Oxone/Co oxidation as an advanced oxidation process: Comparison with traditional Fenton oxidation for treatment of landfill leachate

In this paper, the application of Fenton and Oxone/Co²⁺ oxidation processes for landfill leachate treatment was investigated. The removal of the chemical oxygen demand (COD), suspended substances (SS) and the color of the landfill leachate by Fenton oxidation to that by Oxone/Co²⁺ oxidation were compared under optimal operational conditions. For Fenton oxidation process, the optimal conditions were determined as: [H₂O₂] = 80 mmol L⁻¹, [H₂O₂]/[Fe²⁺] = 2.0, initial pH = 2.5, reaction temperature = 37.5 ± 1 °C, reaction time = 160 min, number of stepwise addition = 3. Under the given conditions, 56.9% of the COD removal efficiency was achieved, but the SS and the color of the treated landfill leachate increased due to the generation of a large quantity of ferric hydroxide sludge. In reference to Oxone/Co²⁺ oxidation process, the optimal conditions were determined as: [Oxone] = 4.5 mmol L⁻¹, [Oxone]/[Co²⁺] = 10⁴, pH = 6.5, reaction temperature = 30 ± 1 °C, reaction time = 300 min, number of stepwise addition = 7, the COD, SS and the color removal efficiencies were 57.5, 53.3 and 83.3%, respectively. From this work, it can be concluded that Oxone/Co²⁺ oxidation process demonstrated higher degradation efficiencies of the COD, SS and color for landfill leachate treatment than that by Fenton oxidation process. It also suggested that Oxone/Co²⁺ oxidation process could be considered as one of the most promising technologies for practical applicability to treat landfill leachate in large scale. For further improving the efficiency of Oxone/Co²⁺ oxidation process, we proposed that combination of it with other technologies in future such as ultraviolet, ultrasound and biological methods.     

Mechanism and kinetics of sulfamethoxazole photocatalytic ozonation in water

The photocatalytic ozonation of sulfamethoxazole (SMT) has been studied in water under different experimental conditions. The effect of gas flow rate, initial concentration of ozone, SMT and TiO₂ has been investigated to establish the importance of mass transfer and chemical reaction. Under the conditions investigated the process is chemically controlled. Both, SMT and TOC kinetics have been considered. Fast and slow kinetic regime of ozone reactions have been observed for SMT and TOC oxidation, respectively. Application of different inhibitors allows for the establishment of reaction mechanism involving direct ozonation, direct photolysis, hydroxyl radical reactions and photocatalytic reactions. Rate constants of the direct reaction between ozone and protonated, non-protonated and anionic SMT species have been determined to be 1.71 × 10⁵, 3.24 × 10⁵ and 4.18 × 10⁵ M⁻¹ s⁻¹, respectively. SMT quantum yield at 313 nm was found to be 0.012 moles per Einstein at pH 5 and 0.003 moles per Einstein at pHs 7 and 9. Main contributions to SMT removal were direct ozone reaction, positive hole oxidation and hydroxyl radical reactions. For TOC removal, main contributions were due to positive hole oxidation and hydroxyl radical reactions.     

Effects of ozone pre-treatment on diclofenac: Intermediates, biodegradability and toxicity assessment

Diclofenac (DCF), a common analgesic, anti-arthritic and anti-rheumatic drug, is one of the most frequently detected compounds in water. This study deals with the degradation of diclofenac in aqueous solution by ozonation. Biodegradability (BOD₅/COD ratio and Zahn-Wellens test), acute ecotoxicity and inhibition of activated sludge activity were determined in ozonated and non-ozonated samples. Liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOF-MS) was used to identify the intermediates formed in 1 h of ozonation. Eighteen intermediates were identified by these techniques and a tentative degradation pathway for DCF ozonation is proposed.Experimental results show that ozone is efficient at removing DCF: > 99% removal (starting from an initial concentration of 0.68 mmol L^− 1) was achieved after 30 min of ozonation (corresponding to an absorbed ozone dose of 0.22 g L^− 1, which is 4.58 mmol L^− 1). However, only 24% of the substrate was mineralized after 1 h of ozonation. The biodegradability, respiration inhibition in activated sludge and acute toxicity tests demonstrate that ozonation promotes a more biocompatible effluent of waters containing DCF.     

The influence of disinfection on aquatic biodegradable organic carbon formation

The aim of this paper was to assess the extent of biodegradable dissolved organic carbon formation upon disinfection of water with chlorine dioxide. Wide diversity of natural waters has been subjected to reactions with various amounts of ClO₂. For comparison examined waters have also been treated with ozone and chlorine. The application of chlorine dioxide and ozone significantly changed the molecular weight distribution of aquatic organic matter. As a result significant amounts of biodegradable carboxylic acids and aldehydes were generated. The formic, acetic, oxalic and ketomalonic acids as well as formaldehyde, acetaldehyde, glyoxal, methylglyoxal were identified. The productivity of aldehydes calculated for all examined waters and disinfectants amounted 12.7-47.7 μg mg⁻¹ DOC in the case of ozonation, 1.3-8.1 μg mg⁻¹ DOC after chlorination and 1.7-9.4 μg mg⁻¹ DOC for ClO₂ treatment. The highest total concentration of carboxylic acids was determined after the ozonation processes. In this case the organic acids' formation potential was in the range 10.8-62.8 μg mg⁻¹ DOC. Relatively high formation potential (5.3-17.9 μg mg⁻¹ DOC) was determined after the oxidation with ClO₂ as well. In the case of chlorination, the productivity of organic acids was low and did not exceed 3.4 μg mg⁻¹ DOC. The relatively high correlation between BDOC formation and carboxylic acids' formation potential was observed. Thus, carboxylic acids' formation potential may be used as a measure of water potential to form BDOC.     

Conventional and (eco) toxicological assessment of batch partial ozone oxidation and subsequent biological treatment of a tank truck cleaning generated concentrate

This paper compares the treatment efficiencies of direct (pH 7.5) and advanced (pH 11.5) partial ozonation followed by biodegradation for the treatment of tank cleaning wastewater concentrate. Both S_COD and toxicity removal efficiencies are examined and direct ozonation is found to perform better in combined toxicity and S_COD removal. Optimal process performance, i.e. the minimal ozone dosage resulting in a maximal removal of S_COD and toxicity in the final effluent, is reached upon reaction of 500 mg O₃/l for both ozonation processes. This ozone dosage results in 60% S_COD reduction for direct ozonation and 64% S_COD reduction for advanced ozonation. A 79% toxicity reduction was achieved using direct ozonation compared to 53% toxicity reduction for advanced ozonation as measured with the standard Pseudokirchneriella subcapitata algal 72 h growth inhibition test. Short-term methods for biodegradability (respirometry) and toxicity (30 min Vibrio fisheri luminescence inhibition) estimation are evaluated in view of process control. The maximal specific oxygen uptake rate of an activated sludge culture (respirometry) is found to relate to the 5-day biochemical oxygen demand (S_BOD,5) but less to the actual S_COD removal during biodegradation. The 30 min Vibrio fisheri luminescence inhibition test is found to be a good short-term estimator for relative changes in toxicity when compared to the standard P. subcapitata algal 72 h growth inhibition test. The 500 mg O₃/l optimal ozone dosage, as determined from P. subcapitata algal 72 h growth inhibition and S_COD removal, could be retrieved using short-term methods.     

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD₅/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L⁻¹, 0.48 for BOD₂₁/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS⁻¹ h⁻¹.     

PAEs and BPA removal in landfill leachate with Fenton process and its relationship with leachate DOM composition

An increasing attention has been paid to the trace endocrine disrupting compounds (EDCs) in landfill leachate. In this paper, the removal of EDCs including phthalic acid esters (PAEs) and bisphenol A (BPA) from the fresh and mature landfill leachate by Fenton treatment was studied. More than 40% of PAEs and about 62% of BPA were removed from the raw mature leachate while only 20% of PAEs and 37% of BPA in the raw fresh leachate were reduced, respectively. After the fresh and mature leachates were spiked with PAEs to 1.5 mg L^− 1 and BPA to 0.08 mg L^− 1, the removal efficiencies of BPA and PAEs increased to more than 88%. The results indicated that the removing efficiencies of the EDCs in the leachate had a relationship with their concentrations, and that the trace levels of EDCs in leachate challenged the treatment capacity of the Fenton process. Most of the EDCs in the enriched leachate were removed by oxidation, which had no clear correlation with the hydrophobicity of the EDCs. The flocculation played an important role in the removal of di-(2-ethylhexyl) phthalate that could not be completely oxidized in the Fenton process, in that the EDCs with high n-octanol/water partition coefficient inclined to precipitate after the Fenton process. The dissolved organic matter (DOM) in the fresh leachate inhibited the EDCs removal more than the DOM in the mature leachate did. Both the composition of the leachate DOM and the characteristics of the EDCs determined the removing efficiencies of the EDCs in the Fenton process.     

Global sensitivity analysis for model-based prediction of oxidative micropollutant transformation during drinking water treatment

This study quantifies the uncertainty involved in predicting micropollutant oxidation during drinking water ozonation in a pilot plant reactor. The analysis is conducted for geosmin, methyl tert-butyl ether (MTBE), isopropylmethoxypyrazine (IPMP), bezafibrate, β-cyclocitral and ciprofloxazin. These compounds are representative for a wide range of substances with second order rate constants between 0.1 and 1.9 × 10⁴ M⁻¹ s⁻¹ for the reaction with ozone and between 2 × 10⁹ and 8 × 10⁹ M⁻¹ s⁻¹ for the reaction with OH-radicals. Uncertainty ranges are derived for second order rate constants, hydraulic parameters, flow- and ozone concentration data, and water characteristic parameters. The uncertain model factors are propagated via Monte Carlo simulation and the resulting probability distributions of the relative residual micropollutant concentrations are assessed. The importance of factors in determining model output variance is quantified using Extended Fourier Amplitude Sensitivity Testing (Extended-FAST). For substances that react slowly with ozone (MTBE, IPMP, geosmin) the water characteristic R_ct-value (ratio of ozone- to OH-radical concentration) is the most influential factor explaining 80% of the output variance. In the case of bezafibrate the R_ct-value and the second order rate constant for the reaction with ozone each contribute about 30% to the output variance. For β-cyclocitral and ciprofloxazin (fast reacting with ozone) the second order rate constant for the reaction with ozone and the hydraulic model structure become the dominating sources of uncertainty.     

Biodegradability enhancement of a pesticide-containing bio-treated wastewater using a solar photo-Fenton treatment step followed by a biological oxidation process

This work proposes an efficient combined treatment for the decontamination of a pesticide-containing wastewater resulting from phytopharmaceutical plastic containers washing, presenting a moderate organic load (COD = 1662-1960 mg O₂ L⁻¹; DOC = 513-696 mg C L⁻¹), with a high biodegradable organic carbon fraction (81%; BOD₅ = 1350-1600 mg O₂ L⁻¹) and a remaining recalcitrant organic carbon mainly due to pesticides. Nineteen pesticides were quantified by LC-MS/MS at concentrations between 0.02 and 45 mg L⁻¹ (14-19% of DOC). The decontamination strategy involved a sequential three-step treatment: (a) biological oxidation process, leading to almost complete removal of the biodegradable organic carbon fraction; (b) solar photo-Fenton process using CPCs, enhancing the bio-treated wastewater biodegradability, mainly due to pesticides degradation into low-molecular-weight carboxylate anions; (c) and a final polishing step to remove the residual biodegradable organic carbon, using a biological oxidation process. Treatment performance was evaluated in terms of mineralization degree (DOC), pesticides content (LC-MS/MS), inorganic ions and low-molecular-weight carboxylate anions (IC) concentrations. The estimated phototreatment energy necessary to reach a biodegradable wastewater, considering pesticides and low-molecular-weight carboxylate anions concentrations, Zahn-Wellens test and BOD₅/COD ratio, was only 2.3 kJ_UV L⁻¹ (45 min of photo-Fenton at a constant solar UV power of 30 W m⁻²), consuming 16 mM of H₂O₂, which pointed to 52% mineralization and an abatement higher than 86% for 18 pesticides. The biological oxidation/solar photo-Fenton/biological oxidation treatment system achieved pesticide removals below the respective detection limits and 79% mineralization, leading to a COD value lower than 150 mg O₂ L⁻¹, which is in agreement with Portuguese discharge limits regarding water bodies.     

Kinetic assessment and modeling of an ozonation step for full-scale municipal wastewater treatment: Micropollutant oxidation, by-product formation and disinfection

The kinetics of oxidation and disinfection processes during ozonation in a full-scale reactor treating secondary wastewater effluent were investigated for seven ozone doses ranging from 0.21 to 1.24 g O₃ g⁻¹ dissolved organic carbon (DOC). Substances reacting fast with ozone, such as diclofenac or carbamazepine (kP,O₃ > 10⁴ M⁻¹ s⁻¹), were eliminated within the gas bubble column, except for the lowest ozone dose of 0.21 g O₃ g⁻¹ DOC. For this low dose, this could be attributed to short-circuiting within the reactor. Substances with lower ozone reactivity (kP,O₃ < 10⁴ M⁻¹ s⁻¹) were only fully eliminated for higher ozone doses.The predictions of micropollutant oxidation based on coupling reactor hydraulics with ozone chemistry and reaction kinetics were up to a factor of 2.5 higher than full-scale measurements. Monte Carlo simulations showed that the observed differences were higher than model uncertainties. The overestimation of micropollutant oxidation was attributed to a protection of micropollutants from ozone attack by the interaction with aquatic colloids. Laboratory-scale batch experiments using wastewater from the same full-scale treatment plant could predict the oxidation of slowly-reacting micropollutants on the full-scale level within a factor of 1.5. The Rct value, the experimentally determined ratio of the concentrations of hydroxyl radicals and ozone, was identified as a major contribution to this difference.An increase in the formation of bromate, a potential human carcinogen, was observed with increasing ozone doses. The final concentration for the highest ozone dose of 1.24 g O₃ g⁻¹ DOC was 7.5 μg L⁻¹, which is below the drinking water standard of 10 μg L⁻¹. N-Nitrosodimethylamine (NDMA) formation of up to 15 ng L⁻¹ was observed in the first compartment of the reactor, followed by a slight elimination during sand filtration. Assimilable organic carbon (AOC) increased up to 740 μg AOC L⁻¹, with no clear trend when correlated to the ozone dose, and decreased by up to 50% during post-sand filtration. The disinfection capacity of the ozone reactor was assessed to be 1-4.5 log units in terms of total cell counts (TCC) and 0.5 to 2.5 log units for Escherichia coli (E. coli). Regrowth of up to 2.5 log units during sand filtration was observed for TCC while no regrowth occurred for E. coli. E. coli inactivation could not be accurately predicted by the model approach, most likely due to shielding of E. coli by flocs.     

Treating landfill leachate using passive aeration trickling filters; effects of leachate characteristics and temperature on rates and process dynamics

Biological ammoniacal-nitrogen (NH₄⁺-N) and organic carbon (TOC) treatment was investigated in replicated mesoscale attached microbial film trickling filters, treating strong and weak strength landfill leachates in batch mode at temperatures of 3, 10, 15 and 30 °C. Comparing leachates, rates of NH₄⁺-N reduction (0.126-0.159 g m^− 2 d^− 1) were predominantly unaffected by leachate characteristics; there were significant differences in TOC rates (0.072-0.194 g m^− 2 d^− 1) but no trend relating to leachate strength. Rates of total oxidised nitrogen (TON) accumulation (0.012-0.144 g m^− 2 d^− 1) were slower for strong leachates. Comparing temperatures, treatment rates varied between 0.029-0.319 g NH₄⁺-N m^− 2 d^− 1 and 0.033-0.251 g C m^− 2 d^− 1 generally increasing with rising temperatures; rates at 3 °C were 9 and 13% of those at 30 °C for NH₄⁺-N and TOC respectively. For the weak leachates (NH₄⁺-N < 140 mg l^− 1) complete oxidation of NH₄⁺-N was achieved. For the strong leachates (NH₄⁺-N 883-1150 mg l^− 1) a biphasic treatment response resulted in NH₄⁺-N removal efficiencies of between 68 and 88% and for one leachate no direct transformation of NH₄⁺-N to TON in bulk leachate. The temporal decoupling of NH₄⁺-N oxidation and TON accumulation in this leachate could not be fully explained by denitrification, volatilisation or anammox, suggesting temporary storage of N within the treatment system. This study demonstrates that passive aeration trickling filters can treat well-buffered high NH₄⁺-N strength landfill leachates under a range of temperatures and that leachate strength has no effect on initial NH₄⁺-N treatment rates. Whether this approach is a practicable option depends on a range of site specific factors.     

Kinetic of benzotriazole oxidation by ozone and hydroxyl radical

Ozonation experiments were performed in batch reactors in order to determine the rate constants for the reaction of molecular ozone and OH radicals with benzotriazole (BT) at different pHs. The first group of ozonation experiments was carried out for the determination of the rate constant for the direct reactions between ozone and BT. Two different kinetic models were used for the determination of kinetic rate constants: (i) the log-reduction of BT with ozone in excess, (ii) the competition kinetic model. The second-order rate constants for BT with molecular ozone were determined to be 36.4 ± 3.8 M⁻¹ s⁻¹ and 18.4 ± 0.8 M⁻¹ s⁻¹ at pH 2 from the two methods respectively. With the competition method, the value at pH 5 was found to be 22.0 ± 2.0 M⁻¹ s⁻¹. In a following stage, the reaction of BT with OH radicals was investigated at pH values ranging from 2 to 10.2. Using a method involving two probe compounds during the ozonation, the second-order rate constants of the BT reaction with hydroxyl radicals were determined. The rate constants were found to vary from 6.2 × 10⁹ M⁻¹ s⁻¹ at pH 10.2 to 1.7 × 10¹⁰ M⁻¹ s⁻¹ at pH 2.     

Evaluation of the prediction of trace organic compound removal during ozonation of secondary effluents using tracer substances and second order rate kinetics

The application of the R_CT-concept for predicting the removal of trace organic compounds (TrOCs) in organic rich WWTP effluents is often problematic due to the fast ozone depletion with instantaneous ozone demand in the range of typically applied ozone dosages. In this study, the determination of OH-radical and ozone exposure from second order rate kinetics with two internal tracer substances was evaluated as alternative approach for these waters. Results from batch and semi-batch experiments showed a linear correlation of OH-radical exposure with ozone consumption, characterized by its slope indicating the formation efficiency of OH-radicals and a lag ozone consumption without significant formation of OH-radicals. Evaluation of data from the project PILOTOX on ozonation of secondary effluent confirmed reasonable prediction of ozone resistant compound removal from relative residual concentration of an internal tracer substance. In contrast, predicting the reduction of TrOCs by direct reactions with ozone from internal tracers was not feasible. Similar removal efficiencies for fast reacting compounds with different rate constants from k_O3 = 10⁴ M⁻¹ s⁻¹ to k_O3 = 10⁶ M⁻¹ s⁻¹ were observed indicating a limitation of the reaction by mass transfer. This effect was observed at low ozone dosages in semi-batch and pilot experiments as well as in batch experiments, where mass transfer from gas to liquid phase is not limiting. It is assumed that consumption of low ozone dosages is faster than sample homogenization in the batch reactors used. Thus, prediction of compound removal by direct reaction with ozone always needs to consider reactor design and geometry.     

Analysis of the mechanism of sludge ozonation by a combination of biological and chemical approaches

Using the practical sludge obtained from municipal sewage treatment plants, the mechanism of the sludge ozonation process was systematically investigated by a combination of biological and chemical approaches, including analysis of the changes in biological response by CFU and PCR-DGGE, bio-macromolecular activity and radical scavenging activity. The results indicated that after the sludge was exposed to ozone at less than 0.02 g O₃/g TSS, the DGGE fingerprint remained constant and there was still some enzyme activity, indicating that the sludge solubilization was the main process. At greater than 0.02 g O₃/g TSS, the bacteria began to be broken down and ozone was used to oxidize the bio-macromolecules such as proteins and DNA released from the sludge. Bacteria belonging to ‘G-Bacteria’ were able to conserve their DNA in the presence of less than 0.08 g O₃/g TSS. At levels higher than 0.10 g O₃/g TSS, the disintegration of the sludge matrix became slow and the microbes lost most of their activity, and ozone was used to transform the bio-macromolecules into small molecules. However, at levels higher than 0.14 g O₃/g TSS, the ozone failed to oxidize the sludge efficiently, because several radical scavengers such as lactic acid and SO₄²⁻ were released from the microbial cells in the sludge.     

Effect of swine manure dilution on ammonia, hydrogen sulfide, carbon dioxide, and sulfur dioxide releases

Animal manure is a significant source of environmental pollution and manure dilution in barn cleaning and slurry storage is a common practice in animal agriculture. The effect of swine manure dilution on releases of four pollutant gases was studied in a 30-day experiment using eight manure reactors divided into two groups. One group was treated with swine manure of 6.71% dry matter and another with manure diluted with water to 3.73% dry matter. Ammonia release from the diluted manure was 3.32 mg min⁻¹ m⁻² and was 71.0% of the 4.67 mg min⁻¹ m⁻² from the undiluted manure (P < 0.01). Because the ammonia release reduction ratio was lower than the manure dilution ratio, dilution could increase the total ammonia emissions from swine manure, especially in lagoons with large liquid surface areas. Carbon dioxide release of 87.3 mg min⁻¹ m⁻² from the diluted manure was 56.4% of the 154.8 mg min⁻¹ m⁻² from the undiluted manure (P < 0.01). Manure dry matter was an important factor for carbon dioxide release from manure. No differences were observed between the treatments (P > 0.05) for both hydrogen sulfide and sulfur dioxide releases. Therefore, dilution could also significantly increase the total releases of hydrogen sulfide and sulfur dioxide to the environment because dilution adds to the total manure volume and usually also increases the total gas release surface area.     

Oxidation kinetics of two pesticides in natural waters by ozonation and ozone combined with hydrogen peroxide

The oxidation of bromoxynil and trifluralin was investigated using ozone (O₃) and O₃ combined with hydrogen peroxide (H₂O₂) in natural waters using batch reactors. The results indicated that these pesticides could not be completely degraded during ozonation, achieving degradation levels lower than 50%. An enhancement of the level of degradation was observed using O₃/H₂O₂ process. A biphasic behaviour of O₃ was also observed. Depending on the experimental conditions, the rate constant for O₃ decomposition was estimated to be between 7.4 × 10⁻⁴ s⁻¹ to 5.8 × 10⁻² s⁻¹, and 3.2 × 10⁻³ s⁻¹ to 4.2 × 10⁻² s⁻¹ for bromoxynil and trifluralin samples, respectively. Acute toxicity analysis performed using Microtox^® showed a decrease in the toxic effects of the samples on the luminescent bacteria during the first few minutes of treatment, followed by an increase of the toxic effects at the end of the reaction for both pesticides. The quantification of oxidation by-products generated during treatment was also addressed. The total molar balances of the degradation by-products versus the initial pesticide concentrations ranged from 60 to 103% under different experimental conditions.     

Degradation of the emerging contaminant ibuprofen in water by photo-Fenton

In this study the degradation of the worldwide Non-Steroidal Anti-Inflammatory Drug (NSAID) ibuprofen (IBP) by photo-Fenton reaction by use of solar artificial irradiation was carried out. Non-photocatalytic experiments (complex formation, photolysis and UV/Vis-H₂O₂ oxidation) were executed to evaluate the isolated effects and additional differentiated degradation pathways of IBP. The solar photolysis cleavage of H₂O₂ generates hydroxylated-IBP byproducts without mineralization. Fenton reaction, however promotes hydroxylation with a 10% contamination in form of a mineralization. In contrast photo-Fenton in addition promotes the decarboxylation of IBP and its total depletion is observed. In absence of H₂O₂ a decrease of IBP was observed in the Fe(II)/UV-Vis process due to the complex formation between iron and the IBP-carboxylic moiety. The degradation pathway can be described as an interconnected and successive principal decarboxylation and hydroxylation steps. TOC depletion of 40% was observed in photo-Fenton degradation. The iron-IBP binding was the key-point of the decarboxylation pathway. Both decarboxylation and hydroxylation mechanisms, as individual or parallel process are responsible for IBP removal in Fenton and photo-Fenton systems. An increase in the biodegradability of the final effluent after photo-Fenton treatment was observed. Final BOD₅ of 25 mg L⁻¹ was reached in contrast to the initial BOD₅ shown by the untreated IBP solution (BOD₅ < 1 mg L⁻¹). The increase in the biodegradability of the photo-Fenton degradation byproducts opens the possibility for a complete remediation with a final post-biological treatment.     

Removal of organics in constructed wetlands with horizontal sub-surface flow: a review of the field experience

Constructed wetlands with horizontal sub-surface flow (HF CWs) have successfully been used for treatment various types of wastewater for more than four decades. Most systems have been designed to treat municipal sewage but the use for wastewaters from agriculture, industry and landfill leachate in HF CWs is getting more attention nowadays. The paper summarizes the results from more than 400 HF CWs from 36 countries around the world. The survey revealed that the highest removal efficiencies for BOD₅ and COD were achieved in systems treating municipal wastewater while the lowest efficiency was recorded for landfill leachate. The survey also revealed that HF CWs are successfully used for both secondary and tertiary treatment. The highest average inflow concentrations of BOD₅ (652 mg l^− 1) and COD (1865 mg l^− 1) were recorded for industrial wastewaters followed by wastewaters from agriculture for BOD₅ (464 mg l^− 1) and landfill leachate for COD (933 mg l^− 1). Hydraulic loading data reveal that the highest loaded systems are those treating wastewaters from agriculture and tertiary municipal wastewaters (average hydraulic loading rate 24.3 cm d^− 1). On the other hand, landfill leachate systems in the survey were loaded with average only 2.7 cm d^− 1. For both BOD₅ and COD, the highest average loadings were recorded for agricultural wastewaters (541 and 1239 kg ha^− 1 d^− 1, respectively) followed by industrial wastewaters (365 and 1212 kg ha^− 1 d^− 1, respectively). The regression equations for BOD₅ and COD inflow/outflow concentrations yielded very loose relationships. Much stronger relationships were found for inflow/outflow loadings and especially for COD. The influence of vegetation on removal of organics in HF CWs is not unanimously agreed but most studies indicated the positive effect of macrophytes.     

Identification of ozonation by-products of 4- and 5-methyl-1H-benzotriazole during the treatment of surface water to drinking water

During the treatment of surface water to drinking water, ozonation is often used for disinfection and to remove organic trace substances, whereby oxidation by-products can be formed. Here we use the example of tolyltriazole to describe an approach for identifying relevant oxidation by-products in the laboratory and subsequently detecting them in an industrial-scale process. The identification process involves ozonation experiments with pure substances at laboratory level (concentration range mg L⁻¹). The reaction solutions from different ozone contact times were analyzed by high performance liquid chromatography - quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS) in full scan mode. Various approaches were used to detect the oxidation by-products: (i) target searches of postulated oxidation by-products, (ii) comparisons of chromatograms (e.g., UV/VIS) of the different samples, and (iii) color-coded abundance time courses (kinetic) of all detected compounds were illustrated in a kind of a heat map. MS/MS, H/D exchange, and derivatization experiments were used for structure elucidation for the detected by-product. Due to the low contaminant concentrations (ng L⁻¹-range) of contaminants in the untreated water, the conversion of results from laboratory experiments to an industrial-scale required the use of HPLC-MS/MS with sample enrichment (e.g., solid phase extraction.) In cases where reference substances were not available or oxidation by-products without clear structures were detected, reaction solutions from laboratory experiments were used to optimize the analytical method to detect ng L⁻¹ in the samples of the industrial processes. We exemplarily demonstrated the effectiveness of the methodology with the industrial chemicals 4- and 5-methyl-1H-benzotriazole (4- and 5-MBT) as an example. Moreover, not only did we identify several oxidation by-products in the laboratory experiments tentatively, but also detected three of the eleven reaction products in the outlet of the full-scale ozonation unit.     

Removal of diatrizoate with catalytically active membranes incorporating microbially produced palladium nanoparticles

There is an increasing concern about the fate of iodinated contrast media (ICM) in the environment. Limited removal efficiencies of currently applied techniques such as advanced oxidation processes require more performant strategies. The aim of this study was to establish an innovative degradation process for diatrizoate, a highly recalcitrant ICM, by using biogenic Pd nanoparticles as free suspension or immobilized in polyvinylidene fluoride (PVDF) and polysulfone (PSf) membranes. As measured by HPLC-UV, the removal of 20 mg L⁻¹ diatrizoate by a 10 mg L⁻¹ Pd suspension was completed after 4 h at a pH of 10. LC-MS analysis provided evidence for the sequential hydrodeiodination of diatrizoate. Pd did not lose its activity after incorporation in the PVDF and PSf matrix and the highest activity (k_cat = 30.0 ± 0.4 h⁻¹ L g⁻¹ Pd) was obtained with a casting solution of 10% PSf and 500 mg L⁻¹ Pd. Subsequently, water containing 20 mg L⁻¹ diatrizoate was treated in a membrane contactor, in which the water was supplied at one side of the membrane while hydrogen was provided at the other side. In a fed batch configuration, a removal efficiency of 77% after a time period of 48 h was obtained. This work showed that membrane contactors with encapsulated biogenic nanoparticles can be instrumental for treatment of water contaminated with diatrizoate.