Biodegradable Chitosan-Based Membranes for Highly Effective Separation of Emulsified Oil/Water.

Efficient separation of oil droplets from oil/water emulsions is necessary for many energy and food industrial processes and for industrial wastewater treatment. Membrane microfiltration has been explored to address this issue because it is simple to operate and low in cost. However, filtration of oil droplets with a size around or less than 1 µm is still a major challenge. Furthermore, the fabrication process for polymeric membranes often uses hazardous organic solvents and petroleum-derived and nonbiodegradable raw materials, which pose additional environmental health and safety risk. In this study, we examined the use of chitosan-based membranes to efficiently remove oil droplets with an average diameter of ∼1 µm. The membranes were fabricated based on the rapid dissolution of chitosan in an alkaline/urea solvent system at a low temperature, thus avoiding the use of any toxic organic solvent. The chitosan membranes were further modified by dopamine and tannic acid (TA). The as-prepared membrane was characterized in terms of surface morphology, pore size distribution, and mechanical strength. The membrane performance was evaluated on a custom-designed crossflow filtration system. The results showed that the modified chitosan membrane with dopamine and TA had a water flux of 230.9 LMH at 1bar transmembrane pressure and oil droplet rejection of 99%. This water flux represented an increase of more than 10 times when compared with the original chitosan membrane without modification. The study also demonstrated excellent antifouling properties of the modified membrane that could achieve near 100% water flux recovery.

Tailoring Polyamide Rejection Layer with Aqueous Carbonate Chemistry for Enhanced Membrane Separation: Mechanistic Insights, Chemistry-Structure-Property Relationship, and Environmental Implications.

Surface roughness and the associated nanosized voids inside the roughness structures have great influence on the separation performance of thin film composite polyamide reverse osmosis (RO) membranes. Inspired by the recent findings that these voids are formed due to the degassing of CO2 nanobubbles during interfacial polymerization, we systematically investigated the role of carbonate chemistry, particularly the solubility of CO2, in the aqueous m-phenylenediamine (MPD) solution for the first time. "Ridge-and-valley" roughness features were obtained when the pH of the MPD solution was between the two acidity constants of the carbonate system (i.e., 6.3 ≤ pH ≤ 10.3), under which condition HCO3- dominates over the other carbonate species. Increasing pH over this range led to both increased water permeability and better rejection of various solutes, thanks to the simultaneously enhanced effective filtration area and cross-linking degree of the polyamide layer. Further increase of pH to 12.5 resulted in more disparate rejection results due to membrane hydrolysis: rejection of neural solutes (B and As(III)) was compromised whereas that of charged solutes (NaCl and As(V)) was maintained. The mechanistic insights gained in the current study reveal the critical need to design RO membranes directly for end applications based on first principles.

Physico-Chemical Processes.

This review is on the research literature published in 2016 related to the physico-chemical processes for water and wastewater treatment. The review is divided into granular and membrane filtration, sedimentation, coagulation/flocculation, flotation, oxidation, and adsorption.

Co-adsorption of Trichloroethylene and Arsenate by Iron-Impregnated Granular Activated Carbon.

Co-adsorption of trichloroethylene (TCE) and arsenate [As(V)] was investigated using modified granular activated carbons (GAC): untreated, sodium hypochlorite-treated (NaClO-GAC), and NaClO with iron-treated GAC (NaClO/Fe-GAC). Batch experiments of single- [TCE or As(V)] and binary- [TCE and As(V)] components solutions are evaluated through Langmuir and Freundlich isotherm models and adsorption kinetic tests. In the single-component system, the adsorption capacity of As(V) was increased by the NaClO-GAC and the NaClO/Fe-GAC. The untreated GAC showed a low adsorption capacity for As(V). Adsorption of TCE by the NaClO/Fe-GAC was maximized, with an increased Freundlich constant. Removal of TCE in the binary-component system was decreased 15% by the untreated GAC, and NaClO- and NaClO/Fe-GAC showed similar efficiency to the single-component system because of the different chemical status of the GAC surfaces. Results of the adsorption isotherms of As(V) in the binary-component system were similar to adsorption isotherms of the single-component system. The adsorption affinities of single- and binary-component systems corresponded with electron transfer, competitive adsorption, and physicochemical properties.

Physico-Chemical Processes.

This review is on the research literature published in 2015 related to the physico-chemical processes for water and wastewater treatment. The review is divided into six sections, including filtration, sedimentation, coagulation/flocculation, flotation, oxidation, and adsorption.

Reducing arsenic accumulation in rice grain through iron oxide amendment.

Effects of soil-arsenic (As), phosphorus and iron oxide on As accumulation in rice grain were investigated. Cultivars that have significantly different sensitivity to As, straighthead-resistant Zhe 733 and straighthead-susceptible Cocodrie, were used to represent different cultivar varieties. The grain accumulation of other elements of concern, selenium (Se), molybdenum (Mo), and cadmium (Cd) was also monitored. Results demonstrated that high soil-As not only resulted in high grain-As, but could also result in high grain-Se, and Zhe 733 had significantly less grain-As than Cocodrie did. However, soil-As did not impact grain-Mo and Cd. Among all elements monitored, iron oxide amendment significantly reduced grain-As for both cultivars, while the phosphate application only reduced grain-Se for Zhe 733. Results also indicated that cultivar type significantly impacted grain accumulation of all monitored trace elements. Therefore, applying iron oxide to As-contaminated land, in addition to choosing appropriate rice cultivar, can effectively reduce the grain accumulation of As.

Physico-Chemical Processes.

This review is on the research literature published in 2014 related to the physico-chemical processes for water and wastewater treatment. The review is divided into six sections, including coagulation/flocculation, filtration, sedimentation, oxidation, flotation, sorption process.

Preliminary Study on Multi-Scale Modeling of Asphalt Materials: Evaluation of Material Behavior through an RVE-Based Approach.

This study employs a microstructure-based finite element modeling approach to understand the mechanical behavior of asphalt mixtures across different length scales. Specifically, this work aims to develop a multi-scale modeling approach employing representative volume elements (RVEs) of optimal size; this is a key issue in asphalt modeling for high-fidelity fracture modeling of heterogeneous asphalt mixtures. To determine the optimal RVE size, a convergence analysis of homogenized elastic properties is conducted using two types of RVEs, one made with polydisperse spherical inclusions, and another made with polydisperse truncated cylindrical inclusions, each aligned with the American Association of State Highway and Transportation Official's maximum density gradation curve for a 12.5 mm Nominal Maximum Aggregate Size (NMAS). The minimum RVE lengths for this NMAS were found to be in the range of 32-34 mm. After the optimal RVE size for each inclusion shape is obtained, computational models of heterogeneous Indirect Tensile Asphalt Cracking Test samples are then generated. These models include the components of viscoelastic mastic, linear elastic aggregates, and cohesive zone modeling to simulate the rate-dependent failure evolution from micro- to macro-cracking. Examination of load-displacement responses at multiple loading rates shows that both heterogeneous models replicate experimentally measured data satisfactorily. Through micro- and macro-level analyses, this study enhances our understanding of the composition-performance relationships in asphalt pavement materials. The procedure proposed in this study allows us to identify the optimal RVE sizes that preserve computational efficiency without significantly compromising their ability to capture the asphalt material behavior under specific operational conditions.

A two-sorbent system for fast uptake of arsenate from water: Batch and column studies.

There is a critical need to use decentralized and/or point-of-use systems to address some challenging water quality issues in society. Sorption-based approaches are uniquely suitable for such applications because of their simplicity in operation; however, the sorbents must possess fast contaminant uptake kinetics to overcome short hydraulic contact times often encountered in small systems. Here we designed a two-sorbent system consisting of Fe2O3-coated mesoporous carbon (FeMC) and nano-Fe2O3-coated activated carbon (FeAC) and demonstrated its ability to remove arsenate with a < 1 min empty bed contact time (EBCT) by a capture-and-storage process. Batch experiments showed rapid capture of arsenate by FeMC, likely occurred on the rod-like structures protruding to the liquid film. The captured arsenate could subsequently be relocated to FeAC for storage, which had a higher apparent sorption capacity. Column studies, operated with a 10 h running time followed by a 14 h pump-off time, showed that with a 102 µg-As/L influent concentration and at 0.85 min EBCT, the column treated 20,022 bed volumes until the 10 µg-As/L breakthrough, corresponding to a sorption density of 2.36 mg-As/g. This capture-and-storage technique resulted in a rapid and high-capacity arsenate removal through a combined effect of facile access to sorption sites on one sorbent and dynamic equilibrium in the two-sorbent system possessing a large total sorption capacity.

Impacts of acute and chronic suspended solids exposure on juvenile freshwater mussels.

Construction activities may affect adjacent water systems by introducing increased levels of suspended solids into the water body and may subsequently affect the survival and growth of freshwater mussels. We tested three sediment types from sites in Missouri, including Spring River sediment (SRS), Osage River bank clay soil (ORC), and quarried limestone from Columbia (LMT). We prepared series of suspensions of each sediment with total suspended solids concentrations ranging from 0 to 5000 mg/L. Juveniles from three mussel species, Fatmucket (Lampsilis siliquoidea), Arkansas Brokenray (Lampsilis reeveiana), and Washboard (Megalonaias nervosa) were exposed to these suspensions in both acute (96-h) and chronic (28-d) tests. No clear impact on survival was observed from the acute or chronic exposures, but chronic test showed that juvenile mussels' growth was strongly affected. Interestingly, growth was enhanced at lower levels of SRS and ORC (≤500 mg/L, p < 0.05), and the juvenile mussels exposed to 500 mg/L SRS exhibited approximately 60 % more dry weight than those reared in the control. LMT did not enhance growth. Growth was slowed by high concentrations (>1000 mg/L) of all three sediments, implying that high suspended solids levels could reduce survival in the long term. Our findings may help to inform regulations and guidelines for construction activities to minimize adverse effects on juvenile mussels.

Ligand-assisted degradation of carbon tetrachloride by microscale zero-valent iron.

Degradation of carbon tetrachloride (CT) by microscale zero-valent iron (ZVI) was investigated in batch systems with or without organic ligands (ethylenediaminetetraacetic acid (EDTA), citric acid, tartaric acid, malic acid and oxalic acid) at pHs from 3.5 to 7.5. The results demonstrated that at 25°C, the dechlorination of CT by microscale ZVI is slow in the absence of organic ligands, with a pseudo-first-order rate constant of 0.0217 h(-1) at pH 3.5 and being further dropped to 0.0052 h(-1) at pH 7.5. However, addition of organic ligands significantly enhanced the rates and the extents of CT removal, as indicated by the rate constant increases of 39, 31, 32, 28 and 18 times in the presence of EDTA, citric acid, tartaric acid, malic acid and oxalic acid, respectively, at pH 3.5 and 25°C. The effect of EDTA was most significant; the dechlorination of CT at an initial concentration of 20 mg l(-1) increased from 16.3% (no ligands) to 89.1% (with EDTA) at the end of 8h reaction. The enhanced CT degradation in the presence of organic ligands was primarily attributed to the elimination of a surface passivation layer of Fe(III) (hydr)oxides on the microscale ZVI through chelating of organic ligands with Fe(III), which maintained the exposure of active sites on ZVI surface to CT.

Medical, Health and Wellness Tourism Research-A Review of the Literature (1970-2020) and Research Agenda.

Medical, health and wellness tourism and travel represent a dynamic and rapidly growing multi-disciplinary economic activity and field of knowledge. This research responds to earlier calls to integrate research on travel medicine and tourism. It critically reviews the literature published on these topics over a 50-year period (1970 to 2020) using CiteSpace software. Some 802 articles were gathered and analyzed from major databases including the Web of Science and Scopus. Markets (demand and behavior), destinations (development and promotion), and development environments (policies and impacts) emerged as the main three research themes in medical-health-wellness tourism. Medical-health-wellness tourism will integrate with other care sectors and become more embedded in policy-making related to sustainable development, especially with regards to quality of life initiatives. A future research agenda for medical-health-tourism is discussed.

Enhanced arsenic removal from water by mass re-equilibrium: kinetics and performance evaluation in a binary-adsorbent system.

Because arsenic (As) is highly toxic and carcinogenic, its efficient removal from drinking water is essential. Considering some adsorption media may adsorb As fast but are too expensive to be applied in a household, while others could be abundantly available at low cost but with slow uptake kinetics, we explored a novel mass re-equilibrium (MRE) process between two media with different adsorption characteristics to enhance the overall As removal. We employed an adsorbent with fast adsorption kinetics to grab As from water, and then allow it to transfer to a second adsorbent with large capacity for As retention. In the system containing two adsorbents separated by a dialysis membrane, the results showed that As associated with a fast-adsorbing iron-based ordered mesoporous carbon could diffuse to a slow-adsorbing but high-capacity iron-based activated carbon. Column tests were further conducted, showing that the mixed medium, composed of the two adsorbents, could be used to adsorb As at a very short empty bed contact time (≤ 1 min) and the removal was improved by the MRE that potentially redistributed solid-phase As during pump-off periods. This study points to a new direction that by the MRE process, novel binary-adsorbent approaches may be developed for contaminant removal, if suitable media and process configuration could be identified.

Photo-oxidation of Cr(III)-citrate complexes forms harmful Cr(VI).

Photo-oxidation is a potential pathway for the transformation of Cr(III) to Cr(VI) in natural environments. In this study, the Cr(III)-citrate complex (Cr(III)-cit) was prepared and its speciation was determined by high performance liquid chromatography (HPLC). Results showed that Cr(III)-cit existed in [Cr(III)-H-cit](+) and [Cr(III)-cit] species in a pH range of 3-5, in [Cr(III)-cit] only from pH 6-8, in [Cr(III)-cit] and [Cr(III)-OH-cit](-) from pH 9-11, and only in [Cr(III)-OH-cit](-) at pH 12. Additional experiments were conducted in batch systems with pHs of 5 to 12 at 25 °C, where aqueous Cr(III) and Cr(III)-cit were fully exposed to light from medium pressure mercury lamps and a xenon lamp mimicking solar light irradiation. Results demonstrated that oxidation of Cr(III) in Cr(III)-cit was much faster than that in aqueous Cr(III). Rates of Cr(III) photo-oxidation were not sensitive to pH in the range from 7 to 9 but increased significantly with further increases in pH, which was consistent with the distribution of Cr(III) forms. It appeared that [Cr(III)-cit-OH](-) was the most photochemically active form and Cr(II), resulting from a ligand-to-metal charge-transfer (LMCT) pathway after light absorption, was a precursor of the oxidation of Cr(III) to Cr(VI). Both dissolved oxygen and the hydroxyl radical ((•)OH), an intermediate, served as oxidants and facilitated the oxidation of Cr(II) to Cr(VI) via a multiple step pathway. The photoproduction of (•)OH was detected by HPLC using benzene as a probe, supporting the proposed reaction mechanism.

Uranium(VI) removal by nanoscale zerovalent iron in anoxic batch systems.

This study investigated the influences of pH, bicarbonate, and calcium on U(VI) removal and reduction by synthetic nanoscale zerovalent iron (nanoFe(0)) particles under anoxic conditions. The results showed that the rates of U(VI) removal and reduction by nanoFe(0) varied significantly with pH and concentrations of bicarbonate and/or calcium. For instance, at pH 6.92 the pseudo-first-order rate constants of U(VI) removal decreased by 78.5% and 81.3%, and U(VI) reduction decreased by 90.3% and 89.3%, when bicarbonate and calcium concentrations were increased from 0 to 1 mM, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of UO(2) and iron (hydr)oxides as a result of the redox interactions between U(VI) and nanoFe(0). The study demonstrated the potential of using nanoFe(0) for U(VI)-contaminated site remediation and highlighted the impacts of pH, bicarbonate, and calcium on the U(VI) removal and reduction processes.

Parallel factor analysis of fluorescence EEM spectra to identify THM precursors in lake waters.

Dissolved organic matter (DOM) can react with chlorine and yield undesirable disinfection byproducts (DBPs), e.g., trihalomethanes (THMs). Numerous studies have demonstrated that various DOM constituents have DBP formation potentials. We explored in this study the use of fluorescence excitation-emission (EEM) spectroscopy to identify THM precursors in 55 lakes in Missouri, USA. EEMs of the lake waters were decomposed into five factors of different origins through parallel factor analysis. The correlations between the component scores of the factors and THM formation potentials reveal that factors 1 and 2 are likely THM precursors and provided better surrogates than SUVA (dissolved organic carbon-normalized UV254) for predicting DBP formation potential. Thus, monitoring the component scores of the DOM-origin factors would provide a practical tool to identify THM precursors and facilitate utilities to choose appropriate techniques for DBP mitigation and optimize the degree of water treatment.

Effects of the Substrate on Interfacial Polymerization: Tuning the Hydrophobicity via Polyelectrolyte Deposition.

Interfacial polymerization (IP) has been the key method for the fabrication of the thin film composite (TFC) membranes that are extensively employed in reverse osmosis (RO) and forward osmosis (FO). However, the role of the substrate surface hydrophilicity in the formation of the IP-film remains a controversial issue to be further addressed. This study characterized the IP films formed on a series of polyacrylonitrile (PAN) substrates whose hydrophilicities (from ~38 to ~93 degrees) were varied via different approaches, including the alkaline treatment and the deposition of various polycations. It was revealed that delamination could occur when the IP film was formed on a relatively hydrophilic surface; the integrity of the TFC membranes was substantially improved, owing to the modification of the polyelectrolyte deposition. On the other hand, the characterization indicated that the TFC membrane could have an enhanced efficiency (with a factor of ~2) when the substrate was relatively hydrophilic. It was established that the polyelectrolyte deposition could be exploited to effectively tune the substrate surface hydrophobicity, thereby providing more degrees of freedom for the optimization of the TFC membranes fabrication.

Role of sulfide and ligand strength in controlling nanosilver toxicity.

Nanosilver has been used broadly in nanotechnology enhanced consumer products because of its strong antimicrobial properties. Silver nanoparticles (AgNPs) released from these products will likely enter wastewater collection and treatment systems. This research evaluated the role of sulfide and ligand strength in controlling nanosilver toxicity to nitrifying bacteria that are important in wastewater treatment. The nanosilver toxicity in the absence and presence of ligands (SO(4)(2-), S(2-), Cl(-), PO(4)(3-), and EDTA(-)) commonly present in wastewater was determined from the oxygen uptake rate measurements. Sulfide appeared to be the only ligand to effectively reduce nanosilver toxicity. By adding a small aliquot of sulfide that was stoichiometrically complexed with AgNPs, the nanosilver toxicity to nitrifying organisms was reduced by up to 80%. Scanning electron microscopy coupled with energy dispersive X-ray analysis indicated that AgNPs were highly reactive with sulfide to form new Ag(x)S(y) complexes or precipitates. These complexes were not oxidized after a prolonged period of aeration (18h). This information is useful for wastewater treatment design and operation to reduce nanosilver toxicity via sulfide complexation. While the biotic ligand model was successful in predicting the toxicity of Ag(+) ions, it could not accurately predict the toxicity of AgNPs. Nevertheless, it could be one of the many tools useful in predicting and controlling nanosilver toxicity to wastewater microorganisms.

Role of Cellulose Micro and Nano Crystals in Thin Film and Support Layer of Nanocomposite Membranes for Brackish Water Desalination.

Reverse osmosis is a major process that produces soft water from saline water, and its output represents the majority of the overall desalination plants production. Developing efficient membranes for this process is the aim of many research groups and companies. In this work, we studied the effect of adding cellulose micro crystals (CMCs) and cellulose nano crystals (CNCs) to the support layer and thin film nanocomposite (TFN) membrane on the desalination performance. SEM, TEM, ATR-FTIR, and contact angle measurements were used to characterize the membrane's properties; and membrane's performance were evaluated by water flux and NaCl rejection. Filling 2% of CNCs gel in the support layer improved the water flux by +40%, while salt rejection maintained almost the same, around 95%. However, no remarkable improvement was gained by adding CNCs gel to m-phenylenediamine (MPD) solution, which was used in TFN membrane preparation. Filling CMCs powder in TFN membrane led to a slight improvement in terms of water flux.

Characterization of dissolved organic matter/nitrogen by fluorescence excitation-emission matrix spectroscopy and X-ray photoelectron spectroscopy for watershed management.

Characterization of dissolved organic matter/nitrogen (DOM/DON) is critical in water quality assessment and nutrient management in watershed or ecosystem. This study was to investigate the link between DOM/DON and its source using fluorescence excitation-emission matrix (EEM) spectroscopy coupled with parallel factor analysis (PARAFAC). Water samples were collected from various aquatic systems in a watershed located in central Missouri, including rural watershed with various land use and land cover (LULC), landfill, and constructed wetland. PARAFAC results based on EEM spectroscopy revealed four DOM components: two humic/fulvic acid-like components, one xenobioic-like component, and one protein-like component (f4). The f4 score was found highly correlated to LULC, indicating its distinctive EEM structure in relation to source. It is believed that the f4 score could be used as a surrogate for DOM/DON source-tracking in complex ecosystems. The nitrogen 1s X-ray photoelectron spectroscopy (XPS) of the solid DOM showed a close relationship between N oxidation state and its origin. The classification of the sample origins by the N oxidation state confirmed the grouping by the f4 score of EEM/PARAFAC. This study demonstrated that EEM/PARAFAC could be used as a tool for DOM/DON source tracking, point or non-point source pollution control, and understanding of DOM/DON fate and transport in complex aquatic ecosystems.