Hiroaki Ozaki

Performance of an ultra-low-pressure reverse osmosis membrane (ULPROM) for separating heavy metal: effects of interference parameters

Abstract An experimental investigation was conducted to study the performance of an aromatic polyamide (ES 20) ultra-low-pressure reverse osmosis membrane (ULPROM) for separating divalent (Cu 2+ , Ni 2+ ) and hexavalent (Cr 6+ ) heavy metals from bulk solution. The influence of operating pressure, feed concentration, pH, and effect of other ions (Ca 2+ and Mg 2+ ) on the ULPROM performance was studied. The investigation was conducted for synthetic wastewater and wastewater from the heavy metal industry. Experimental results show that the rejection increases with increasing feed pressure, it is dependent on feed pH and is higher at higher pH. Increasing concentration of other ions slightly decreased the rejection of heavy metals. Generally, rejection of heavy metal is found to be greater than 95% for the ULPROM tested, which suggests the suitability of such membranes for industrial application for recovery of heavy metal and reclaiming wastewater.

Rejection of organic compounds by ultra-low pressure reverse osmosis membrane

The introduction of ultra-low pressure reverse osmosis (ULPRO) membrane has widened the horizon of reverse osmosis (RO) in purification of surface water and wastewater as well as desalination of brackish water. The ULPRO membrane chemistry can provide a high water flux at low operating pressure, while maintaining a very good salt and organics rejection. This paper deals with the investigation on the rejection of low molecular weight organic compounds by ULPRO membrane. Laboratory scale experiments were carried out at a pressure of 3 kg/cm2 with a feed flow rate of 1.20 l/min. The rejection of undissociated organic compounds did not show a close relationship with the feed pH. The percentage removal of undissociated organic compounds increased linearly with the molecular weight as well as with the molecular width. The removal efficiency can be predicted by these relationships. But neither molecular weight nor molecular width can be considered as an absolute factor for rejection. The feed pH also influenced the removal efficiency of dissociated organic compounds. The efficiency decreased linearly with the increase in the dissociation constant.

Degradation of common pharmaceuticals and personal care products in mixed solutions by advanced oxidation techniques

Widespread detection of pharmaceutical compounds in water environment has been a serious concern recently, while conventional sewage treatments are ineffective for their elimination. But, advanced oxidation techniques are very promising to remove varieties of organic contaminants in water. This research aims to elucidate oxidation potentials of sixteen commonly used pharmaceutical compounds in mixed solutions by seven advanced oxidation techniques in laboratory batch experiments. The removal profiles exhibited four distinct patterns: a) easily degradable by all seven techniques, b) not easily degradable by all seven techniques, c) easily degradable by ozone-based techniques, but not by ultraviolet radiation-based techniques and d) easily degradable by ultraviolet radiation-based techniques, but not by ozone-based techniques. Ozone-based techniques rather than ultraviolet radiation-based techniques were very powerful for simultaneous removal of the compounds efficiently. Moreover, ozonation combined with ultraviolet radiation was the most appropriate technique for simultaneous removal of the tested compounds efficiently. Increased ozone dissolution and decomposition with ozone-based techniques did not always enhance the compounds’ removal. Physicochemical properties of the compounds and solution pH also presumably played an important role on the removal which merits further attention.

Bioregeneration by mixed microorganisms of granular activated carbon loaded with a mixture of phenols

The role of mixed microorganisms on the bioregeneration of granular activated carbon (GAC) loaded with a mixture of phenol and 2,4-dichlorophenol was investigated. In a biological activated-carbon, sequencing batch reactor (BAC-SBR), bioregeneration efficiency for phenol was enhanced from 39 to 48% and for 2,4-dichlorophenol from 38 to 43% by increasing solid retention time from 3 to 8xa0days. Prolonging the sludge retention time induced both progressive desorption of adsorbates due to biodegradation in the bulk solution and direct assimilation of adsorbates on GAC by attached microorganisms.

PHOTOCATALYTIC OZONATION OF 2, 4-DICHLOROPHENOXYACETIC ACID IN WATER WITH A NEW TIO2 FIBER

More effective techniques are required to mineralize the increasing number of recalcitrant organic contaminants at low concentrations in the water environment using advanced oxidation process. Though relatively new, photocatalytic ozonation (O3/UV/TiO2) is considered superior to ozonation (O3) and photocatalysis (UV/TiO2), due to synergistic effects and use of immobilized TiO2 photocatalysts is a milestone in advance oxidation process. This article aimed to elucidate 2, 4-dichlorophenoxyacetic acid (2, 4-D) mineralization characteristics in low aqueous solutions by O3/UV/TiO2 using the world’s first high-strength TiO2 fiber catalyst in laboratory experiments. 2, 4-D degradation and TOC removal in O3, UV/TiO2 and O3/UV/TiO2 followed pseudo-first order reaction kinetic. The removal rates for 2, 4-D and TOC in O3/UV/TiO2 were respectively about 1.5 and 2.4-fold larger than the summation of the corresponding values in O3 and UV/TiO2. The O3/UV/TiO2 process was characterized by short-lived few aromatic intermediates, faster degradations of aliphatic intermediates and dechlorination as a major step in 2, 4-D mineralization. The significantly enhanced 2, 4-D mineralization in the process was attributed to increased ozone decomposition and reduced electron-hole recombination on TiO2 surface resulting to a large number of OH generation. The O3/UV/TiO2 process with the TiO2 fiber catalyst was very promising with respect to the major challenges being faced in AOP involving TiO2, namely separation of powder catalyst in suspension and reduced efficiency of immobilized catalysts (e.g. TiO2 film/fiber).

A novel use of TiO2 fiber for photocatalytic ozonation of 2,4-dichlorophenoxyacetic acid in aqueous solution.

More efficient oxidation methods are needed to degrade especially newly emerging recalcitrant organic contaminants at low concentrations in the water environment. Reduced photonic efficiency of immobilized TiO2 is a major challenge in TiO2-assisted advanced oxidation processes (AOP). Mineralization of 2,4-dichllorophenoxyacetic acid (2,4-D) in low aqueous solution by O3/UV/TiO2 using the worlds first high-strength TiO2 fiber was investigated and compared with O3, UV/TiO2, and O3/TiO2 in laboratory batch experiments. The 2,4-D degradation and total organic carbon (TOC) removal followed pseudo first-order reaction kinetic, while their rates in O3/UV/TiO2 were respectively about 1.5 and 2.4 times larger than the summation of the values in 03 and UV/TiO2. The O3/UV/TiO2 was characterized by few aromatics with very low abundance, fast disappearance of aliphatics and more than 95% dechlorination. The discrepancies in organic carbon mass balance among the intermediates and 2,4-D were attributed mainly to few apparently major unidentified intermediates. The significantly enhanced 2,4-D mineralization in O3/UV/TiO2 was attributed to increased ozone dissolution followed by its decomposition, and reduced electron-hole recombination in presence of dissolved ozone resulting in a large number of hydroxyl radical (*OH) generation from more than one parallel path. The removal efficiencies of the systems can further be enhanced by optimizing design parameters, and O3/UV/TiO2 with the TiO2 fiber is promising to mineralize recalcitrant organic contaminants in water at low concentrations.

UV photolysis of perfluorooctanoic acid (PFOA) in dilute aqueous solution

Perfluorooctanoic acid (PFOA) is very persistent in the environment and widely detected in the water environment. Only some advanced methods with extreme reaction conditions are shown to be capable of degrading the compound efficiently, and almost all the earlier investigations used very high PFOA concentrations. The compound is detected normally at very low concentrations in the water environment, while mild reaction conditions for its degradation are preferable. This article aimed to elucidate photodegradation of PFOA in dilute aqueous solutions by combined UV wavelengths (185 nm+254 nm) and 254 nm using a newly designed UV jacket. PFOA degradation was greatly enhanced with the combined wavelengths with almost one hundred percent PFOA removals in four-hour reaction. The removals were well described by the first-order reaction kinetic. The removal efficiencies and rate values significantly decreased with smaller initial PFOA concentrations. But defluorination was greatly enhanced with smaller PFOA concentrations possibly due to accelerated decomposition of fluorinated intermediates of PFOA. Formic acid and acetic acid were two tentatively identified intermediates of PFOA photolysis while the former was a major intermediate predominantly controlling solution pH during the oxidation. The results demonstrated that PFOA photolysis by the combined wavelengths with mild reaction conditions can be greatly enhanced by proper design of UV jacket and reactor system.

Efficacy of ultraviolet radiation and hydrogen peroxide oxidation to eliminate large number of pharmaceutical compounds in mixed solution

Ultraviolet photolysis and ultraviolet and hydrogen peroxide oxidation of fourteen commonly used pharmaceutical compounds and two personal care products in mixed solution using low pressure ultraviolet lamp was investigated in laboratory batch experiments. Removal of the compounds followed the first-order reaction kinetic. Three distinct impacts of hydrogen peroxide on ultraviolet and hydrogen peroxide oxidation of the compounds (positive, negative and no significant effect) were observed. Removal behavior of the several tested compounds in mixed solution varied significantly than their respective behavior in absence of coexisting compounds. Clofibric acid, diclofenac, fenoprofen, isopropylantipyrine, ketoprofen, phenytoin and triclosan were removed very efficiently (> 96 %) by ultraviolet photolysis alone. Residual hydrogen peroxide during ultraviolet and hydrogen peroxide oxidation was quantitated for the first time. Hydrogen peroxide addition to ultraviolet photolysis was not worthy for majority of the tested compounds as their removal did not increase significantly and very big fractions (> 85 %) of the added hydrogen peroxide (0.29 ∼ 1.47 mM) remained unused presumably due to small fluence of the lamp, very small molar absorption for hydrogen peroxide at 254 nm (27.06 /M.cm) and acidic pH of reaction solution (< 5.7). Further exploration on ultraviolet and hydrogen peroxide oxidation with higher fluence lamp and alkaline solution pH will clarify usefulness of the method to treat pharmaceutical contaminated waters.

Rejection of pharmaceuticals and personal care products (PPCPs) and endocrine disrupting chemicals (EDCs) by low pressure reverse osmosis membranes

This paper aims to elucidate retention characteristics of some pharmaceuticals and personal care products (PPCPs), and endocrine disrupting chemicals (EDCs), by two polyamide low pressure reverse osmosis (LPRO) membranes. Feed solution pH did not have an influence on rejections of undissociated solutes, which was most likely governed by adsorption, size exclusion and diffusion simultaneously. Size exclusion was presumably dominant, especially with tight membranes (UTC-70U). Rejections of the solutes with low dipole moment (<1.0 debye) decreased with increasing octanol-water partition coefficient (K(ow)). The solutes with large K(ow) values were most likely adsorbed on membrane and subsequently passed through it resulting in larger diffusion coefficient (D(p)). The rejections decreased with increasing D(p) values irrespective of their dipole moments. Rejections of solutes with comparatively larger dipole moments might be dominated by diffusion and/or convection rather than their hydrophobicity. However, rejections of solutes with hydroxyl and carboxyl functional groups by UTC-60 increased with solution pH. More than 80% rejections were obtained for degree of dissociation (alpha)>0.5. Electrostatic repulsion played a key role for rejection of dissociated solutes, especially by loose LPRO membranes. Therefore, assessing the dissociation degree at desired pH values can be a key step to obtain an insight of rejection mechanisms by polyamide membranes.

Heterogeneous photocatalytic ozonation of 2,4-D in dilute aqueous solution with TiO2 fiber

Photocatalytic ozonation (O(3)/UV/TiO2) is an emerging oxidation method for recalcitrant organic contaminants in water. However, immobilised TiO2 catalysts suffer from reduced photonic efficiency. Therefore, TiO2 catalysts with excellent mechanical and thermal properties and enhanced photonic efficiencies are sought. This paper aimed to elucidate the mineralisation of low concentration 2,4-D (45.0 microM) by O(3)/UV/TiO2 using the worlds first high-strength TiO2 fibre in laboratory batch experiments. 2,4-D degradation and TOC removal followed pseudo first-order reaction kinetic. The removal rates for 2,4-D and TOC in O(3)/UV/TiO2 were 1.5 and 2.4-fold larger than the summation of the values for ozonation (O3)) and photocatalysis (UV/TiO2), respectively. O(3)/UV/TiO2 was characterised by few aromatic intermediates with low abundance, fast degradations of aliphatic intermediates and dechlorination as a major step. The significantly enhanced 2,4-D mineralisation in O(3)/UV/TiO2 was attributed to increased ozone dissolution and decomposition, and reduced electron-hole recombination resulting in large number of hydroxyl radical (*OH) formation from more than one parallel path. The discrepancies in the organic carbon mass budget were attributed to few apparently major unidentified intermediates, while chlorine mass balance was reasonably acceptable. The mineralisation efficiency of O(3)/UV/TiO2 with the TiO2 fibre can further be enhanced by optimisation of experimental design parameters. The new TiO2 fibre is very promising to overcome the problem of reduced efficiency of TiO2 catalyst in an immobilised state.