Article

The potential of using UV photolysis in an aquifer thermal energy storage system to remediate groundwater contaminated with chloro ethenes

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Abstract

In several places in The Netherlands, industrial areas are redeveloped into residential areas with sustainable heating systems based on aquifer thermal energy storages (ATES). At these sites, groundwater is contaminated with chlorinated ethenes. In this project various pilot set-ups were tested as a non-invasive technique to remove chlorinated ethenes from contaminated groundwater by integrating a UV reactor into the ATES system. It was demonstrated that per- and trichloro ethenes (PCE and TCE) can be photolyzed by LP UV-lamps up to 10–20% at a relatively high dose of 500 mJ/cm². However, the photolysis of cis-dichloro ethene (DCE) and vinyl chloride (VC) was limited to maximum 5%. In addition, it was found that, during the photolysis trans-DCE may be formed, which usually is not observed in biodegradation pathways of chloroethenes. As the groundwater composition at a certain location may show significant variations in time (concentration differences of a factor 2–3 were no exception during the various experiments) it is important to adjust the system to the range of concentrations that can be expected.

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... The main recommendations to the authorities were to limit the maximum injection temperature to 25°C and to intensify underground management [287]. In this context, there has been also a growing interest in the combination of enhanced groundwater remediation and ATES [309,[325][326][327][328][329][330][331][332][333][334][335]. ...
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Emerging organic contaminants (pharmaceutical compounds, personal care products, pesticides, hormones, surfactants, fire retardants, fuel additives etc.) are increasingly found in water sources and therefore need to be controlled by water treatment technology. UV advanced oxidation technologies are often used as an effective barrier against organic contaminants. The combined operation of direct photolysis and reaction with hydroxyl radicals ensures good results for a wide range of contaminants. In this review, an overview is provided of the photochemical reaction parameters (quantum yield, molar absorption, OH radical reaction rate constant) of more than 100 organic micropollutants. These parameters allow for a prediction of organic contaminant removal by UV advanced oxidation systems. An example of contaminant degradation is elaborated for a simplified UV/H(2)O(2) system.
Article
The photolysis half-life of aqueous chlorine in clear sky, summer noon sunlit (47°N) water of pH 8 is 12 min when measured at the surface. It increases with decreasing pH due to the decreasing ratio of OCl−/HOCl to 60 min at pH 5. The pseudo-first-order rate constant for the photolysis of HOCl becomes 2 × 10−4 s−1 and that of OCl− 1.2 × 10−3 s−1. The variation of the rate of photolysis with depth was calculated for water columns exhibiting different light absorption coefficients by taking into account that, for both HOCl and OCl−, the most effective wavelength for photolysis in sunlight is approx. 330 nm. These results show that in water treatment, chlorine photolysis should be minimized whenever possible by operating at low pH, sun shielding or night-time addition of chlorine or avoiding storage in shallow reservoirs. The rate of chlorine photolysis controls the formation of OH radical which acts as a secondary highly reactive photooxidant (see Part II).On u.v. (255 nm) irradiation both HOCl and OCl− photolyze at comparable rates and slowly enough that chlorine depletion will not occur during the time of irradiation typical in u.v. disinfection.Photolysis can also contribute to the depletion of chlorine in atmospheric waters whenever chlorine is formed by (slow) ozonation of chloride.
Article
The search for environmental transformation products of organic pollutants (like drugs) is a difficult task and usually only few compounds are detected. This might be due to effective degradation but could also be a result of analytical deficits dealing with complex matrices. Especially transformation products of very low concentrations in sludge were difficult to identify so far. Additionally, the use of standard separation techniques might lead to the loss of isomeric compounds, which possess identical spectroscopic and spectrometric properties. To date no complete study investigating the environmental fate of any tricyclic antipsychotic drug has been reported. Therefore, this study investigated the popular neuroleptic drug chlorpromazine and its potential transformation by all main environmental pathways: aerobic and anaerobic biodegradation as well as abiotic photolytic degradation by sunlight. Analysis of test samples by high performance liquid chromatography coupled to multiple stage mass-spectrometry (HPLC-MS(n)) allowed the detection of numerous compounds. Further, the use of a special software allowed distinguishing between transformation products of small intensities and background "noise" caused by sludge or matrix. Three aerobic tests of different bacterial density (the Closed Bottle test, OECD 301D; the Manometric Respiratory test, OECD 301F; the modified Zahn-Wellens test, 302B; one anaerobic test (a modified anaerobic degradation test according to ISO 11734) as well as a photodegradation test were performed in the present study. According to the individual test guidelines, chlorpromazine had to be classified as not biodegradable in all of the biodegradation tests. However, a special chromatographic column and gradient along with mass spectrometric fragmentation experiments of higher order uncovered the presence of a total of 61 abiotic and biotic transformation products which where formed during the course of the tests. The structures of three aerobic and one anaerobic biotransformation products were elucidated by HPLC-UV-Flourescence-MS(n). Photodegradation showed almost complete elimination of chlorpromazine after 4h of irradiation with a xenon arc lamp. 57 photoproducts were found and for 28 of them LC-MS(n) fragmentation experiments (n=4) were performed. The molecular structures of the three main photolysis products were elucidated. The identified transformation products are expected to be found in the aquatic environment, yet nothing is known about their ecotoxicological properties. As some of the performed tests showed toxic effects of chlorpromazine or its transformation products on bacteria, further risk assessment upon this drug and its fate is strongly recommended.
Article
UV/chlorine (UV/HOCl and UV/ClO(2)) Advanced Oxidation Processes (AOPs) were assessed with varying process layout and compared to the state of the art UV/H(2)O(2) AOP. The process comparison focused on the economical and energy saving potential of the UV/chlorine AOP. Therefore the experiments were performed at technical scale (250 L/h continuous flow reactor) and at process energies, oxidant and model contaminant concentrations expected in full scale reference plants. As model compounds the emerging contaminants (ECs): desethylatrazine, sulfamethoxazole, carbamazepine, diclofenac, benzotriazole, tolyltriazole, iopamidole and 17α-ethinylestradiol (EE2) were degraded at initial compound concentrations of 1 μg/L in tap water and matrixes with increased organic load (46 mg/L DOC). UV/chlorine AOP organic by-product forming potential was assessed for trihalomethanes (THMs) and N-Nitrosodimethylamine (NDMA). A process design was evaluated which can considerably reduce process costs, energy consumption and by-product generation from UV/HOCl AOPs.
Article
The energy consumptions of conventional ozonation and the AOPs O(3)/H(2)O(2) and UV/H(2)O(2) for transformation of organic micropollutants, namely atrazine (ATR), sulfamethoxazole (SMX) and N-nitrosodimethylamine (NDMA) were compared. Three lake waters and a wastewater were assessed. With p-chlorobenzoic acid (pCBA) as a hydroxyl radical ((•)OH) probe compound, we experimentally determined the rate constants of organic matter of the selected waters for their reaction with (•)OH (k(OH,DOM)), which varied from 2.0 × 10(4) to 3.5 × 10(4) L mgC(-1) s(-1). Based on these data we calculated (•)OH scavenging rates of the various water matrices, which were in the range 6.1-20 × 10(4) s(-1). The varying scavenging rates influenced the required oxidant dose for the same degree of micropollutant transformation. In ozonation, for 90% pCBA transformation in the water with the lowest scavenging rate (lake Zürich water) the required O(3) dose was roughly 2.3 mg/L, and in the water with the highest scavenging rate (Dübendorf wastewater) it was 13.2 mg/L, corresponding to an energy consumption of 0.035 and 0.2 kWh/m(3), respectively. The use of O(3)/H(2)O(2) increased the rate of micropollutant transformation and reduced bromate formation by 70%, but the H(2)O(2) production increased the energy requirements by 20-25%. UV/H(2)O(2) efficiently oxidized all examined micropollutants but energy requirements were substantially higher (For 90% pCBA conversion in lake Zürich water, 0.17-0.75 kWh/m(3) were required, depending on the optical path length). Energy requirements between ozonation and UV/H(2)O(2) were similar only in the case of NDMA, a compound that reacts slowly with ozone and (•)OH but is transformed efficiently by direct photolysis.
Article
Advanced oxidation treatment using low pressure UV light coupled with hydrogen peroxide (UV/H(2)O(2)) was evaluated for the oxidation of six pharmaceuticals in three wastewater effluents. The removal of these six pharmaceuticals (meprobamate, carbamazepine, dilantin, atenolol, primidone and trimethoprim) varied between no observed removal and >90%. The role of the water quality (i.e., alkalinity, nitrite, and specifically effluent organic matter (EfOM)) on hydroxyl radical (OH) exposure was evaluated and used to explain the differences in pharmaceutical removal between the three wastewaters. Results indicated that the efficacy of UV/H(2)O(2) treatment for the removal of pharmaceuticals from wastewater was a function of not only the concentration of EfOM but also its inherent reactivity towards OH. The removal of pharmaceuticals also correlated with reductions in ultraviolet absorbance at 254nm (UV(254)), which offers utilities a surrogate to assess pharmaceutical removal efficiency during UV/H(2)O(2) treatment.
Article
The photodegradation rates of seven chlorinated hydrocarbons; C2Cl4, C2HCl3, C2H4Cl2, 1,1,1-C2H3Cl3, 1,1,2-C2H3Cl3, CHCl3, CCl4 were investigated under the UV bandwidths of 185 and 254 nm in the presence and absence of dissolved oxygen (DO) in water. These hydrocarbons are possible contaminants of groundwater. This study confirms that the degradation rates of all chlorinated hydrocarbons are elevated in the absence of DO. This was especially apparent for chlorinated methane and ethane. Tetrachloroethylene's rate was the highest among the seven hydrocarbons regardless of the DO levels. It was clear that the concentration of intermediate trichloroethylene produced by photodegradation of tetrachloroethylene in the absence of DO was 1/50th of that in the presence of DO. Photodegradation in the presence of DO resulted in the formation of O3 and hydroxyl radicals. Alternatively, the photodegradation in the absence of DO resulted in the formation of organic radicals and a dissociation of the bond. It is discussed that DO acts as an "inner filter" or "scavenger" that reduces the UV light intensity in the photoreactor. Molecular O2 has absorption bands at 185 and 254 nm, the former being stronger. The processes of degradation depend on the degradation rate relative to the presence and absence of DO.
Article
Our goal was to create a photodegradation model based on the META expert system [G. Klopman, M. Dimayuga, J. Talafous, J. Chem. Inf. Comput. Sci. 34 (1994a) 1320-1325]. This requires the development of a dictionary of photodegradation pathways. Equipped with such a dictionary, we found that META successfully predicts degradation pathways of organic compounds under UV light. Our model was tested on a wide range of industrial compounds for which literature data exists. The results were excellent as the hit/miss ratio was better than 92%. This work complements our previous elaboration of equivalent mammal metabolism, aerobic and anaerobic biodegradation models.
Article
Degradation of chlorobenzene using various photoinduced oxidation processes such as direct ultraviolet light-induced photolysis (UV), UV-H2O2, UV-O3, and UV-H2O2-O3 was investigated under aerobic and anaerobic conditions. Kinetics and mechanisms of the degradation process were studied using high performance liquid chromatorgraphy (HPLC) and gas chromatorgraphy-mass spectrometry (GC-MS). In all cases, loss of chlorobenzene followed first-order kinetics. For UV-induced degradation of chlorobenzene, the observed pseudo first-order rate constant, k(obs), ranged from 1.8 x 10(-4) s(-1) under anaerobic conditions to 6.4 x 10(-4) s(-1) for oxygen-saturated solution. Among the four systems studied, under identical conditions, the degradation rates for UV-H2O2 and UV-H2O2-O3 were very similar and were an order of magnitude higher than the one observed for UV. For the UV-H202 system, the observed pseudo first-order rate constant varied linearly with [H2O2] and followed the rate expression k(obs) = kOH[H2O2], where kOH is the observed second-order rate constant for the reaction of OH radical with cholorbenzene. A plot of k(obs) vs. [H2O2] gave a value of 0.17+/-0.02 M(-1) s(-1) for kOH. Both HPLC and GC-MS studies showed that depending upon the time of photolysis and the advanced oxidation processes (AOP) method employed, various intermediates were formed during the degradation process. For the UV process, these intermediates were identified as phenol, biphenyl, chlorobiphenyl isomers, and benzaldehyde. For the other three systems, chlorophenol, and various isomers of chlorobiphenyl and dichlorobiphenyl, were observed as the intermediates. The initial pH of the solution decreased from 5.8 to 3.5, showing the release of chlorine from cholobenzene. The HPLC results also showed that at longer times, the subsequent degradation of the intermediates also took place. Carbon dioxide and water are suspected to be the likely end products. Mechanistic schemes for the formation of such intermediates are proposed.
Article
The photochemistry of 2-chloropyrimidine (ClPy) was investigated by means of nanosecond laser flash photolysis, HPLC, mass spectrometry, polarography and absorption spectroscopy. Two major products were formed on low-intensity UV irradiation (lambda = 254 nm) of ClPy in anaerobic aqueous solution: 2-hydroxypyrimidine (quantum yield approximately 0.01) and a compound identified as 2-chloro-4,2'-bipyrimidine (quantum yield approximately 0.005). Only the former of these products was obtained under aerobic conditions. Investigation by nanosecond flash photolysis revealed the occurrence of efficient intersystem crossing to the ClPy triplet state; the deactivation processes from this state were determined. Photosensitised generation of the ClPy triplet state showed that the triplet is involved in the formation of the bipyrimidine. A reaction scheme is proposed comprising two reaction channels: heterolytic rupture of the C-Cl bond in the excited singlet state of ClPy leading to formation of 2-hydroxypyrimidine, and homolytic C-Cl rupture in the triplet state with creation of pyrimidinyl radicals, which react with excess ClPy to give 2-chloro-4,2'-bipyrimidine.
Article
The kinetics of Ultraviolet C (UV-C)-induced direct phototransformation of four representative pharmaceuticals, i.e., 17alpha-ethinylestradiol (EE2), diclofenac, sulfamethoxazole, and iopromide, was investigated in dilute solutions of pure water buffered at various pH values using a low-pressure and a medium-pressure mercury arc lamp. Except for iopromide, pH-dependent rate constants were observed, which could be related to acid-base equilibria. Quantum yields for direct phototransformation were found to be largely wavelength-independent, except for EE2. This compound, which also had a rather inefficient direct phototransformation, mainly underwent indirect phototransformation in natural water samples, while the UV-induced depletion of the other pharmaceuticals appeared to be unaffected by the presence of natural water components. At the UV-C (254 nm) drinking-water disinfection fluence (dose) of 400 Jm(-2), the degree of depletion of the select pharmaceuticals at pH=7.0 in pure water was 0.4% for EE2, 27% for diclofenac, 15% for sulfamethoxazole, and 15% for iopromide, indicating that phototransformation should be seriously taken into account when evaluating the possibility of formation of UV transformation products from pharmaceuticals present as micropollutants.
Article
Chlorinated solvents are common groundwater contaminants that threaten surface water quality and benthic health when present in groundwater seeps. Aquatic sediments can act as natural biobarriers to detoxify chlorinated solvent plumes via reductive dechlorination. In situ sediment capping, a remedial technique in which clean material is placed at the sediment-water interface, may alter sedimentary natural attenuation processes. This research explores the potential of Anacostia River sediment to naturally attenuate chlorinated solvents under simulated capping conditions. Results of microcosm studies demonstrated that intrinsic dechlorination of dissolved-phase PCE to ethene was possible, with electron donor availability controlling microbial activity. A diverse microbial community was present in the sediment, including multiple Dehalococcoides strains indicated by the amplification of the reductive dehalogenases tceA, vcrA, and bvcA. An upflow column simulating a capped sediment bed subject to PCE-contaminated groundwater seepage lost dechlorination activity with time and only achieved complete dechlorination when microorganisms present in the sediment were provided electron donor. Increases in effluent chloroethene concentrations during the period of biostimulation were attributed to biologically enhanced desorption and the formation of less sorptive dechlorination products. These findings suggest that in situ caps should be designed to account for reductions in natural biobarrier reactivity and for the potential breakthrough of groundwater contaminants.