Degradation of reactive dyes in a photocatalytic circulating-bed biofilm reactor

Decolorization and mineralization of reactive dyes by intimately coupled TiO₂‐photocatalysis and biodegradation (ICPB) on a novel TiO₂‐coated biofilm carrier were investigated in a photocatalytic circulating‐bed biofilm reactor (PCBBR). Two typical reactive dyes—Reactive Black 5 (RB5) and Reactive Yellow 86 (RY86)—showed similar first‐order kinetics when being photocatalytically decolorized at low pH (～4–5) in batch experiments. Photocatalytic decolorization was inhibited at neutral pH in the presence of phosphate or carbonate buffer, presumably due to electrostatic repulsion from negatively charged surface sites on TiO₂, radical scavenging by phosphate or carbonate, or both. Therefore, continuous PCBBR experiments were carried out at a low pH (～4.5) to maintain high photocatalytic efficiency. In the PCBBR, photocatalysis alone with TiO₂‐coated carriers could remove target compound RB5 and COD by 97% and 47%, respectively. Addition of biofilm inside macroporous carriers maintained a similar RB5 removal efficiency, but COD removal increased to 65%, which is evidence of ICPB despite the low pH. ICPB was further proven by finding microorganisms inside carriers at the end of the PCBBR experiments. A proposed ICPB pathway for RB5 suggests that a major intermediate, a naphthol derivative, was responsible for most of the residual COD, while most of the nitrogen in the azo‐bonds (? N?N? ) was oxidized to N₂. Biotechnol. Bioeng. 2012; 109:884–893. © 2011 Wiley Periodicals, Inc.     

Integrated photocatalytic-biological reactor for accelerated 2,4,6-trichlorophenol degradation and mineralization

An integrated photocatalytic-biological reactor (IPBR) was used for accelerated degradation and mineralization of 2,4,6-trichlorophenol (TCP) through simultaneous, intimate coupling of photocatalysis and biodegradation in one reactor. Intimate coupling was realized by circulating the IPBR’s liquid contents between a TiO₂ film on mat glass illuminated by UV light and honeycomb ceramics as biofilm carriers. Three protocols—photocatalysis alone (P), biodegradation alone (B), and integrated photocatalysis and biodegradation (photobiodegradation, P&B)—were used for degradation of different initial TCP concentrations. Intimately coupled P&B also was compared with sequential P and B. TCP removal by intimately coupled P&B was faster than that by P and B alone or sequentially coupled P and B. Because photocatalysis relieved TCP inhibition to biodegradation by decreasing its concentration, TCP biodegradation could become more important over the full batch P&B experiments. When phenol, an easy biodegradable compounds, was added to TCP in order to promote TCP mineralization by means of secondary utilization, P&B was superior to P and B in terms of mineralization of TCP, giving 95% removal of chemical oxygen demand. Cl⁻ was only partially released during P experiments (24%), and this corresponded to its poor mineralization in P experiments (32%). Thus, intimately coupled P&B in the IPBR made it possible obtain the best features of each: rapid photocatalytic transformation in parallel with mineralization of photocatalytic products.     

Photobiodegradation of phenol with ultraviolet irradiation of new ceramic biofilm carriers

Activated sludge acclimated to biodegrade phenol was allowed to attach on and in light porous ceramic carriers and to function as a biofilm in a photolytic circulating-bed bioreactor (PCBBR). Phenol degradation in the PCBBR was investigated following three protocols: photolysis with ultraviolet light alone (P), biodegradation alone (B), and the two mechanisms operating simultaneously (P/B). Phenol was degraded at approximately equal rates by B and P/B, each of which was much faster than the rate by P. Furthermore, phenol was mineralized to a significantly greater extent with P/B than with either P or B. SEM showed that the biofilm survived well inside macropores that presumably shaded the microorganisms from UV irradiation, even though the UV light greatly reduced biofilm on outer surface of the carriers in the P/B experiments. Rapid biodegradation of phenol, enhanced mineralization, and survival of bacteria inside macropores demonstrated that being in a biofilm inside the porous carriers protected the bacteria from UV-light toxicity, allowing intimate coupling of photolysis and biodegradation.     

2,4-DNT removal in intimately coupled photobiocatalysis: the roles of adsorption, photolysis, photocatalysis, and biotransformation

The removal of 2,4-dinitrotoluene (2,4-DNT) by simultaneous UV-photo(cata)lysis and biodegradation was explored using intimately coupled photolysis/photocatalysis and biodegradation (ICPB) with two novel porous carriers. First, a porous ceramic carrier was used to attach the photocatalyst (TiO?) on its exterior and accumulate biomass in its interior. UV irradiation alone decomposed 71% of the 2,4-DNT in 60 h, and TiO? catalyst improved the photolysis to 77%. Second, a macroporous sponge carrier was used to strongly adsorb 2,4-DNT and protect microorganisms from 2,4-DNT inhibition and UV irradiation. The main photolytic reactions were reduction of the nitryl to amino and hydrolysis of the amino to release NH??. The main biodegradation reactions were oxidative release of NO?? and accelerated reductive release of NH??. ICPB more thoroughly released inorganic N, with nearly equal amounts being oxidized to nitrate and reduced to ammonium. The genera Burkholderia and Bacillus were found inside the sponge carriers, and they are associated with biodegradation of DNT and its photolysis intermediates. Therefore, using an adsorbent and macroporous biofilm carrier enabled the effective removal of 2,4-DNT by ICPB.     

Integrated photocatalytic-biological reactor for accelerated phenol mineralization

An integrated photocatalytic-biological reactor (IPBR) was developed for accelerated phenol degradation and mineralization. In the IPBR, photodegradation and biodegradation occurred simultaneously, but in two separated zones: a piece of mat-glass plate coated with TiO₂ film and illuminated by UV light was connected by internal circulation to a honeycomb ceramic that was the biofilm carrier for biodegradation. This arrangement was designed to give intimate coupling of photocatalysis and biodegradation. Phenol degradation was investigated by following three protocols: photocatlysis with TiO₂ film under ultraviolet light, but no biofilm (photodegradation); biofilm biodegradation with no UV light (biodegradation); and simultaneous photodegradation and biodegradation (intimately coupled photobiodegradation). Photodegradation alone could partly degrade phenol, but was not able to achieve significant mineralization, even with an HRT of 10 h. Biodegradation alone could completely degrade phenol, but it did not mineralize the COD by more than 74%. Photobiodegradation allowed continuous rapid degradation of phenol, but it also led to more complete mineralization of phenol (up to 92%) than the other protocols. The results demonstrate that intimate coupling was achieved by protecting the biofilm from UV and free-radical inhibition. With phenol as the target compound, the main advantage of intimate coupling in the IPBR was increased mineralization, presumably because photocatalysis made soluble microbial products more rapidly biodegradable.     

2,4,6-trichlorophenol (TCP) photobiodegradation and its effect on community structure

The mechanisms occurring in a photolytic circulating-bed biofilm reactor (PCBBR) treating 2,4,6-trichlorophenol (TCP) were investigated using batch experiments following three protocols: photodegradation alone (P), biodegradation alone (B), and intimately coupled photodegradation and biodegradation (P&B). Initially, the ceramic particles used as biofilm carriers rapidly adsorbed TCP, particularly in the B experiments. During the first 10 min, the TCP removal rate for P&B was equal to the sum of the rates for P and B, and P&B continued to have the greatest TCP removal, with the TCP concentration approaching zero only in the P&B experiments. When phenol, an easily biodegradable compound, was added along with TCP in order to promote TCP mineralization by means of secondary utilization, P&B was superior to P and B in terms of mineralization of TCP, giving 95% removal of chemical oxygen demand (COD). The microbial communities, examined by clone libraries, changed dramatically during the P&B experiments. Whereas Burkholderia xenovorans, a known degrader of chlorinated aromatics, was the dominant strain in the TCP-acclimated inoculum, it was replaced in the P&B biofilm by strains noted for biofilm formation and biodegrading non-chlorinated aromatics.     

Photocatalytic inactivation of influenza virus by titanium dioxide thin film

Titanium dioxide (TiO(2)) under ultraviolet (UV) light produces a strong oxidative effect and may therefore be used as a photocatalytic disinfectant. Although many studies on the photocatalytic inactivation of bacteria have been reported, few studies have addressed virus inactivation. In the present study, we demonstrated the inactivation of influenza virus through TiO(2) photocatalysis using TiO(2) nanoparticles immobilized on a glass plate. The influences of the UV intensity, UV irradiation time and bovine serum albumin (BSA) concentration in the viral suspensions on the inactivation kinetics were investigated. Additionally, we also determined whether the International Organization for Standardization (ISO) methodology for the evaluation of antibacterial activity of TiO(2) photocatalysis could be applied to the evaluation of antiviral activity. The viral titers were dramatically reduced by the photocatalytic reaction. Even with a low intensity of UV-A (0.01 mW cm(-2)), a viral reduction of approximately 4-log(10) was observed within a short irradiation time. The viral inactivation kinetics were associated with the exposure time, the UV intensity and the BSA concentration in virus suspensions. These results show that TiO(2) photocatalysis could be used to inactivate the influenza virus. Furthermore, a minor modification of the ISO test method for anti-bacterial effects of TiO(2) photocatalysis could be useful for the evaluation of antiviral activity.     

Development of photocatalytic biosensor for the evaluation of biochemical oxygen demand

The photocatalytic biosensor of flow system using semiconductor TiO2 was developed to evaluate biochemical oxygen demand (BOD) levels in river water. Photocatalysis of sample was carried out in a photoreactor with TiO2 and a 6W black-light blue fluorescent tube as light source. Sample from a photoreactor outlet was measured by an oxygen electrode with a biofilm. The sensor response of photocatalytic biosensor was between 5 and 10 min depending on concentration of biochemical in the samples. At BOD of 1 mgl-1, the sensor response increased 1.33-fold in comparison with that without photocatalysis. The degradation of tannic acid and humic acid with photocatalysis were 51.8 and 38.4%, respectively. Gum arabic and linear alkylbenzene sulfonate (LAS) were degraded a little, but gave the responses of more than double to the sensor. Free radicals yielded by photocatalysis in a photoreactor did not affect the sensor response because their lifetime is extremely short. Fairly good correlation (r=0.983) between the sensor method and the conventional method was obtained for test samples. This biosensor using photocatalytic pretreatment improved the sensitivity.     

石油添加剂甲基叔丁基醚的污染治理技术研究进展

甲基叔丁基醚是一种石油添加剂,广泛应用于中高档汽油中.其对环境造成的污染和对人体健康造成的危害已日益引起人们的高度重视.本文综述了近年来国外有关甲基叔丁基醚的污染治理技术研究进展,主要是高级氧化技术和微生物降解.已用于处理甲基叔丁基醚的高级氧化技术包括;多相光催化氧化法、紫外光加强的过氧化氢氧化法、臭氧法与臭氧-过氧化氢联合氧化法、超声法与超声-臭氧联合氧化法、芬顿法与光芬顿氧化法、氧气的还原性活化和水的γ射线辐射.微生物降解主要涉及有氧代谢和无氧代谢两大途径.     

Photocatalytic inactivation of bacteriophages by TiO2-coated glass plates under low-intensity, long-wavelength UV irradiation

The International Organization for Standardization (ISO) was used to evaluate antibacterial activity by titanium dioxide (TiO(2)) photocatalysis since 2006. We evaluated photocatalytic inactivation of Qβ and T4 bacteriophages induced by low-intensity, long-wavelength ultraviolet A (UVA; 0.1 mW cm(-2) and 0.001 mW cm(-2)) irradiation on a TiO(2)-coated glass plate using the ISO methodology. The results indicated that both bacteriophages were inactivated at 0.001 mW cm(-2) UVA. The intensity of UV light, including long-wavelength light (UVA), is very low in an actual indoor environment. Thus, TiO(2) photocatalysis can be beneficial for inactivating viruses in an indoor environment. Experiments using qPCR and bovine serum albumin degradation assume that viral inactivation is caused by outer viral protein disorder and not by viral RNA reduction by reactive oxygen species produced during TiO(2) photocatalysis. Furthermore, we showed that the ISO methodology for standard testing of antibacterial activity by TiO(2) photocatalysis can be applied to assess antiviral activity.     

Protection of biofilms against toxic shocks by the adsorption and desorption capacity of carriers in anaerobic fluidized bed reactors

The aim of this study was to select a support medium for an anaerobic biofilm fluidized bed reactor (AFBR) for waste water treatment. Six materials, shale, pumice, porous glass, quartz sand, activated carbon and anthracite were used as carriers for the biofilm. The reactors were operated in parallel for several months with vapour condensate from a sulfite cellulose process as feed. The criteria used for the evaluation were: a) Reproducibility of the reactor performance, b) performance of the different carriers under various loading rates, c) stability against toxic shock loadings using 2,4,6-trichlorophenol (TCP) as toxicant, d) recovery capacity after intoxication and starvation, e) adsorption/desorption behavior of the carriers.A comparison between four runs showed good reproducibility of the steady state removal rates. The performance of the reactors and the stability of the degradation rates were tested for a range of loading conditions. Unbuffered, buffered and pH controlled conditions were compared. The pumice carrier was best with respect to the degradation rate achieved per carrier mass. The response of the reactors to massive TCP step loadings was tested. Loadings less than 1.5 kg TCP/m³d resulted in initially normal gas production rates for all the systems, except the activated carbon, whose gas production was partially inhibited from the start. After increasing the load to 1.5 kg TCP/m³d the gas production rates of all the other reactors fell abruptly to zero. Restarting after 2 months, all reactors showed methanogenic activity without requiring new inoculum.Adsorption and desorption experiments with TCP showed that only the anthracite and activated carbon adsorbed appreciable amounts. The activated carbon had the greatest adsorption capacity but did not release the TCP by desorption, as did the anthracite.A bicomponent (pumice and anthracite) carrier mixture was compared in biological experiments with pumice and anthracite carrier alone, with and without TCP loading. The pumice and the carrier-mix performed equally well under non-toxic-loading conditions. With TCP toxic loading, the performance of the anthracite was superior. The anthracite carrier could be regenerated, owing mainly to its capacity for desorption.     

Photochemical UV/TiO2 treatment of olive mill wastewater (OMW)

Olive mill wastewater (OMW) was treated by photocatalysis using TiO2 under UV irradiation on the laboratory scale. The chemical oxygen demand, the coloration at 330nm, and the level of phenols all showed decreases which, after a 24-h treatment, reached 22%, 57% and 94%, respectively. The differences between these three values indicate the persistence of colourless, non-phenolic compounds. Application of the novel Fictitious Atomic-Group Separation method showed an increase in carbon oxidation state and confirmed that the attack primarily concerns, aromatic moieties. A fine spectroscopic study revealed the occurrence of three successive phases during the degradation process, thought to correspond to three different categories of molecules in the OMW and the presence of pectin compounds.     

Βeta-carotene protects sudan IV from photocatalytic degradation in a micellar model system: Insights into the antioxidant properties of the “golden” <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

Sterilization using titanium dioxide-mediated photocatalysis has been shown to be a powerful biocidal process due to the production of reactive redox species (RRS). More specifically, these RRS generated from TiO₂ photocatalysis are able to completely oxidize organic material, including microorganisms. Photocatalysis is a potentially useful application for the production of u.v.-illuminated self-sterilizing surfaces such as in surgical suites or water purification. Some organisms are able to protect themselves from radicals and oxidants by producing carotenoid pigments which scavenge free radicals and oxidants. In this work we have created a micellar model with a target dye and used the model to demonstrate that when β-carotene is incorporated into the system it will protect the target dye from photocatalytic destruction. Our model will help to predict how difficult it will be to destroy microbes when exposed to photocatalysis. Our data showed that 50% of the target dye was protected after 5 min of photocatalytic oxidation when β-carotene was present in the micellar system. However, when the micellar system lacked β-carotene protection, 82% of the dye was destroyed via photocatalysis. As a frame of reference, we subjected our model system to standard oxidative Fenton conditions namely, Fe(NO₃)₃/H₂O₂. We demonstrated that after 90 min exposure to the above reagents 80% of the target dye remained when β-carotene was present in the micellar system. However, when no β-carotene was present 62% of the dye was destroyed under Fenton conditions.     

微生物降解3,5,6-三氯-2-吡啶醇的研究进展

随着高毒性有机磷杀虫剂的限制和禁止使用,近年来以毒死蜱为代表的低毒性有机磷杀虫剂的市场份额有所增加。然而,毒死蜱的使用也导致了环境中3,5,6-三氯-2-吡啶醇(TCP)的产生,因为TCP是毒死蜱和甲基毒死蜱在环境中降解的主要中间代谢产物。它具有较高的水溶性和迁移性,容易进入深层土壤及水体环境,从而引起广泛的污染。释放到环境中的TCP不仅可以抑制TCP及其母体化合物毒死蜱和甲基毒死蜱的生物降解,而且也能抑制其他有机污染物的生物降解,从而进一步加重环境中TCP以及其他有机污染物的累积残留,影响环境系统的自我修复功能。本文概述了TCP及其母体化合物的结构、TCP的生态毒性、TCP降解菌的多样性及其微生物降解的最新研究进展,为毒死蜱和TCP污染地区进行经济可行的生物修复提供参考。     

UV photolysis for enhanced phenol biodegradation in the presence of 2,4,6-trichlorophenol (TCP)

A bacterial strain isolated from activated sludge and identified as Bacillus amyloliquefaciens could biodegrade phenol, but 2,4,6-trichlorophenol (TCP) inhibited phenol biodegradation and biomass growth. UV photolysis converted TCP into dichlorocatechol, monochlorophenol, and dichlorophenol, and this relieved inhibition by TCP. Phenol-removal and biomass-growth rates were significantly accelerated after UV photolysis: the monod maximum specific growth rate (μ _max) increased by 9 % after TCP photolysis, and the half-maximum-rate concentration (K _S) decreased by 36 %. Thus, the major benefit of UV photolysis in this case was to transform TCP into a set of much-less-inhibitory products.     

A Pseudomonas putida Strain Genetically Engineered for 1,2,3-Trichloropropane Bioremediation

1,2,3-Trichloropropane (TCP) is a toxic compound that is recalcitrant to biodegradation in the environment. Attempts to isolate TCP-degrading organisms using enrichment cultivation have failed. A potential biodegradation pathway starts with hydrolytic dehalogenation to 2,3-dichloro-1-propanol (DCP), followed by oxidative metabolism. To obtain a practically applicable TCP-degrading organism, we introduced an engineered haloalkane dehalogenase with improved TCP degradation activity into the DCP-degrading bacterium Pseudomonas putida MC4. For this purpose, the dehalogenase gene (dhaA31) was cloned behind the constitutive dhlA promoter and was introduced into the genome of strain MC4 using a transposon delivery system. The transposon-located antibiotic resistance marker was subsequently removed using a resolvase step. Growth of the resulting engineered bacterium, P. putida MC4-5222, on TCP was indeed observed, and all organic chlorine was released as chloride. A packed-bed reactor with immobilized cells of strain MC4-5222 degraded >95% of influent TCP (0.33 mM) under continuous-flow conditions, with stoichiometric release of inorganic chloride. The results demonstrate the successful use of a laboratory-evolved dehalogenase and genetic engineering to produce an effective, plasmid-free, and stable whole-cell biocatalyst for the aerobic bioremediation of a recalcitrant chlorinated hydrocarbon.     

How UV photolysis accelerates the biodegradation and mineralization of sulfadiazine (SD)

Sulfadiazine (SD), one of broad-spectrum antibiotics, exhibits limited biodegradation in wastewater treatment due to its chemical structure, which requires initial mono-oxygenation reactions to initiate its biodegradation. Intimately coupling UV photolysis with biodegradation, realized with the internal loop photobiodegradation reactor, accelerated SD biodegradation and mineralization by 35 and 71 %, respectively. The main organic products from photolysis were 2-aminopyrimidine (2-AP), p-aminobenzenesulfonic acid (ABS), and aniline (An), and an SD-photolysis pathway could be identified using C, N, and S balances. Adding An or ABS (but not 2-AP) into the SD solution during biodegradation experiments (no UV photolysis) gave SD removal and mineralization rates similar to intimately coupled photolysis and biodegradation. An SD biodegradation pathway, based on a diverse set of the experimental results, explains how the mineralization of ABS and An (but not 2-AP) provided internal electron carriers that accelerated the initial mono-oxygenation reactions of SD biodegradation. Thus, multiple lines of evidence support that the mechanism by which intimately coupled photolysis and biodegradation accelerated SD removal and mineralization was through producing co-substrates whose oxidation produced electron equivalents that stimulated the initial mono-oxygenation reactions for SD biodegradation.     

Iridium Oxide‐Assisted Plasmon‐Induced Hot Carriers: Improvement on Kinetics and Thermodynamics of Hot Carriers

Plasmonic nanostructures are capable of driving photocatalysis through absorbing photons in the visible region of the solar spectrum. Unfortunately, the short lifetime of plasmon‐induced hot carriers and sluggish surface chemical reactions significantly limit their photocatalytic efficiencies. Moreover, the thermodynamically favored excitation mechanism of plasmonic photocatalytic reactions is unclear. The mechanism of how the plasmonic catalyst could enhance the performance of chemical reaction and the limitation of localized surface plasmon resonance devices is proposed. In addition, a design is demonstrated through co‐catalyst decorated plasmonic nanoparticles Au/IrO_X upon a semiconductor nanowire‐array TiO₂ electrode that are able to considerably improve the lifetime of plasmon‐induced charge‐carriers and further facilitate the kinetics of chemical reaction. A thermodynamically favored excitation with improved kinetics of hot carriers is revealed through electrochemical studies and characterization of X‐ray absorption spectrum. This discovery provides an opportunity to efficiently manage hot carriers that are generated from metal nanostructures through surface plasmon effects for photocatalysis applications.     

High-rate acidophilic ferrous iron oxidation in a biofilm airlift reactor and the role of the carrier material

In this study, the feasibility and engineering aspects of acidophilic ferrous iron oxidation in a continuous biofilm airlift reactor inoculated with a mixed culture of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans bacteria were investigated. Specific attention was paid to biofilm formation, competition between both types of bacteria, ferrous iron oxidation rate, and gas liquid mass transfer limitations. The reactor was operated at a constant temperature of 30 degrees C and at pH values of 0-1.8. Startup of the reactor was performed with basalt carrier material. During the experiments the basalt was slowly removed and the ferric iron precipitates formed served as a biofilm carrier. These precipitates have highly suitable characteristics as a carrier material for the immobilization of ferrous iron-oxidizing bacteria and dense conglomerates were observed. Lowering the pH (0.6-1) resulted in dissolution of the ferric precipitates and induced granular sludge formation. The maximum ferrous iron oxidation rate achieved in this study was about 145 molFe(2+)/m(3).h at a hydraulic residence time of 0.25 h. Optimal treatment performance was obtained at a loading rate of 100 mol/m(3).h at a conversion efficiency as high as 98%. Fluorescent in situ hybridization (FISH) studies showed that when the reactor was operated at high ferrous iron conversion (>85%) for 1 month, the desirable L. ferrooxidans species could out-compete A. ferrooxidans due to the low Fe(2+) and high Fe(3+) concentrations.     

The influence of cell immobilization by biofilm forming on the biodegradation capabilities of bacterial consortia

Recent biodegradation researches are focused on improving the deterioration efficiency and maintaining the stability of microbial activity during the process. Immobilizing bacterial cells by using the adhesive method is a simple way to achieve both objectives. The purpose of this study was to evaluate how the immobilization of bacterial cells by the biofilm forming method influences the biodegradation efficiency of two different bacterial consortia—low diesel oil degraders (base deterioration efficiency < 40%) and high phenol degraders (base deterioration efficiency > 90%). The degradation tests were carried out on four different carriers (expanded clay pellets, polypropylene, polyvinyl chloride rings and paperboard). The obtained results show that biofilms may considerably increase the efficiency of low degraders. The best diesel oil deterioration (80%) was achieved when paperboard was used as a carrier. However, the immobilization of high degraders did not significantly influence their base biodegradation potential. A 6% increase was noted only for the expanded clay pellets.