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Ozonation is known to generate biodegradable organic matter, which is typically reduced by biological filtration to avoid bacterial regrowth in distribution systems. Post-chlorination generates halogenated disinfection byproducts (DBPs) but little is known about the biodegradability of their precursors. This study determined the effect of ozonation and biofiltration conditions, specifically ozone exposure and empty bed contact time (EBCT), on the control of DBP formation potentials in drinking water. Ozone exposure was varied through addition of H 2 O 2 during ozonation at 1 mgO 3 /mgDOC followed by biological filtration using either activated carbon (BAC) or anthracite. Ozonation led to a 10% decrease in dissolved organic carbon (DOC), without further improvement from H 2 O 2 addition. Raising H 2 O 2 concentrations from 0 to 2 mmol/mmolO 3 resulted in increased DBP formation potentials during post-chlorination of the ozonated water (target Cl 2 residual after 24 h = 1-2 mg/L) as follows: 4 trihalomethanes (THM4, 37%), 8 haloacetic acids (HAA8, 44%), chloral hydrate (CH, 107%), 2 haloketones (HK2, 97%), 4 haloacetonitriles (HAN4, 33%), trichloroacetamide (TCAM, 43%), and adsorbable organic halogen (AOX, 27%), but a decrease in the concentrations of 2 trihalonitromethanes (THNM2, 43%). Coupling ozonation with biofiltration prior to chlorination effectively lowered the formation potentials of all DBPs including CH, HK2, and THNM2, all of which increased after ozonation. The dynamics of DBP formation potentials during BAC filtration at different EBCTs followed first-order reaction kinetics. Minimum steady-state concentrations were attained at an EBCT of about 10-20 min, depending on the DBP species. The rate of reduction in DBP formation potentials varied among individual species before reaching their minimum concentrations. CH, HK2, and THNM2 had the highest rate constants of between 0.5 and 0.6 min -1 followed by HAN4 (0.4 min -1 ), THM4 (0.3 min -1 ), HAA8 (0.2 min -1 ), and AOX (0.1 min -1 ). At an EBCT of 15 min, the reduction in formation potential for most DBPs was less than 50% but was higher than 70% for CH, HK2, and THNM2. The formation of bromine-containing DBPs increased with increasing EBCT, most likely due to an increase in Br - /DOC ratio. Overall, this study demonstrated that the combination of ozonation and biofiltration is an effective approach to mitigate DBP formation during drinking water treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

UV-C radiation is the U.S. EPA recommended technology to remove N-nitrosodimethylamine (NDMA) during drinking and recycled water production. Frequently, H(2)O(2) is added to the treatment to remove other recalcitrant compounds and to prevent NDMA reformation. However, the transformation of NDMA precursors during the UV and UV/H(2)O(2) process and the consequences for NDMA formation potential are currently not well understood, in particular in the presence of monochloramine. In this study, doxylamine has been chosen as a model compound to elucidate its degradation byproducts in the UV and UV/H(2)O(2) process and correlate those with changes to the NDMA formation potential. This study shows that during UV treatment in the presence and absence of monochloramine, NDMA formation potential can be halved. However, an increase of more than 30% was observed when hydrogen peroxide was added. Ultrafast liquid chromatography coupled to quadrupole-linear ion trap mass spectrometer was used for screening and structural elucidation of degradation byproducts identifying 21 chemical structures from the original parent compound. This work shows that further oxidation of NDMA precursors does not necessarily lead to a decrease in NDMA formation potential. Degradation byproducts with increased electron density in the vicinity of the dimethylamino moiety, for example induced by hydroxylation, may have a higher yield of nucleophilic substitution and subsequent NDMA formation compared to the parent compound during chloramination. This work demonstrates the need to consider the formation of oxidation byproducts and associated implications for the control and management of NDMA formation in downstream processes and distribution when integrating oxidative treatments into a treatment train generating either drinking water or recycled water for potable reuse.

This study evaluates the effect of UV-C and UV-C/H(2)O(2) in the presence of chloramines on the N-nitrosodimethylamine formation potential (NDMA FP) of tramadol as a model precursor. The experiments were performed at high initial concentrations of TMDL (i.e., 20 mg/L) in order to elucidate the structures of TMDL byproducts. Twenty-four byproducts were identified in UV-C, UV-C/monochloramine, and UV/H(2)O(2)/monochloramine oxidation of tramadol using MS(3) capabilities of a hybrid quadrupole-linear ion trap mass spectrometer, combined with online hydrogen/deuterium (H/D) exchange experiments. Oxidative cleavage of methoxy and methoxybenzene moiety, O-demethylation, hydroxylation, and cyclohexane ring-opening were identified as major reaction mechanisms of tramadol in UV oxidation. Addition of monochloramine decreased the degradation rates of tramadol and its byproducts and yielded several monochlorinated derivatives. The oxidation rates were significantly enhanced in the presence of H(2)O(2), and byproducts of oxidative benzene ring-opening were detected. The majority of the identified byproducts are likely to have a higher NDMA FP than the parent compound due to a reduced steric hindrance and/or insertion of electron-donating hydroxyl groups in the N,N-dimethylamine side chain. This was confirmed by the results of NDMA FP tests, which showed that the formation of NDMA was enhanced up to four times depending on the process conditions in UV alone and in UV and UV/H(2)O(2) in the presence of monochloramine. Prolonged oxidation by hydroxyl radicals in UV/H(2)O(2)/monochloramine process mineralized some of the byproducts and slightly reduced the NDMA FP at the end of the treatment. The obtained degradation pathway of tramadol allowed the correlation of changes in NDMA FP during oxidation with its major oxidative transformation reactions. This manuscript demonstrates the significance of oxidation byproducts as NDMA precursors and emphasizes the need for their consideration when evaluating the evolution of NDMA FP during oxidative treatment.

This work assessed the solar photo-Fenton degradation of nalidixic acid (NXA), a quinolone antibacterial agent, in several different aqueous solutions. It has been proven that the composition of the water clearly affects the efficiency of the photo-Fenton process. The presence of chlorine ions induces the concurrence of different mechanisms involving Cl() and Cl(2)(-) radicals, which slow down the process. Up to 35 transformation products (TPs) were identified and their structures characterized by accurate LC-TOF-MS mass measurements during treatment of the different model waters. Photocatalytic degradation was thus observed to proceed mainly through the attack of the hydroxyl radicals on the double bond C((2))C((3)) which induce further ring opening. All the TPs identified persisted after total degradation of NXA. NXA in real pharmaceutical effluent was treated by photo-Fenton as a first stage before biological treatment. As NXA has been demonstrated to be recalcitrant to biological treatment, photo-Fenton treatment of the effluent was continued until its total degradation. Although NXA was efficiently degraded, LC-MS analyses demonstrated that some of the TPs identified after the photo-Fenton treatment were also recalcitrant to biological treatment, persisting after the combined treatment. These results show that analytical assessment of photocatalytic water treatments is essential to assure they are functioning as intended., (© 2010 Elsevier Ltd. All rights reserved.)

The purpose of this work was to determine the degradation products and pathway of chlorfenvinphos (CFVP) in water treated by photo-Fenton driven by solar irradiation, as well as to develop an analytical procedure for the degradation experiments. Degradation products and pathway were determined in a laboratory experimental setup. Routine water sample analysis was done by standard laboratory wet chemistry procedures and the use of laboratory equipment such as HPLC-UV and ionic chromatography (IC). Solid-phase extraction (SPE) was used to extract analytes from an aqueous matrix, and GC-MS was used to identify intermediate degradation products. The use of an HPLC-TOF-MS provided more results on degradation products and more insight was gained into how degradation takes place. In all experiments, strong mineralisation and degradation of CFVP was observed. CFVP and its degradation products, like 2,4-dichlorophenol, 2,4-dichlorobenzoic acid and triethylphosphate were decomposed into organic substances like acetate, formate, maleate, and inorganic ions like chloride and phosphate, within the detection limits (12.5 microg/L for CFVP in the GC-MS and 40 microg/L in HPLC-UV) of the equipment used. In fact, Cl(-) emerges in nearly stoichiometric concentrations and PO(4)(3)(-) is precipitated as FePO(4). The remarkably complete absence of chlorinated aliphatic substances and chlorinated acids leads to the conclusion that chlorine is removed very quickly, and that residual DOC does not correspond to any chlorinated compound.

A coupled solar photo-Fenton (chemical) and biological treatment has been used to remove biorecalcitrant diuron (42 mg l(-1)) and linuron (75 mg l(-1)) herbicides from water at pilot plant scale. The chemical process has been carried out in a 82 l solar pilot plant made up by four compound parabolic collector units, and it was followed by a biological treatment performed in a 40 l sequencing batch reactor. Two Fe(II) doses (2 and 5 mg l(-1)) and sequential additions of H2O2 (20 mg l(-1)) have been used to chemically degrade the initially polluted effluent. Next, biodegradability at different oxidation states has been assessed by means of BOD/COD ratio. A reagent dose of Fe=5 mg l(-1) and H2O2=100 mg l(-1) has been required to obtain a biodegradable effluent after 100 min of irradiation time. Finally, the organic content of the photo-treated solution has been completely assimilated by a biomass consortium in the sequencing batch reactor using a total suspended solids concentration of 0.2 g l(-1) and a hydraulic retention time of 24h. Comparison between the data obtained at pilot plant scale (specially the one corresponding to the chemical step) and previously published data from a similar system performing at laboratory scale, has been carried out.

In this paper, we present the photo-Fenton treatment in a solar pilot-plant scale of several EU priority hazardous substances (Alachlor, Atrazine, Chlorfenvinphos, Diuron and Isoproturon) dissolved in water. The results have been evaluated not only from the point of view of contaminant disappearance and mineralisation, but also of toxicity reduction and enhancement of biodegradability. Degradation was monitored by total organic carbon, pesticide concentration by HPLC-UV, inorganics released by ion chromatography, and biodegradability by the Zahn-Wellens (Z-W) test. The total volume of the solar photoreactor, composed of compound parabolic collectors with a total area of 4.16m2, was between 70 and 82 L. The treatment was shown to be effective, mineralising all of the pesticides tested, both alone and in mixtures. In order to find out the conditions for biocompatibility using the photo-Fenton reaction as a pre-treatment step, wastewater inoculated with unacclimated municipal sludge containing pesticides after certain degradation time was evaluated by the Z-W test. Biodegradability was enhanced (70% considered biodegradable) by the photo-Fenton treatment after 12-25min. It may be concluded that the photo-Fenton treatment consistently enhances biodegradability of wastewater containing pesticides.

Phenolic compounds are known to be present in high concentrations in various types of agro-industrial wastes. As they are highly biorecalcitrant, the possibility of treatment by advanced oxidation processes should be investigated. In this work, six model phenolic compounds (vanillin, protocatechuic acid, syringic acid, p-coumaric acid, gallic acid and L-tyrosine) were chosen for a demonstration of degradation by photo-Fenton reaction, under artificial light in laboratory experiments in Vienna and under sunlight in pilot-plant experiments at the Plataforma Solar de Almería in Spain. All compounds were completely mineralised. No non-degradable intermediates were produced, either in experiments with single substances or in a more complex matrix of a mixture of phenolic compounds. The expected selectivity of the photo-Fenton reaction for aromatic compounds was proven by comparison of the decrease in total organic carbon with the removal of total phenolic content.

In this paper, we present pilot-scale solar Photo-Fenton and TiO2 treatment of a model compound (α-methylphenylglycine) dissolved in 500 mg/l concentration in water. Not only contaminant disappearance and mineralisation were evaluated, but also enhancement of biodegradability. The solar photoreactors, composed of 4.16 m2 of compound parabolic collectors, had a total volume of 82 l (44.6 l illuminated). Treatment was successful with both Advanced Oxidation Processes (AOPs) tested, but photo-Fenton was shown to be by far more efficient from the kinetic and practical point of view. To find out the conditions for biocompatibility using the AOPs as a pre-treatment, waste water after certain degradation time, unacclimated municipal sludge and mineral nutrients were placed together and evaluated by the Zahn–Wellens (Z-W) test. Biodegradability was enhanced (70% biodegradable) by both AOPs, but photo-Fenton was demonstrated to be more efficient, requiring a treatment time one order of magnitude shorter than TiO2. Hydrogen peroxide management for reduced consumption and elimination prior to discharging water to the biotreatment step is also discussed in detail. [ABSTRACT FROM AUTHOR]

UV–C radiation is the U.S. EPA recommended technology to remove N-nitrosodimethylamine (NDMA) during drinking and recycled water production. Frequently, H2O2 is added to the treatment to remove other recalcitrant compounds and to prevent NDMA reformation. However, the transformation of NDMA precursors during the UV and UV/H2O2 process and the consequences for NDMA formation potential are currently not well understood, in particular in the presence of monochloramine. In this study, doxylamine has been chosen as a model compound to elucidate its degradation byproducts in the UV and UV/H2O2 process and correlate those with changes to the NDMA formation potential. This study shows that during UV treatment in the presence and absence of monochloramine, NDMA formation potential can be halved. However, an increase of more than 30% was observed when hydrogen peroxide was added. Ultrafast liquid chromatography coupled to quadrupole-linear ion trap mass spectrometer was used for screening and structural elucidation of degradation byproducts identifying 21 chemical structures from the original parent compound. This work shows that further oxidation of NDMA precursors does not necessarily lead to a decrease in NDMA formation potential. Degradation byproducts with increased electron density in the vicinity of the dimethylamino moiety, for example induced by hydroxylation, may have a higher yield of nucleophilic substitution and subsequent NDMA formation compared to the parent compound during chloramination. This work demonstrates the need to consider the formation of oxidation byproducts and associated implications for the control and management of NDMA formation in downstream processes and distribution when integrating oxidative treatments into a treatment train generating either drinking water or recycled water for potable reuse. [ABSTRACT FROM AUTHOR]

This study evaluates the effect of UV-C and UV-C/H2O2 in the presence of chloramines on the N-nitrosodimethylamine formation potential (NDMA FP) of tramadol as a model precursor. The experiments were performed at high initial concentrations of TMDL (i.e., 20 mg/L) in order to elucidate the structures of TMDL byproducts. Twenty-four byproducts were identified in UV-C, UV-C/monochloramine, and UV/H2O2/monochloramine oxidation of tramadol using MS3 capabilities of a hybrid quadrupole-linear ion trap mass spectrometer, combined with online hydrogen/deuterium (H/D) exchange experiments. Oxidative cleavage of methoxy and methoxybenzene moiety, O-demethylation, hydroxylation, and cyclohexane ring-opening were identified as major reaction mechanisms of tramadol in UV oxidation. Addition of monochloramine decreased the degradation rates of tramadol and its byproducts and yielded several monochlorinated derivatives. The oxidation rates were significantly enhanced in the presence of H2O2, and byproducts of oxidative benzene ring-opening were detected. The majority of the identified byproducts are likely to have a higher NDMA FP than the parent compound due to a reduced steric hindrance and/or insertion of electron-donating hydroxyl groups in the N,N-dimethylamine side chain. This was confirmed by the results of NDMA FP tests, which showed that the formation of NDMA was enhanced up to four times depending on the process conditions in UV alone and in UV and UV/H2O2 in the presence of monochloramine. Prolonged oxidation by hydroxyl radicals in UV/H2O2/monochloramine process mineralized some of the byproducts and slightly reduced the NDMA FP at the end of the treatment. The obtained degradation pathway of tramadol allowed the correlation of changes in NDMA FP during oxidation with its major oxidative transformation reactions. This manuscript demonstrates the significance of oxidation byproducts as NDMA precursors and emphasizes the need for their consideration when evaluating the evolution of NDMA FP during oxidative treatment. [ABSTRACT FROM AUTHOR]

Abstract: A multivariate analysis using experimental design techniques was performed to determine the effect of iron, hydrogen peroxide and titanium dioxide in the solar photodegradation of dichloroacetic acid in a combined TiO2/photo-Fenton process. The study was carried out at pilot-plant scale, using TiO2 supported on silica as the heterogeneous photocatalyst to facilitate separation of the solids after the reaction, and iron concentrations of less than 3mgL−1 to avoid removal of iron from the effluent. The results show that iron is the most important factor influencing the reaction rate, which suggests that in strongly acidic solutions, the Fenton mechanism controls the process even at such low iron concentrations. Under these conditions, the expected synergism between TiO2 and iron degradation pathways seems to be negligible compared to the antagonistic effect between hydrogen peroxide and TiO2, which reduces the activity of the combined system. However, in the absence of hydrogen peroxide, the activity achieved by the combined Fe/TiO2 system is similar to that of the photo-Fenton process, with the advantage that H2O2 is replaced by a reusable TiO2-based catalytic material. Consequently, the analysis of pilot-plant operation economics took not only the degradation rate, but also the cost of chemicals into account. [Copyright &y& Elsevier]

This paper reports on the combined solar photo-Fenton/biological treatment of an industrial effluent (initial total organic carbon, TOC, around 500mgL−1) containing a non-biodegradable organic substance (α-methylphenylglycine at 500mgL−1), focusing on pilot plant tests performed for design of an industrial plant, the design itself and the plant layout. Pilot plant tests have demonstrated that biodegradability enhancement is closely related to disappearance of the parent compound, for which a certain illumination time and hydrogen peroxide consumption are required, working at pH 2.8 and adding Fe2+ =20mgL−1. Based on pilot plant results, an industrial plant with 100m2 of CPC collectors for a 250L/h treatment capacity has been designed. The solar system discharges the wastewater (WW) pre-treated by photo-Fenton into a biotreatment based on an immobilized biomass reactor. First, results of the industrial plant are also presented, demonstrating that it is able to treat up to 500Lh−1 at an average solar ultraviolet radiation of 22.9Wm−2, under the same conditions (pH, hydrogen peroxide consumption) tested in the pilot plant. [Copyright &y& Elsevier]