Anion Exchange on Cationic Surfactant Micelles, and a Speciation Model for Estimating Anion Removal on Micelles during Ultrafiltration of Water

Removal of Algae and Algal Toxins from a Drinking Water Source Using a Two-Stage Polymeric Ultrafiltration Membrane Process

The release of algal toxins in algae-containing water sources poses a serious threat to drinking water safety and human health. The conventional water treatment processes of water plants have a limited ability to remove algae and algal toxins, especially algal toxins with a molecular weight (MW) of less than 1000 Da. To eliminate algal pollution from a water source, a two-stage ultrafiltration (UF) process with a large polysulfone hollow fiber membrane with a MW cut-off of 200 kDa and a small aromatic polyamide roll membrane with a MW cut-off of 1 kDa were applied after a traditional sand filter in a water treatment plant. UF operation conditions, including the operating time, pressure, and membrane flux, were investigated. With an operating pressure of 0.05-0.08 MPa, the polysulfone hollow fiber membrane removed algae effectively, as the influent algal cell concentration ranged from 1-30 cells/mL but exhibited a limited removal of algal toxins. With an operating pressure of 0.3-0.4 MPa, the elimination of microcystins (MCs) reached 96.3% with the aromatic polyamide roll membrane. The operating pressure, membrane flux, and operating time were selected as the experimental factors, and the effects on the UF efficiency to remove algal toxins and biodegradable dissolved organic carbon were investigated by the response surface methodology. The model showed that the order of influence on the membrane operating efficiency was operating pressure > membrane flux > running time. The optimal UF operating conditions were an operating pressure of 0.3 MPa, a membrane flux of 17.5 L/(m2·h), and a running time of 80 min.

Chemically cross-linked keratin and nanochitosan based sorbents for heavy metals remediation

Biosorbents for water remediation were prepared using keratin biopolymer cross-linked with nanochitosan (NC). Keratin proteins were dissolved using reducing agents and NC was incorporated with concentrations of 1, 3 and 5 % individually into the keratin solution. The mixtures were thermally treated at 75°C overnight, which promoted the formation of ester bonds between the hydroxyl groups of nanochitosan and the carboxylic groups of the keratin biopolymer. The resulting keratin derived biosorbents were characterized by X-Ray photoelectron spectroscopy, confirming the cross-linking between keratin and nanochitosan. The chicken feathers keratin (CFK) surface modifications with nanochitosan were examined with Brunauer-Emmett-Teller, scanning and transmission electron microscopies. The sorption capacity of biosorbents was tested for eight different metals simultaneously at different contact times (15, 30, 60, 120, 240, 280 mins) and pH (5.5, 7.5 and 8.5), including arsenic, selenium, chromium, nickel, cobalt, lead, cadmium and zinc, using simulated industrial wastewater water containing 600 μg L^-1 concentration of each metal. The synthesized environmentally benign biosorbents exhibited biosorption of metals upto 98 % at pH 7.5 and a contact time of 24 h, showing their potential for industrial wastewater remediation.

Biodegradable Dissolved Organic Carbon (BDOC) Removal from Micro-Polluted Water Source Using Ultrafiltration: Comparison with Conventional Processes, Operation Conditions and Membrane Fouling Control

The biodegradable dissolved organic carbon (BDOC) in micro-polluted water sources affects the drinking water quality and safety in the urban water supply. The conventional technology of “coagulation-sedimentation-filtration” in a water plant located in the lower reaches of the Yangtze River removed dissolved organic carbon (DOC) with a molecular weight (MW) > 30 kDa effectively, but the BDOC elimination only ranged 27.4−58.1%, due to their predominant smaller MW (<1 kDa), leading to a high residual BDOC of 0.22−0.33 mg/L. To ensure the biological stability of drinking water, i.e., the inability to support microbial growth (BDOC < 0.2 mg/L), a pilot-scale ultrafiltration process (UF, made of aromatic polyamide with MW cut-off of 1 kDa) was operated to remove BDOC as an advanced treatment after sand-filtration. Results showed the membrane flux decreased with the increase in the influent BDOC concentration and decrease in operating pressure. With an operating pressure of 0.25 MPa, the BDOC removal by UF reached 80.7%, leading to a biologically stable BDOC concentration of 0.08 mg/L. The fouling of the membrane was mainly caused by organic pollution. The H2O2−HCl immersion washing method effectively cleaned the membrane surface fouling, with a recovery of membrane flux of 98%.

Novel development of cationic surfactant-based mucoadhesive nanovaccine for direct immersion vaccination against Francisella noatunensis subsp. orientalis in red tilapia (Oreochromis sp.)

Francisella noatunensis subsp. orientalis (Fno) is one of the infectious diseases that causes economic losses associated with tilapia mortality. Even though direct immersion administration of vaccines is more practicable for small fish and fry compared with oral and injection vaccination in the fields, the efficacy is still insufficient due to lower potency of antigen uptake. Herein, we accomplished the development of a mucoadhesive nanovaccine platform using cetyltrimethylammonium bromide (CTAB), a cationic surfactant, to improve the efficiency of immersion vaccination against Fno in tilapia. Cationic Fno nanovaccine (CAT-Fno-NV) was prepared though emulsification using an ultrasonic method. In our investigation, the CAT-Fno-NV increased the opportunity of Fno vaccine uptake by extending the contact time between vaccine and mucosal surface of fish gills and enhancing the protective efficacy against Fno infection. Fish were vaccinated with the CAT-Fno-NV by a direct immersion protocol. The challenge trial by Fno injection revealed that CAT-Fno-NV at the concentration 1:100 ratio (approximately 1 × 10⁶ cfu/mL) had the highest efficacy to protect fish from Fno infection at day 30 after post challenge period according to the total number of Fno detected in head kidney, spleen and liver. A significant upregulation of IgM gene was observed in gills, skin, head kidney, serum and peripheral blood lymphocytes (PBLs) and spleen tissues treated with WC and CAT-Fno-NV (1:100) vaccines, while IgT gene was highly expressed in only gills and skin tissues for treated WC and CAT-Fno-NV (1:100) groups. We anticipate that the cationic surfactant-based nanovaccine developed in this study could become an efficient alternative for direct immersion vaccination to induce humoral immune responses against Fno in vaccinated tilapia.

Boron removal by electrocoagulation: Removal mechanism, adsorption models and factors influencing removal

Boron (B), normally present in ground water and sea water, is a vital micronutrient for plants, but is also toxic in excessive amounts. Under typical conditions, aqueous boron is present as boric acid (H₃BO₃), which is uncharged, making B particularly challenging to remove by mechanisms commonly applicable to removal of trace constituents. Adsorption of B onto aluminum hydroxide solids (Al(OH)₃(s)) generated using aluminum-based electrocoagulation (EC) is a promising strategy for B removal. Infrared spectroscopy analysis indicated complexation of B(OH)₃ with aluminum hydroxide solids via surface hydroxyl groups, while X-ray and infrared spectroscopy results indicated that the structure of the Al(OH)₃(s) was influenced both by EC operating conditions and by water quality. A linear adsorption model predicted B removal well when initial concentrations were lower than 50 mg/L, but fit the experimental data poorly at higher initial B concentrations. The Langmuir adsorption model provided a good fit for a broader range of initial B concentrations (5-1000 mg/L). Factors affecting B adsorption during the EC process, including current intensity, Al dissolution rate, boron concentration, pH, and total dissolved solid (TDS), were investigated. Increasing current intensity initially led to a higher Al dissolution rate, and therefore higher B adsorption, but there was a limit, as further increases in current intensity caused rapid formation of Al(OH)₃(s) having a large particle size and a low capacity to complex B. Boron removal decreased as its concentration increased. The best removal of B occurred at pH 8, corresponding to a slightly positive zeta potential for aluminum hydroxide and a small but significant fraction of negatively charged B species. Higher TDS concentrations facilitated the use of higher current intensities, i.e., the limit on the effective Al dissolution rate increased with increasing TDS. Two real water samples (river water and oilfield produced water) spiked with B were treated using EC, resulting in up to 50% B removal from river water (C₀ = 10 mg/L, current = 0.2 A) in 2 h, and 80% B removal from produced water (C₀ = 50 mg/L, current = 1.0 A) in 2 h.

Modeling arsenic (V) removal from water by micellar enhanced ultrafiltration in the presence of competing anions

With increasing arsenic (As) contamination incidents reported around the world, better processes for As removal from industrial wastewater and other contaminated waters are required to protect drinking water sources. Complexation of As with cetylpyridinium chloride (CPC) cationic surfactant micelles, coupled with ultrafiltration (UF), has the potential to improve As removal, but competition from other anions could be a limiting factor. Using a binary-system ion-exchange model, the selectivity coefficients for binding of the monovalent and divalent forms of arsenate (As (V)) to cationic cetylpyridinium (CP⁺) micelles, relative to Cl^-, were determined to be 0.55 for H₂AsO₄^- and 0.047 mol L^-1 for HAsO₄^2-, respectively. The affinity sequence for binding of commonly occurring monovalent anions by CP⁺ micelles was found to be NO₃^- > Cl^- > HCO₃^- > H₂AsO₄^-, and for divalent anions, SO₄^2- > HAsO₄^2-. Distribution of As (V) between the micellar and aqueous phases was explored using ion exchange isotherms, with higher pH and lower concentrations of competing anions increasing rejection of As (V) across UF membranes. A model accounting for these effects, based on mass balances across UF membranes and selectivity coefficients for binding of anions to the CP⁺ micelles, was used to predict As (V) removal during micellar-enhanced ultrafiltration (MEUF) of mixtures of competing anions. Model predictions agreed well with experiment results for both artificial and spiked natural river water samples. Arsenic (≈0.1 mM) removals of 91% and 84% were achieved from artificial waters and spiked natural river waters, respectively, by adding 20 mM CPC prior to UF.

Development of Nanostructured Water Treatment Membranes Based on Thermotropic Liquid Crystals: Molecular Design of Sub-Nanoporous Materials

Supply of safe fresh water is currently one of the most important global issues. Membranes technologies are essential to treat water efficiently with low costs and energy consumption. Here, the development of self-organized nanostructured water treatment membranes based on ionic liquid crystals composed of ammonium, imidazolium, and pyridinium moieties is reported. Membranes with preserved 1D or 3D self-organized sub-nanopores are obtained by photopolymerization of ionic columnar or bicontinuous cubic liquid crystals. These membranes show salt rejection ability, ion selectivity, and excellent water permeability. The relationships between the structures and the transport properties of water molecules and ionic solutes in the sub-nanopores in the membranes are examined by molecular dynamics simulations. The results suggest that the volume of vacant space in the nanochannel greatly affects the water and ion permeability.