Jenyuk Lohwacharin

Hybrid ferrihydrite-MF/UF membrane filtration for the simultaneous removal of dissolved organic matter and phosphate

Dissolved organic matter (DOM) and phosphorus promote microbial regrowth in water distribution networks. Ferrihydrite (Fh) has a high adsorption affinity with DOM and phosphate. Hence, a lab-scale unit of the hybrid Fh-MF/UF membrane filtration system was used to evaluate membrane fouling and the removal efficiency of DOM and phosphate. Suwannee River natural organic matter (SRNOM) was used as a surrogate for DOM in natural water. The Fh-membrane system demonstrated removal rates of dissolved organic carbon (DOC), UV254 and phosphate up to 50%, 80% and 90%, respectively, at the Fh dose of 17.5 mg/L. The effect of phosphate on the removal of DOM was different without or with the addition of Fh; namely, phosphate increased the DOM removal without Fh by interacting with the UF membrane made of regenerated cellulose (RC), but phosphate decreased the DOM removal by Fh due to the strong affinity of phosphate with Fh. Size exclusion chromatography revealed that phosphate mainly competed against smaller DOM molecules for Fh adsorption sites. Although the addition of Fh caused only a moderate flux decline with the RC membranes, the deposition of positively charged Fh on the surface of a negatively charged high-flux membrane, i.e., polyethersulfone (PES), caused a rapid decline of the permeation flux.

Ultrafiltration of natural organic matter and black carbon: factors influencing aggregation and membrane fouling.

There are concerns about black carbon (BC), due to its potential for sorption of toxic pollutants and inevitably entering drinking water sources. This study aimed to evaluate factors affecting BC aggregation and membrane fouling in the ultrafiltration of river water. Hydrophilic carbon black (CB) was selected as a surrogate of submicron BC in natural waters. Calcium, pH, and natural organic matter (NOM) were found to influence CB aggregation. Calcium induced interparticle interactions in a pH range of 4.3-7.7. In river water at 0.3mM Ca2+, CB remained as fine aggregates (<300 nm) that caused substantial filtration resistance. At 1.3mM Ca2+, CB size increased to 2.2-3.3 microm and membrane fouling was reduced. Interactions between particles and NOM enhanced organic rejection and eliminated irreversible membrane fouling. BC in water resources is a noxious substance, but it was easily aggregated in hard waters and could enhance NOM removal in the ultrafiltration process.

Analysis of trihalomethane precursor removal from sub-tropical reservoir waters by a magnetic ion exchange resin using a combined method of chloride concentration variation and surrogate organic molecules

In small reservoirs in tropical islands in Japan, the disinfection by-product formation potential is high due to elevated concentrations of dissolved organic matter (DOM) and bromide. We employed a combined method of variation of chloride concentrations and the use of DOM surrogates to investigate removal mechanisms of bromide and different fractions of DOM by chloride-based magnetic ion exchange (MIEX®) resin. The DOM in reservoir waters was fractionated by resins based on their hydrophobicity, and characterized by size-exclusion chromatography and fluorescence excitation-emission matrix spectrophotometry. The hydrophobic acid (HPO acid) fraction was found to be the largest contributor of the trihalomethane (THM) precursors, while hydrophilic acid (HPI acid) was the most reactive precursors of all the four THM species. Bromide and DOM with a molecular weight (MW) greater than 1kDa, representing HPO acid (MW 1-3kDa) and HPI acid (MW 1-2kDa), were effectively removed by MIEX® resin; however, DOM with a MW lower than 1kDa, representing HPI non-acid, was only moderately removed. The removal of THM precursors by MIEX® resin was interfered by high chloride concentrations, which was similar to the removal of glutamic acid (HPI acid surrogate) and bromide. However, elevated chloride concentrations had only a minor effect on tannic acid (HPO acid surrogate) removal, indicating that HPO acid fraction was removed by a combination of ion exchange and physical adsorption on MIEX® resin. Our study demonstrated that the combined use of DOM surrogates and elevated chloride concentrations is an effective method to estimate the removal mechanisms of various DOM fractions by MIEX® resin.

Simultaneous removal of dissolved organic matter and bromide from drinking water source by anion exchange resins for controlling disinfection by-products.

Anion exchange resins (AERs) with different properties were evaluated for their ability to remove dissolved organic matter (DOM) and bromide, and to reduce disinfection by-product (DBP) formation potentials of water collected from a eutrophic surface water source in Japan. DOM and bromide were simultaneously removed by all selected AERs in batch adsorption experiments. A polyacrylic magnetic ion exchange resin (MIEX®) showed faster dissolved organic carbon (DOC) removal than other AERs because it had the smallest resin bead size. Aromatic DOM fractions with molecular weight larger than 1600 Da and fluorescent organic fractions of fulvic acid- and humic acid-like compounds were efficiently removed by all AERs. Polystyrene AERs were more effective in bromide removal than polyacrylic AERs. This result implied that the properties of AERs, i.e. material and resin size, influenced not only DOM removal but also bromide removal efficiency. MIEX® showed significant chlorinated DBP removal because it had the highest DOC removal within 30 min, whereas polystyrene AERs efficiently removed brominated DBPs, especially brominated trihalomethane species. The results suggested that, depending on source water DOM and bromide concentration, selecting a suitable AER is a key factor in effective control of chlorinated and brominated DBPs in drinking water.

Ultrafiltration of Humic Acid Solution: Effects of Self‐dispersible Carbon Black and Cations

Abstract Effects of carbon black (CB) addition on membrane fouling and rejection of macromolecular humic acids (HA) were evaluated by a stirred‐cell ultrafiltration unit. Stable CB dispersions increased filtration resistances, but enhanced HA rejection by the membranes. Monovalent and divalent ions affected the filtration resistance of CB solution differently; namely, NaCl solution showed a very high resistance due to the concentration of CB in the diffusion boundary layer near the membrane surface, whereas CaCl2 and MgCl2 solutions showed only cake resistance. The cake layer containing both CB and HA was more easily removed from the membranes than HA‐cake layer.

Properties of residual titanium dioxide nanoparticles after extended periods of mixing and settling in synthetic and natural waters

Titanium dioxide nanoparticle (TiO2 NP) discharged into water bodies can affect ecosystems and human health adversely. We studied the properties of residual TiO2 NPs with and without gentle mixing (to simulate a natural environment more closely) and after settling for 12-h periods. Surface complexation, dynamic particle size changes, and TiO2 NP destabilization in synthetic and lake waters were investigated. The accumulation of inert ions (Na+ and Cl−) in the diffuse layer which was not discussed in other studies was supposed to be the main reason that aggregation occurred slowly and continuously. PO43− stabilized and destabilized TiO2 NPs at 10 mM and 100 mM, respectively. Destabilization occurred because high ionic strength overwhelmed increased negative charges of TiO2 NPs by complexation with PO43−. TiO2 NP destabilization was achieved in approximately 12 h in synthetic and lake waters, and is attributed to the slow diffusion of ions into aggregates. Despite the presence of moderately high concentrations of natural organic matter, which tends to stabilize TiO2 NPs, the addition of 20 mM PO43− destabilized the TiO2 NPs in lake water. Smaller aggregate sizes formed compared with those before destabilization, which indicates that stable residual TiO2 NPs could exist in aquatic environments after extended periods.

Performance of integrated ferrate–polyaluminum chloride coagulation as a treatment technology for removing freshwater humic substances

Ferrate-based technologies can play versatile roles in water treatment because of their potential for in situ production and because they do not form any harmful by-products. We compared the oxidative performance of Fe(VI) generated by an electrochemical process, with H2O2-UV irradiation (a standard oxidation process) for removing Suwannee River natural organic matter. It took only 5 min for Fe(VI) (Fe: 1.67 × 10-4 M) to reduce the fluorescence intensity of a humic-like fluorophore by 36% of the original value; in contrast, it took 120 min of irradiation using H2O2-UV ([OH] ∼ 1.8 × 10-13 M) to remove 68% of the original value. In addition to the short reaction time, ferrate can also form aggregates that can remove turbidity and adsorb organics and other contaminants present in water. Simultaneous addition of ferrate and polyaluminum chloride (PACl) to unfiltered natural water displayed the most efficient reduction of UVA254, primarily under acidic conditions. Ferrate pre-oxidation followed by PACl coagulation was the most effective process for reducing turbidity and chromaticity, because of the effects arising from the coagulation of ferrate that resulted in Fe(III)(s) species. Ferrate pre-oxidation generated low-molecular-weight UVA254-absorbing organics, whose dissolved organic matter (DOM) peak at 1250 Da was removed by PACl coagulation. Neither the initial pH nor the process order significantly affected the removal of organic carbon by the integrated ferrate-PACl process.

Analysis of adsorption processes of dissolved organic matter (DOM) on ferrihydrite using surrogate organic compounds

Ferrihydrite (Fh) has been recently used in water treatment for removing dissolved organic matter (DOM), but its governing interactions with low-molecular weight DOM are largely unknown. This study aimed to elucidate the influence of chemical structure of DOM on the interactions between functional groups of DOM and Fh using various surrogates representing DOM in natural waters. We tested four surrogate compounds: l-glutamic acid, resorcinol, l-serine, and tannic acid, which represent the main chemical groups of carboxylic and hydroxyl groups; and the Suwannee River NOM (SRNOM) that represents the composition of DOM in natural aquatic systems. Batch adsorption experiments revealed that the DOM adsorption onto Fh was significantly influenced by the steric arrangements of –COOH and –OH functional groups. Both l-serine with α-carboxyl group and resorcinol with hydroxyl groups in meta-position were marginally removed by Fh, indicating that the adsorption of DOM on Fh was determined by their chemical structures and the relative positions of carboxylate and hydroxyl groups. The adsorption of l-glutamic acid was controlled by the pH-dependent ligand exchange of γ-carboxyl groups, which was similar to the SRNOM adsorption. In contrast, adsorption of tannic acid was not affected by pH, which can be explained by a two-step adsorption, namely, ligand exchange followed by multi-layer adsorption to the partitioning phase. The results of kinetic experiments demonstrated that adsorption of DOM by Fh was significant and rapid. The kinetic adsorption data can be expressed by the pseudo-second-order equation, indicating that the adsorption step might be the rate-limiting step.