紫外光照射与生物降解耦合用于PCBs降解的研究

介绍了PCBs紫外光降解的机理及研究进展 ,讨论了影响PCBs光降解的主要因素 ,即环上的氯原子数目、取代位置及所处的微环境均显著地影响PCBs的光降解速率。简述了PCBs生物降解的研究进展 ,重点概述了好氧降解、厌氧降解及好氧厌氧协同作用的机理及特点。最后 ,讨论了PCBs生物降解和光降解的互补性 ,介绍了最近的研究进展 ,指出光降解和生物降解耦合将加快PCBs的移走速率 ,提出了PCBs污染土壤原位修复需要进一步解决的问题。     

Molecular perspectives and recent advances in microbial remediation of persistent organic pollutants

Nutrition and pollution stress stimulate genetic adaptation in microorganisms and assist in evolution of diverse metabolic pathways for their survival on several complex organic compounds. Persistent organic pollutants (POPs) are highly lipophilic in nature and cause adverse effects to the environment and human health by biomagnification through the food chain. Diverse microorganisms, harboring numerous plasmids and catabolic genes, acclimatize to these environmentally unfavorable conditions by gene duplication, mutational drift, hypermutation, and recombination. Genetic aspects of some major POP catabolic genes such as biphenyl dioxygenase (bph), DDT 2,3-dioxygenase, and angular dioxygenase assist in degradation of biphenyl, organochlorine pesticides, and dioxins/furans, respectively. Microbial metagenome constitutes the largest genetic reservoir with miscellaneous enzymatic activities implicated in degradation. To tap the metabolic potential of microorganisms, recent techniques like sequence and function-based screening and substrate-induced gene expression are proficient in tracing out novel catabolic genes from the entire metagenome for utilization in enhanced biodegradation. The major endeavor of today’s scientific world is to characterize the exact genetic mechanisms of microbes for bioremediation of these toxic compounds by excavating into the uncultured plethora. This review entails the effect of POPs on the environment and involvement of microbial catabolic genes for their removal with the advanced techniques of bioremediation.     

Increase in biodegradation of dimethyl phthalate by Closterium lunula using inorganic carbon

The effect and mechanism of inorganic carbon (IC) on the biodegradation of dimethyl phthalate (DMP) by a green microalga Closterium lunula was investigated. The growth of this microalga and the biodegradation of DMP were significantly enhanced when the initial IC was increased. An intermediate product of DMP biodegradation was identified as phthalic acid (PA) that was accumulated and caused a sharp decrease in pH of microalgal culture medium, which inhibited both the growth of microalga and the biodegradation of DMP. A suggested second-order kinetic equation of organic pollutant biodegradation by microalgae (-dC/dt = kNr) fitted well with the experimental data. The increase of IC caused a decline in biodegradation rate constant for organic carbon (k) and an increase in growth (N) by supplying a favorite carbon source and mitigating the decrease of pH. As the net effect, the overall biodegradation rate of DMP was promoted as IC increased, which was dominated by the increase of microalgal growth.     

Biodegradation of four phthalate esters in sludge

This study investigated the effects of ultrasonic pretreatment and various treatments on the aerobic degradation of four phthalic acid esters (PAEs) such as diethyl phthalate (DEP), benzyl butyl phthalate (BBP), di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl)phthalate (DEHP) in sludge. The effect on PAE degradation of treating sludge with a 20 min sonication period at a power level of 0.1 W ml(-1) was evaluated. The degradation rates of the four PAEs were DBP>BBP>DEP>DEHP. Degradation rate constants (k(1)) and half-lives (t(1/2)) for the four PAEs (50 mg kg(-1)) ranged from 0.182 to 0.379 day(-1) and 1.8 to 3.8 days, respectively. The optimal pH for PAE degradation in sludge was 7.0 at 30 degrees C. PAE degradation was enhanced by the addition of yeast extract, brij 30 or brij 35 and inhibited by the addition of hydrogen peroxide. Our results show that a combination of ultrasonic pretreatment and biodegradation can effectively remove PAE from sludge.     

Influence of humic substances on the photolysis of aqueous pesticide residues

The present work investigated the direct and indirect photolysis of pesticide residues (atrazine, imazaquin, iprodione), in aqueous solutions and under UV-visible radiation (280-480nm). Different kinds of humic substances (HS) were added to samples in order to evaluate their behaviour as possible photocatalysts and their effect on the photolysis of pesticides. The fulvic acids were purchased from the International Humic Substances Society, and they were added to samples in concentrations ranging from 1 to 150 mgl(-1). Titanium dioxide was used as the photocatalyst, in concentration ranging from 10 to 150 mgl(-1). Pesticides photolysis were measured by UV-visible absorption spectroscopy and differential pulse polarography with all used pesticides, reaching total degradation after 2h of irradiation, thus indicating a fast direct photolysis. Photocatalysis by TiO(2) could increase the pesticides photolysis rate up to 40%. This effect, however, was not observed for imazaquin photolysis. Again, except for imazaquin, HS presence showed a positive effect in increasing pesticide degradation, but only within specific concentration ranges (below 10mg l(-1) for iprodione and about 30mgl(-1) for atrazine). Above these ranges HS induce a decrease in the pesticides photolysis rate. Spin-trapping measurements by electronic paramagnetic resonance spectroscopy, using the spin-trap DMPO, showed that HS are able to photogenerate hydroxyl radicals, increasing the pesticides molecule degradation. However, the HS also react with the photogenerated hydroxyl radical, influencing the pesticide photolysis, leading to a decrease in the photolysis rate and causing it to be strongly dependent on the nature and concentration of residues in the water to be treated.     

Biofiltration Kinetics of a Gaseous Aldehyde Mixture Using a Synthetic Matrix

Abstract

Although aldehydes contribute to ozone and particulate matter formation, there has been little research on the biofiltration of these volatile organic compounds (VOCs), especially as mixtures. Biofiltration degradation kinetics of an aldehyde mixture containing hexanal, 2-methylbutanal (2-MB), and 3-methylbutanal (3-MB) was investigated using a bench-scale, synthetic, media-based biofilter. The adsorption capacity of the synthetic media for a model VOC, 3-methylbutanal, was 10 times that of compost. Periodic residence time distribution analysis (over the course of 1 yr) via a tracer study (84–99% recovery), indicated plug flow without channeling in the synthetic media and lack of compaction in the reactor. Simple first-order and zero-order kinetic models both equally fit the experimental data, yet analysis of the measured rate constants versus fractional conversion suggested an overall first-order model was more appropriate. Kinetic analysis indicated that hexanal had a significantly higher reaction rate (k = 0.09 ± 0.005 1/sec; 23 ± 1.3 ppmv) compared with the branched aldehydes (k = 0.04 ± 0.0036 1/sec; 31 ± 1.6 ppmv for 2-MB and 0.03 ± 0.0051 1/sec; 22 ± 1.3 ppmv for 3-MB). After 3 months of operation, all three compounds reached 100% removal (50 sec residence time, 18–46 ppmv inlet). Media samples withdrawn from the biofilter and observed under scanning electron microscopy analysis indicated microbial growth, suggesting removal of the aldehydes could be attributed to biodegradation.     

Primary biodegradation of veterinary antibiotics in aerobic and anaerobic surface water simulation systems

The primary aerobic and anaerobic biodegradability at intermediate concentrations (50-5000 microg/l) of the antibiotics olaquindox (OLA), metronidazole (MET), tylosin (TYL) and oxytetracycline (OTC) was studied in a simple shake flask system simulating the conditions in surface waters. The purpose of the study was to provide rate data for primary biodegradation in the scenario where antibiotics pollute surface waters as a result of run-off from arable land. The source of antibiotics may be application of manure as fertilizer or excreta of grazing animals. Assuming first-order degradation kinetics, ranges of half-lives for aerobic degradation of the four antibiotics studied were 4-8 days (OLA), 9.5-40 days (TYL), 14-104 days (MET) and 42-46 days (OTC). OLA and OTC were degraded with no initial lag phase whereas lag phases from 2 to 34 days (MET) and 31 to 40 days (TYL) were observed for other substances. The biodegradation behaviour was influenced by neither the concentrations of antibiotics nor the time of the year and location for sampling of surface water. Addition of 1 g/l of sediment or 3 mg/l of activated sludge from wastewater treatment increased the biodegradation potential which is believed to be the result of increased bacterial concentration in the test solution. Biodegradation was significantly slower in tests conducted in absence of oxygen. Assessments of the toxic properties of antibiotics by studying the influence on the biodegradation rates of 14C-aniline at different concentrations of antibiotics showed that no tests were conducted at toxic concentrations.     

Kinetic studies of the reaction of hydroxyl radicals with trichloroethylene and tetrachloroethylene

Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C2HCl3 (k(1)) and C2Cl4 (k2) over an extended temperature range at 740+/-10 Torr in a He bath gas. These absolute rate measurements were accomplished using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. The simple Arrhenius equation adequately describes the low temperature data for k1 (<650 K) and the entire data set for k2 and is given by (in units of cm3 molecule(-1) s(-1)): k1(291 - 650 K) = (9.73+/-1.15) x 10(-13) exp (158.7+/-44.0)/T, k2(293 - 720 K ) = (1.53+/-0.14) x 10(-12) exp (-688.2+/-67.5)/T. Error limits are 2sigma values. The room temperature values for k1 and k2 are within +/-2sigma of previous data using different techniques. The Arrhenius activation energies for k1 and k2 are a factor of 2-3 lower than previously reported values. The experimental measurements for both k1 and k2 in conjunction with transition state and variation transition state theory calculations infer an OH addition mechanism. The lack of a measurable kinetic isotope effect for k1 is consistent with this mechanism. Insight into the subsequent reactions of the chemically activated intermediate are presented in the form of potential energy diagrams derived from ab initio calculations.     

Biofiltration kinetics of a gaseous aldehyde mixture using a synthetic matrix

Although aldehydes contribute to ozone and particulate matter formation, there has been little research on the biofiltration of these volatile organic compounds (VOCs), especially as mixtures. Biofiltration degradation kinetics of an aldehyde mixture containing hexanal, 2-methylbutanal (2-MB), and 3-methylbutanal (3-MB) was investigated using a bench-scale, synthetic, media-based biofilter. The adsorption capacity of the synthetic media for a model VOC, 3-methylbutanal, was 10 times that of compost. Periodic residence time distribution analysis (over the course of 1 yr) via a tracer study (84-99% recovery), indicated plug flow without channeling in the synthetic media and lack of compaction in the reactor. Simple first-order and zero-order kinetic models both equally fit the experimental data, yet analysis of the measured rate constants versus fractional conversion suggested an overall first-order model was more appropriate. Kinetic analysis indicated that hexanal had a significantly higher reaction rate (k = 0.09 +/- 0.005 1/sec; 23 +/- 1.3 ppmv) compared with the branched aldehydes (k = 0.04 +/- 0.0036 1/sec; 31 +/- 1.6 ppmv for 2-MB and 0.03 +/- 0.0051 1/sec; 22 +/- 1.3 ppmv for 3-MB). After 3 months of operation, all three compounds reached 100% removal (50 sec residence time, 18-46 ppmv inlet). Media samples withdrawn from the biofilter and observed under scanning electron microscopy analysis indicated microbial growth, suggesting removal of the aldehydes could be attributed to biodegradation.     

Biodegradation of nonylphenol in river sediment

We investigated the biodegradation of nonylphenol monoethoxylate (NP1EO) and nonylphenol (NP) by aerobic microbes in sediment samples collected at four sites along the Erren River in southern Taiwan. Aerobic degradation rate constants (k1) and half-lives (t1/2) for NP (2 microg g(-1)) ranged from 0.007 to 0.051 day(-1) and 13.6 to 99.0 days, respectively; for NP1EO (2 microg g(-1)) the ranges were 0.006 to 0.010 day(-1) and 69.3 to 115.5 days. Aerobic degradation rates for NP and NP1EO were enhanced by shaking and increased temperature, and delayed by the addition of Pb, Cd, Cu, Zn, phthalic acid esters (PAEs), and NaCl, as well as by reduced levels of ammonium, phosphate, and sulfate. Of the microorganism strains isolated from the sediment samples, we found that strain JC1 (identified as Pseudomonas sp.) expressed the best biodegrading ability. Also noted was the presence of 4'-amino-acetophenone, an intermediate product resulting from the aerobic degradation of NP by Pseudomonas sp.     

Biodegradation of benzene, toluene, and xylene (BTX) in liquid culture and in soil by Bacillus subtilis and Pseudomonas aeruginosa strains and a formulated bacterial consortium

Purpose

The major aromatic constituents of petroleum products viz. benzene, toluene, and mixture of xylenes (BTX) are responsible for environmental pollution and inflict serious public concern. Therefore, BTX biodegradation potential of individual as well as formulated bacterial consortium was evaluated. This study highlighted the role of hydrogen peroxide (H₂O₂), nitrate, and phosphate in stimulating the biodegradation of BTX compounds under hypoxic condition.

Materials and methods

The individual bacterium viz. Bacillus subtilis DM-04 and Pseudomonas aeruginosa M and NM strains and a consortium comprising of the above bacteria were inoculated to BTX-containing liquid medium and in soil. The bioremediation experiment was carried out for 120?h in BTX-containing liquid culture and for 90?days in BTX-contaminated soil. The kinetics of BTX degradation either in presence or absence of H₂O₂, nitrate, and phosphate was analyzed using biochemical and gas chromatographic (GC) technique.

Results

Bacterial consortium was found to be superior in degrading BTX either in soil or in liquid medium as compared to degradation of same compounds by individual strains of the consortium. The rate of BTX biodegradation was further enhanced when the liquid medium/soil was exogenously supplemented with 0.01?% (v/v) H₂O₂, phosphate, and nitrate_. The GC analysis of BTX biodegradation (90?days post-inoculation) in soil by bacterial consortium confirmed the preferential degradation of benzene compared to m-xylene and toluene.

Conclusions

It may be concluded that the bacterial consortium in the present study can degrade BTX compounds at a significantly higher rate as compared to the degradation of the same compounds by individual members of the consortium. Further, addition of H₂O₂ in the culture medium as an additional source of oxygen, and nitrate and phosphate as an alternative electron acceptor and macronutrient, respectively, significantly enhanced the rate of BTX biodegradation under oxygen-limited condition.     

共代谢基质对芽孢杆菌Y-4降解异喹啉的影响

以吡啶，葡萄糖和邻苯二甲酸作为共代谢基质，研究了它们对芽孢杆菌Y_4降解异喹啉的影响。实验结果表明各降解过程均遵循二级反应动力学方程：-dS／dt=K2S2＋K1S＋K0。吡啶的加入会抑制异喹啉的降解，并且吡啶的浓度越高，抑制作用越明显。反应体系中葡萄糖的浓度为100-800mg／L时，葡萄糖的加入会促进异喹啉的降解，且葡萄糖浓度越大，异喹啉降解速率P越大，当葡萄糖的浓度为800mg／L时，其降解率速率P可由未加葡萄糖的0．1924h。上升为0．2255h-1。适宜浓度的邻苯二甲酸会对异喹啉的降解产生促进作用，邻苯二甲酸的浓度为50mg／L时，异喹啉的降解速率可由原来的0．1924h-1增加到0．2145h-1，邻苯二甲酸浓度过高反而会抑制异喹啉的降解。     

Biodegradation of phenanthrene in river sediment

The aerobic biodegradation potential of phenanthrene (a polycyclic aromatic hydrocarbon [PAH]) in river sediment was investigated in the laboratory. Biodegradation rate constants (k1) and half-lives (t1/2) for phenanthrene (5 microg/g) in sediment samples collected at five sites along the Keelung River in densely populated northern Taiwan ranged from 0.12 to 1.13 l/day and 0.61 to 5.78 day, respectively. Higher biodegradation rate constants were noted in the absence of sediment. Two of the sediment samples were capable of biodegrading phenanthrene at initial concentrations 5-100 microg/g; lower biodegradation rates occurred at higher concentrations. Optimal biodegradation conditions were determined as 30 degreesC and pH 7.0. Biodegradation was not significantly influenced by the addition of such carbon sources as acetate, pyruvate, and yeast extract, but was significantly influenced by the addition of ammonium, sulfate, and phosphate. Results show that anthracene, fluorene, and pyrene biodegradation was enhanced by the presence of phenanthrene, but that phenanthrene treatment did not induce benzo[a]pyrene biodegradation during a 12-day incubation period.     

Reductive dechlorination and biodegradation of 2,4,6-trichlorophenol using sequential permeable reactive barriers: laboratory studies

The reductive dechlorination and biodegradation of 2,4,6-trichlorophenol (2,4,6-TCP) was investigated in a laboratory-scale sequential barrier system consisting of a chemical and biological reactive barrier. Palladium coated iron (Pd/Fe) was used as a reactive barrier medium for the chemical degradation of 2,4,6-TCP, and a sand column seeded with anaerobic microbes was used as a biobarrier following the chemical reactive barrier in this study. Only phenol was detected in the effluent from the Pd/Fe column reactor, indicating that the complete dechlorination of 2,4,6-TCP was achieved. The residence time of 30.2-21.2h was required for the complete dechlorination of 2,4,6-TCP of 100 mg l(-1) in the column reactor. The surface area-normalized rate constant (k(SA)) is 3.84 (+/-0.48)x10(-5)lm(-2)h(-1). The reaction rate in the column tests was one order of magnitude slower than that in the batch test. In the operation of the biobarrier, about 100 microM of phenol was completely removed with a residence time of 7-8d. Consequently, the dechlorination prior to biodegradation turns out to increase the overall treatability. Moreover, the sequential permeable reactive barriers, consisting of iron barrier and biobarrier, could be recommended for groundwater contaminated with toxic organic compounds such as chlorophenols.     

Photodegradation of the antimicrobial triclocarban in aqueous systems under ultraviolet radiation

This work aimed to investigate the effectiveness of ultraviolet (UV) radiation on the degradation of the antimicrobial triclocarban (TCC). We investigated the effects of several operational parameters, including solution pH, initial TCC concentration, photocatalyst TiO₂ loading, presence of natural organic matter, and most common anions in surface waters (e.g., bicarbonate, nitrate, and sulfate). The results showed that UV radiation was very effective for TCC photodegradation and that the photolysis followed pseudo-first-order kinetics. The TCC photolysis rate was pH dependent and favored at high pH. A higher TCC photolysis rate was observed by direct photolysis than TiO₂ photocatalysis. The presence of the inorganic ions bicarbonate, nitrate, and sulfate hindered TCC photolysis. Negative effects on TCC photolysis were also observed by the addition of humic acid due to competitive UV absorbance. The main degradation products of TCC were tentatively identified by gas chromatograph with mass spectrometer, and a possible degradation pathway of TCC was also proposed.     

Biodegradation of juvenoid diastereoisomers: radio-HPLC and MS analysis

Microbial degradation of two diastereoisomeric forms 2 and 3 of a selected juvenoid (insect juvenile hormone bioanalog), ethyl N-{2-{4-[(2-hydroxycyclohexyl)methyl]phenoxy}ethyl}carbamate was studied and the degradation products analyzed. Degradation experiments were performed using simple modeling under laboratory conditions. A Candida sp. strain T1, isolated from soil, was chosen as a biodegradation species. Radiolabeling of the studied compounds 2 and 3 was used in combination with radio-HPLC and MS analysis to increase the limits of detection, monitoring and isolation of trace quantities of the products of degradation and/or transformation. Resulting from the microbial processes using 2 or 3 as source compounds, three identical products (4-6) of their biodegradation were produced. Compound 2 also afforded two additional products (7, 8). Radio-HPLC analysis and separation, and subsequent MS analysis of the degradation mixtures resulted in identification of the degradation products. The degree and the rate of biodegradation of 2 and 3 were analyzed after 1, 3 and 7 days from the beginning of the experiment.     

Kinetics of OH radical reactions with dibenzo-p-dioxin and selected chlorinated dibenzo-p-dioxins

The pulsed laser photolysis/pulsed laser-induced fluorescence (PLP/PLIF) technique has been applied to obtain rate coefficients for OH + dioxin (DD) (k1), OH + 2-chlorodibenzo-p-dioxin (2-CDD) (k2), OH + 2,3-dichlorodibenzo-p-dioxin (2,3-DCDD) (k3), OH + 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD) (k4), OH + 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) (k5), OH + 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) (k6), and OH + octachlorodibenzo-p-dioxin (OCDD) (k7) over an extended range of temperature. The atmospheric pressure (740 +/- 10 Torr) rate measurements are characterized by the following Arrhenius parameters (in units of cm3 molecule(-1) s(-1), error limits are 1 omega): k1(326-907 K) = (1.70+/-0.22) x 10(-12)exp(979+/-55)/T, k2(346-905 K) = (2.79+/-0.27) x 10(-12)exp(784+/-54)/T, k3(400-927 K) = 10(-12)exp(742+/-67)/T, k4(390-769 K) = (1.10+/-0.10) x 10(-12)exp(569+/-53)/T, k5(379-931 K) = (1.02+/-0.10) x 10(-12)exp(580+/-68)/T, k6(409-936 K) = (1.66+/-0.38) x 10(-12)exp(713+/-114)/T, k7(514-928 K) = (3.18+/-0.54) x 10(-12)exp(-667+/-115)/T. The overall uncertainty in the measurements, taking into account systematic errors dominated by uncertainty in the substrate reactor concentration, range from a factor of 2 for DD, 2-CDD, 2,3-DCDD, 2,7-DCDD, and 2,8-DCDD to +/- a factor of 4 for 1,2,3,4-TCDD and OCDD. Negative activation energies characteristic of an OH addition mechanism were observed for k1-k6. k7 exhibited a positive activation energy. Cl substitution was found to reduce OH reactivity, as observed in prior studies at lower temperatures. At elevated temperatures (500 K < T < 500 K), there was no experimental evidence for a change in reaction mechanism from OH addition to H abstraction. Theoretical calculations suggest that H abstraction will dominate OH reactivity for most if not all dioxins (excluding OCDD) at combustion temperatures (>1000 K). For OCDD, the dominant reaction mechanism at all temperatures is OH addition followed by Cl elimination.     

Photocatalytic degradation of the herbicide erioglaucine in the presence of nanosized titanium dioxide: comparison and modeling of reaction kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm-1 and 0.984 ppm min-1, respectively. In this work, we also compared the reactivity between the commercial TiO2 Degussa P-25 and a rutile TiO2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO2.     

Photoassisted and photocatalytic degradation of sulfur mustard using TiO2 nanoparticles and polyoxometalates

The decomposition of highly toxic chemical warfare agent, sulfur mustard (bis(2-chloroethyl) sulfide or HD), has been studied by homogeneous photolysis and heterogeneous photocatalytic degradation on titania nanoparticles. Direct photolysis degradation of HD with irradiation system was investigated. The photocatalytic degradation of HD was investigated in the presence of TiO₂ nanoparticles and polyoxometalates embedded in titania nanoparticles in liquid phase at room temperature (33?±?2 °C). Degradation products during the treatment were identified by gas chromatography–mass spectrometry. Whereas apparent first-order kinetics of ultraviolet (UV) photolysis were slow (0.0091 min^?1), the highest degradation rate is obtained in the presence of TiO₂ nanoparticles as nanophotocatalyst. Simultaneous photolysis and photocatalysis under the full UV radiation leads to HD complete destruction in 3 h. No degradation products observed in the presence of nanophotocatalyst without irradiation in 3 h. It was found that up to 90 % of agent was decomposed under of UV irradiation without TiO₂, in 6 h. The decontamination mechanisms are often quite complex and multiple mechanisms can be operable such as hydrolysis, oxidation, and elimination. By simultaneously carrying out photolysis and photocatalysis in hexane, we have succeeded in achieving faster HD decontamination after 90 min with low catalyst loading. TiO₂ nanoparticles proved to be a superior photocatalyst under UV irradiation for HD decontamination.     

Hydrolysis and photolysis of oxytetracycline in aqueous solution

Oxytetracycline ((2Z,4S,4aR,5S,5aR,6S,12aS)-2-(amino-hydroxy-methylidene)-4-dimethylamino-5,6,10,11,12a-pentahydroxy-6-methyl-4,4a,5,5a-tetrahydrotetracene-1,3,12-trione) is a member of tetracycline antibiotics family and is widely administered to farm animals for the purpose of therapeutical treatment and health protection. Increasing attention has been paid to the environmental fate of oxytetracycline and other veterinary antibiotics with the occurrence of these antibiotics in the environment. The hydrolysis and photolysis degradation of oxytetracycline was investigated in this study. Oxytetracycline hydrolysis was found to obey the first-order model and similar rate constant values ranging from 0.094 ± 0.001 to 0.106 ± 0.003 day^{? 1} were obtained at different initial concentration ranging from 10 to 230 μ M. Solution pH and temperature were shown to have remarked effects on oxytetracycline hydrolysis. The hydrolysis in pH neutral solution appeared to be much faster than in both acidic and alkaline solutions. Oxytetracycline half-life decreased from 1.2 × 10² to 0.15 day with the increasing temperature from 4 ± 0.8 to 60 ± 1°C. The presence of Ca^{2 +} made oxytetracycline hydrolytic degradation kinetics deviate from the simple first-order model to the availability-adjusted first-order model and greatly slowed down the hydrolysis. Oxytetracycline photolysis was found to be very fast with a degradation rate constant at 3.61 ± 0.06 day^{? 1}, which is comparable to that of hydrolysis at 60°C. The presence of Ca^{2 +} accelerated oxytetracycline photolysis, implying that oxytetracycline become more vulnerable to sunlight irradiation after chelating with Ca^{2 +}. The photolysis may be the dominant degradation pathway of oxytetracycline in shallow transparent water environment.