Removal of 1,4-dioxane from landfill leachate by a rotating advanced oxidation contactor equipped with activated carbon/TiO2 composite sheets.

A rotating advanced oxidation contactor (RAOC) equipped with activated carbon (AC)/TiO2 composite sheets for 1,4-dioxane removal from biologically treated landfill leachate (BTLL) was developed. The performance of the RAOC in 1,4-dioxane removal was compared to that of a TiO2 slurry reactor by evaluating the removal efficiencies in pure water (PW) and the BTLL. In the TiO2 slurry reactor, 1,4-dioxane was hardly degraded in the BTLL during 66 h of treatment because of strong inhibition by coexisting substances in the BTLL. In contrast, the RAOC successfully removed 1,4-dioxane from the BTLL by 89% through adsorption and by 81% through photocatalysis during treatment for 66 h. The ratio of the rate constants for degrading 1,4-dioxane in the BTLL and PW by the RAOC was two orders of magnitude higher than that for a TiO2 slurry reactor. This shows that the RAOC greatly mitigated the inhibition by coexisting substances in the BTLL. The electrical energy required for 1,4-dioxane degradation in the BTLL by the RAOC was much lower than that required for degradation by the TiO2 slurry reactor. The results show that the RAOC equipped with AC/TiO2 composite sheets effectively removed 1,4-dioxane from BTLL.

Removal mechanism of sulfamethazine and its intermediates from water by a rotating advanced oxidation contactor equipped with TiO2-high-silica zeolite composite sheets.

The removal of antibiotic sulfamethazine (SMT) and its intermediates from water was investigated using a rotating advanced oxidation contactor (RAOC) equipped with TiO2-high-silica zeolite composite sheets. SMT was readily removed from water through adsorption onto high-silica zeolite and photocatalytic decomposition by TiO2 inside the composite sheet. Some degradation intermediates were retained and photocatalytically decomposed inside the composite sheet. Relatively hydrophobic intermediates such as hydroxylated SMT were captured inside the sheets, whereas hydrophilic intermediates were distributed in water. This was attributed to the hydrophobic interactions in the adsorption mechanism of high-silica zeolite. The time courses of the NH4+, NO3-, and SO42- ion concentration during the RAOC treatment of SMT were evaluated. After treatment by RAOC for 24 h, approximately 94% of nitrogen derived from the amino and sulfanilamide groups and 39% of sulfur from the sulfanilamide group were mineralized, which indicated that the mineralization behavior of SMT treated by RAOC was different from that treated by TiO2 powder. These results strongly suggested that the dissociation of the amino group and cleavage of the sulfonamide group and subsequent dissociation of the amino group preferentially proceeded inside the composite sheets.

Removal of crotamiton and its degradation intermediates from secondary effluent using TiO2-zeolite composites.

Crotamiton, a scabicide and antipruritic agent persistent during biological treatment processes, is frequently detected in secondary effluent. In this study, titanium dioxide (TiO2) and high-silica zeolite (HSZ-385) composites were synthesized and applied for the treatment of crotamiton in secondary effluent. Crotamiton was rapidly adsorbed by HSZ-385, and the adsorption performance of crotamiton in the secondary effluent was quite close to that in the test using ultrapure water. Even though the TiO2-zeolite composites showed lower adsorption rates than that of HSZ-385, similar crotamiton adsorption capacities were revealed using both test materials. The photocatalytic decomposition of crotamiton was significantly inhibited by the water matrix at low initial concentrations. The TiO2-zeolite composites rapidly adsorbed crotamiton from secondary effluent, and then the crotamiton was gradually decomposed under ultraviolet irradiation. Importantly, when using TiO2-zeolite composites, coexisting material in the secondary effluent did not markedly inhibit crotamiton removal at low initial crotamiton concentration. The behaviors of the main intermediates during treatment demonstrated that the main degradation intermediates of crotamiton were also captured by the composites.

Removal behaviors of sulfamonomethoxine and its degradation intermediates in fresh aquaculture wastewater using zeolite/TiO2 composites.

Removal efficiencies of sulfamonomethoxine (SMM) and its degradation intermediates formed by treatment with zeolite/TiO2 composites through adsorption and photocatalysis were investigated in fresh aquaculture wastewater (FAWW). Coexistent substances in the FAWW showed no inhibitory effects against SMM adsorption. Although coexistent substances in the FAWW inhibited the photocatalytic decomposition of SMM, the composites mitigated the inhibition, possibly because of concentration of SMM on their surface by adsorption. LC/MS/MS analyses revealed that hydroxylation of amino phenyl and pyrimidinyl portions, transformation of the amino group in the amino phenyl portion into a nitroso group, and substitution of the methoxy group with a hydroxyl group occurring in the initial reaction resulted in the formation of various intermediates during the photocatalysis of SMM. All detected intermediates had a ring structure, and almost all intermediates disappeared at the same time SMM was completely decomposed. Ph-OH formed by hydroxylation of the phenyl portion was detected upon decomposition of SMM during photocatalysis. The removal of Ph-OH by the composites proceeded more rapidly than that by TiO2 alone under ultraviolet irradiation. The SMM and Ph-OH were completely degraded by the composites within 30min, showing that the zeolite/TiO2 composites were effective in removing SMM and its intermediates from FAWW.

Photocatalytic decomposition behavior and reaction pathway of sulfamethazine antibiotic using TiO2.

The photocatalytic degradation of sulfanethazine (SMT), one of the sulfonamide antibiotics, in aqueous solution by TiO2 was investigated. The time courses of SMT concentration, the amount of non-purgeable organic carbon, and the concentrations of ions such as SO4(2-), NH4(+), and NO3(-) formed during the photocatalytic reaction were measured and the structures of seven intermediates formed with the disappearance of SMT were also estimated by LC/MS/MS analyses. In addition to that of SMT, the decomposition behaviors of model compounds sulfanilic acid (SA) and 4-amino-2, 6-dimethylpyrimidine (ADMP) were investigated using the TiO2/UV system. The observed photocatalytic degradation behaviors of SMT, SA, and ADMP gave new insight into the degradation pathway of SMT. Especially, the formation of p-aminophenol during SMT decomposition, which until now has not been reported in previous studies concerning the photocatalytic decomposition of SMT and other sulfonamide antibiotics. These results indicate the existence of a novel photocatalytic degradation pathway for sulfonamides. The direct substitution of the sulfonamide group with a hydroxyl group is suggested.

Factors affecting the adsorptive removal of bisphenol A in landfill leachate by high silica Y-type zeolite.

Although bisphenol A (BPA), a representative endocrine-disrupting compound, has been detected frequently in landfill leachate, effective technologies for BPA removal from landfill leachates are limited. We used high silica Y-type zeolite (HSZ-385) for the selective adsorption of BPA from landfill leachate, and factors affecting this adsorption are discussed. Higher removal efficiencies at pH 5.0-9.0 imply that neutral BPA is adsorbed more easily onto HSZ-385 than monomeric or divalent BPA anions. An increase in ionic strength and sodium acetate concentration did not affect BPA adsorption significantly, while the removal efficiency decreased slightly when more than 50 mgC/L of humic acid was added. HSZ-385 was applied to synthetic leachates that simulate the composition of landfill leachate at various degradation stages. In young acidic leachates that contain sodium acetate, the use of HSZ-385 for the adsorptive removal of BPA appears to be more effective than in old alkaline leachates, which contain large amounts of humic acid. In addition, 82 % BPA removal was achieved from young raw leachates using HSZ-385, which demonstrates that selective BPA removal from actual landfill leachate has been achieved.

Modeling of sulfonamide antibiotic removal by TiO(2)/high-silica zeolite HSZ-385 composite.

TiO(2)/high-silica zeolite composite synthesized by a sol-gel method was applied for the removal of sulfamethazine (SMT) antibiotic from water, and simple models including both adsorption and photocatalytic decomposition were developed. In this study, two types of models were constructed: a synergistic model that included the interaction between the zeolite and TiO(2) in the composite, and an individual model, which did not include the interaction. We obtained rate constants for adsorption, desorption and photocatalytic decomposition experimentally, and compared them with the results calculated using the synergistic and individual models. The individual model predicted that ca. 55% of SMT would be removed from the system after 6h of treatment; however, our experiments showed that 80% of the SMT was removed, suggesting the existence of another reaction pathway. Therefore, a synergistic model was constructed, in which, part of the SMT was adsorbed onto the zeolite within the composite, desorbed from the zeolite and migrated to the TiO(2), and was then photocatalytically decomposed. Experiments were carried out with varying amounts of the TiO2-zeolite composite, and the synergistic model was validated. We estimated that 10% of the desorbed SMT was photocatalytically decomposed without being released into the water. When TiO(2)-zeolite composite concentrations were 0.04, 0.12 and 0.20g/L, and the treatment time was 6h, the proportions of the total decomposition of SMT that occurred via this synergistic reaction pathway were calculated as 52.2%, 58.6% and 66.7%, respectively. In other words, over half of the SMT was decomposed through the synergistic reaction, which played a very significant role in the overall removal of SMT (the remainder of the SMT was decomposed through simple photocatalysis on the TiO(2)).

Adsorptive removal and photocatalytic decomposition of sulfamethazine in secondary effluent using TiO2-zeolite composites.

We investigated the adsorption and decomposition of sulfamethazine (SMT), which is used as a synthetic antibacterial agent and discharged into environmental water, using high-silica Y-type zeolite (HSZ-385), titanium dioxide (TiO2), and TiO2-zeolite composites. By using ultrapure water and secondary effluent as solvents, we prepared SMT solutions (10 µg/L and 10 mg/L) and used them for adsorption and photocatalytic decomposition experiments. When HSZ-385 was used as an adsorbent, rapid adsorption of SMT in the secondary effluent was confirmed, and the adsorption reached equilibrium within 10 min. The photocatalytic decomposition rate using TiO2 in the secondary effluent was lower than that in ultrapure water, and we clarified the inhibitory effect of ions and organic matter contained in the secondary effluent on the reaction. We synthesized TiO2-zeolite composites and applied them to the removal of SMT. During the treatment of 10 µg/L SMT in the secondary effluent using the composites, 76% and more than 99% of the SMT were decomposed within 2 and 4 h by photocatalysis. The SMT was selectively adsorbed onto high-silica Y-type zeolite in the composites. Resultantly, the inhibitory effect of the coexisting materials was reduced, and the composites could remove SMT more effectively compared with TiO2 alone in the secondary effluent.

Photocatalytic decomposition of crotamiton over aqueous TiO(2) suspensions: determination of intermediates and the reaction pathway.

The photocatalytic degradation of crotamiton in aqueous solution using TiO(2) was investigated. To investigate the effect of initial pH, the photodegradation behaviors of three types of pharmaceuticals were compared (crotamiton, clofibric acid, sulfamethoxazole). The degradation rates of crotamiton in the pH range 3-9 were nearly equal, but those of clofibric acid and sulfamethoxazole were affected by pH. At pH>6.5, TiO(2) particles, clofibric acid and sulfamethoxazole had negative charge, therefore, the repulsive force between TiO(2) particles and anionic pharmaceuticals occurred and a low reaction rate at high pH was observed. The effect of UV intensity and TiO(2) concentration on photodegradation efficiency was also investigated. Linear and logarithmical relationships between UV intensity, TiO(2) concentration and the reaction rate constant were confirmed. Furthermore, the structures of photodegradation intermediates formed concomitantly with the disappearance of crotamiton were estimated. Seven intermediates were characterized by LC/MS/MS analyses, and it was assumed that the photocatalytic degradation of crotamiton was initiated by the attack of electrophilic hydroxyl radicals on aromatic rings and alkyl chains.

Effect of void structure of photocatalyst paper on VOC decomposition.

TiO2 powder-containing paper composites, called TiO2 paper, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO2 paper has a porous structure originating from the layered pulp fiber network, with TiO2 powders scattered on the fiber matrix. Under UV irradiation, the TiO2 paper decomposed gaseous acetaldehyde more effectively than powdery TiO2 and a pulp/TiO2 mixture not in paper form. Scanning electron microscopy and mercury intrusion analysis revealed that the TiO2 paper had characteristic unique voids ca. 10 microm in diameter, which might have contributed to the improved photocatalytic performance. TiO2 paper composites having different void structures were prepared by using beaten pulp fibers with different degrees of freeness and/or ceramic fibers. The photodecomposition efficiency was affected by the void structure of the photocatalyst paper, and the initial degradation rate of acetaldehyde increased with an increase in the total pore volume of TiO2 paper. The paper voids presumably provided suitable conditions for TiO2 catalysis, resulting in higher photocatalytic performance by TiO2 paper than by TiO2 powder and a pulp/TiO2 mixture not in paper form.

Photocatalytic decomposition of bisphenol A in water using composite TiO2-zeolite sheets prepared by a papermaking technique.

Titanium dioxide (TiO2) photocatalyst and zeolite adsorbent were made into a paper-like composite by a papermaking technique using pulp and ceramic fibers as sheet matrix. The photocatalytic performance for the degradation of bisphenol A (BPA) dissolved in water was investigated under UV irradiation. The TiO2 sheet prepared was easier to handle than the original TiO2 powders in aqueous media. The TiO2 sheet could decompose the BPA under UV irradiation, although at a lower degradation efficiency than the TiO2 suspension. The TiO2-free zeolite sheet could not remove the BPA from water completely because of its adsorption equilibrium. Furthermore, the composite TiO2-zeolite sheets exhibited a higher efficiency for BPA removal than the zeolite-free TiO2 sheets, the efficiency of the former being equivalent to that of the TiO2 suspension. The enhancement in removal efficiency was not attributed to the simple adsorption of BPA on zeolite but rather to the synergistic effect obtained through the combined use of TiO2 photocatalyst and zeolite adsorbent in the paper-like composite sheet, which is believed to accelerate the BPA photodegradation in water.