocs. With the addition of the maximum motion step in the representative two-dimensional diffusion-limited aggregation (DLA) model, there was a transition for flocs from isotropic to anisotropic as the maximum motion step increased. The strength of flocs was mainly affected by the distribution of particles near the aggregated core rather than distant particles. A simplified breakage model, which found that broken flocs provided more chances for diffused particles to access the inner parts of flocs and to be uniformly packed around the aggregated core, was first proposed. Moreover, an important result showed that the floc fragments formed with a larger value of the maximum motion step had more growing sites than did those with a smaller msa value, which was a benefit of following the re-forming procedure.

Evaluation of emulsion electrospun polycaprolactone/hyaluronan/epidermal growth factor nanofibrous scaffolds for wound healing.

Wound healing scaffolds provide cells with structural integrity and can also deliver biological agents to establish a skin tissue-specific microenvironment to regulate cell functions and to accelerate the healing process. In this study, we fabricated biodegradable nanofibrous scaffolds with an emulsion electrospinning technique. The scaffolds were composed of polycaprolactone, hyaluronan and encapsulating epidermal growth factor. The morphology and core-sheath structure of the nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. The scaffolds were also characterized for chemical composition and hydrophilicity with a Fourier-transform infrared analysis, energy dispersive spectroscopy and the water contact angle. An in vitro model protein bovine serum albumin and epidermal growth factor release study was conducted to evaluate the sustained release potential of the core-sheath structured nanofibers with and without the hyaluronan component. Additionally, an in vitro cultivation of human skin keratinocytes (HaCaT) and fibroblasts on polycaprolactone/hyaluronan and polycaprolactone/hyaluronan-epidermal growth factor scaffolds showed a significant synergistic effect of hyaluronan and epidermal growth factor on cell proliferation and infiltration. Furthermore, there was an up-regulation of the wound-healing-related genes collagen I, collagen III and TGF-ß in polycaprolactone/hyaluronan/epidermal growth factor scaffolds compared with control groups. In the full-thickness wound model, the enhanced regeneration of fully functional skin was facilitated by epidermal regeneration in the polycaprolactone/hyaluronan/epidermal growth factor treatment group. Our findings suggest that bioactivity and hemostasis of the hyaluronan-based nanofibrous scaffolds have the capability to encapsulate and control the release of growth factors that can serve as skin tissue engineering scaffolds for wound healing.