三种不同组合电极催化还原高浓度硝酸盐氮的研究

以重金属Cu或Cu/Pd为催化剂对阴极进行改性,采用三种不同组合电极形式(以电镀方式改性的无孔钛板为阴极,阳极为炭板;经吸附负载改性的活性炭纤维绑缚在钛网上形成阴极.阳极为相同面积的钛网;以负载改性的多孔钛板为阴极,以相同面积的多孔钛板为阳极),考察了其对硝酸盐氯的去除效果以及反应副产物氨氮的生成情况.试验结果表明,将催化剂吸附负载于电极上对硝酸盐氮的去除效果比电镀负载方式好;负载催化剂的ACF电极系统会有黑色絮体脱落,影响处理水体水质;负载钯/铜的多孔钛板具有较高的安全性,适于饮用水中硝酸盐氮的处理.     

有机羧酸胺阻锈剂在3.5%NaCl饱和Ca(OH)2溶液中对碳钢的阻锈作用

采用干湿循环试验,线性极化(LPR),电化学阻抗谱(EIS)以及扫描电子显微镜(SEM)方法研究有机羧酸胺(ZX)与Ca(NO₂)₂在3.5%NaCl饱和Ca(OH)₂溶液中对碳钢的阻锈效果。试验结果表明,在溶液中加入阻锈剂0.2%~1.2%时,有机羧酸胺与Ca(NO₂)₂均有抑制碳钢锈蚀的作用,但在干湿循环试验中Ca(NO₂)₂的阻锈效果与其含量不成比例关系,而ZX与其含量有良好的相关性。此外,在电化学试验中,随着ZX与Ca(NO₂)₂含量的增加,阻锈效果越明显,且在3.5%NaCl饱和Ca(OH)₂溶液中ZX的阻锈效果优于Ca(NO₂)₂。     

Electro-oxidation of pistachio processing wastewater using Ti/Pt mesh-type anodes in batch system

In this study, the treatment of pistachio processing wastewater (PPW) by electro-oxidation method was investigated. Ti/Pt-plated electrodes were used for the anode material, and stainless steel electrodes were used for cathode material. Experimental studies were carried out in batch mode. Stirring speed, supporting electrolyte species and concentration, initial pH value, current density, temperature and dilution ratio were selected as experimental parameters effecting removal efficiency. In Ti/Pt electrode experimental studies on the optimum conditions, chemical oxygen demand (COD), total organic carbon (TOC) and total phenols (TP) removal efficiencies were obtained, respectively, as 99.98%, 70.74% and 100%, and energy consumption value was obtained as 297.5 kW-h/m³ (12.39 kW-h/kg COD, 51.29 kW-h/kg TOC and 64.68 kW-h/kg TP). As a result of the experimental studies, the PPW can be treated by electro-oxidation. Given the results of removal efficiency and energy consumption values, it was concluded the electro-oxidation using Ti/Pt anode very appropriate treatment of PPW.     

Removal of chromium from aqueous solutions and plating bath rinse by an electrochemical method

In this work, a bipolar packed bed electrolytic cell having steel Raschig rings behaving as electrodes has been used to remove chromium in the form of Cr(VI) from aqueous solutions and a sample of plating bath rinse.

Fe²⁺ ions generated at the anode side of the electrodes have reacted with OH^‐ ions generated at the cathode side forming Fe(OH)₂ in this electrolytic cell.Cr(VI) have coprecipitated as Cr(OH)₃ with Fe(OH)₃ forming after the redox reaction between Fe(OH)₂ and Cr(VI). Meanwhile other impurities have also removed besides Cr(VI) using this process. Removal rate of 100% for Cr(VI) has been achieved in the experiments done with different initial Cr(VI) concentration, duration of electrolysis and applied potential. Fully removal of Cr(VI) has also been achieved from the sample of plating bath rinse.     

Chlorbromuron urea herbicide removal by electro-Fenton reaction in aqueous effluents

The removal of low concentration of chlorbromuron herbicide in aqueous systems was carried out by electro-Fenton process comprised of three-electrode divided and undivided cell with a reticulated vitreous carbon cathode and platinum anode. The electro-Fenton was also carried out in a two-electrode undivided cell in which ferrous ion forms from a sacrificial iron anode. It was observed that the total organic carbon (TOC) removal efficiency was influenced by the cell voltage, the pH of the solution and initial herbicide concentration during the electro-Fenton treatment with a stainless steel anode. The Fe²⁺/Fe³⁺ activity in the Fenton chemistry (regardless if it is hydroxyl radical or ferryl ion) was improved by the electrochemical catalysis leading to a TOC analysis below the detection limit (0.2 mg l⁻¹) corresponding to a TOC removal over 98%. It was found that TOC removal during chlorbromuron degradation followed apparent first order kinetics. The rate constant was increased by decreasing the initial concentration of chlorbromuron.     

Electrochemical removal of bisphenol A based on the anodic polymerization using a column type carbon fiber electrode

Electrochemical removal based on the polymerization of organic pollutants on an anode surface was performed on bisphenol A (BPA) and its derivatives, bisphenol S (BPS) and diphenolic acid (DPA). It was confirmed by voltammetric techniques that the electrochemical oxidation of these compounds leads to the formation of a polymeric film on a carbon electrode surface. The electrochemical removals of BPA, BPS and DPA based on the anodic polymerization were attempted in the batch type cell. A carbon fiber (CF) was used as an anode with a very large surface area. The high removal efficiency for BPA, BPS, and DPA was obtained by applying a potential at 0.75-, 1.0-, and 0.8-V, respectively. The removal efficiency for BPA does not decrease in the presence of 10ppm humic acid. The electropolymerized BPA film formed on the CF surface was characterized by FT-IR and UV/vis. The continuous treatment of BPA was achieved by using the flow system with a column type of CF electrode. The applicability of this method for removal of BPA from aqueous solution was tested at several different conditions, i.e., flow rate of solution and concentration of electrolyte and BPA. This system can be applied for removal of a low concentration BPA even from low electrolyte concentrations of aqueous solution.     

两种碳基材料对二级出水中有机物的去除特性

针对活性炭与活性焦两种碳基吸附材料,分别开展静态吸附与动态过滤实验,考察了两者对城镇再生水厂二级出水中有机物的去除效果。结果表明:活性焦介孔及大孔丰富,对应孔体积为0.436 cm³/g,为活性炭的1.6倍;准二级动力学模型更适用于两种材料对COD的吸附动力学拟合,活性焦动力学吸附速率常数k₂为活性炭的2倍;水温为22℃时,活性焦与活性炭对COD的Langmuir饱和吸附量分别为230.38、94.14 mg/g。在近4个月的连续运行中,活性焦滤柱对有机物的去除效果全程优于活性炭滤柱,尽管两滤柱在由单纯吸附向生物吸附降解转化的过程中对有机物的去除率有所降低,但对COD的去除率仍可分别稳定在28.43%和22.26%。活性焦颗粒与活性炭颗粒表面ATP含量最高分别为7032.94、5753.52 ng/g。此外,活性焦滤柱对1~10 ku有机物组分,以及腐殖酸类物质、溶解性微生物代谢产物等不同荧光特性有机物均有较好的去除效果。与活性炭相比,活性焦对再生水厂二级出水中有机物的去除效果更优。     

Oxidising and disinfecting by hydrogen peroxide produced in a two-electrode cell

Hydrogen peroxide was produced by direct current electrolysis using two electrodes only, a carbon felt cathode and a dimensional stabilised anode (titanium coated with RuO2), without adding any chemical. The required oxygen was supplied by water oxidation and by transfer from the atmosphere. The intensity should be maintained under a maximum value to avoid peroxide reduction. High peroxide production rate and concentration were then reached. Electroperoxidation partially removed dissolved organic carbon (DOC) contained in solutions of phenol, salicylic acid, benzoic acid and humic acids. The DOC removal in effluent of municipal sewage plant corresponded to a breakage of the double bonds. Real effluents were significantly disinfected owing to the direct effect of electric current and the indirect effect of peroxide. Moreover, a remnant effect was ensured.     

Electro-photocatalytic degradation of acid orange II using a novel TiO2/ACF photoanode

A novel photoanode was prepared by immobilizing TiO₂ film onto activated carbon fibers (TiO₂/ACF) using liquid phase deposition (LPD) to study the electro-photocatalytic (EPC) degradation of organic compounds exemplified by an azo-dye, namely, Acid Orange II (AOII). Results demonstrated that by applying a 0.5 V bias (vs. SCE) across the TiO₂/ACF electrode, the AOII degradation rate was increased significantly compared to that of photocatalytic (PC) oxidation. The application of an electric field promotes the separation of photogenerated electrons and holes as confirmed by electrochemical impedance spectroscopy (EIS) measurements. The structural and surface morphology of the TiO₂/ACF electrode was characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). SEM images showed that TiO₂ was deposited on almost every carbon fiber with an average thickness of about 200 nm with the inner space between neighboring fibers being maintained unfilled. The morphological features of the photo-anode facilitated the passage of solution as well as UV light through the felt-form electrode and created a three-dimensional environment favorable to EPC oxidation. Both the large outer surface area of the 3D electrode and the good organic adsorption capacity of the ACF support promoted high contact efficiency between AOII and TiO₂ surface. Anatase was the major crystalline TiO₂ deposited. UV-vis spectrophotometry, TOC (total organic carbon) analysis, and HPLC technique were used to monitor the concentration change of AOII and intermediates as to gain insight into the EPC degradation of AOII using the TiO₂/ACF electrode.     

Surfactant-coated aluminum hydroxide for the rapid removal and biodegradation of hydrophobic organic pollutants in water

The removal of hydrophobic organic pollutants in water to surfactant-coated aluminum hydroxide [surfactant-Al(OH)₃] was investigated. Anionic surfactants such as sodium dodecyl sulfate (SDS), sodium bis(2-ethylhexyl)sulfosuccinate (AOT), and sodium oleate were sorbed on positively charged aluminum hydroxide at pH 7 and formed hydrophobic aggregates that can incorporate hydrophobic organic pollutants in water. Because of the hydrophobic interaction and decrease in the positive charge, surfactant-Al(OH)₃ was coagulated into precipitates that can readily be separated from water. Hydrophobic organic pollutants such as alkylphenols, polycyclic aromatic hydrocarbons, estrogens, chlorinated antifungals, and pesticides were well collected to the precipitates and thus efficiently removed from water. The collection of hydrophobic organic pollutants was correlated to their aqueous-octanol distribution coefficient. The decomposition of hydrophobic organic pollutants was examined using a bacterial agent (Bacillus subtilis). Hydrophobic organic compounds collected to AOT-Al(OH)₃ or sodium oleate-Al(OH)₃ were insufficiently decomposed. On the other hand, nonylphenol, octylphenol, and pendimethalin collected to SDS-Al(OH)₃ were decomposed within 1 week. The decomposition was accelerated by the collection to SDS-Al(OH)₃.     

Equilibrium adsorption of fulvic acids on activated carbon and its dependance on preozonization of solutions

The impact of ozonization on the equilibrium adsorption of fulvic acids (FA) on activated carbon has been studied. The possibility of multicomponent approach to describe the adsorption equilibrium by using two hypothetical components: weakly and strongly adsorbable fractions of FA was examined. The ozone treatment was shown to equalize the ability of FA fractions to adsorption as compared with the unozonized solution. It was established that the variation of the free energy of adsorption of FA destruction products correlated with changes of the share of organic carbon, subjected to biological impact, in the total organic carbon. The efficiency prediction of the ozone treatment of solutions of natural organic compounds prior to their filtration through the biologically activated carbon can be expediently performed by determining the variation of the free energy of adsorption.     

Chemical characterization of different typologies of mucilaginous aggregates in the Northern Adriatic Sea

The chemical composition of mucilage aggregates found during summer 2000, 2001 and 2002 in the North Adriatic Sea depends on the nature of the organic matter during aggregation, on the environmental conditions of the site of formation and on the transformations during ageing. The mucilages were composed of organic matter, together with a significant inorganic fraction. Elemental analysis revealed 12.5-32.2% of organic carbon, 0-7.3% of inorganic carbon and 1.0-3.7% of nitrogen. The C(org)/N ratios of most aggregates were between 7.5 and 12.6, values close to those found in the suspended matter; higher ratios were found in large-size (>5 m) aggregates which are probably older. The content of carbohydrates and proteins determined in the aggregates, respectively, 15.4+/-8.9% and 7.9+/-4.8%, w/w, showed a prevalence of carbohydrates over proteins. Neutral carbohydrate analysis of purified polysaccharides from mucilage samples showed very similar signatures with high relative abundance of galactose and glucose. Humic, fulvic and humin substances extracted from the mucilages constitute an important fraction of the organic matter in the aggregates. The humin (a fraction insoluble in acidic and basic media) was present in all mucilage samples, indicating the refractory nature of a part of the organic matter in the mucilage. The iron and calcium could play a role during the aggregation process to form a complex with polysaccharides and humic fractions. The C(org)/N ratio 10+/-2 found in the humic acids extracted from the Adriatic aggregates disclosed a marine origin. The low phosphorus content and the high C(org)/P ratio found in the aggregates might depend from high bacteria activity or from the aggregation of organic fractions depleted of phosphorus. The principal inorganic species contained aluminium and silicon, part of which was of biogenic origin and was more significant in the offshore mucilage aggregates than in the coastal ones. The Si(biog)/C(org) ratio showed that diatoms were always present in the aggregates, although it cannot be established whether these are the producers or these develop within the aggregates.     

DBPs removal in GAC filter-adsorber

A rapid sand filter and granular activated carbon filter-adsorber (GAC FA) were compared in terms of dissolved organic carbon (DOC) and disinfection by-products (DBPs) removal. A water treatment plant (WTP) that had a high ammonia concentration and DOC in raw water, which, in turn, led to a high concentration of DBPs because of a high dose of pre-chlorination, was investigated. To remove DBPs and DOC simultaneously, a conventional rapid sand filter had been retrofitted to a GAC FA at the Buyeo WTP in Korea. The overall removal efficiency of DBPs and DOC was higher in the GAC FA than in the sand filter, as expected. Breakthrough of trihalomethanes (THMs) was noticed after 3 months of GAC FA operation, and then removal of THMs was minimal (<10%). On the other hand, the removal efficiency of five haloacetic acids (HAA(5)) in the GAC FA was better than that of THMs, though adsorption of HAA(5) decreased rapidly after 3.5 months of GAC FA operation. And then, gradual improvement (>90%) in HAA(5) removal efficiency was again observed, which could be attributed to biodegradation. At the early stage of GAC FA operation, HAA(5) removal was largely due to physical adsorption, but later on biodegradation appeared to prevail. Biodegradation of HAA(5) was significantly influenced by water temperature. Similar turbidity removal was noticed in both filters, while better manganese removal was confirmed in the sand filter rather than in the GAC FA.     

Electro‐oxidation of phenol in petroleum wastewater using a novel pilot‐scale electrochemical cell with graphite and stainless‐steel electrodes

This work investigated the removal of phenol from petroleum wastewater by the electro‐oxidation process. The experimental design was developed on a pilot‐scale electro‐oxidation system equipped with a cylindrical shape of graphite electrodes as an anode and stainless‐steel electrodes as a cathode. An initial study was performed based on operating variables such as current density and time on real petroleum wastewater. The optimum conditions were obtained as a current density of 3 mA/cm² and time 15 min. Under these applied optimum conditions, complete phenol removal from an initial concentration of about 6.8 mg/L was achieved. Also, 50–60% removal of organic matter in terms of chemical oxygen demand (COD) and biological oxygen demand (BOD). The removal of organic matter using electro‐oxidation requires a long reaction time. Also, the economic study indicated that the energy consumption was determined to be 0.79 kWh/m³ and the operating cost was 0.051 $/m³ which is very economical compared with conventional methods.     

Theoretical study on fulvic acid structure, conformation and aggregation. A molecular modelling approach

The ubiquitous presence of humic substances (HS), combined with their ability to provide multiple sites for chemical reaction, makes them relevant to numerous biogeochemical processes such as mineral weathering, nutrient bioavailability, and contaminant transport. The reactivity of HS depends on their functional group chemistry and microstructure, which are in turn influenced by the composition of the surrounding media. In order to help towards an understanding of structure conformations and aggregation process of HS in soils and waters and to get a better knowledge of these kinds of materials, a fulvic acid (FA) has been modelled as a function of its ionic state under different conditions. Our proposed theoretical model based on the Temple-Northeastern-Birmingham (TNB) monomer fits well with experimental observations on the solubility (dipolar moment) and electronic and vibrational spectra of FAs. The presence of water molecules has a great stabilization effect on the electrostatic energy; this effect is greater as ionized rate increases. In vacuum, the non-ionized aggregated species are more stable than monomers because of the increase in their interaction due to H-bonding and non-bonding forces. When the molecules are ionized, no aggregation process takes place. In solution, the FA concentration is a critical factor for the aggregation. The system containing two FA molecules probably did not form aggregates because its equivalent concentration was too low. When the concentration was increased, the system gave rise to the formation of aggregates. The ionic state is another critical factor in the aggregation process. The ionized FA has a higher electric negative charge, which increases the energetic barriers and inhibits the approximation of FA caused by the Brownian movement.     

Dynamic pesticide removal with activated carbon fibers

Rapid small-scale minicolumn tests were carried out to simulate the atrazine adsorption in water phase with three pelletized pitch-based activated carbon fibers (ACF) and one commercial granular activated carbon (GAC). Initial atrazine solutions were prepared with pretreated ground water. Minicolumn tests showed that the performance of highly activated carbon fibers (surface area of 1700 m2/g) is around 7 times better than the commercial GAC (with surface area at around 1100 m2/g), whereas carbon fibers with medium activation degree (surface area of 1500 m2/g) had a removal efficiency worse than the commercial carbon. The high removal efficiency of the highly activated ACF is due to the wide-opened microstructure of the material, with an appreciable contribution of the low size mesopores, maintaining at these conditions a fast kinetic adsorption rate rather than a selective adsorbent for micropollutants vs. natural organic matter.     

A kinetic study of 3-chlorophenol enhanced hydroxyl radical generation during ozonation

Hydroxyl (OH) radical is proposed as an important factor in the ozonation of water. In the present study, the enhancing effect of 3-chlorophenol on OH radical generation was mathematically evaluated using electron spin resonance (ESR)/spin-trapping technique. OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO–OH. The initial velocity of DMPO–OH generation in ozonated water containing 3-chlorophenol was quantitatively measured using a combined system of ESR spectroscopy with stopped-flow apparatus which was controlled by home-made software. The initial velocity of DMPO–OH generation increased as a function of the concentration of ozone and the more effectively of 3-chlorophenol concentration. The relation among ozone concentration, amount of 3-chlorophenol and the initial velocity (ν₀) of DMPO–OH generation was mathematically analyzed and the following equation was obtained, ν₀ (10⁻⁶M/s)={9.7×[3-chlorophenol (10⁻⁹M)]+0.0005} exp(57×[ozone (10⁻⁹M)]). The equation fitted very well with the experimental results, and the correlation coefficient was larger than 0.99. The equation for the enhancing effect by 3-chlorophenol should provide useful information to optimize the condition in ozone treatment process of water containing phenolic pollutants.     

Adsorption of dissolved natural organic matter by modified activated carbons

Adsorption of dissolved natural organic matter (DOM) by virgin and modified granular activated carbons (GACs) was studied. DOM samples were obtained from two water treatment plants before (i.e., raw water) and after coagulation/flocculation/sedimentation processes (i.e., treated water). A granular activated carbon (GAC) was modified by high temperature helium or ammonia treatment, or iron impregnation followed by high temperature ammonia treatment. Two activated carbon fibers (ACFs) were also used, with no modification, to examine the effect of carbon porosity on DOM adsorption. Size exclusion chromatography (SEC) and specific ultraviolet absorbance (SUVA(254)) were employed to characterize the DOMs before and after adsorption. Iron-impregnated (HDFe) and ammonia-treated (HDN) activated carbons showed significantly higher DOM uptakes than the virgin GAC. The enhanced DOM uptake by HDFe was due to the presence of iron species on the carbon surface. The higher uptake of HDN was attributed to the enlarged carbon pores and basic surface created during ammonia treatment. The SEC and SUVA(254) results showed no specific selectivity in the removal of different DOM components as a result of carbon modification. The removal of DOM from both raw and treated waters was negligible by ACF10, having 96% of its surface area in pores smaller than 1 nm. Small molecular weight (MW) DOM components were preferentially removed by ACF20H, having 33% of its surface area in 1--3 nm pores. DOM components with MWs larger than 1600, 2000, and 2700 Da of Charleston raw, Charleston-treated, and Spartanburg-treated waters, respectively, were excluded from the pores of ACF20H. In contrast to carbon fibers, DOM components from entire MW range were removed from waters by virgin and modified GACs.     

Ultrafiltration of natural organic matter and black carbon: Factors influencing aggregation and membrane fouling

There are concerns about black carbon (BC), due to its potential for sorption of toxic pollutants and inevitably entering drinking water sources. This study aimed to evaluate factors affecting BC aggregation and membrane fouling in the ultrafiltration of river water. Hydrophilic carbon black (CB) was selected as a surrogate of submicron BC in natural waters. Calcium, pH, and natural organic matter (NOM) were found to influence CB aggregation. Calcium induced interparticle interactions in a pH range of 4.3-7.7. In river water at 0.3 mM Ca²⁺, CB remained as fine aggregates (<300 nm) that caused substantial filtration resistance. At 1.3 mM Ca²⁺, CB size increased to 2.2-3.3 μm and membrane fouling was reduced. Interactions between particles and NOM enhanced organic rejection and eliminated irreversible membrane fouling. BC in water resources is a noxious substance, but it was easily aggregated in hard waters and could enhance NOM removal in the ultrafiltration process.     

A bench study on lead removal from battery manufacturing wastewater by carbonate precipitation

A residual soluble Pb ≤ 0.2 mg/l has been measured after hydrocerussite precipitation in the range of pH 9–10 and filtration with 0.45 μm filter, at a total carbonate concentration (C_T) of about 1.5 × 10⁻⁴ M. Filterability and sedimentation were optimized by minimizing the “relative supersaturation” coefficient during precipitation. Pb abatement was implemented in the pH range 9–9.5, following a preliminary precipitation step consisting of a slow, gradual change of pH from 6.8 to 7.8 with 0.1 M NaOH solution. The crystals formed may settle within 24 h, allowing Pb to be recovered as Pb₃(CO₃)₂(OH)₂.