Arsenic — a Review. Part II: Oxidation of Arsenic and its Removal in Water Treatment

In natural waters arsenic normally occurs in the oxidation states +III (arsenite) and +V (arsenate). The removal of As(III) is more difficult than the removal of As(V). Therefore, As(III) has to be oxidized to As(V) prior to its removal. The oxidation in the presence of air or pure oxygen is slow. The oxidation rate can be increased by ozone, chlorine, hypochlorite, chlorine dioxide, or H₂O₂. The oxidation of As(III) is also possible in the presence of manganese oxide coated sands or by advanced oxidation processes. Arsenic can be removed from waters by coprecipitation with Fe(OH)₃, MnO₂ or during water softening. Fixed‐bed filters have successfully been applied for the removal of arsenic.The effectiveness of arsenic removal was tested in the presence of adsorbents such as FeOOH, activated alumina, ferruginous manganese ore, granular activated carbon, or natural zeolites. Other removal technologies are anion exchange, electrocoagulation, and membrane filtration by ultrafiltration, nanofiltration or reverse osmosis.     

Field Treatment of MTBE‐Contaminated Groundwater Using Ozone/UV Oxidation

Methyl‐tertiary butyl ether (MTBE) is often found in groundwater as a result of gasoline spills and leaking underground storage tanks. An extrapolation of occurrence data in 2008 estimated at least one detection of MTBE in approximately 165 small and large public water systems serving 896,000 people nationally (United States Environmental Protection Agency [U.S. EPA] 2008). The objective of this collaborative field study was to evaluate a small groundwater treatment system to determine the effectiveness of ultraviolet (UV)/ozone treatment in removing MTBE from contaminated drinking water wells. A pilot‐scale advanced oxidation process (AOP) system was tested to evaluate the oxidation efficiency of MTBE and intermediates under field conditions. This system used ozone as an oxidizer in the presence of UV light at hydraulic retention times varying from 1 to 3 min. MTBE removal efficiencies approaching 97% were possible with this system, even with low retention times. The intermediate t‐butyl alcohol (TBA) was removed to a lesser extent (71%) under the same test conditions. The main intermediate formed in the oxidation process of the contaminated groundwater in these studies was acetone. The concentrations of the other anticipated intermediates t‐butyl formate (TBF), isopropyl alcohol (IPA), methyl acetate (MAc), and possible co‐occurring aromatics (BTEX) in the effluent were negligible.     

Pump‐and‐Treat Groundwater Remediation Using Chlorine/Ultraviolet Advanced Oxidation Processes

Comparative studies of the use of chlorine/ultraviolet (Cl₂/UV) and hydrogen peroxide/ultraviolet (H₂O₂/UV) Advanced oxidation processes (AOPs) to remove trichloroethylene (TCE) from groundwater in a pump‐and‐treat application were conducted for the first time at the full‐scale operational level at two water treatment facilities in Northern California. In these studies, aqueous chlorine replaced hydrogen peroxide in the AOP treatment step, where the oxidant is exposed to UV light to produce highly reactive radical species that degrade groundwater contaminants. TCE removal rates as a function of initial chlorine dose and pH were then determined. At the site where the natural pH of the water was 7.1, TCE was removed (to a concentration of less than 0.5 µg/L) for nearly every chlorine dose point tested, and pH adjustment slightly enhanced the treatment process at this facility. The second site had a high natural pH of 7.7, and here, TCE was not completely removed for any chlorine dose up to 5.7 mg/L, although TCE removal did increase when the chlorine dose increased between 0.9 and 3.6 mg/L. Residual TCE remaining in the water post‐Cl₂/UV was readily removed using active carbon filtration, which is part of the overall treatment train at this facility. These studies also verified that Cl₂/UV AOP did not interfere with the photolysis of N‐nitrosodimethylamine or result in an effluent acutely toxic toward Ceriodaphnia dubia. Comparative economic analysis revealed that the chemical costs associated with Cl₂/UV AOP were 25 to 50% of the costs associated with in place H₂O₂/UV AOP treatment.     

Performance of A Combination Process of UV/H2O2/Micro‐Aeration for Oxidation of Dichloroacetic Acid in Drinking Water

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.     

Analysis and occurrence of bromate in raw water and drinking water

A method for the trace-level determination of bromate in raw and drinking water is reported. The procedure combines the quantitation of bromate by ion chromatography with a concentration step which in the main is composed of an unselective enrichment of all water constituents by means of a rotatory evaporator and a selective removal of the chloride ions. With this method, the reliable determination of bromate in raw and drinking waters is possible down to concentrations of at least 1 μg/L. The method is used for systematic examinations in several German waterworks which use ozone for the preparation of drinking water. The resulting data clearly prove that during the ozonation of bromide-containing waters, bromate is produced, whereby the concentration of bromate in the ozonated raw water can exceed 10 μg/L. Some correlations between the amount of bromate and the respective conditions of ozonation are pointed out.     

Hydrologic and geologic control of carbonate water chemistry in the subarctic nahanni karst,canada

There are six classes of water and five geologic environments in the subarctic Nahanni karst. During the summers of 1972 and 1973, 214 water samples were collected from 15 of the 30 hydrogeologic categories. Linear discriminant function analysis, using five measured and two derived chemical variables, indicates that there are statistically significant (0.005 level) differences in water chemistry between similar waters in different geologic environments, between waters in the same geologic environment, and between waters in different hydrogeological categories. Geological environment labels a natural water because it determines the availability of soil CO₂ and of soluble minerals. Measurements indicate that mean soil log PCO₂ is greatest in areas of shale mantled by till (?2.39), and least in areas of sandy fluvioglacial drift (?3.27). Low values on the sandy drift are due to the sparse shrub vegetation, and to the high degree of soil aeration; soils in areas of shale are clay-rich and support a dense boreal forest. Hydrology influences water chemistry because it determines how much CO₂ natural waters pick up from the environment and how much they subsequently lose to the atmosphere, and as a result, whether they dissolve or deposit soluble materials. The similarity between mean calculated log PCO₂ in natural waters (?2.92) and mean measured soil log PCO₂ (?2.80) suggests that natural waters in Nahanni are dose to equilibrium with mean soil CO₂ levels.     

Nanofiltration in Combination with Limestone Filtration for Treating a Soft Spring Water Containing High Amounts of Humic Substances

The paper presented here describes experiments with a nanofiltration pilot plant treating spring water which contains high amounts of humic substances. With this process, water components such as humic substances, iron, manganese, and aluminum may be very well removed. However, the low pH value of the NF filtrate does not conform with the German standards. This is why the pH value will be increased in a second treatment step by limestone filtration. Prior to limestone filtration, CO₂ dosage is required in order to make sure that the pH value stays below the upper limit of the German standards of 9.5. With this treatment, a drinking water results which meets the German standards and has good chemical properties with respect to corrosion. The operation of the nanofiltration pilot plant for the treatment of the very soft spring water did not require the continuous addition of chemicals in order to prevent scaling. Although the spring water entered the NF without chemical pretreatment, there was no decrease in filtrate capacity observed over a period of six months. This is in contrast to other investigations involving colour reduction from very hard surface waters. When treating very hard waters by nanofiltration, the addition of complexing agents or acid is required in order to prevent scaling of the membranes. Such intricate pretreatment procedures cause doubt of the application of nanofiltration for the treatment of hard waters in large plants. However, in the case presented here, the application of NF in combination with the hardening step is quite simple, so that the full-scale plant may be operated mainly automatically and will require only little maintenance.     

曝气充氧对城市污染河道内源铵态氮释放的控制

以城市污染河道沉积物和上覆水为研究对象,利用模拟实验方法,探讨不同曝气充氧方式(水曝气EW、底泥曝气ES)对污染河道內源铵态氮(NH4+-N)释放的影响.研究结果发现:从间隙水和沉积物中NH4+-N的削减效果来看,底泥曝气均要优于水曝气;实验结束后,底泥曝气组沉积物与间隙水中NH4+-N含量分别减少63.39%和43.33%,水曝气组分别减少了7.54%和13.98%;从沉积物-水界面NH4+-N的扩散通量变化来看,水曝气组界面通量高于对照组,其变化规律与对照组相似;底泥曝气组沉积物-水界面NH4+-N扩散通量变化过程完全不同于其它两组,在整个试验周期内(除第5 d以外),底泥曝气组的通量低于水曝气组,在第15 d最低,为13.73 mg/(m2.d),仅为水曝气组和对照组的14.68%和19.93%,表明底泥曝气组沉积物NH4+-N的释放潜力低于水曝气组沉积物.     

Significance of an In Vivo Genotoxicity Test for Surface Waters Is Increased when the Physiological Characteristics of the Test Organism (Bivalvia: Mollusca) Are Taken into Account?

The alkaline filter elution assay using the gills of the freshwater clam species Corbicula fluminea detects breaks in single‐stranded DNA and is thus a good method for determining the genotoxic potential of surface waters. In attempting to standardize the procedure, a wide range of factors which could have an influence on the uptake of genotoxic substances by the exposed clams were studied. The most important parameters of the static exposure in relation to the rate of filtration by the animals turned out to be the temperature, the volume of the water, and the exposure time. Differences in body size and in the amount of suspended particles in surface waters did not play a significant role. The results demonstrate that the in vivo test system can be quite sensitive and its results reproducible when the relevant species‐specific characteristics of the test organisms are brought into consideration, even if the test organism belongs to a biologically more advanced group. A clear dose‐response relationship to the reference substances 4‐nitroquinoline‐1‐oxide (NQO) and N‐methyl‐N‐nitro‐N‐nitrosoguanidine (MNNG) can be observed even after a short exposure time of between four and twenty hours. No genotoxic effects were observed when using this method on surface waters from the area of Cologne (including water from the Rhine River and within the protection zone 2 of the Cologne waterworks).     

Zum Auftreten von leichtflüchtigen Halogenkohlenwasserstoffen im Badewasser

110 samples from two swimming-pools were gas-chromatographically investigated for halogenated hydrocarbons. In spite of varying chlorine concentrations between 0.1 and 2.5 mg/l Cl₂ the bacteriological results were unobjectionable. The total of the haloforms was between 1.2 and 182 μg/l, with the average value of 90 μg/l. Besides CHCl₃, CHBrCl₂, CHBr₂Cl and CCl₃NO₂ there were observed other, still unidentified compounds in the chlorinated bathing water which clearly are successive products of disinfection, too. The water treatment by flocculation and filtration does not bring about any elimination of trihalomethanes. Of special importance is the occurrence of trichloronitromethane in concentrations of 0.13 … 1.2 μg/l, whose LC₅₀ in the Daphnia test is 189 μg/l, at a threshold concentration of 160 μg/l. To limit the pollution of water and air to a minimum, specific conditions must be adhered to in the operation of indoor swimming-pools.     

Removal of Elongated Particle Aggregates on Fibrous Filters

Elongated aerosol particle removal on fibrous filters has been investigated. It was shown that particle agglomerates are removed much more efficiently compared to the regularly shaped single particles with identical electrical mobility diameter at two filtration velocities tested. The experimental results were compared with the classical filtration theory and it was shown that the theoretical predictions, which are based on the assumption that the particles are spherical, are significantly different compared to an agglomerate filtration efficiency value. In order to account for a particle shape non-regularity, dominating nanoparticle removal mechanisms were firstly evaluated for a regular particle of certain size and then adjusted by fitting coefficients k₁ (for diffusion component) and k₂ (for interception). These coefficients were determined by fitting the theoretical values that gives the best coincidence with the measured data points. As was further demonstrated theoretically, the coefficient k₁ is identical to the ratio of the actual particle surface area to the surface area of the spherical particle of the equivalent diameter. On the other hand, the coefficient k₂ was found to be equal to the ratio of the projection of a given particle on a plane perpendicular to a streamline, to that of the spherical particle of the equivalent diameter. The reported findings would allow undertaking more accurate evaluation of the removal efficiency of non-regular aerosol particle, which is especially important for industrial applications where non-regular aerosols are frequently met.     

Adsorption of Cadmium Ions from Aqueous Solution Using Granular Activated Carbon and Activated Clay

The present study was aimed at removing cadmium ions from aqueous solution through batch studies using adsorbents, such as, granular activated carbon (GAC) and activated clay (A‐clay). GAC was of commercial grade where as the A‐clay was prepared by acid treatment of clay with 1 mol/L of H₂SO₄. Bulk densities of A‐clay and GAC were 1132 and 599 kg/m³, respectively. The surface areas were 358 m²/g for GAC and 90 m²/g for A‐clay. The adsorption studies were carried out to optimize the process parameters, such as, pH, adsorbent dosage, and contact time. The results obtained were analyzed for kinetics and adsorption isotherm studies. The pH value was optimized at pH 6 giving maximum Cd removal of 84 and 75.2% with GAC and A‐clay, respectively. The adsorbent dosage was optimized and was found to be 5 g/L for GAC and 10 g/L for A‐clay. Batch adsorption studies were carried out with initial adsorbate (Cd) concentration of 100 mg/L and adsorbent dosage of 10 g/L at pH 6. The optimum contact time was found to be 5 h for both the adsorbents. Kinetic studies showed Cd removal a pseudo second order process. The isotherm studies revealed Langmuir isotherm to better fit the data than Freundlich isotherm.     

Treatment of Arsenic Contaminated Groundwater Using Calcium Impregnated Granular Activated Carbon in a Batch Reactor: Optimization of Process Parameters

This paper is an experimental investigation into the removal of arsenic species from simulated groundwater by adsorption onto Ca²⁺ impregnated granular activated carbon (GAC‐Ca) in the presence of impurities like Fe and Mn. The effects of adsorbent concentration, pH and temperature on the percentage removal of total arsenic (As(T)), As(III) and As(V) have been discussed. Under the experimental conditions, the optimum adsorbent concentration of GAC‐Ca was found to be 8 g/L with an agitation time of 24 h, which reduced As(T) concentration from 188 to 10 μg/L. Maximum removal of As(V) and As(III) was observed in a pH range of 7–11 and 9–11, respectively. Removal of all the above arsenic species decreased slightly with increasing temperature. The presence of Fe and Mn increased the adsorption of arsenic species. Under the experimental conditions at 30°C, the maximum percentage removals of As(T), As(III), As(V), Fe, and Mn were found to be ca. 94.3, 90.6, 98.0, 100 and 63%, respectively. It was also observed that amongst the various regenerating liquids used, a 5 N H₂SO₄ solution exhibited maximum regeneration (ca. 91%) of the spent GAC‐Ca.     

Reduzierung von Bakterien- und Coliphagen-Konzentrationen auf der Fließstrecke eines Klärwerksableiters

Reduction of the Concentration of Bacteria and Coliphages along the Flowing Stretch of a Treated Sewage Channel The efficiency of surface waters to eliminate E. coli, fecal streptococci, Salmonella spp., and coliphages was evaluated in a small river which receives treated wastewater and which is rich in submerged macrophytes. The study took place between April and December, 1994. Total colony count, BOD₅, O₂ concentration and water temperature were determined in the river as well. As the river does not receive additional water downwards along its 17.2 km course, dilution effects could be ruled out as the cause for the elimination of the microorganisms. The reduction is assumed to happen rather due to sedimentation, grazing, and adsorption to the submerged waterplants. Immediately after discharge of the wastewater, the river water contained about 10⁵ cfu/100 mL E. coli and 10⁴ cfu/100 mL fecal streptococci, about 1000 pfu/100 mL coliphages, and, as a rule, was positive for salmonella in 10 mL. The reduction of E. coli, fecal streptococci, salmonella, clostridia, and coliphages at the end of the course was 1 to 2 orders of magnitude. This reduction took place mainly within the first 4.7 km, a part in which, due to low flowing velocities, suspended solids settle down efficiently. Besides, at the end of this part the submerged waterplants are especially abundant. The reduction of suspended solids correlated positively with that of BOD₅, bacteria, and coliphages. The reduction of microorganisms was not sufficient to fulfill the requirements of the European Community guidelines for bathing waters and for surface waters used as drinking water source. The regenerating capacity of surface waters is not sufficient to eliminate pathogens from convenionally treated wastewater. Therefore, tertiary treatment is necessary to keep receiving waters reasonably free from pathogens.     

Control of Hydrogen Sulfide by a Wire‐Tube Dielectric Barrier Discharge AC Plasma Reactor

Destruction of hydrogen sulfide by a wire‐tube dielectric barrier discharge (DBD) AC plasma reactor was carried out at atmospheric pressure and room temperature. Six aspects, effect of applied voltage, initial H₂S concentration, gas flow rate, pellets in the reactor, DBD reactor materials, and DBD dielectric thickness on H₂S removal efficiency were investigated. Furthermore, specific energy density (SED), absolute removal amount (ARA), and energy yield (EY) during the discharge process were investigated at the same time. In addition, ozone generation during the decomposition of H₂S was also studied. Experimental results demonstrated the application of DBD AC plasma was an effective technology for odor elimination.     

Remediation of the Wells G & H Superfund Site,Woburn, Massachusetts

Remediation of ground water and soil contamination at the Wells G & H Superfund Site, Woburn, Massachusetts, uses technologies that reflect differences in hydrogeologic settings, concentrations of volatile organic compounds (VOCs), and costs of treatment. The poorly permeable glacial materials that overlie fractured bedrock at the W.R. Grace property necessitate use of closely spaced recovery wells. Contaminated ground water is treated with hydrogen peroxide and ultraviolet (UV) oxidation. At UniFirst, a deep well completed in fractured bedrock removes contaminated ground water, which is treated by hydrogen peroxide, UV oxidation, and granular activated carbon (GAC). The remediation system at Wildwood integrates air sparging, soil-vapor extraction, and ground water pumping. Air stripping and GAC are used to treat contaminated water; GAC is used to treat contaminated air. New England Plastics (NEP) uses air sparging and soil-vapor extraction to remove VOCs from the unsaturated zone and shallow ground water. Contaminated air and water are treated using separate GAC systems. After nine years of operation at W.R. Grace and UniFirst, 30 and 786 kg, respectively, of VOCs have been removed. In three years of operation, 866 kg of VOCs have been removed at Wildwood. In 15 months of operation, 36 kg of VOCs were removed at NEP. Characterization work continues at the Olympia Nominee Trust, Whitney Barrel, Murphy Waste Oil, and Aberjona Auto Parts properties. Risk assessments are being finalized that address heavy metals in the floodplain sediments along the Aberjona River that are mobilized from the Industri-Plex Superfund Site located a few miles upstream.     

On the Treatment of Industrial Wastewaters Carrying Oily Emulsions,Surfactans and Sulphates

The successful purification of waste waters from the leather and textile industries is possible by flocculation with aluminium sulphate and alkaline-earth chlorides. BaCl₂ proved very successful among the applied alkaline-earth chlorides. The removal of oily emulsions and tensides was very effective when the waste waters were treated by a two-stage flocculation process. By an excessive application of BaCl₂ also a reduction of sulphate was obtained. Wastewaters treated in the neutral range showed a purification effect of 98 %, so that the effluents were clear and colourless. The time of sedimentation amounted to 1 h only. Segregated oil was successfully removed with the aid of a very absorptive polyurethane foam.     

Removal of Selenium by Adsorption onto Granular Activated Carbon (GAC) and Powdered Activated Carbon (PAC)

The present work involves the study of Se(IV) adsorption onto granular activated carbon (GAC) and powdered activated carbon (PAC). The adsorbents are coated with ferric chloride solution for the effective removal of selenium. The physico-chemical characterization of the adsorbents is carried out using standard methods, e. g., proximate analysis, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), thermo-gravimetric (TGA) and differential thermal analysis (DTA), etc. The FTIR spectra of the GAC and PAC indicate the presence of various types of functional groups, e. g., free and hydrogen bonded OH groups, silanol groups (Si-OH), alkenes, and CO group stretching from aldehydes and ketones on the surface of adsorbents. Batch experiments are carried out to determine the effect of various factors such as adsorbent dose (w), initial pH, contact time (t), and temperature (T) on the adsorption process. The optimum GAC and PAC dosage is found to be 10 g/L and 8 g/L, respectively, for Se(IV) removal with C₀ = 100 mg/L. The percent removal of Se(IV) increases with increasing adsorbent concentration, while removal per unit weight of adsorbent increases with decreasing adsorbent concentration. Se(IV) adsorption onto both the GAC and PAC adsorbents is high at low pH values, and decreases with increased initial pH. The results obtained are analyzed by various kinetic models. The parameters of pseudo-first order, pseudo-second order kinetics, and Weber-Morris intra particle kinetics are determined. It is seen that the sorption kinetics of Se(IV) onto GAC and PAC can be best represented by the pseudo-second order kinetic model.     

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.     

Use of Magnet Technology for Phosphate Elimination from Municipal Sewage

The present report describes the set-up and first operation results of a novel carousel magnetic separator. This carousel magnetic separator is suitable for continuous separation of magnetized particles from water. Continuous operation is achieved by a segmented rotating separation matrix. This matrix also allows the use of low-cost permanent magnets, by means of which magnetic fields of up to 0.5 T can be generated without energy consumption. The suitability of a first prototype of this carousel magnetic separator was tested for elimination of magnetite-containing iron phosphate and iron hydroxide flocs. These flocs result from conventional precipitation/flocculation of municipal sewage with FeCl₃ and the addition of magnetite particles generated by wet-chemical processes. First results demonstrate that the carousel magnetic separator can reduce phosphate concentrations of up to 14 mg/L PO₄^3–-P in the inlet to below 1 mg/L PO₄^3–-P in the outlet at filtration rates of about 40 m/h. Magnetite dosage in the range of 50 mg/L affects phosphate precipitation positively via a slight reduction of the precipitant volume. However, the total amount of chemicals required for phosphate elimination is increased by the substances needed for magnetite production. Therefore, a further reduction of magnetite dosage must be achieved.