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Query: UMLS:C1835664 (TOC)
 2,763 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Highway stormwater runoff quality data were collected from throughout California during 2000-2003. Samples were analyzed for conventional pollutants (pH, conductivity, hardness, and temperature); aggregates (TSS, TDS, TOC, DOC); total and dissolved metals (As, Cd, Cr, Cu, Ni, Pb, and Zn); and nutrients (NO(3)-N, TKN, total P, and ortho-P). Storm event and site characteristics for each sampling site were recorded. A statistical summary for chemical characteristics of highway runoff is provided based on statewide urban and non-urban highways. Constituent event mean concentrations (EMCs) were generally higher in urban highways than in non-urban highways. The chemical characteristics of highway runoff in California were compared with national highway runoff chemical characterization data. The results obtained in California were generally similar to those found in other states. The median EMC for Pb measured in studies conducted in previous decades was much higher than the current median Pb EMC in California. The lower Pb EMC in California compared to previous highway runoff monitoring is believed to be due to the elimination of leaded gasoline. An attempt was also made to identify surrogate constituents within a general family of water quality categories using Spearman correlations and selected pairs with Spearman coefficients greater than 0.8. The strongest correlations were observed among parameters associated with dissolved minerals (EC, TDS, and chloride); organic carbon (TOC and DOC); petroleum hydrocarbons (TPH and O & G); and particulate matter (TSS and turbidity). Within the metals category, total iron concentration was highly correlated with most total metal concentrations. The correlations between total and dissolved concentrations were all less than 0.8, even between total and dissolved concentrations of the same metals. Multiple linear regression (MLR) analyses were performed to evaluate the impact of various site and storm event variables on highway runoff constituent EMCs. Parameters found to have significant impacts on highway runoff constituent EMCs include: total event rainfall (TER); cumulative seasonal rainfall (CSR); antecedent dry period (ADP); contributing drainage area (DA); and annual average daily traffic (AADT). Surrounding land use and geographic regions were also determined to have a significant impact on runoff quality. The MLR model was also used to predict constituent EMCs. Model performance determined by comparing predicted and measured values showed good agreement for most constituents.
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PMID:Characterization and prediction of highway runoff constituent event mean concentration. 1716 4

In this research, we investigated the variation of transmembrane pressure and permeate water quality in pre-coagulation and sedimentation with iron based coagulant, and chlorination of feed water for PVDF (Polyvinylidene fluoride) based MF membrane filtration. NaCIO was fed to the membrane module at a dosage of 0.5 mg/L and maintained during filtration. To observe the effect of raw water, three types of raw and processed waters, including river surface water, coagulated water and coagulated-settled water, were employed. In the case of river surface water, the transmembrane pressure increased abruptly in 500 hours operation. On the contrary, no significant increase in transmembrane pressure was observed for coagulated water and coagulated-settled water for 1200 hours operation. The turbidity of permeate was lower than the detection limit for all applied waters. The removal efficiency for humic substances in coagulated water and coagulated-settled water was approximately ten times higher than that in surface river water. And, the removal efficiency for TOC and DOC was approximately two times higher than that in surface river water. From the results of the operation, it can be observed that it is possible to maintain stable operation at 0.9 m(3)/m(2)-day filtration flux through a combination of pre-coagulation and pre-chlorination. However, the water quality of permeate was the best when the pre-coagulation-sedimentation process was combined with pre-chlorination. With respect to fouling reduction and operation efficiency increase in membrane filtration, the pre-coagulation/sedimentation process is a promising alternative.
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PMID:Evaluation of a MF membrane system composed of pre coagulation-sedimentation and chlorination for water reuse. 1716 54

A soil column filled with sandy soil was constructed to investigate redox buffering capacity of aquifer sediments and its variation in different redox zones. Results indicated that with the aggravating of landfill leachate pollution, the oxidation capacity (OXC) of sediments was decrease, and the reduction capacity (RDC) of sediments was increase. In uncontaminated aquifer sediments, Fe3 + was a main component of OXC, and account for about 70.5 % of OXC; TOC was a main component of RDC, and account for about 98.7% of RDC. In anaerobic environment, large fraction of amorphous Fe3+ and part of crystalline Fe3+ were reduced, and the reduced product was mainly precipitated as FeCO3 and FeS. In methanogenic zone/sulfate reduction zone and iron reduction zone, deposit of Fe2 + led to ion-exchangeable Fe2+ content increased from 0.5 % of uncontaminated aquifer sediments to 3% and 1.84% respectively. Therefore, sediment-bound iron may act as a very significant redox buffer in polluted aquifer, the reduction of Fe3 + and fowling precipitation and ion exchange onto the sediment of Fe2+ substantially reduces the size of the anaerobic leachate pollution plume, which may contribute substantially to the buffering of entering reduced species.
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PMID:[Study on redox buffering of landfill leachate contaminated aquifer sediments]. 1730 58

This paper presents experimental results on the imidacloprid removal from wastewater using homogeneous photo-Fenton reactions illuminated with black light lamps. Multivariate experimental design was used to identify the effect of initial Fe(II) and H(2)O(2) concentrations on process performance. The initial iron concentration played a key role in the process kinetics, whereas hydrogen peroxide concentration directly affected the extent of the oxidation process. Imidacloprid degradation proceeded via two distinctive kinetics regimes, an initial stage of rapid imidacloprid reduction, followed by a slower oxidation process until complete removal. Under optimal conditions, more than 50% imidacloprid degradation was observed after less than 1 min treatment, and TOC and COD removal up to 65% and 80%, respectively, were measured after all hydrogen peroxide was consumed. Raw imidacloprid samples presented significant acute toxicity to Daphnia magna and genotoxic effects on Bacillus subtilis sp. Such toxic effects remained detectable even after significant pesticide removal had been achieved, due to the presence of toxic by-products. Both acute toxicity and genotoxicity disappeared after considerable mineralization resulting in final low molecular weight by-products. Results obtained here confirm that design and operation of photo-Fenton processes should focus on toxicity removal rather than on specific target pollutants.
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PMID:Imidacloprid oxidation by photo-Fenton reaction. 1757 40

The mineralisation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the presence of zero-valent iron and hydrogen peroxide (the advanced Fenton process--AFP) whilst being subjected to acoustic or hydrodynamic cavitation is reported. If the reaction is merely stirred then there is 57% removal of TOC whilst on irradiation the figure is 64% although the latter reaction is more rapid. Use of ultrasound alone results in only 11% TOC removal in 60 min of treatment time. Addition of iron powder marginally enhances the extent of degradation but an appreciable increase is observed in the presence of hydrogen peroxide which acts as a source for hydroxyl radicals by Fenton chemistry as well as by dissociation in the presence of ultrasound. The use of hydrodynamic cavitation in conjunction with the advanced Fenton process has also been found to be a useful tool for continuous remediation of water contaminated with 2,4-D. After 20 min of treatment the residual TOC is reduced to 30% and this probably represents the remaining highly recalcitrant small organic molecules.
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PMID:Mineralisation of 2,4-dichlorophenoxyacetic acid by acoustic or hydrodynamic cavitation in conjunction with the advanced Fenton process. 1766 35

Iron-containing mesostructured materials (Fe-SBA-15) are suitable for continuous treatment of phenolic aqueous solutions by means of catalytic wet peroxide oxidation (CWPO) in a packed-bed reactor. These materials were successfully extruded, crushed and sieved with a particle size ranging from 1 to 1.6 mm using mineral clay and methyl cellulose as binders. Non-significant changes have been found in the textural and structural properties of the extruded material in comparison to the parent powder Fe-SBA-15 material. Activity of extruded catalyst in terms of phenol degradation and TOC reduction has been monitored in a continuous mode. The increase of residence time enhances significantly the TOC degradation. The catalyst stability, taking into account the loss of iron species from the catalyst into the aqueous solution, has also been examined. The catalytic results of Fe-SBA-15 material in comparison to a homogeneous catalytic test prove the relevant role of the solid catalyst in the oxidation process.
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PMID:Catalytic wet peroxidation of phenol in a fixed bed reactor. 1767 30

Degradation of bisphenol A (BPA) and simultaneous formation of hydrogen peroxide induced by glow discharge plasma in contact with aqueous solution were investigated. Experimental results indicated that the BPA degradation rate was higher in sodium chloride solution than that in sodium sulfate or phosphate solutions. However, the formation rates of hydrogen peroxide were on the opposite case. Both the BPA removal and the hydrogen peroxide production rates decreased in the presence of hydroxyl radical scavengers, indicating that hydroxyl radicals are the most probable oxidants responsible for BPA degradation and the precursors of hydrogen peroxide. Ferric ion showed better catalytic effect than that of ferrous ion, suggesting that the ferric ion was reduced by the intermediates formed during BPA degradation, which was confirmed by following the production of ferrous ion in the system. TOC of the solution gradually reduced with discharge time; however, without catalysts, the solution COD increased with discharge time and sharply decreased in the presence of iron salts. The major intermediate products were identified by LC/MS and the possible degradation mechanism was discussed.
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PMID:Degradation of bisphenol A and formation of hydrogen peroxide induced by glow discharge plasma in aqueous solutions. 1808 47

Many nitroaromatic compounds (NACs) are considered toxic and potential carcinogens. The purpose of this study was to develop an integrated reductive/oxidative process for treating NACs contaminated waters. The process consists of the combination of zero-valent iron and an ozonation based treatment technique. Corrosion promoters are added to the contaminated water to minimize passivation of the metallic species. Water contaminated with 2,4-dinitrotoluene (DNT) was treated with the integrated process using a recirculated batch reactor. It was demonstrated that addition of corrosion promoters to the contaminated water enhances the reduction of 2,4-DNT with zero-valent iron. The addition of corrosion promoters resulted in 62% decrease in 2,4-DNT concentration to 2,4-diaminotoluene. The data shows that iron reduced the 2,4-DNT and ozone oxidized these products resulting in a 73% removal of TOC and a 96% decrease in 2,4-DNT concentration.
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PMID:Single-step treatment of 2,4-dinitrotoluene via zero-valent metal reduction and chemical oxidation. 1816 66

This study investigated the effect of ultrasound (US) enhancement on the degradation of 2,4-DCP in a new Fenton like system. An obviously synergistic effect was observed after introduction of US into the Fe/EDTA system. Good correspondences with pseudo-first-order kinetic were found in each reaction system. It was demonstrated that the degradation rate constant (kobs) of DCP in US/Fe/EDTA was 7 and 32 times higher than those in Fe/EDTA and US system alone. Simultaneously, lower first-order kobs was also obtained in the investigation of decomposition of EDTA. At 60 min reaction time, Removals of 81% TOC, complete DCP and 89% EDTA were achieved. Low molecular weight organic acids are identified as the main products, which contribute to the solution self-buffer at about pH 6.5 along with the reaction. In addition, the effect of initials condition, i.e., iron addition, EDTA dosage, DCP concentration and US input power as well as reaction temperature were studied and reaction activation energy (Ea) was also calculated.
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PMID:Enhanced degradation of 2,4-dichlorophenol by ultrasound in a new Fenton like system (Fe/EDTA) at ambient circumstance. 1832 14

Catalytic effects of iron salts on phenol degradation induced by glow discharge plasma (GDP) were examined. It was found that ferric ions showed much better catalytic effect than that of ferrous ions. The reason was that GDP could produce hydroxyl radicals and hydrogen peroxide simultaneously; the hydroxyl radicals reacted with phenol to produce dihydroxycyclohexadienyl radicals which reduced the ferric ions to ferrous ions and the newly formed ferrous ions catalyzed the hydrogen peroxide to produce more hydroxyl radicals. Without iron salts, TOC of the solution gradually decreased with treatment time while COD of the solution increased due to the accumulation of the hydrogen peroxide. Without iron salts, catechol, hydroquinone, and hydroxylhydroquinone were major by-products. However, large amounts of catechol, hydroquinone and benzoquinone yielded in the presence of iron salts. The present study presents some new information related to Fenton's reaction.
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PMID:Unusual catalytic effects of iron salts on phenol degradation by glow discharge plasma in aqueous solution. 1850 6


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