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1.
The decomposition of dichloroacetic acid (DCAA) in water using a UV/H2O2/micro‐aeration process was investigated in this paper. DCAA cannot be removed by UV radiation, H2O2 oxidation or micro‐aeration alone, while UV/H2O2/micro‐aeration combination processes have proved effective and can degrade this compound completely. With initial concentrations of about 110 μg/L, more than 95.1% of DCAA can be removed in 180 min under UV intensity of 1048.7 μW/cm2, H2O2 dosage of 30 mg/L and micro‐aeration flow rate of 2 L/min. However, more than 30 μg/L of DCAA was left after 180 min by UV/H2O2 combination process without micro‐aeration with the same UV intensity and H2O2 dosage. The effects of applied UV radiation intensity, H2O2 dose, initial DCAA concentration and pH on the degradation of DCAA have been examined in this study. Degradation mechanisms of DCAA with hydroxyl radical oxidation have been discussed. The removal rate of DCAA was sensitive to operational parameters. There was a linear relationship between rate constant k and UV intensity and initial H2O2 concentration, which indicated that a higher removal capacity can be achieved by improvement of both factors. A newly found nitrogenous disinfection by‐product (N‐DBP)‐DCAcAm, which has the potential to form DCAA, was easier to remove than DCAA by UV/H2O2 and UV/H2O2/micro‐aeration processes. Finally, a preliminary cost comparison revealed that the UV/H2O2/micro‐aeration process was more cost‐effective than the UV/H2O2 process in the removal of DCAA from drinking water. 相似文献
2.
AOX‐formation by the Sonochemical Treatment of Salicylic Acid in Presence of Chloride Ultrasound shows great potential for improving water, wastewater and sludge treatment processes. However, a number of questions exist: for example the influence of suspended solids or salts. In this paper the influence of chloride in view of AOX‐formation should be investigated. As organic model compound salicylic acid (0.05…1 mmol/L) was used. Formation of AOX (adsorbable organically bound halogens) was measured in dependence upon chloride concentrations (1.4…141 mmol/L) and pH 2 and 9. Ultrasound irradiation was performed in glass reactor (500 mL) at 206 kHz and 353 kHz by continuous bubbling argon:oxgen (4:1) at a flow rate of 1 L/min into the solutions. The elimination of salicylic acid and the formation of hydrogen peroxide were not influenced by the presence of chloride (up to 56 mmol/L). The rate of salicylic acid elimination and the formation rate of hydrogen peroxide are at concentrations of mmol/(L min) levels but those of AOX formation of μmol/(L min) levels. The reactions leading to chlorinated by‐products can be seen as minor reaction paths. The yield of AOX depending on frequency, pH and chloride concentration lies between 10 μg/L and 900 μg/L. In acidic medium they were twice as high as in basic medium. Below the ratio chloride : salicylic acid of 2 mol/mol, AOX could not be identified. 相似文献
3.
Elimination of Swimming Pool Water Disinfection By‐products with Advanced Oxidation Processes (AOPs)
Ozonation is a treatment step which was first applied in the 1960s in pool water treatment for disinfection as well as for oxidation of pool water contaminants. Contact time between ozone and pool water was identified to be of significance with an increased elimination efficiency regarding chloramines, trihalogenmethane formation potential and the permanganate index for longer reaction times. Oxidation via OH radicals might be the dominating pathway. In this study ozonation was compared with the ozone based advanced oxidation processes ozone/UV and ozone/hydrogen peroxide regarding the elimination efficiency of both disinfection by‐products (DBPs) and DBP precursors. It was observed that AOPs in comparison to ozonation showed an increased elimination efficiency regarding total organic carbon (TOC), the organically bound halogens adsorbable on activated carbon (AOX) and AOX formation potential. A contact time of 3 minutes between pool water and oxidant turned out to be practically sufficient. Just for the trihalomethane (THM) formation potential ozonation showed a slight advantage compared to the AOPs because ozonation is a highly selective oxidant and OH radical reactions are known to produce small reactive molecules which are easier transformed to THMs. Combination of membrane filtration and AOPs resulted in an elimination of 10 to 90 % of the DBPs and their precursors. The ozone/hydrogen peroxide process is suggested for pool water treatment because of the higher elimination rates compared to ozonation and of economic reasons compared to the ozone/UV process. 相似文献
4.
The purpose of the study is to gain a better understanding about the formation of THM (trihalomethanes), HAA (haloacetic acids), and AOX (adsorbable organic halogen) in river water (river Ruhr, Essen) through a chlorination kinetics approach. The effect of chlorination time and preozonation on the formation of THM, HAA, and AOX substances was studied. Preozonation can reduce the chlorine demand and the precursors for AOX and THM. THM generation was reduced further, when the ozone dosage consumed increased from 3.5 to 12.5 mg in the 1.4 L reaction vessel. AOX and TCAA (trichloroacetic acid) concentrations also decreased dramatically when 3.5 mg of ozone had reacted with the river water, but a higher dose of ozone did not further reduce AOX and TCAA formations. Besides, the characteristics of organic matter in raw water, ozonated water, and preozonated/chlorinated water was investigated. The results suggest the formation of low‐molecular‐weight acids with low UV absorbance when high‐molecular refractive matter is oxidized. 相似文献
5.
The degradation pathway for the oxidation of EDTA in the UV/H2O2-process was investigated. In absence of iron ions, the mineralization of EDTA is dominated by the reaction of the HO-radicals generated by the photolysis of H2O2. The organic degradation products iminodiacetate (IMDA), glycinate, oxamate, glyoxylate, oxalate and formate, and the inorganic degradation products carbon dioxide, ammonia, nitrate, nitrite, and cyanate were found. In the presence of iron ions, photolytic decarboxylation processes inside the complex get an important role during degradation, and the organic degradation products ethylenediaminetriacetate (ED3A), ethylenediaminediacetate (EDDA), ethylenediaminemonoacetate (EDMA) were also found. By combining product studies with balances of carbon and nitrogen, the degradation pathway in the UV/H2O2-process could be elucidated. The degradation of EDTA was fast (kdeg = 0.012 s–1), and no toxic degradation products were identified. Therefore, the process is well suited for the elimination of EDTA in water treatment. 相似文献
6.
The degradation reactions of two monoazo pigments, namely, Red 53:1 and Red 48:2, by Fenton, photo‐Fenton and UV/H2O2 systems have been studied. The efficiencies of the Fenton reactions increased with temperature, but the formation of solid agglomerates was observed when the reactions were carried out above 50°C indicating a coagulant action of Fe+2 or Fe+3. Photo‐Fenton reactions irradiated by sunlight presented the best rate constants for cleavage of the azo bond and the naphthalene rings. The UV/H2O2 system exhibited the highest efficiency with respect to the consumption of H2O2. The presence of a carbonyl group in the ortho position of the naphthol ring hampered the oxidation of pigment Red 48:2 by hydroxyl radicals. This finding may be explained in terms of the acceptor character of the COOH group, and suggests the formation of a complex containing two six‐membered rings between Fe+3 and the pigment molecule. 相似文献
7.
Hydrophilic xenobiotics can be eliminated in the UV/H2O2-process. The oxidation in this process is enhanced by the photolytically generated HO radicals. Bicarbonate is able to scavenge HO radicals. So it was expected that the degradation rates of the investigated xenobiotics were affected by the influence of bicarbonate. In contrast to the widely described decrease of the degradation rate, a much more complex situation was found in this investigation. The degradation rates of 2-amino-1-naphthalenesulfonate and diphenyl-4-sulfonate were decreased and reached for high concentrations of bicarbonate the values of the photolytical degradation rate. The degradation of 4,4′-diaminostilbene-2,2′-disulfonate was accelerated significantly in the presence of bicarbonate. The degradation rate of EDTA was increased at small concentrations of bicarbonate and decreased at higher concentrations. 相似文献
8.
In this work, the treatment of actual agro‐industrial wastewaters (IWW) by a UV/H2O2 process has been investigated. The aqueous wastes were received from industrial olive oil mills and then treated by laboratory scale physicochemical methods, i. e., coagulation using ferrous and aluminum sulfate, decantation, filtration and adsorption on activated carbon. These wastes are brown colored effluents and have a residual chemical oxygen demand (COD) in the range of 1800 to 3500 mgO2 L–1, which cannot be further eliminated with physicochemical processes. The UV/H2O2 treatments were carried out under monochromatic irradiation at 254 nm using a thermostated reactor equipped with a mercury vapor lamp located in an axial position. The effects of initial H2O2 concentration, initial COD, pH and temperature have been studied in order to determine the optimum conditions for maximum color and COD removals. The experimental results reveal the suitability of the UV/H2O2 process for both removal of high levels of COD and effectively decolorizing the solution. In particular, 95% of color removal and 90% of COD removal were obtained under conditions of pH = 5 and 32°C using 2.75 g H2O2 g–1 COD L–1 during 6 h of UV‐irradiation. The treatment is unaffected by pH over the range 2 to 9. In addition, the COD removal is improved by increasing the temperature, whereas the color removal has not been affected by this parameter. The results show that the hydroxyl radicals generated from the catalytic decomposition of H2O2 by UV‐irradiation of the solution could be successfully used to mineralize the organics contained in IWW. The mineralization of the organics seems to occur in three main sequential steps: the first is the rapid decomposition of tannins leading to aromatic compounds, which are confirmed by the decolorization of the IWW; the second step corresponds to the oxidation of aromatics leading to aliphatic intermediates, which occurs by the cleavage of an aromatic ring, and is established by the removal of aromatics, and the final step is the slow oxidation of the aliphatic intermediates, which is measured by the COD removal. 相似文献
9.
A characterization method for AOX in surface water samples was developed and tested. The method involves fractionation using a hydrophobic C18 resin and a weak anionic exchange resin and allows the fractionation of the AOX pool of surface water samples into four fractions: (1) hydrophilic acidic, (2) hydrophilic non‐acidic, (3) hydrophobic acidic, and (4) hydrophobic non‐acidic. The adsorption analysis was verified with AOX‐relevant model compounds and was applied to characterize the AOX pool of a stream sample from the Moskva river (Russia). In addition to the fractionation analysis, size‐exclusion chromatography was used to characterize the AOX pool of the sample studied. Hydrophilic acids made up the major fraction of the AOX pool (55 %). Among this fraction chlorinated high‐molecular acids (humic substances) made up the main fraction (35 %). 相似文献
10.
Wido Schmidt 《洁净——土壤、空气、水》2004,32(1):48-60
Chlorine dioxide stock solutions for the disinfection of drinking water are made by the application of chlorite/chlorine process in many waterworks. In such cases the stock solution is always characterised by a mixture of chlorine and chlorine dioxide. The disinfection of waters of different origin with a mixture of chlorine dioxide and chlorine showed the formation of odours of different intensity. The reasons are the re‐formation of chlorine dioxide and the formation of odorous disinfection by‐products. Applying the chlorine dioxide for disinfection, its re‐formation caused by the reaction of chlorite with chlorine is the dominant reason of odour formation. When chlorine is used, the formation of odorous by‐products becomes more relevant. In order to quantify the sensitivity of water concerning odour, the odour indicator coefficient OI was defined. The decreased demand of chlorine dioxide by applying chlorine and chlorine dioxide in combination is recognised to be the key in order to avoid the formation of odour after the disinfection of drinking water with chlorine dioxide. 相似文献
11.
The relative ability of Coriolus versicolor to grow on coir fiber as a ligninocellulosic material was examined. Addition of yeast extract to the culture increased laccase activity, which was further enhanced to the level of 1976 U/L by addition of 1 mM copper sulfate. Laccase thus produced was used without further purification for the decolorization of various dye solutions. Decolorization efficiency was compared with the conventional environment friendly oxidation technique using hydrogen peroxide in the presence of UV radiations. Laccase showed good decolorization in most of the cases. Excellent results were achieved when the dye solution was treated successively with laccase and UV/H2O2 wherein more than 80% decolorization was achieved. This value is remarkably higher than that attained either by the enzyme or UV/H2O2 photolysis alone. 相似文献
12.
The degradation of dissolved organic matter (DOM) was studied in alkaline solution. The products were characterised using UV/vis spectroscopy, size‐exclusion chromatography (SEC), and by the analysis of low‐molecular‐weight organic acids (LMWOA). The degradation experiments were performed with water from a brown water lake or its isolated fulvic acid fraction and sodium hydroxide at different reaction times and temperatures. Depending on the wavelength and the reaction time, the UV/vis absorbance between 230 nm and 600 nm increased or decreased. The behaviour of model compounds during reactions in alkaline media was compared to the UV/vis spectroscopic behaviour of DOM. The release of LMWOA was described by kinetic data and compared to the data of model reactions. Evidence was given for the carboxylic esters playing a significant role in the release of LMWOA only during the beginning of the alkaline degradation. The results gained by SEC with on‐line UV and DOC detection showed that the average size of DOM was decreasing, and that a major part of the degradation products consisted of low‐molecular‐weight mono‐ and dicarboxylic acids. 相似文献
13.
Granular activated carbon (GAC) adsorption of two representative taste and odor (T & O) compounds, 2‐isopropyl‐3‐methoxy pyrazine (IPMP), and 2‐isobutyl‐3‐methoxy pyrazine (IBMP), in drinking water was investigated. Results show that the modified Freundlich equation best fit the experimental data during the adsorption isotherm tests, and the pseudo first‐order kinetics and intra‐particle diffusion kinetics well described the adsorption kinetics pattern. The calculated thermodynamic parameters (ΔH0, ΔS0, and ΔG0) indicated a spontaneous and endothermic adsorption process. Factors affecting the treatment efficiency were carefully evaluated. Acidic and alkaline conditions both favored GAC adsorption of IPMP and IBMP, especially the former. With the GAC dosage increasing, the first order adsorption rates increased, while the intra‐particle adsorption rates decreased. Within 12 h, 200 mg/L GAC could remove >90% of 150 µg/L IPMP and IBMP via adsorption at pH 3–11. Therefore, GAC is a promising treatment technology to control the T & O compounds associated water pollution. 相似文献
14.
The degradation of two pesticides: atrazine and metazachlor was investigated in aqueous solution under UV-irradiation with and without H2O2. Rate constants of the photochemical degradation were determined applying a first order kinetics and quantum yields of the processes were calculated. This approach leads to an apparent decrease of the quantum yield with increasing initial pesticide concentration. At low H2O2 initial concentrations, the pesticide degradation was shown to be much more efficient than the degradation under UV-irradiation only. However, at high H2O2 concentrations (>2 mmol L?1), the efficiency of the UV/H2O2 system dropped down and the quantum yields of degradation were lower than for the direct photolysis. In the absence of H2O2, no influence of the pH value on the photodegradation of the pesticides could be noticed in a range between pH 3 and pH 11. At low H2O2 initial concentrations, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH 11. The results emphasize the potential of optimized reaction conditions in advanced oxidation. 相似文献
15.
Degradations of reactive brilliant red X‐3B solution by both conventional UV irradiation and microwave electrodeless UV irradiation were investigated. Degradation processes were studied by UV–VIS spectrophotometry, total organic carbon (TOC), high performance capillary electrophoresis (HPCE), conductivity, pH value, and ion chromatography. The results of color removal (%) and TOC removal (%) showed that the degradation by microwave electrodeless UV irradiation was more effective than by conventional UV irradiation. The results of UV–VIS absorption spectra and HPCE analyses indicated that the degradation of reactive brilliant red X‐3B was occurred at the conjugation system first, the benzene ring and the naphthalene ring later. The reactive brilliant red X‐3B was cleaved into some new small compounds and eventually most of the organic substances were mineralized to CO2 and H2O. The results of the conductivity analysis suggested that the degradation has mainly occurred in the first 40 min of reaction. The pH value of reactive brilliant red X‐3B solution was decreased first and then was increased. The results of inorganic anions analysis hinted that many of the N, Cl, and S elements from reactive brilliant red X‐3B were still attached in organic molecules. 相似文献
16.
Factors Influencing the Release of DOC and AOX out of Former Wastewater Infiltration Soils The influence of soil and of infiltration water quality on the release of dissolved organic carbon (DOC) and adsorbable organic halogens (AOX) from two former wastewater infiltration sites was investigated in laboratory column studies. Desorption was the most important factor influencing release processes. It depends on the amount of sorbent and sorbate and the strength of binding. Therefore, for constant irrigation rates a higher soil organic carbon content coincided with higher DOC-contents of the column effluent, while the irrigation water quality was of minor importance. Within one system the dependencies of AOX release and DOC mobilization were found to be similar. Transferring these dependencies on other systems has its limitations because of a different binding quality between sorbent and sorbate. 相似文献
17.
Erik Oerter Eric Slessarev Ate Visser Kyungjin Min Megan Kan Karis J. McFarlane Malay C. Saha Asmeret Asefaw Berhe Jennifer Pett-Ridge Erin Nuccio 《水文研究》2021,35(9):e14366
Perennial bioenergy crops with deep (>1 m) rooting systems, such as switchgrass (Panicum virgatum L.), are hypothesized to increase carbon storage in deep soil. Deeply rooted plants may also affect soil hydrology by accessing deep soil water for transpiration, which can affect soil water content and infiltration in deep soil layers, thereby affecting groundwater recharge. Using stable H and O isotope (δ2H and δ18O) and 3H values, we studied the soil water conditions at 20–30 cm intervals to depths of 2.4–3.6 m in paired fields of switchgrass and shallow rooted crops at three sites in the southern Great Plains of North America. We found that soil under switchgrass had consistently higher soil water content than nearby soil under shallow-rooted annual crops by a margin of 15%–100%. Soil water content and isotopic depth profiles indicated that hydraulic redistribution of deep soil water by switchgrass roots explained these observed soil water differences. To our knowledge, these are the first observations of hydraulic redistribution in deeply rooted grasses, and complement earlier observations of dynamic soil water fluxes under shallow-rooted grasses. Hydraulic redistribution by switchgrass may be a strategy for drought avoidance, wherein the plant may actively prevent water limitation. This raises the possibility that deeply rooted grasses may be used to passively subsidize soil water to more shallow-rooted species in inter-cropping arrangements. 相似文献
18.
The inactivation of enzymes is of great interest for many industrial applications. The effectiveness of photoinactivation of alpha‐amylase, catalase, and urease with 222 nm radiation was investigated in comparison to that at 254 nm. The enzymes were irradiated with different fluence rates of 222 nm radiation emitted by a KrCl‐excimer lamp and with 254 nm radiation produced by a low‐pressure mercury lamp. The relative activities were calculated before and after irradiation. Degradation caused by UV‐radiation was assessed by SDS‐PAGE analysis. The results clearly demonstrated that inactivation of the proteins is much more effective with the 222 nm excimer lamp compared to the 254 nm mercury lamp. Irradiation with the excimer lamp and a UV‐fluence rate of 1000 J/m2 was sufficient to reduce the relative activities of amylase and urease to 15% and that of catalase to 60%. After irradiation with 4000 J/m2, the enzyme activity was almost completely inhibited. In contrast, after irradiation with the mercury lamp with an UV‐fluence rate of 4000 J/m2, the relative activity was still above 85%. The gel patterns showed no visible degradation after irradiation at 254 nm, but a strong and unspecific degradation was obvious after treatment at 222 nm, presumably caused by cleavage of the peptide bonds. 相似文献
19.
Photochemical oxidation methods are able to eliminate hydrophilic xenobiotics with a high efficiency. In waters with high DOC values caused by humic substances (HS) which are able to absorb UV light, problems can result. The degradation rates of the micropollutants using irradiation wavelengths in the range between λ = 200 nm to λ = 260 nm are significantly influenced by HS. This is mainly caused by the high absorption of the HS at shorter wavelength. In the presence of HS, the photolytic degradation of EDTA and FeEDTA was slowed down by an inner filter effect. A similar tendency could be seen for the photolytic degradation of 2-amino-1-naphthalenesulfonate where additional effects to the inner filter effect were also operating. In the UV/H2O2-process, the decrease of the degradation rate could be assigned to the ability of the HS to scavenge HO radicals. 相似文献
20.
The water solubility of benzopyrene in the presence of ionic detergents is investigated. The power of n-alkyl benzene sulfonates to dissolve benzopyrene in increased quantities grows with the elongation of their m-alkyl chain (from C8 to C12) and decreases with temperature between 10 and 40°C. The properties of the detergents determine their solvent effect, the substance-specific coefficient Kbind being decisive, as is demonstrated by the example of the cation-active detergents cetyltrimethylammonium bromide, sodium n-decyl benzene sulfonate and sodium lauryl sulfonate. 相似文献