Thin-film fixed-bed reactor (TFFBR) for solar photocatalytic inactivation of aquaculture pathogen <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

Background  

Outbreaks of infectious diseases by microbial pathogens can cause substantial losses of stock in aquaculture systems. There are several ways to eliminate these pathogens including the use of antibiotics, biocides and conventional disinfectants, but these leave undesirable chemical residues. Conversely, using sunlight for disinfection has the advantage of leaving no chemical residue and is particularly suited to countries with sunny climates. Titanium dioxide (TiO₂) is a photocatalyst that increases the effectiveness of solar disinfection. In recent years, several different types of solar photocatalytic reactors coated with TiO₂ have been developed for waste water and drinking water treatment. In this study a thin-film fixed-bed reactor (TFFBR), designed as a sloping flat plate reactor coated with P25 DEGUSSA TiO₂, was used.     

Gas phase photocatalytic degradation on TIO2 pellets of volatile chlorinated organic compounds from a soil vapor extraction well

The degradation of trichloroethylene (TCE, Cl₂C=CHCl) and tetrachloroethylene (PCE, Cl₂C=CCI₂) in a gas stream from a soil vapor extraction (SVE) well was demonstrated with an annular photocatalytic reactor packed with porous TiO₂ pellets in a field trial at the Savannah River Site in Aiken, SC. The TiO₂ pellets were prepared using a sol‐gel method. The experiments were performed at 55 to 60°C using space times of 10⁸ to 10¹⁰ g ? s ? mol^‐1 for TCE and PCE. Chloroform (CHCl₃) and carbon tetrachloride (CCl₄) were detected as minor products from side reactions. On a molar basis, the amounts CCl₄ and CHCl₃ produced were about 2 and 0.2% of the reactants, respectively.     

Grazers and vitamins shape chain formation in a bloom-forming dinoflagellate, Cochlodinium polykrikoides

Predators influence the phenotype of prey through both natural selection and induction. We investigated the effects of grazers and nutrients on chain formation in a dinoflagellate, Cochlodinium polykrikoides, which forms dense blooms and has deleterious effects on marine ecosystems around the world. Field populations of C. polykrikoides formed longer chains than laboratory cultures without grazers. In the field, chain length of C. polykrikoides was positively correlated with the abundance of the copepod Acartia tonsa. Chain length of C. polykrikoides increased when exposed to live females of A. tonsa or its fresh (<24 h post-isolation) exudates for 48 h. These results suggest that dissolved chemical cues released by A. tonsa induce chain formation in C. polykrikoides. Ingestion rate of A. tonsa on four-cell chains of C. polykrikoides was lower than on single cells, suggesting that chain formation may be an effective anti-grazing defense. Finally, nutrient amendment experiments demonstrated that vitamins (B₁, B₇, and B₁₂) increased the chain length of C. polykrikoides both singly and collectively, while trace metals and inorganic nutrients did not, showing that vitamins may also influence chain formation in this species.     

Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity

The photocatalytic properties of titanium dioxide are well known and have many applications including the removal of organic contaminants and production of self-cleaning glass. There is an increasing interest in the application of the photocatalytic properties of TiO₂ for disinfection of surfaces, air and water. Reviews of the applications of photocatalysis in disinfection (Gamage and Zhang 2010; Chong et al., Wat Res 44(10):2997–3027, 2010) and of modelling of TiO₂ action have recently been published (Dalrymple et al. , Appl Catal B 98(1–2):27–38, 2010). In this review, we give an overview of the effects of photoactivated TiO₂ on microorganisms. The activity has been shown to be capable of killing a wide range of Gram-negative and Gram-positive bacteria, filamentous and unicellular fungi, algae, protozoa, mammalian viruses and bacteriophage. Resting stages, particularly bacterial endospores, fungal spores and protozoan cysts, are generally more resistant than the vegetative forms, possibly due to the increased cell wall thickness. The killing mechanism involves degradation of the cell wall and cytoplasmic membrane due to the production of reactive oxygen species such as hydroxyl radicals and hydrogen peroxide. This initially leads to leakage of cellular contents then cell lysis and may be followed by complete mineralisation of the organism. Killing is most efficient when there is close contact between the organisms and the TiO₂ catalyst. The killing activity is enhanced by the presence of other antimicrobial agents such as Cu and Ag.     

The Photocatalytic Activity of TiO<Subscript>2</Subscript> Thin Film Deposited on Al Plate Together with Cu(II) and Ag(I)

Cu (II) and Ag(I) together with TiO₂ powder were deposited on conducting support substrates to enhance the photocatalytic ability. The catalytic efficiency was tested by monitoring the photocatalytic degradation and detriment of methylene blue (MB) and bovine serum albumin (BSA). The conformational change of BSA induced by catalysts was also observed by circular dichroism spectroscopy.The antibacterial activities were studied by Escherichia coli. Both MB and BSA could be degraded more efficiently than pure TiO₂. After treatment with catalyst, the morphology of cells became twisted and rougher. Regular wrinkles were damaged and groove-like rift appeared on the surface. The fluorescence polarization has shown a significant decrease in membrane fluidity and the increase of permeability of cell membrane. Changes of the spectral profile of E. coli were observed, which suggested the damages of surface groups on the cell membrane.     

Comparative effects of TiO2-immobilized photocatalytic supporters on the bactericidal efficiency of a novel photoreactor

A novel and highly effective UV-TiO₂ photocatalytic reactor was developed for killing microorganisms, including Escherichia coli. Among tested four types of TiO₂-immobilized photocatalytic supporters (glass bead, muscovite bead, alginate bead, and TiO₂ thin film coated quartz tube), the muscovite bead had a 99.9% percent bactericidal activity within 5 min along with permanent longevity. Adding air bubbles or H₂O₂ (<50 mg l^–1) to the sample solution significantly enhanced the killing activity in that 100% percent of bacterial cells were killed within 3 min.     

A Facile Method to Improve the Photocatalytic and Lithium‐Ion Rechargeable Battery Performance of TiO2 Nanocrystals

TiO₂ has been well studied as an ultraviolet (UV) photocatalyst and electrode material for lithium‐ion rechargeable batteries. Recent studies have shown that hydrogenated TiO₂ displayed better photocatalytic and lithium ion battery performances. Here it is demonstrated that the photocatalytic and battery performances of TiO₂ nanocrystals can be successfully improved with a facile low‐temperature vacuum process. These TiO₂ nanocrystals extend their optical absorption far into the visible‐light region, display nanometer‐scale surface atomic rearrangement, possess superoxide ion characteristics at room temperature without light irradiation, show a 4‐fold improvement in photocatalytic activity, and has 30% better performance in capacity and charge/discharge rates for lithium ion battery. This facile method could provide an alternative and effective approach to improve the performance of TiO₂ and other materials towards their practical applications.     

Long‐Lived,Visible‐Light‐Excited Charge Carriers of TiO2/BiVO4 Nanocomposites and their Unexpected Photoactivity for Water Splitting

Different mole ratios of TiO₂/BiVO₄ nanocomposites with effective contacts have are fabricated by putting BiVO₄ nanoparticles into the TiO₂ sol, followed by thermal treatment at 450 °C. Based on the transient‐state surface photovoltage responses and the atmosphere‐controlled steady‐state surface photovoltage spectra, it is concluded that the photogenerated charge carriers in the TiO₂/BiVO₄ nanocomposite with a proper mole ratio (5%) display much longer lifetime and higher separation than those in the BiVO₄ alone. This is responsible for the unexpected activity for photoelectrochemical oxidation of water, for photocatalytic production of H₂, and for photocatalytic degradation of phenol as a model pollutant under visible irradiation. Moreover, it is suggested that the prolonged lifetime and increased separation of photogenerated charges in the fabricated TiO₂/BiVO₄ nanocomposite is attributed to the unusual spatial transfer of visible‐excited high‐energy electrons of BiVO₄ to TiO₂. This work will provide feasible routes to synthesize visible‐light responsive nanomaterials for efficient solar utilization.     

Enhanced catalase synthesis by a novel combined system of photocatalytic reactor and fermentor

A novel combined system of a photocatalytic reactor, with UV and titanium dioxide as photocatalyst, and a fermentor with Bacillus sp. F26 as catalase producer was developed. Production of catalase was enhanced by 14% to 18.5 U ml⁻¹ without affecting cell growth.Nomenclature q_s: specific glucose consumption rate; μ: specific growth rate; q_p: specific CAT production rate     

Sterilization effects of a TiO<Subscript>2</Subscript> photocatalytic film against a<Emphasis Type="Italic">Streptococcus mutans</Emphasis> culture

Streptococcus mutans is one of the more significant pathogens involved in the development of dental caries in humans. The purpose of this research was to design a TiO₂-coated dental instrument and to determine the bactericidal effects of the instrument onS. mutants. TiO₂ photocatalytic films were prepared by the low-pressure metal-organic chemical vapor deposition (LPMOCVD) method using titanium tetraisopropoxide (TTIP) as precursor. The photocatalytic reaction was carried out on a TiO₂-coated pyrex petri dish with an ultraviolet (UV) light emitting diode (LED) illuminator or a fluorescent lamp light source. Our data indicates that the relative survival ratio ofS. mutans when plated onto TiO₂ photocatalytic films and under exposure to UV-A light for 15 min was 0.01%. In addition, a fluorescent lamp light source also had bactericidal effects on theS. mutans plated TiO₂ photocatalytic films. These results indicate that TiO₂-coated dental materials or devices may be useful in dental treatments for the prevention of carious or enamel demineralization.     

Satellite detection of harmful algal bloom occurrences in Korean waters

Cochlodinium polykrikoides (p) is a planktonic dinoflagellate known to produce red tides responsible for massive fish kills and thereby serious economic loss in Korean coastal waters, particularly during summer and fall seasons. The present study involved analyzing chlorophyll-a (Chl-a) from SeaWiFS ocean color imagery collected over the period 1998–2002 to understand the spatial and temporal aspects of C. polykrikoides blooms that occurred in the enclosed and semi-enclosed bays of the Korean Southeast Sea. NOAA-AVHRR data were used to derive Sea Surface Temperature (SST) to elucidate physical factors affecting the spatial distribution and abundance of C. polykrikoides blooms. The time series of SeaWiFS-derived Chl-a gave an impression that recent red tide events with higher concentrations appeared to span more than 8 weeks during summer and fall seasons and were widespread in most of the Korean Southeast Sea coastal bays and neighboring oceanic waters. Coupled eutrophication and certain oceanic processes were thought to give rise to the formation of massive C. polykrikoides blooms with cell abundances ranging from 1000 to 30,000 cells ml⁻¹, causing heavy mortalities of aquaculture fish and other marine organisms in these areas. Our analysis indicated that Chl-a estimates from SeaWiFS ocean color imagery appeared to be useful in demarcating the locality, spatial extent and distribution of these blooms, but unique identification of C. polykrikoides from non-bloom and sediment dominated waters remains unsuccessful with this data alone. Thus, the classical spectral enhancement and classification techniques such as Forward Principal Component Analysis (FPCA) and Minimum Spectral Distance (MSD) to uniquely identify and better understand C. polykrikoides blooms characteristics from other optical water types were attempted on both low spatial resolution SeaWiFS ocean color imagery and high spatial resolution Landsat-7 ETM+ imagery. Application of these techniques could capture intricate and striking patterns of C. polykrikoides blooms from surrounding non-bloom and sediment dominated waters, providing improved capability of detecting, predicting and monitoring C. polykrikoides bloom in such optically complex waters. The result obtained from MSD classification showed that retrieval of C. polykrikoides bloom from the mixed phase of this bloom with turbid waters was not feasible with the SeaWiFS ocean color imagery, but feasible with Landsat-7 ETM+ imagery that provided more accurate and comparable spatial C. polykrikoides patterns consistent with in situ observations. The dense phase of the bloom estimated from these imageries occupied an area of more than 25 km² around the coastal bays and the mixed phase extended over several hundreds kilometers towards the Southeast Sea offshore due to exchange of water masses caused by coastal and oceanic processes. Sea surface temperature analyzed from AVHRR infrared data captured the northeastward flow of Tsushima Warm Current (TWC) waters that provided favorable environmental conditions for the rapid growth and subsequent southward initiation of C. polykrikoides blooms in hydrodynamically active regions in the Korean Southeast Sea offshore.     

Enhancement of the biodegradability of model wastewater containing recalcitrant or inhibitory chemical compounds by photocatalytic pre-oxidation

m-Dinitrobenzene, diphenylamine and resorcinol, threearomatic compounds found inhibitory or recalcitrant tobiological treatments, were chosen as model chemicalsfor this study on the integration ofphotocatalytic-biological treatments. The degradationof each of these compounds was achieved by ultravioletphotocatalytic oxidation, leading to the formation ofintermediate compounds. The photocatalytic treatmentwas performed in a TiO₂ slurry reactor containingan aqueous solution of one of the three chemicals. Thebiodegradability of model wastewater treatedphotocatalytically was measured in terms ofBOD₁/TOC. Intermediate compounds that appeared atearly stages of the photocatalytic degradation ofm-dinitrobenzene or diphenylamine seemed to be moreinhibitory than the parent compounds but this was notthe case for resorcinol. A substantial improvement inBOD₁/TOC could be achieved, but it required themineralization of at least 80% of the organic carbonoriginally in the water. Microtox® toxicityresults confirmed the BOD₁/TOC trends fordiphenylamine.     

Alteration of plankton communities and biogeochemical cycles by harmful Cochlodinium polykrikoides (Dinophyceae) blooms

Cochlodinium polykrikoides is a globally distributed, ichthyotoxic, bloom-forming dinoflagellate. Blooms of C. polykrikoides manifest themselves as large (many km²) and distinct patches with cell densities exceeding 10³ ml⁻¹ while water adjacent to these patches can have low cell densities (<100 cells ml⁻¹). While the effect of these blooms on fish and shellfish is well-known, their impacts on microbial communities and biogeochemical cycles are poorly understood. Here, we investigated plankton communities and the cycling of carbon, nitrogen, and B-vitamins within blooms of C. polykrikoides and compared them to areas in close proximity (<100 m) with low C. polykrikoides densities. Within blooms, C. polykrikoides represented more than 90% of microplankton (>20 μm) cells, and there were significantly more heterotrophic bacteria and picoeukaryotic phytoplankton but fewer Synechococcus. Terminal restriction fragment length polymorphism analysis of 16S and 18S rRNA genes revealed significant differences in community composition between bloom and non-bloom samples. Inside the bloom patches, concentrations of vitamin B₁₂ were significantly lower while concentrations of dissolved oxygen were significantly higher. Carbon fixation and nitrogen uptake rates were up to ten times higher within C. polykrikoides bloom patches. Ammonium was a more important source of nitrogen, relative to nitrate and urea, for microplankton within bloom patches compared to non-bloom communities. While uptake rates of vitamin B₁ were similar in bloom and non-bloom samples, vitamin B₁₂ was taken up at rates five-fold higher (>100 pmol⁻¹ L⁻¹ d⁻¹) in bloom samples, resulting in turn-over times of hours during blooms. This high vitamin demand likely led to the vitamin B₁₂ limitation of C. polykrikoides observed during nutrient amendment experiments conducted with bloom water. Collectively, this study revealed that C. polykrikoides blooms fundamentally change microbial communities and accelerate the cycling of carbon, some nutrients, and vitamin B₁₂.     

Physiochemical properties of n-n heterostructured TiO2/Mo-TiO2 composites and their photocatalytic degradation of gaseous toluene

The composite TiO₂/Mo-TiO₂ were prepared by a modified sol-gel method. The prepared catalysts were characterized by X-ray diffraction, BET analysis, SEM, X-ray photoelectron spectroscopy, and UV–vis diffused reflectance spectroscopy techniques. The structural characterization results demonstrated that Mo was successfully doped into the TiO₂ lattice and caused slight changes in the physiochemical properties. The UV–vis DRS showed a red shift of the adsorption edge to the visible region. The photocatalytic decomposition efficiencies of the catalysts were examined with toluene as a typical VOC in a continuous flow reactor. The photocatalytic activity of the n-n heterogeneous TiO₂/Mo-TiO₂ was greater than that of pure TiO₂ and Mo-TiO₂, and the catalyst containing a Mo/Ti mole ratio of 2.5% exhibited optimum photocatalytic properties. In general, a relative humidity of 35%, a higher oxygen content, a lower initial toluene concentration, and a higher UV intensity were beneficial for toluene decomposition.     

TiO2 Photocatalysis Damages Lipids and Proteins in Escherichia coli

This study investigates the mechanisms of UV-A (315 to 400 nm) photocatalysis with titanium dioxide (TiO₂) applied to the degradation of Escherichia coli and their effects on two key cellular components: lipids and proteins. The impact of TiO₂ photocatalysis on E. coli survival was monitored by counting on agar plate and by assessing lipid peroxidation and performing proteomic analysis. We observed through malondialdehyde quantification that lipid peroxidation occurred during the photocatalytic process, and the addition of superoxide dismutase, which acts as a scavenger of the superoxide anion radical (O₂·⁻), inhibited this effect by half, showing us that O₂·⁻ radicals participate in the photocatalytic antimicrobial effect. Qualitative analysis using two-dimensional electrophoresis allowed selection of proteins for which spot modifications were observed during the applied treatments. Two-dimensional electrophoresis highlighted that among the selected protein spots, 7 and 19 spots had already disappeared in the dark in the presence of 0.1 g/liter and 0.4 g/liter TiO₂, respectively, which is accounted for by the cytotoxic effect of TiO₂. Exposure to 30 min of UV-A radiation in the presence of 0.1 g/liter and 0.4 g/liter TiO₂ increased the numbers of missing spots to 14 and 22, respectively. The proteins affected by photocatalytic oxidation were strongly heterogeneous in terms of location and functional category. We identified several porins, proteins implicated in stress response, in transport, and in bacterial metabolism. This study reveals the simultaneous effects of O₂·⁻ on lipid peroxidation and on the proteome during photocatalytic treatment and therefore contributes to a better understanding of molecular mechanisms in antibacterial photocatalytic treatment.     

Cochlodinium fulvescens sp. nov. (Gymnodiniales, Dinophyceae), a new chain-forming unarmored dinoflagellate from Asian coasts

Cellular morphology and the phylogenetic position of a new unarmored photosynthetic dinoflagellate Cochlodinium fulvescens Iwataki, Kawami et Matsuoka sp. nov. were examined by light microscopy and molecular phylogenetic analyses based on partial large subunit ribosomal DNA (LSU rDNA) and small subunit ribosomal DNA (SSU rDNA) sequences. The cells of C. fulvescens closely resemble C. polykrikoides, one of the most harmful red tide forming dinoflagellates, due to it possessing a cingulum encircling the cell approximately twice, a spherical nucleus positioned in the anterior part of the cell and an eyespot‐like orange pigmented body located in the dorsal side of the epicone, as well as formation of cell‐chains. However, this species is clearly distinguished from C. polykrikoides based on several morphological characteristics, namely, cell size, shape of chloroplasts and the position of narrow sulcus situated in the cell surface. The sulcus of C. fulvescens is located at the intermediate position of the cingulum in the dorsal side, whereas that of C. polykrikoides is situated immediately beneath the cingulum. LSU rDNA phylogenies indicated that C. fulvescens is clearly distinct from, but closely related to C. polykrikoides among dinoflagellates.     

Controllable Synthesis of Mesoporous TiO2 Polymorphs with Tunable Crystal Structure for Enhanced Photocatalytic H2 Production

Multiphasic titanium dioxide (TiO₂) possessing abundant heterophase junctions have been widely used for various photocatalytic applications. Current synthesis of multiphasic TiO₂ mainly involves the process of thermal treatment and multiple steps of rigorous reactions, which is adverse to controlling the crystal phases and phase ratios of multiphasic TiO₂. Meanwhile, the resulting products have relatively low surface area and nonporous structure. Here, a facile polymer‐assisted coordination‐mediated self‐assembly method to synthesize mesoporous TiO₂ polymorphs with controllable heterophase junctions and large surface area by using polyethylenimine as the porogen in an acidic aqueous synthesis system is reported. Using this approach, the crystal phases (triphase, biphase, and monophase) and phase compositions (0–100%) are easily tailored by selecting the suitable acidic media. Furthermore, the specific surface areas (77–228 m² g^?1) and pore sizes (2.9–10.1 nm) are readily tailored by changing the reaction temperature. The photocatalytic activity of mesoporous TiO₂ polymorphs is evaluated by photocatalytic hydrogen evolution. The triphasic TiO₂ exhibits an excellent photocatalytic H₂ generation rate of 3.57 mmol h^?1 g^?1 as compared to other polymorphs, which is attributed to the synergistic effects of heterophase junctions and mesostructure. The band diagram of possible electron transfer pathway for triphasic TiO₂ is also elucidated.     

Morphology and taxonomy of chain-forming species of the genus Cochlodinium (Dinophyceae)

The morphology of an unarmored chain-forming harmful dinoflagellate Cochlodinium polykrikoides and its similar species such as Cochlodinium catenatum, Cochlodinium fulvescens, and Cochlodinium convolutum was carefully observed, emphasizing the single cell stage for clarifying taxonomically important morphological features. To differentiate C. polykrikoides from C. convolutum, the shape and the position of the nucleus are useful characters. C. polykrikoides also differs from C. fulvescens in being smaller in size, possessing many rod-shaped chloroplasts and having the sulcus running just below the cingulum on the dorsal surface. Careful observation of the ichnotype of C. catenatum suggests that C. catenatum sensu Kofoid and Swezy collected from off La Jolla, CA, USA, is not identical to C. catenatum sensu Okamura and is probably a different species, in having no chloroplasts and a nucleus positioned at the center of the cell. In addition, C. polykrikoides has many morphological features in common with C. catenatum sensu Okamura except for slightly elongate cells and is probably a junior synonym of this species.     

Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces

The aim of the present work was to explore possibilities of photocatalytic TiO₂ coating for reducing biofilms on non-living surfaces. The model organism, Deinococcus geothermalis, known to initiate growth of durable, colored biofilms on machine surfaces in the paper industry, was allowed to form biofilms on stainless steel, glass and TiO₂ film coated glass or titanium. Field emission electron microscopy revealed that the cells in the biofilm formed at 45°C under vigorous shaking were connected to the surface by means of numerous adhesion threads of 0.1--0.3 μm in length. Adjacent cells were connected to one another by threads of 0.5--1 μm in length. An ultrastructural analysis gave no indication for the involvement of amorphous extracellular materials (e.g., slime) in the biofilm. When biofilms on photocatalytic TiO₂ surfaces, submerged in water, were exposed to 20 W h m⁻² of 360 nm light, both kinds of adhesion threads were completely destroyed and the D. geothermalis cells were extensively removed (from >10⁷ down to below 10⁶ cells cm⁻²). TiO₂ films prepared by the sol-gel technique were slightly more effective than those prepared by the ALD technique. Doping of the TiO₂ with sulfur did not enhance its biofilm-destroying capacity. The results show that photocatalytic TiO₂ surfaces have potential as a self-cleaning technology for warm water using industries.     

Effects of the algicides CuSO4 and NaOCl on various physiological parameters in the harmful dinoflagellate Cochlodinium polykrikoides

The marine dinoflagellate Cochlodinium polykrikoides has spread worldwide and is responsible for harmful algal blooms. The chemical biocides, copper sulfate (CuSO₄) and sodium hypochlorite (NaOCl), are known to be effective in removing bloom-forming or biofouling organisms. Here, we assessed the biocidal efficiency and toxicological properties of NaOCl and CuSO₄ on the physiological and catalase responses of C. polykrikoides. The endpoints used were cell counts, pigment content, chlorophyll autofluorescence (CAF), and antioxidant catalase (CAT) activity. The test organism showed a dose-dependent decrease in growth rate against the algicides; 72-h median effective concentrations (EC₅₀) were 0.584 and 0.633 mg L^–1 for NaOCl and CuSO₄, respectively. The decrease in pigment levels and CAF intensity showed that NaOCl and CuSO₄ might affect the photosynthetic processes of the exposed cells. Furthermore, a considerable increase in CAT activity in the cells was detected, indicating that the algicides might generate reactive oxygen species, thereby markedly damaging the cells. These results suggest that the test algicides are very effective in removing C. polykrikoides by inducing cellular stress and inhibiting cell recovery at higher concentrations.