Effects of polyelectrolytes on reduction of model compounds via coagulation

The objective of this research work was to evaluate the performance of enhanced coagulation by alum and polymer. Synthetic source waters containing high molecular weight humic acids, medium molecular weight tannic acids and low molecular weight p-hydroxybenzoic acid were formulated by adjusting the concentration of turbidity and pH; and jar tests were used to study the effect of various types and dosages of polymer on reducing the above model compounds. At a specific pH condition, the applied alum dosage would efficiently decrease the turbidity to 2 NTU follows the order: humic>tannic>p-hydroxybenzoic acid. Adjustment of pH influenced the performance of alum obviously but not of p-DADMAC. High p-DADMAC dosage overwhelming the effects of alum is less affected by pH adjustment. The results of this investigation reveal that enhanced coagulation with p-DADMAC was founded to be very effective for removing high-molecular-weight THM precursors, i.e., humic acid and tannic acid, and markedly reduced the alum dosages required for turbidity removal. The other two polymers, i.e., cationic PAM and non-ionic PAM, which had higher molecular weight but lower charge density than p-DADMAC, were not capable of removing organic precursors. It was thus concluded that enhanced coagulation with polymer, p-DADMAC, could be considered as a promising technique for removal of NOMs with hydrophobic and higher-molar-mass (>1K) in water treatment plants.     

Numerical simulation of the thermal destruction of some chlorinated C1 and C2 hydrocarbons

We have numerically modeled the breakdown of small quantities of several chlorinated hydrocarbons (CH3Cl, CH2Cl2, CHCl3, CCl4, C2H3Cl, and C2H5Cl) in a lean mixture of combustion products between 800 and 1480 K. This simulates the fate of poorly atomized waste in a liquid-injection incinerator. Kinetics calculations were performed using the CHEMKIN and SENKIN programs, with a reaction mechanism that was developed at Louisiana State University to model flat-flame burner experiments. A 99.99-percent destruction efficiency was attained in one second at temperatures ranging from 1280 to 960 K, with CCl4 requiring the highest temperature for destruction and C2H5Cl the lowest. For all compounds except C2H5Cl, there was a range of temperatures at which byproducts accounted for several percent of the elemental chlorine at the outlet. The more heavily chlorinated compounds formed more byproducts even though the amount of elemental chlorine was the same in all cases. The sensitivity of results to residence time, equivalence ratio, temperature profile, and the presence of additional chlorine, was examined for the case of CHCl3.     

Decomposition of halogenated methanes in oxygen-free gas mixtures by the use of a silent electric discharge

A silent electric discharge was applied to decompose halogenated methanes including CCl4, CHCl3, CFCl3, CF2Cl2 and CF3Cl, in argon-containing gas mixtures. The decompositions of the target compounds were studied in static reactors at a fixed electric field and room temperature. The reaction products were analyzed by FT-IR spectroscopy, gas chromatography and UV spectrophotometry. The results demonstrated, that the radical-type decomposition of chlorofluoromethanes led to products formed by realignment of the halogen atoms. The decomposition of CCl4 was faster than that of the cholorofluoromethanes, and produced perchloroethane and chlorine. CHCl3 exhibited the highest decomposition rate and produced a large variety of products.     

电化学方法用于酸性红B模拟废水脱色试验研究

本文研究了两种电极材料 (SnO2 Ti和RuO2 Ti)对酸性红B模拟废水的脱色效果 ,考察了不同 pH、电流密度(j)及外加电解质 (Na2 SO4/NaCl)对处理过程的影响。结果表明 ,两种电极材料都能对酸性红B染料废水进行有效脱色 ,主要是Cl-在电解过程中的间接氧化作用 ,同时也包括电极表面的直接氧化作用。     

Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4

Aqueous solutions of reactive blue 4 textile dye are totally mineralised when irradiated with TiO2 photocatalyst. A solution containing 4 x 10(-4) M dye was completely degraded in 24 h irradiation time. The intensity of the solar light was measured using Lux meter. The results showed that the dye molecules were completely degraded to CO2, SO4(2-), NO3-, NH4+ and H2O under solar irradiation. The addition of hydrogen peroxide and potassium persulphate influenced the photodegradation efficiency. The rapidity of photodegradation of dye intermediates were observed in the presence of hydrogen peroxide than in its absence. The auxiliary chemicals such as sodium carbonate and sodium chloride substantially affected the photodegradation efficiency. High performance liquid chromatography and chemical oxygen demand were used to study the mineralisation and degradation of the dye respectively. It is concluded that solar light induced degradation of textile dye in wastewater is a viable technique for wastewater treatment.     

Electrochemical combustion of herbicide mecoprop in aqueous medium using a flow reactor with a boron-doped diamond anode

The anodic oxidation of 1.8l of solutions with mecoprop (2-(4-chloro-2-methylphenoxy)-propionic acid or MCPP) up to 0.64 g l(-1) in Na2SO4 as background electrolyte within the pH range 2.0-12.0 has been studied using a flow plant containing a one-compartment filter-press electrolytic reactor with a boron-doped diamond (BDD) anode and a stainless steel cathode, both of 20-cm2 area. Electrolyses carried out in batch under steady conditions and operating at constant current density between 50 and 150 mA cm(-2) always yield complete mineralization due to the great concentration of hydroxyl radical generated at the BDD anode. The degradation rate is practically independent of pH and Na2SO4 concentration, but it becomes faster with increasing MCPP concentration, current density, temperature and liquid flow rate. The effect of these parameters on current efficiency and energy cost has also been investigated. Generated weak oxidants such as H2O2 and peroxodisulfate ion have little influence on the mineralization process. The kinetics for the herbicide decay follows a pseudo first-order reaction with a higher rate constant when current density increases. Aromatic products such as 4-chloro-o-cresol, 2-methylhydroquinone and 2-methyl-p-benzoquinone, and generated carboxylic acids such as maleic, fumaric, lactic, pyruvic, tartronic, acetic and oxalic, have been identified as intermediates by chromatographic techniques. The initial chlorine is completely released in the form of chloride ion, which is slowly oxidized to Cl2 at the BDD anode. A reaction pathway for MCPP mineralization involving all products detected is proposed.     

优化混凝处理低温低浊黄河水及对余铝的控制

考察了4种混凝剂,高效聚合氯化铝（HPAC）,聚合氯化铝（PACl）,硫酸铝（Al2（SO4）3）,混合PACl和氯化铁（FeCl3）,对低温低浊黄河原水的混凝效果与沉后水残留铝含量的关系。结果表明,当采用Al2（SO4）3或PACl做混凝剂时,在取得较好浊度去除的投药量下,水中余铝浓度会超过国家标准（0．2131g／L）。而采用HPAC或FeCl3和PACl复配药剂,在取得与Al2（SO4）3或PACl类似的浊度去除效果的同时,也能较好地控制水中的余铝含量。当HPAC投加量为21mg／L时,沉后水浊度降至1．3NTU,残留铝含量为0．147mg／L。复配投加PACl 15mg／L和FeCl3 12mg／L后,沉后水浊度为1．18NTU,残留铝含量为0．074mg／L。PACl和氯化铁的复配比例需要精确的调控,否则容易导致出水余铁余铝含量增加。而HPAC投加量小于21mtg／L时出水余铝浓度均低于国家标准。因此,在这4种混凝剂中,就混凝效果及余铝控制而言,HPAC更适合充当低温低浊水源水的混凝处理药剂。     

Thermodynamic analysis and kinetic modelling of dioxin formation and emissions from power boilers firing salt-laden hog fuel

Both organic chlorine (e.g. PVC) and inorganic chlorides (e.g. NaCl) can be significant chlorine sources for dioxin and furan (PCDD/F) formation in combustion processes. This paper presents a thermodynamic analysis of high temperature salt chemistry. Its influence on PCDD/F formation in power boilers burning salt-laden wood waste is examined through the relationships between Cl2, HCl, NaCl(g) and NaCl(c). These analyses show that while HCl is a product of combustion of PVC-laden municipal solid waste, NaCl can be converted to HCl in hog fuel boilers by reactions with SO2 or alumino-silicate materials. Cl2 is a strong chlorinating agent for PCDD/F formation. HCl can be oxidized to Cl2 by O2, and Cl2 can be reduced back to HCl by SO2. The presence of sulphur at low concentrations thus enhances PCDD/F formation by increasing HCl concentrations. At high concentrations, sulphur inhibits de novo formation of PCDD/Fs through Cl2 reduction by excess SO2. The effect of NH3, CO and NOx on PCDD/F formation is also discussed. A semi-empirical kinetic model is proposed. This model considers both precursor and de novo formation mechanisms. A simplified version is used as a stack emission model. The kinetic model indicates that stack dioxin emissions will increase linearly with decreasing electrostatic precipitator (ESP) efficiency and exponentially with increasing ESP temperature.     

Effect of SO4 2-/Al3+ ratio and OH-/Al3+ value on the characterization of coagulant poly-aluminum-chloride-sulfate (PACS) and its coagulation performance in water treatment

A poly-aluminum-chloride-sulfate (PACS) was prepared at various experimental conditions. It was found that the coagulation performance of PACS in water treatment was affected by the PACS particle size distribution and zeta potential value. The experimental results indicated that the PACS particle size distribution and zeta potential value were highly influenced by SO(4)(2-)/Al(3+) molar ratio and bacicities (gamma,gamma=[OH]/[Al]) value. At a fixed gamma value of 2.0, the average PACS particle size increased from 25 to 80nm with the increase of SO(4)(2-)/Al(3+) ratio from 0 to 0.1. Further increase of the SO(4)(2-)/Al(3+) ratio resulted in acute increment particle size of PACS extremely, which can be attributed to its aggregation. At a fixed SO(4)(2-)/Al(3+) ratio of 0.0664, the largest average size of PACS occurred at gamma=2.0. It was also found that the zeta potential value of PACS was strongly influenced by the SO(4)(2-)/Al(3+) ratio, gamma value and pH of the aquatic solution. The zeta potential value of PACS increased with increasing of SO(4)(2-)/Al(3+) ratio. At a fixed SO(4)(2-)/Al(3+) ratio of 0.0664, PACS achieved greatest zeta potential value at gamma value of around 2.0. The maximum positive zeta potential value of PACS was found at pH5.3. At a fixed gamma value of 2.0 and SO(4)(2-)/Al(3+) ratio of 0.0664, the PACS achieved an optimum natural organic matter and turbidity removal efficiency.     

Direct VUV photolysis of chlorinated methanes and their mixtures in an oxygen stream using an ozone producing low-pressure mercury vapour lamp

The gas-phase photooxidations of CCl(4), CHCl(3), CH(2)Cl(2) and their binary mixtures in an O(2) stream were studied in a flow reactor under various experimental conditions using a low-pressure mercury lamp as light source covered with a high-purity silica sleeve being used. The 184.9 nm VUV irradiation emitted is responsible for the Cl-C bond rupture in the chlorinated methanes and for the formation of O(3) from O(2). The rate of degradation of H-containing chlorinated methanes increased sharply on increase of their initial concentrations, most probably of a (*)Cl chain reaction, as indicated by the increase in the molar ratio of the amount of HCl formed to the amount of H-containing target substance decomposed. The experimental results suggested that the further transformations of the radicals and products formed play an important role as (*)Cl sources, causing a considerably higher rate of decomposition of the H-containing target substances. In a humidified O(2) stream, the (*)OH formed opens up another route for oxidation of the target substances. Thus, the rates of degradation of CH(2)Cl(2) and CHCl(3) increased on increase of the relative humidity, whereas the water vapour had no effect at all on the decomposition of CCl(4). At the same time, competition occurs between (*)Cl or (*)OH for reactions with the target substance. The photooxidation of binary mixtures was investigated too. The addition of CCl(4) or CHCl(3) to CH(2)Cl(2) strongly increased its degradation rate. The addition of CH(2)Cl(2) did not have a considerable effect on the rate of degradation of CHCl(3).     

吸附-电化学氧化耦合处理对氯苯酚废水及动力学

以毡状活性炭纤维为阳极,不锈钢为阴极,吸附-电化学氧化耦合降解对氯苯酚废水进行了研究。考察了吸附或耦合电化学氧化过程、电流密度、支持电解质硫酸钠浓度和活性炭纤维重复使用对废水COD去除率的影响,结果表明,采用吸附-电化学氧化耦合方法,当电流密度7.6 mA/cm2支持电解质（硫酸钠）浓度为1 g/L,处理时间为180 min,4-CP废水COD去除率可达97.09%。毡状活性炭纤维对4-CP的静态吸附过程符合Langmiu吸附等温方程。建立了吸附-电化学氧化COD去除动力学模型,动力学模型参数表明,对于COD的去除,电化学氧化作用比吸附作用大。     

Direct VUV photolysis of chlorinated methanes and their mixtures in a nitrogen stream

The gas-phase decomposition of CCl(4), CHCl(3) and CH(2)Cl(2) and their binary mixtures was studied in a flow-type reactor in a nitrogen gas stream, using a low-pressure mercury vapour lamp covered with a high-purity silica quartz sleeve. The 184.9 nm vacuum-ultraviolet (VUV) light emitted is able to rupture the C-Cl bond in these target substances. For H-containing compounds, the decomposition takes place not only by direct photolysis, but also by H abstraction by .Cl formed during the direct photolysis of the target substances. The relative contributions of direct photolysis and .Cl-sensitized reactions to the decomposition were estimated at different initial concentrations. The addition of CCl(4) to CHCl(3) or CH(2)Cl(2) increased their decomposition rates via increase of the .Cl concentration, whereas the addition of CH(2)Cl(2) to CHCl(3) decreased its degradation rate, suggesting that CH(2)Cl(2) acts as a .Cl radical scavenger. The variation of the product distribution confirms the effect of the composition of the irradiated gas mixtures on the relative contributions of .Cl-sensitized reactions and direct photolysis.     

Identification and behavior of reaction products formed by chlorination of ethynylestradiol

Six products were formed by reaction of ethynylestradiol (EE2) with sodium hypochlorite in buffered solutions. 4-Chloroethynylestradiol (4-ClEE2) and 2,4-dichloroethynylestradiol (2,4-diClEE2) were identified as the two major reaction products, using preparative HPLC, MS, and NMR. When EE2 reacted with chlorine at different pHs (pH 5, 7, and 9) or chlorine concentrations (0.2, 1, 2, and 5 mmol/l, corresponding to molar ratios to EE2, 1, 5, 10, and 25, respectively), the formation of 4-ClEE2 and 2,4-diClEE2 was observed under the above conditions, and the highest yields were 20 and 52 mol%, respectively. EE2 was consumed almost completely within 5 min of chlorination by addition of chlorine of more than 1 mmol/l (molar ratio to EE2, 5). On the other hand, the two products existed in highly chlorinated solutions after 60 min (4ClEE2, 1-6 mol%; 2,4-diClEE2, 3-25 mol%). The estrogenic activities of 4-ClEE2 by estrogen receptor alpha or beta binding assay were similar to those of the parent EE2, and the activities of 2,4-diClEE2 were lower about 10 times.     

Analysis of a summertime PM2.5 and haze episode in the mid-Atlantic region

Observations of the mass and chemical composition of particles less than 2.5 microm in aerodynamic diameter (PM2.5), light extinction, and meteorology in the urban Baltimore-Washington corridor during July 1999 and July 2000 are presented and analyzed to study summertime haze formation in the mid-Atlantic region. The mass fraction of ammoniated sulfate (SO4(2-)) and carbonaceous material in PM2.5 were each approximately 50% for cleaner air (PM2.5< 10 microg/m3) but changed to approximately 60% and approximately 20%, respectively, for more polluted air (PM2.5>30 microg/m3). This signifies the role of SO4(2-) in haze formation. Comparisons of data from this study with the Interagency Monitoring of Protected Visual Environments network suggest that SO4(2-) is more regional than carbonaceous material and originates in part from upwind source regions. The light extinction coefficient is well correlated to PM2.5 mass plus water associated with inorganic salt, leading to a mass extinction efficiency of 7.6 +/- 1.7 m2/g for hydrated aerosol. The most serious haze episode occurring between July 15 and 19, 1999, was characterized by westerly transport and recirculation slowing removal of pollutants. At the peak of this episode, 1-hr PM2.5 concentration reached approximately 45 microg/m3, visual range dropped to approximately 5 km, and aerosol water likely contributed to approximately 40% of the light extinction coefficient.     

Relationship between chlorine consumption and chlorination by-products formation for model compounds

The objective of this research is to investigate the relationship between chlorine decay and the formations of disinfection by-products (DBP), including trichloromethane (TCM) and chloroacetic acid (CAA) in the presence of four model compounds, i.e., resorcinol, phloroglucinol, p-hydroxybenzoic acid, and m-hydroxybenzoic acid. The chlorine degradation in model compounds with OH and/or COOH functional groups were rapid after chlorination. The TCM yields of carboxylic group substituted compounds (3-hydroxybenzoic acid [3-HBA], 4-hydroxybenzoic acid [4-HBA]) were found to be lower than that of the m-dihydroxy substituted compounds. Phloroglucinol, with one more OH substitution group than resorcinol, tends to form significant amounts of CAA after chlorination. However, it was observed that with the COOH substitution of 3-HBA and 4-HBA tend to exhibit more CAA formation potential than resorcinol. The developed parallel second and first-order reaction model for chlorine demand has been successfully utilized for TCM, CAA and DBP formation modeling. A high correlation between CAA and TCM was observed for the model compounds.     

Extraction of chlorinated aliphatic hydrocarbons from groundwater at micromolar concentrations for isotopic analysis of chlorine.

A method is described for near-quantitative extraction of micromolar concentrations of chlorinated aliphatic hydrocarbons (CAHs) from water for determination of chlorine (Cl) isotope ratios. A low pressure, carrier-gas procedure of extraction was proven to be applicable to CH2Cl2, CCl4, C2H2Cl2, and C2HCl3. The pH of the water was adjusted with NaOH to prevent extraction of CO2 from air and/or dissolved inorganic carbonate species. Recoveries of CAH samples (approximately 15 mumol), added to and extracted from approximately 340 ml of water, averaged approximately 96%. Average changes in the delta 37Cl values of the CAHs, attributable to the extraction process, were -0.01 +/- 0.06@1000. Significant isotopic fractionation of Cl was measured during partial extraction of C2CHCl3 from water, indicating that near-quantitative extraction is required for reliable stable Cl isotope analysis of CAHs. This method is also suitable for the extraction of dissolved CAH for gas chromatography-combustion-isotope ratio mass spectrometric measurements of hydrogen and carbon.     

Breakpoint chlorination curves of greywater.

A study on chlorination of raw greywater with hypochlorite is reported in this paper. Samples were chlorinated in a variety of conditions, and residual chlorine (Cl2) was measured spectrophotometrically. For each sample, the chlorination curve (chlorine residuals versus chlorine dose) was obtained. Curves showed the typical hump-and-dip profile attributable to the formation and destruction of chloramines. It was observed that, after reactions with strong reductants and chloramines-forming compounds, the remaining organic matter exerted a certain demand of chlorine. The evolution of chlorination curves with addition of ammonia and dodecylbencene sulfonate sodium salt and with dilution of the greywater sample were studied. In addition, chlorination curves at several contact times have been obtained, resulting in slower chlorine decay in the hump zone than in the dip zone. In addition, the decay of coliforms in chlorinated samples was also investigated. It was found that, for a chlorination dosage corresponding to the maximum of the hump zone (average 8.9 mg Cl2/ L), samples were negative in coliforms after 10 to 30 minutes of contact time. After-growth was not observed within 3 days after chlorination. Implications in chlorination treatments of raw greywater can be derived from these results.     

Second-order chlorine decay and trihalomethanes formation in a pilot-scale water distribution systems

It is well known that model-building of chlorine decay in real water distribution systems is difficult because chlorine decay is influenced by many factors (e.g., bulk water demand, pipe-wall demand, piping material, flow velocity, and residence time). In this paper, experiments were run to investigate the kinetic model of chlorine decay and the formation model of trihalomethanes (THMs) in pilot-scale water distribution systems. Experimental results show that the rate constants of chlorine decay, including wall decay and bulk decay, increasing with temperature. Moreover, the kinetic model of chlorine decay and the formation model of THMs describe experiment data of pilot-scale water distribution systems. The effect of different piping material on chlorine decay and THMs formation were also investigated. The rate constants of chlorine decay are ranked in order: stainless steel pipe, ductile iron pipe, and last, polyethelene pipe because wall decay is the largest in stainless steel pipe than that in other piping material. Correspondingly, the rate of THMs formation follows the order of stainless steel pipe, ductile iron pipe, and last, polyethelene pipe because of less chlorine in bulk water reacting with the trihalomethane formation potential (THMFP).     

钛基IrO2-SnO2电极在烟气海水脱硫恢复系统中的应用

采用浸渍-热分解法制备了含IrOx-TiO2中间层的IrO2-SnO2电极,得到的电极具有较高的析氯电催化活性和较强的稳定性,并通过电化学氧化法对Na2SO3海水脱硫模拟液进行处理,考察了电流密度、温度、pH值和电解时间等电解工艺参数对Na2SO3去除率和化学需氧量COD的影响。结果表明,在电流密度为200 mA/cm^2,pH值为3.5,电解440 mg/L的Na2SO3海水脱硫模拟液,15 min时Na2SO3去除率可达96.5%,COD去除率可达82.6%。     

Mineralization of CCl4 by the UVC-photolysis of hydrogen peroxide in the presence of methanol

A method for a photochemically induced mineralization of CCl4 is described in which use is made of reductive radicals. The UVC-photolysis (254 nm) of H2O2 added to aqueous solutions of CCl4 is leading to the homolysis of the oxidant yielding hydroxyl radicals (HO) that subsequently react with added methanol to generate hydroxymethyl radicals (CH2OH). The latter radicals initiate mineralization of CCl4 by reductive C-Cl bond splitting. CHCl3, C2Cl4 and C2Cl6 were found as reaction intermediates, but are quantitatively depleted in a parallel oxidative reaction manifold leading to mineralization. Carbon dioxide radical anion, CO2(-), an intermediate in the mineralization pathway of methanol, is also shown to initiate the mineralization of CCl4 by reductive dechlorination. A reaction mechanism is proposed and validated with computer simulations of all the experimental results.