Isolation and characterization of an Alcaligenes sp. strain DG-5 capable of degrading DDTs under aerobic conditions

In this study, an Alcaligenes sp. strain DG-5 that can effectively degrade dichlorodiphenyltrichloro-ethanes (DDTs) under aerobic conditions was isolated from DDTs-contaminated sediment. Various factors that affect the biodegradation of DDTs by DG-5 were investigated. About 88 %, 65 % and 45 % of the total DDTs were consumed within 120 h when their initial concentrations were 0.5, 5 and 15 mg L?1, respectively. However, almost no degradation was observed when their concentration was increased to 30 mg L?1, but the addition of nutrients significantly improved the degradation, and 66 % and 90 % of the total DDTs were degraded at 336 h in the presence of 5 g L?1 peptone and yeast extract, respectively. Moreover, the addition of 20 mM formate also enhanced the ability of DG-5 to transform DDTs, and its DDT transformation capacity (T(c)) value was increased by 1.8 - 2.7 fold for the pure (p,p'-DDT or o,p'-DDT only) and mixed systems (p,p'-DDT, o,p'-DDT, p,p'-DDD and p,p'-DDE). Furthermore, it was found that competitive inhibition in the biodegradation by DDT compounds occurred in the mixed system.     

Comparison of biotic and abiotic treatment approaches for co-mingled perchlorate, nitrate, and nitramine explosives in groundwater

Biological and abiotic approaches for treating co-mingled perchlorate, nitrate, and nitramine explosives in groundwater were compared in microcosm and column studies. In microcosms, microscale zero-valent iron (mZVI), nanoscale zero-valent iron (nZVI), and nickel catalyzed the reduction of RDX and HMX from initial concentrations of 9 and 1 mg/L, respectively, to below detection (0.02 mg/L), within 2 h. The mZVI and nZVI also degraded nitrate (3 mg/L) to below 0.4 mg/L, but none of the metal catalysts were observed to appreciably reduce perchlorate ( approximately 5 mg/L) in microcosms. Perchlorate losses were observed after approximately 2 months in columns of aquifer solids treated with mZVI, but this decline appears to be the result of biodegradation rather than abiotic reduction. An emulsified vegetable oil substrate was observed to effectively promote the biological reduction of nitrate, RDX and perchlorate in microcosms, and all four target contaminants in the flow-through columns. Nitrate and perchlorate were biodegraded most rapidly, followed by RDX and then HMX, although the rates of biological reduction for the nitramine explosives were appreciably slower than observed for mZVI or nickel. A model was developed to compare contaminant degradation mechanisms and rates between the biotic and abiotic treatments.     

Residues and chiral signatures of organochlorine pesticides in sediments from Xiangshan Bay, East China Sea

Residual levels and enantiomeric signatures of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in surface sediments from Xiangshan Bay, East China Sea were investigated. The concentrations of ∑HCHs (sums of α-, β-, γ-, and δ-HCH) and ∑DDTs (sums of p, p'-DDT, p, p'-DDD,p, p'-DDE, o, p'-DDT, and o, p'-DDD) ranged from 0.14 to 0.67 ng g?1 and 0.61 to 22.38 ng g?1, respectively. A slight potential health risk to the organism was then indicated for the residual levels of DDTs according to the ERL/ERM guidelines. Moreover, the predominant β-HCH implied that the technical HCH contamination was mainly due to the historical usage. But the high ratio of DDT/∑DDTs depicted a cocktail input pattern of fresh and weathered DDTs. The enantiomeric fractions (EFs) of α-HCH, o, p'-DDT, and o, p'-DDD were also determined. The degradation of α-HCH was enantioselective in all sediments samples, resulting in an enrichment of (-)-enantiomers. However, the racemic residues of o, p'-DDT and o, p'-DDD were observed in all sediments samples.     

Assessing copper thresholds for phytotoxicity and potential dietary toxicity in selected vegetable crops

Copper pollution in soils is widespread, and its accumulation in crop products could pose a risk on human health. In this paper, bioavailability of added copper (Cu) and critical Cu concentrations in a vegetable garden soil was evaluated for Chinese cabbage (Brassica chinensis L.), pakchoi (Brassica chinensis L.), and celery (Apiumg graveolens L. var. dulce DC) based on human dietary toxicity. The availability of added Cu in the soil decreased with incubation time, and had minimal change after 10-12 weeks. After incubated for 12 weeks, about 60% of added Cu was not extractable by DTPA. The same crops were also grown in sand culture to determine their responses to solution Cu. Shoot growth was significantly inhibited at Cu concentrations above 10 mg kg(-1) in the solution or above 150 mg kg(-1) (DTPA-Cu) in the soil. The sensitivity of the crops to Cu toxicity differed among the three vegetable crops. Copper concentration in shoots and edible parts varied with Cu supply levels and type of the vegetables. Negative correlations (r=-0.90-0.99**) were noted between Cu concentration in shoots and fresh matter yields, but Cu concentrations in the edible parts were positively correlated with available and total Cu in the soil (r=0.91-0.99**). The critical tissue Cu concentrations at 10% shoot DM reduction were 19.4, 5.5, 30.9 mg kg(-1) for Chinese cabbage, pakchoi, and celery, respectively. Based on the threshold of human dietary toxicity for Cu (10 mg kg(-1)), the critical concentrations of total and available Cu in the soil were 430 and 269 mg kg(-1) for pakchoi, 608 and 313 mg kg(-1) for celery, and 835 and 339 mg kg(-1) for Chinese cabbage, respectively.     

Effects of elevated soil copper on phenology,growth and reproduction of five ruderal plant species

The repeated use of copper (Cu) fungicides to control vine downy mildew, caused by Plasmopara viticola, has been responsible for the heavy increase of Cu concentration in the upper layers of vineyard soils. To determine the effects of elevated soil Cu on plant development, we created an artificial soil gradient with Cu enrichments ranging from 0 to 400 mg kg-1. On this gradient, and for five ruderal plant species commonly found in vineyards in southern France (Poa annua L., Dactylis glomerata L., Senecio vulgaris L., Hypochoeris radicata L., and Andryala integriflolia L.), we quantified survival, growth, and reproduction throughout one flowering season. High concentrations of Cu in the soil resulted in low survival, low total plant biomass, delay in flowering and fruiting, and low seed set. However, the effects differed among species. Furthermore, high soil Cu concentrations had contrasting effects on patterns of resource allocation depending on the plant species.     

Biodegradation of nicosulfuron by the bacterium Serratia marcescens N80

By enrichment culturing of the sludge collected from the industrial wastewater treatment pond, we isolated a highly efficient nicosulfuron degrading bacterium Serratia marcescens N80. In liquid medium, Serratia marcescens N80 grows using nicosulfuron as the sole nitrogen source, and the optimal temperature, pH values, and inoculation for degradation are 30-35°C, 6.0-7.0, and 3.0% (v/v), respectively. With the initial concentration of 10 mg L?1, the degradation rate is 93.6% in 96 hours; as the initial concentrations are higher than 10 mg L?1, the biodegradation rates decrease as the nicosulfuron concentrations increase; when the concentration is 400 mg L?1, the degradation rate is only 53.1%. Degradation follows the pesticide degradation kinetic equation at concentrations between 5 mg L?1 and 50 mg L?1. Identification of the metabolites by the liquid chromatography/mass spectrometry (LC/MS) indicates that the degradation of nicosulfuron is achieved by breaking the sulfonylurea bridge. The strain N80 also degraded some other sulfonylurea herbicides, including ethametsulfuron, tribenuron-methyl, metsulfuron-methyl, chlorimuron-ethyl,and rimsulfuron.     

Metallothionein induction, antioxidative responses, glycogen and growth changes in Tubifex tubifex (Oligochaete) exposed to the fungicide, fenhexamid

Laboratory studies were conducted to determine the effects of different concentrations of fenhexamid (0.1, 1, and 10 mg L(-1)) on growth, oxidative stress, protein, glycogen, and metallothionein (MT) contents in Tubifex tubifex after an exposure of 2, 4, and 7 days. In addition, residues of the fungicide were followed in water and in the worms. In water, fenhexamid concentration decreased slowly (maximum -2 +/- 0.03% after 2 days for 1 mg L(-1)). In the worms, it increased after 4 days and decreased thereafter, confirming that the worms were exposed to the fungicide and not to a degradation product. LC50 values were between 95.22 +/- 5.36 and 32.11 +/- 1.8 mg L(-1) depending on exposure time. Exposure to fenhexamid had a negative effect on T. tubifex growth (maximum effect -12.2 +/- 0.8% after 7 days with 10 mg L(-1)) demonstrating the toxic effect of the pesticide. This growth rate decrease was accompanied by a reduction in protein and glycogen contents. The activity of catalase (CAT), and glutathione reductase (GR) increased in response to the fungicide demonstrating an oxidative stress in the worms. In contrast glutathion-S-transferase activity (GST) decreased. Exposure to fenhexamid also induced synthesis of MT (maximum +78 +/- 8% after 2 days for 10 mg L(-1)). The specificity of MT concentration increase in response to metals is discussed.     

水葱修复土壤镉污染潜力的研究

野外观察与研究发现水葱(Scirpus tabernaemontani G.)可以耐受土壤中高浓度的重金属污染,并对镉(Cd)有很高的生物富集量.实验室水培试验研究了两个主要因素,营养液pH与Cd含量,对水葱生物量以及Cd富集效果的影响.结果表明,它可耐受高浓度Cd (30 mg/L)和大范围pH变化 (3.7～7.7).当营养液pH为4.7, Cd为25 mg/L时,水葱富集的Cd达到最大值:地上部分264.71 mg/kg,地下部分234.39 mg/kg,平均转运系数1.13.这显示了它用于植物修复Cd污染土壤的潜力.     

Influence of pH and ozone dose on the content and structure of haloacetic acid precursors in groundwater

This study investigated the effects of pH (6-10) and ozone dose [0.4-3.0?mg O(3)/mg dissolved organic carbon (DOC)] on the content and structure of haloacetic acid (HAA) precursors in groundwater rich in natural organic matter (NOM; DOC 9.85?±?0.18?mg/L) during drinking water treatment. The raw water was ozonated in a 2 L glass column. NOM fractionation was carried out using XAD resins. HAA formation potential (HAAFP) was determined according to standard EPA Method 552. NOM characterization revealed it is mostly hydrophobic (65?% fulvic and 14?% humic acids). Hydrophobic NOM significantly influences HAA formation, as confirmed by the high HAAFP (309?±?15?μg/L). Ozonation at pH?6-10 led to changes in NOM structure, i.e. complete humic acid oxidation, and increased the hydrophilic NOM fraction content (65-90?% achieved using 3.0?mg O(3)/mg DOC). The highest degree of NOM oxidation and HAA precursor removal was achieved at pH?10 (up to 68?% HAAFP). Ozonation pH influenced the distribution of HAA precursor content, as increasing the pH from 6 to 10 increased the reactivity of the hydrophilic fraction, with the HAAFP increasing from 19.1?±?6.0?μg/mg DOC in raw water to 152?±?8?μg/mg DOC in ozonated water. The degree of HAA precursor removal depends on the dominant oxidation mechanism, which is related to the applied ozone dose and the pH of the oxidation process. Ozonation at pH?10 favours the mechanism of radical NOM oxidation and was the most effective for HAAFP reduction, with the efficacy of the process improving with increasing ozone dose.     

Neutralization/prevention of acid rock drainage using mixtures of alkaline by-products and sulfidic mine wastes

Backfilling of open pit with sulfidic waste rock followed by inundation is a common method for reducing sulfide oxidation after mine closure. This approach can be complemented by mixing the waste rock with alkaline materials from pulp and steel mills to increase the system’s neutralization potential. Leachates from 1 m³ tanks containing sulfide-rich (ca.30 wt %) waste rock formed under dry and water saturated conditions under laboratory conditions were characterized and compared to those formed from mixtures. The waste rock leachate produced an acidic leachate (pH?<?2) with high concentrations of As (65 mg/L), Cu (6 mg/L), and Zn (150 mg/L) after 258 days. The leachate from water-saturated waste rock had lower concentrations of As and Cu (<2 μg/L), Pb and Zn (20 μg/L and 5 mg/L), respectively, and its pH was around 6. Crushed (<6 mm) waste rock mixed with different fractions (1–5 wt %) of green liquid dregs, fly ash, mesa lime, and argon oxygen decarburization (AOD) slag was leached on a small scale for 65 day, and showed near-neutral pH values, except for mixtures of waste rock with AOD slag and fly ash (5 % w/w) which were more basic (pH?>?9). The decrease of elemental concentration in the leachate was most pronounced for Pb and Zn, while Al and S were relatively high. Overall, the results obtained were promising and suggest that alkaline by-products could be useful additives for minimizing ARD formation.     

Gas chromatographic methods for monitoring of wastewater chlorophenol degradation in anaerobic reactors

Wastewater samples from an anaerobic reactor were extracted with hexane and derivatized with diazomethane (method 1) and with acetic anidride (method 2). Gas chromatography with electron-capture detection (ECD) was employed for separating the parent compound and intermediates trichlorophenols (TCP) and dichlorophenols (DCP) which originated from the penta chlorophenol (PCP) degradation process. The relations between concentrations of PCP, TCP and DCP areas were linear in the range of concentrations of 0.2 to 8 mg/L and 0.025 mg/L to 5 mg/L for methods 1 and 2, respectively. The repeatability of the extraction methods was satisfactory, with variation coefficients lower than 11%. For method 1, at the fortification level of 0.2 mg/L, recovery of PCP, TCP, and DCP was 112%, 74% and 45%, respectively. For method 2, the corresponding recovery values at the fortification level of 0.1 mg/L were 91%, 93% and 103%, respectively. Storage of the frozen samples did not alter their PCP determination properties. The chromatographic methods adapted for chlorophenol determination in wastewater were suitable with relatively simple manipulation techniques. The obtained results were reproducible and allowed identification of intermediates formed during the PCP degradation process.     

Gas chromatographic methods for monitoring of wastewater chlorophenol degradation in anaerobic reactors

Wastewater samples from an anaerobic reactor were extracted with hexane and derivatized with diazomethane (method 1) and with acetic anidride (method 2). Gas chromatography with electron-capture detection (ECD) was employed for separating the parent compound and intermediates trichlorophenols (TCP) and dichlorophenols (DCP) which originated from the penta chlorophenol (PCP) degradation process. The relations between concentrations of PCP, TCP and DCP areas were linear in the range of concentrations of 0.2 to 8 mg/L and 0.025 mg/L to 5 mg/L for methods 1 and 2, respectively. The repeatability of the extraction methods was satisfactory, with variation coefficients lower than 11%. For method 1, at the fortification level of 0.2 mg/L, recovery of PCP, TCP, and DCP was 112%, 74% and 45%, respectively. For method 2, the corresponding recovery values at the fortification level of 0.1 mg/L were 91%, 93% and 103%, respectively. Storage of the frozen samples did not alter their PCP determination properties. The chromatographic methods adapted for chlorophenol determination in wastewater were suitable with relatively simple manipulation techniques. The obtained results were reproducible and allowed identification of intermediates formed during the PCP degradation process.     

Organochlorine pesticides and metabolites in young leaves of Mangifera indica from sites near a point source in Coast region, Tanzania

Young leaves of Mangifera indica (mango tree) from nine sites were used as bioindicators of local atmospheric contamination by organochlorine pesticides and metabolites from a point source, an old storage site at Vikuge farm in Tanzania. Sample extracts were analysed by GC-ECD and GC-MS. The concentrations ranged 2.7-649 ng g(-1)p,p'-DDT, below detection limit (bdl)-290 ng g(-1) o,p'-DDT, 0.4-13 ng g(-1) p,p'-DDE, bdl to 4 ng g(-1) o,p'-DDE, 1-231 ng g(-1) p,p'-DDD and 0.5-55 ng g(-1) o,p'-DDD. The concentrations of other compounds were up to 3.9 ng g(-1) pentachloroanisole, 1.3 ng g(-1) alpha-HCH, 12 ng g(-1) beta-HCH and 2 ng g(-1) gamma-HCH, on fresh weight basis. The compounds p,p'-DDT, p,p'-DDE, p,p'DDD and o,p'-DDD were found in 100% of the samples, while pentachloroanisole, o,p'-DDT and o,p'-DDE were detected in 78%, 56% and 67% of the samples, respectively. The low DDE/DDT ratios (0.01-0.20) in all samples indicate recent input of significantly non-degraded DDT from the point source. The low alpha-/gamma-HCH ratios (<0.3-0.7) in most samples indicate recent input of lindane (99% gamma-HCH). The slightly high alpha-/gamma-HCH ratios in some samples might be due to photochemical or bacterial transformation of gamma-HCH to alpha-HCH, or could reflect input of technical HCH. The very strong positive correlations in the concentrations of p,p'-DDT, p,p'-DDE, p,p'-DDD, o,p'-DDT, o,p'-DDE and o,p'-DDD (r=0.91-0.98, n=18, p<0.01) indicate that they have a common source. The results suggest that young mango leaves are suitable bioindicators of recent inputs of organochlorine contaminants from a point source.     

Reducing plant uptake of PAHs by cationic surfactant-enhanced soil retention

Reducing the transfer of contaminants from soils to plants is a promising approach to produce safe agricultural products grown on contaminated soils. In this study, 0-400 mg/kg cetyltrimethylammonium bromide (CTMAB) and dodecylpyridinium bromide (DDPB) were separately utilized to enhance the sorption of PAHs onto soils, thereby reducing the transfer of PAHs from soil to soil solution and subsequently to plants. Concentrations of phenanthrene and pyrene in vegetables grown in contaminated soils treated with the cationic surfactants were lower than those grown in the surfactant-free control. The maximum reductions of phenanthrene and pyrene were 66% and 51% for chrysanthemum (Chrysanthemum coronarium L.), 62% and 71% for cabbage (Brassica campestris L.), and 34% and 53% for lettuce (Lactuca sativa L.), respectively. Considering the impacts of cationic surfactants on plant growth and soil microbial activity, CTMAB was more appropriate to employ, and the most effective dose was 100-200 mg/kg.     

Effect of inorganic and organic solutes on zero-valent aluminum-activated hydrogen peroxide and persulfate oxidation of bisphenol A

The effect of varying inorganic (chloride, nitrate, sulfate, and phosphate) and organic (represented by humic acid) solutes on the removal of aqueous micropollutant bisphenol A (BPA; 8.8 μM; 2 mg/L) with the oxidizing agents hydrogen peroxide (HP; 0.25 mM) and persulfate (PS; 0.25 mM) activated using zero-valent aluminum (ZVA) nanoparticles (1 g/L) was investigated at a pH of 3. In the absence of the solutes, the PS/ZVA treatment system was superior to the HP/ZVA system in terms of BPA removal rates and kinetics. Further, the HP/ZVA process was not affected by nitrate (50 mg/L) addition, whereas chloride (250 mg/L) exhibited no effect on the PS/ZVA process. The negative effect of inorganic anions on BPA removal generally speaking increased with increasing charge in the following order: NO₃^? (no inhibition)?<?Cl^? (250 mg/L)?=?SO₄^2??<?PO₄^3? for HP/ZVA and Cl^? (250 mg/L; no inhibition)?<?NO₃^??<?SO₄^2??<?PO₄^3? for PS/ZVA. Upon addition of 20 mg/L humic acid representing natural organic matter, BPA removals decreased from 72 and 100% in the absence of solutes to 24 and 57% for HP/ZVA and PS/ZVA treatments, respectively. The solute mixture containing all inorganic and organic solutes together partly suppressed the inhibitory effects of phosphate and humic acid on BPA removals decreasing to 46 and 43% after HP/ZVA and PS/ZVA treatments, respectively. Dissolved organic carbon removals were obtained in the range of 30 and 47% (the HP/ZVA process), as well as 47 and 57% (the PS/ZVA process) for the experiments in the presence of 20 mg/L humic acid and solute mixture, respectively. The relative Vibrio fischeri photoluminescence inhibition decreased particularly for the PS/ZVA treatment system, which exhibited a higher treatment performance than the HP/ZVA treatment system.     

Effect of tris-(2-chloroethyl)-phosphate (TCEP) at environmental concentration on the levels of cell cycle regulatory protein expression in primary cultured rabbit renal proximal tubule cells

Tris-(2-chloroethyl)-phosphate (TCEP) is a typical organophosphate flame retardant and has been designated as a micropollutant in aquatic environment. However, the potential effect of TCEP at environmental concentration is mostly unknown. Thus, the purpose of this study was to investigate the renal effect of TCEP at environmental concentration using primary cultured rabbit renal proximal tubule cells (PTCs). The results showed that TCEP at 10 mg L(-1) decreased cell viability, 84.2% of the control, but increased lactate dehydrogenase, 150% fold of the control. TCEP at 10 mg L(-1) also inhibited expression of CDK4, cyclin D1, CDK2, and cyclin E (79.3%, 77.7%, 73.3%, and 67.8% of the control, respectively), but increased expression of p21(WAF/Cip1) and p27(Kip1) (167.7% and 141.3% of the control, respectively). TCEP decreased DNA synthesis and cell number, 77% and 70% of the control, respectively. Through study of cell viability, cell damage, cell cycle regulator expression, DNA synthesis and cell number, TCEP at 10 microg L(-1) only affected the cells that TCEP increased expression of p21(WAF/Cip1) and p27(Kip1), 118.6% and 121.5% of the control, respectively, but decreased DNA synthesis, 91.5% of the control. In conclusion, TCEP at 10 microg L(-1) significantly increased cell cycle regulatory protein expression (p21(WAF/Cip1) and p27(Kip1)), but slightly decreased DNA synthesis in primary cultured rabbit renal PTCs.     

Toxicity mechanism of cerium oxide nanoparticles on cyanobacteria Microcystis aeruginosa and their ecological risks

The extensive application of cerium oxide nanoparticles (CeO₂ NPs), a type of rare earth nanomaterial, led to pollution into aquatic environments. Cyanobacteria, a significant component of freshwater ecosystems, can interact with CeO₂ NPs. However, little attention has been paid as to whether CeO₂ NPs will have adverse effects on cyanobacteria. In the present study, Microcystis aeruginosa (FACHB-942) was exposed to different concentrations (0, 1, 10, and 50 mg/L) of CeO₂ NPs. Results showed 50 mg/L CeO₂ NPs inhibited algal growth (11.48%?±?5.76%), suppressed photosynthesis and induced the generation of reactive oxygen species (ROS) after 72 h exposure. The toxicity mechanism is the adsorption of CeO₂ NPs on cell surface, the ROS formation and the intracellular Ce. Additionally, the intracellular microcystins (MCs) content was significantly induced (11.84%?±?1.47%) by 50 mg/L CeO₂ NPs, while no significance was found in 1 and 10 mg/L CeO₂ NP treatments. Results indicated high concentrations of CeO₂ NPs could be toxic to algae through the adverse effects on algal growth and photosynthesis. Moreover, the promoted MCs production could also pose a threat to freshwater ecosystems due to the possible release into the environment.

     

Phytoremediation of ethylene glycol and its derivatives by the burhead plant (Echinodorus cordifolius (L.)): effect of molecular size

Ethylene glycol (EG) is a group of dihydroxy alcohol that has been utilised in a variety of industrial and residential settings. EG contaminated wastewater has a high chemical oxygen demand (COD), which causes environmental problems. The aim of this research was to investigate the efficiency of the burhead plant (Echinodorus cordifolius (L.)) in the removal of mono-, di- and triethylene glycol (MEG, DEG and TEG), the first three members of the dihydroxy alcohol group, from synthetic wastewaters, to examine the toxic effect of EG on the plant and to identify differences among MEG, DEG, and TEG removal. It was found that the COD of synthetic wastewaters decreased to levels below the standard effluent (COD=120 mg L?1) on day 18, 21 and 33 for MEG, DEG and TEG, respectively. On day 18 of the experiment, the burhead plant removed approximately 2000, 1950 and 730 mg L?1 of MEG, DEG and TEG, respectively. The removal rate of MEG was faster than that of DEG and TEG, suggesting that the molecular size of the EG had affected its rate of removal. The concentrations of MEG, DEG, and TEG in plant tissue were measured to show that burhead can take up EG, and the major site of EG accumulation is the leaf. The molar of MEG that was taken up into the plant leaf was higher than that of DEG and TEG. This suggested that EG of smaller molecular sizes can be taken up more rapidly by the plant than EG of larger molecular sizes. EG concentrations in the leaf increased to a peak concentration and then slowly decreased. GC-MS analysis of DEG-treated plant tissue found MEG, 1,4-dioxan-2-one, neophytadiene, and 2-propenamide, that may be DEG-degradation products and/or compounds that are induced when plants are exposed to DEG. The result indicates that burhead can potentially be used for EG removal.     

Nutrient and tetracycline removal from simulated biogas slurry and biogas upgrading by microalgae cultivation under different carbon nanotubes concentrations

Environmental Science and Pollution Research - The present study sought to determine the effects of multi-walled carbon nanotubes (MWCNTs) concentrations (0–10 mg L?1) on tetracycline...     

Photocatalytic degradation of p,p′-DDT under UV and visible light using interstitial N-doped TiO2

1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (or p,p′-DDT) is one of the most persistent pesticides. It is resistant to breakdown in nature and cause the water contamination problem. In this work, a major objective was to demonstrate the application of N-doped TiO₂ in degradation and mineralization of the p,p′-DDT under UV and visible light in aqueous solution. The N-doped TiO₂ nanopowders were prepared by a simple modified sol–gel procedure using diethanolamine (DEA) as a nitrogen source. The catalyst characteristics were investigated using XRD, SEM, TEM, and XPS. The adsorption and photocatalytic oxidation of p,p′-DDT using the synthesized N-doped TiO₂ under UV and visible light were conducted in a batch photocatalytic experiment. The kinetics and p,p′-DDT degradation performance of the N-doped TiO₂ were evaluated. Results show that the N-doped TiO₂ can degrade p,p′-DDT effectively under both UV and visible lights. The rate constant of the p,p′-DDT degradation under UV light was only 0.0121 min^?1, whereas the rate constant of the p,p′-DDT degradation under visible light was 0.1282 min^?1. Under visible light, the 100% degradation of p,p′-DDT were obtained from N-doped TiO₂ catalyst. The reaction rate of p,p′-DDT degradation using N-doped TiO₂ under visible light was sixfold higher than that under UV light. According to Langmuir-Hinshelwood model, the adsorption equilibrium constant (K) for the N-doped TiO₂ under visible light was 0.03078 L mg^?1, and the apparent reaction rate constant (k) was 1.3941 mg L^?1-min. Major intermediates detected during the p,p′-DDT degradation were p,p′-DDE, o,p′-DDE, p,p′-DDD and p,p′-DDD. Results from this work can be applied further for the breakdown of p,p′-DDT molecule in the real contaminated water using this technology.