Solar treatment of cork boiling and bleaching wastewaters in a pilot plant

This paper reports on cork boiling and bleaching wastewaters treatment by solar photocatalytic processes, TiO₂/UV and Fe²⁺/H₂O₂/UV (TiO₂-only for bleaching wastewater), in a pilot plant with compound parabolic collectors. The photo-Fenton reaction (k = 0.12 L/kJ_UV, r₀ = 59.4 mg/kJ_UV) is much more efficient that TiO₂ photocatalysis and TiO₂ + S₂O₈²⁻ (k = 0.0024 L/kJ_UV, r₀ = 1.36 mg/kJ_UV), leading to 94% mineralization of the bleaching wastewater after 31.5 kJ_UV/L, consuming 77.1 mM of H₂O₂ (3.0 mmol/kJ_UV) and using 20 mg/L of iron. For the cork boiling wastewater, after a slow initial reaction rate, the DOC degradation curve shows a first-order kinetics behaviour (k = 0.015 L/kJ_UV, r₀ = 20.8 mg/kJ_UV) until 173 kJ_UV/L (≈300 mg C/L). According to the average oxidation state (AOS), toxicity profiles, respirometry and kinetic results obtained in two solar CPCs plants, the optimal energy dose estimated for phototreatment to reach a biodegradable effluent is 15 kJ_UV/L and 114 kJ_UV/L, consuming 33 mM and 151 mM of H₂OT:/PGN/ELSEVIER/WR/web/00007490/₂, achieving almost 49% and 48% mineralization of the wastewaters, respectively for the cork bleaching and boiling wastewaters.     

Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L⁻¹, and a real global quantity of micropollutants of 29.5 μg L⁻¹. The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV₂₅₄) alone, dark Fenton (Fe^2+,3+/H₂O₂) and photo-Fenton (Fe^2+,3+/H₂O₂/light). Different irradiation sources were used for the photo-Fenton experiences: UV₂₅₄ and simulated sunlight. Iron and H₂O₂ concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV₂₅₄, 50 mg L⁻¹ of H₂O₂, with and without adding iron (5 mg L⁻¹ of Fe²⁺ added or 1.48 mg L⁻¹ of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H₂O₂ concentration increased (10, 25 and 50 mg L⁻¹), best degradations were observed. UV₂₅₄, Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal.The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.     

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.     

Comparative effect of simulated solar light,UV, UV/H2O2 and photo-Fenton treatment (UV–Vis/H2O2/Fe) in the Escherichia coli inactivation in artificial seawater

Innovative disinfection technologies are being studied for seawater, seeking a viable alternative to chlorination. This study proposes the use of H₂O₂/UV₂₅₄ and photo-Fenton as disinfection treatment in seawater. The irradiations were carried out using a sunlight simulator (Suntest) and a cylindrical UV reactor. The efficiency of the treatment was compared for Milli-Q water, Leman Lake water and artificial seawater. The presence of bicarbonates and organic matter was investigated in order to evaluate possible effects on the photo-Fenton disinfection treatment. The photo-Fenton treatment, employing 1 mg L⁻¹ Fe²⁺ and 10 mg L⁻¹ of H₂O₂, led to the fastest bacterial inactivation kinetics. Using H₂O₂/UV₂₅₄ high disinfection rates were obtained similar to those obtained with photo-Fenton under UV₂₅₄ light. In Milli-Q water, the rate of inactivation for Escherichia coli was higher than in Leman Lake water and seawater due to the lack of inorganic ions affecting negatively bacteria inactivation. The presence of bicarbonate showed scavenging of the OH^• radicals generated in the treatment of photo-Fenton and H₂O₂/UV₂₅₄. Despite the negative effect of inorganic ions, especially HCO₃^-, the disinfection treatments with AOPs in lake water and seawater improved significantly the disinfection compared to light alone (simulated sunlight and UV₂₅₄). In the treatment of photo-Fenton with simulated sunlight, dissolved organic matter had a beneficial effect by increasing the rate of inactivation. This is associated with the formation of Fe³⁺-organo photosensitive complexes leading to the formation of ROS able to inactivate bacteria. This effect was not observed in the photo-Fenton with UV₂₅₄. Growth of E. coli surviving in seawater was observed 24 and 48 h after treatment with UV light. However, growth of surviving bacteria was not detected after photo-Fenton with UV₂₅₄ and H₂O₂/UV₂₅₄ treatments.     

Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor - IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H₂O₂ (kinetic study) and another with controlled H₂O₂ dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H₂O₂, nalidixic acid degradation was complete at 66 mM of H₂O₂ consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H₂O₂ dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO₃⁻ generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.     

Degradation of sulfamethoxazole in water by solar photo-Fenton. Chemical and toxicological evaluation

In this work, the photocatalytic degradation of the antibiotic sulfamethoxazole (SMX) by solar photo-Fenton at pilot plant scale was evaluated in distilled water (DW) and in seawater (SW). Degradation and mineralization of SMX were strongly hindered in SW compared to DW. The influence of H₂O₂ and iron concentration on the efficiency of the photocatalytic process was evaluated. An increase in iron concentration from 2.6 to 10.4 mg L⁻¹ showed only a slight improvement in SMX degradation and mineralization. However, an increase in H₂O₂ concentration up to 120 mg L⁻¹ during photo-Fenton in DW decreased SMX solution toxicity from 85% to 20%, according to results of Daphnia magna bioassays. The same behaviour was not observed after photo-Fenton treatment in SW. Despite 45% mineralization in SW, toxicity increased from 16% to 86% as shown by Vibrio fischeri bioassays, which suggests that the intermediates generated in SW are different from those in DW. A SMX degradation pathway during the photo-Fenton treatment in DW is proposed.     

Solar photo-Fenton process on the abatement of antibiotics at a pilot scale: Degradation kinetics, ecotoxicity and phytotoxicity assessment and removal of antibiotic resistant enterococci

This work investigated the application of a solar driven advanced oxidation process (solar photo-Fenton), for the degradation of antibiotics at low concentration level (μg L⁻¹) in secondary treated domestic effluents at a pilot-scale. The examined antibiotics were ofloxacin (OFX) and trimethoprim (TMP). A compound parabolic collector (CPC) pilot plant was used for the photocatalytic experiments. The process was mainly evaluated by a fast and reliable analytical method based on a UPLC-MS/MS system. Solar photo-Fenton process using low iron and hydrogen peroxide doses ([Fe²⁺]₀ = 5 mg L⁻¹; [H₂O₂]₀ = 75 mg L⁻¹) was proved to be an efficient method for the elimination of these compounds with relatively high degradation rates. The photocatalytic degradation of OFX and TMP with the solar photo-Fenton process followed apparent first-order kinetics. A modification of the first-order kinetic expression was proposed and has been successfully used to explain the degradation kinetics of the compounds during the solar photo-Fenton treatment. The results demonstrated the capacity of the applied advanced process to reduce the initial wastewater toxicity against the examined plant species (Sorghum saccharatum, Lepidium sativum, Sinapis alba) and the water flea Daphnia magna. The phytotoxicity of the treated samples, expressed as root growth inhibition, was higher compared to that observed on the inhibition of seed germination. Enterococci, including those resistant to OFX and TMP, were completely eliminated at the end of the treatment. The total cost of the full scale unit for the treatment of 150 m³ day⁻¹ of secondary wastewater effluent was found to be 0.85 € m⁻³.     

Decolorization of dark brown colored coffee effluent by solar photo-Fenton reaction: effect of solar light dose on decolorization kinetics

The decolorization of dark brown colored coffee effluent by solar photo-Fenton process has been studied. Effects of accumulated solar light energy and dosage of Fenton reagents (iron and hydrogen peroxide) on the color removal have been examined. With increasing Fe dosage the rate of the decolorization increased but the enhancement was not pronounced beyond 10 mg L⁻¹. Although addition of H₂O₂ increased the decolorization rate up to around 1000 mg L⁻¹ of H₂O₂, further addition of H₂O₂ could not enhance the color removal. At excess dosages of Fenton reagents, the color removal was not improved due to their scavenging of hydroxyl radicals. It was found that the pseudo-first order decolorization kinetic constant based on the accumulated solar energy is a sole parameter unifying solar photo-Fenton decolorization processes under the different weather conditions. The kinetic constant can be readily used to calculate the amount of solar energy required to achieve a certain degree of color removal. The mineralization was rather slower as compared with the decolorization. The decolorization capability with solar irradiation was found to be comparable to UV light irradiation. The present results suggest that abundant solar energy driving decolorization of coffee effluent by photo-Fenton reaction is highly efficient.     

Floc-based sequential partial nitritation and anammox at full scale with contrasting N2O emissions

New Activated Sludge (NAS^®) is a hybrid, floc-based nitrogen removal process without carbon addition, based on the control of sludge retention times (SRT) and dissolved oxygen (DO) levels. The aim of this study was to examine the performance of a retrofitted four-stage NAS^® plant, including on-line measurements of greenhouse gas emissions (N₂O and CH₄). The plant treated anaerobically digested industrial wastewater, containing 264 mg N L⁻¹, 1154 mg chemical oxygen demand (COD) L⁻¹ and an inorganic carbon alkalinity of 34 meq L⁻¹. The batch-fed partial nitritation step received an overall nitrogen loading rate of 0.18-0.22 kg N m⁻³ d⁻¹, thereby oxidized nitrogen to nitrite (45-47%) and some nitrate (13-15%), but also to N₂O (5.1-6.6%). This was achieved at a SRT of 1.7 d and DO around 1.0 mg O₂ L⁻¹. Subsequently, anammox, denitrification and nitrification compartments were followed by a final settler, at an overall SRT of 46 d. None of the latter three reactors emitted N₂O. In the anammox step, 0.26 kg N m⁻³ d⁻¹ was removed, with an estimated contribution of 71% by the genus Kuenenia, which constituted 3.1% of the biomass. Overall, a nitrogen removal efficiency of 95% was obtained, yielding a dischargeable effluent. Retrofitting floc-based nitrification/denitrification with carbon addition to NAS^® allowed to save 40% of the operational wastewater treatment costs. Yet, a decrease of the N₂O emissions by about 50% is necessary in order to obtain a CO₂ neutral footprint. The impact of emitted CH₄ was 20 times lower.     

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.     

Performance of a Sequencing Batch Biofilm Reactor for the treatment of pre-oxidized Sulfamethoxazole solutions

A combined strategy of a photo-Fenton pretreatment followed by a Sequencing Batch Biofilm Reactor (SBBR) was evaluated for total C and N removal from a synthetic wastewater containing exclusively 200 mg L⁻¹ of the antibiotic Sulfamethoxazole (SMX). Photo-Fenton reaction was optimized at the minimum reagent doses in order to improve the biocompatibility of effluents with the subsequent biological reactor. Consequently, the pretreatment was performed with two different initial H₂O₂ concentrations (300 and 400 mg L⁻¹) and 10 mg L⁻¹ of Fe²⁺. The pre-treated effluents with the antibiotic intermediates as sole carbon source were used as feed for the biological reactor. The SBBR was operated under aerobic conditions to mineralize the organic carbon, and the Hydraulic Retention Time (HRT) was optimized down to 8 h reaching a removal of 75.7% of the initial Total Organic Carbon (TOC). The total denitrification of the NO₃⁻ generated along the chemical-biological treatment was achieved by means of the inclusion of a 24-h anoxic stage in the SBBR strategy. In addition, the Activated Sludge Model No. 1 (ASM1) was successfully used to complete the N balance determining the N fate in the SBBR.The characterization and the good performance of the SBBR allow presenting the assessed combination as an efficient way for the treatment of wastewaters contaminated with biorecalcitrant pharmaceuticals as the SMX.     

An innovative ultrasound, Fe and TiO2 photoassisted process for bisphenol a mineralization

This paper explores the degradation of a model pollutant, bisphenol A, by an advanced oxidation process that combines sonolysis, Fe²⁺, and TiO₂ in a photoassisted process. Experiments were done under saturated oxygen conditions. The effect of different Fe²⁺ (0.56 and 5.6 mg/L) and TiO₂ (10 and 50 mg/L) concentrations was investigated on both the elimination and mineralization of the pollutant. A pronounced synergistic effect that led to the complete and rapid elimination of dissolved organic carbon (DOC) was observed even at low catalyst loadings. In this system, almost a complete removal of DOC (93%) was observed after 4 h using 10 and 5.6 mg/L of TiO₂ and Fe²⁺, respectively, whereas at the same time, only 5, 6, and 22% of DOC was removed by an individual process alone (TiO₂ photocatalysis, ultrasound, and photo-Fenton, respectively). In this system, ultrasound has the principal role of eliminating the initial substrate and providing hydrogen peroxide for the photocatalytic systems, while photo-Fenton and TiO₂ photocatalysis are mainly responsible for the transformation of the intermediates in CO₂ and H₂O. The role of H₂O₂ generated from the sonochemical process is also discussed.     

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.     

Total and stable washout of nitrite oxidizing bacteria from a nitrifying continuous activated sludge system using automatic control based on Oxygen Uptake Rate measurements

Partial nitrification (ammonium oxidation to nitrite) has gained a lot of interest among researchers in the last years because of its advantages with respect to complete nitrification (ammonium oxidation to nitrate): decrease of oxygen requirements for nitrification, reduction of COD demand and CO₂ emissions during denitrification and higher denitrification rate and lower biomass production during anoxic growth.In this study, an extremely high-strength ammonium wastewater (3000-4000 mg N L⁻¹) was treated in a continuous pilot plant with a configuration of three reactors in series plus a settler. The system was operated under the maximum possible volumetric nitrogen loading rate, at mild temperature (around 25 °C), with high sludge retention time (around 30 d) and significant nitrifying biomass concentration (average of 1800 ± 600 mg VSS L⁻¹). The implemented control loops transformed the system, which was operating with complete nitrification, into a continuous partial nitrification system. Nitrite oxidizing bacteria (NOB) washout was accomplished with local control loops for pH and dissolved oxygen (DO) with proper setpoints for NOB inhibition (pH = 8.3 and DO = 1.2-1.9 mg O₂ L⁻¹) and with an inflow control loop based on Oxygen Uptake Rate (OUR) measurements, which allowed working at the maximum ammonium oxidation capacity of the pilot plant in each moment. This operational strategy maximized the difference between ammonia oxidizing bacteria (AOB) and NOB growth rates, which is the key point to achieve a fast and stable NOB washout. The results showed a stable operation of the partial nitrification system during more than 100 days and NOB washout was corroborated with fluorescence in-situ hybridization (FISH) analysis.     

Phosphorus limitation in nitrifying groundwater filters

Phosphorus limitation has been demonstrated for heterotrophic growth in groundwater, in drinking water production and distribution systems, and for nitrification of surface water treatment at low temperatures. In this study, phosphorus limitation was tested, in the Netherlands, for nitrification of anaerobic groundwater rich in iron, ammonium and orthophosphate. The bioassay method developed by Lehtola et al. (1999) was adapted to determine the microbially available phosphorus (MAP) for nitrification. In standardized batch experiments with an enriched mixed culture inoculum, the formation of nitrite and nitrate and ATP and the growth of ammonia-oxidizing bacteria (AOB; as indicated by qPCR targeting the amoA-coding gene) were determined for MAP concentrations between 0 and 100 μg PO₄-P L⁻¹. The nitrification and microbial growth rates were limited at under 100 μg PO₄-P L⁻¹ and virtually stopped at under 10 μg PO₄-P L⁻¹. In the range between 10 and 50 μg PO₄-P L⁻¹, a linear relationship was found between MAP and the maximum nitrification rate. AOB cell growth and ATP formation were proportional to the total ammonia oxidized. Contrary to Lehtola et al. (1999), biological growth was very slow for MAP concentrations less than 25 μg PO₄-P L⁻¹. No full conversion nor maximum cell numbers were reached within 19 days. In full-scale groundwater filters, most of the orthophosphate was removed alongside with iron. The remaining orthophosphate appeared to have only limited availability for microbial growth and activity. In some groundwater filters, nitrification was almost totally prevented by limitation of MAP. In batch experiments with filtrate water from these filters, the nitrification process could be effectively stimulated by adding phosphoric acid.     

Iron amendment and Fenton oxidation of MTBE-spent granular activated carbon

Fenton-driven regeneration of methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) involves an Fe amendment step to increase the Fe content and to enhance the extent of MTBE oxidation and GAC regeneration. Four forms of iron (ferric sulfate, ferric chloride, ferric nitrate, ferrous sulfate) were amended separately to GAC. Following Fe amendment, MTBE was adsorbed to the GAC followed by multiple applications of H₂O₂. Fe retention in GAC was high (83.8-99.9%) and decreased in the following order, FeSO₄·7H₂O > Fe₂(SO₄)₃·9H₂O > Fe(NO₃)₃·9H₂O > FeCl₃. A correlation was established between the post-sorption aqueous MTBE concentrations and Fe on the GAC for all forms of Fe investigated indicating that Fe amendment interfered with MTBE adsorption. However, the mass of MTBE adsorbed to the GAC was minimally affected by Fe loading. Relative to ferric iron amendments to GAC, ferrous iron amendment resulted in lower residual iron in solution, greater Fe immobilization in the GAC, and less interference with MTBE adsorption. MTBE oxidation was Fe limited and no clear trend was established between the counter-ion (SO₄²⁻, Cl⁻, NO₃⁻) of the ferric Fe amended to GAC and H₂O₂ reaction, MTBE adsorption, or MTBE oxidation, suggesting these processes are anion independent.     

Effects of UV/H2O2 advanced oxidation on chemical characteristics and chlorine reactivity of surface water natural organic matter

The advanced oxidation process utilizing ultraviolet and hydrogen peroxide (UV/H₂O₂) is currently applied in commercial drinking water applications for the removal of various organic pollutants. Natural organic matter (NOM) present in the source water can also be oxidized and undergo changes at the fluence and H₂O₂ concentrations applied in commercial drinking water UV/H₂O₂ applications (fluences less than 2000 mJ cm⁻², initial H₂O₂ concentrations less than 15 mg L⁻¹). In this study, the impact of UV/H₂O₂ on NOM’s aromaticity, hydrophobicity, and potential to form trihalomethanes (THMs) and haloacetic acids (HAAs) was investigated for raw surface water and the same water with the very hydrophobic acid (VHA) fraction of NOM removed. During UV/H₂O₂ treatments, NOM in the raw surface water was partially oxidized to less aromatic and hydrophobic characteristics, but was not mineralized, confirming findings from past research. Below fluences of 1500 mJ cm⁻² UV/H₂O₂ treatment of the raw water did not lead to reduction in the formation potential of THMs. The formation potential of HAAs was reduced at a fluence of 500 mJ cm⁻² with only small additional reductions as fluence further increased. For the water from which the VHA fraction was removed, UV/H₂O₂ treatment led to mineralization of NOM suggesting that, when coupled with a pre-treatment capable of removing the VHA fraction, UV/H₂O₂ could achieve further reductions in NOM. These subsequent reductions in NOM led to continuous reductions in the formation potentials of THMs and HAAs as fluence increased.     

Disinfection and formation of disinfection by-products in a photoelectrocatalytic system

In this study, disinfection and formation of disinfection by-products (DBPs) were studied in a photoelectrocatalytic (PEC) treatment system. Disinfection performance of titanium dioxide (TiO₂) in the PEC system was determined through Escherichia coli (E. coli) inactivation. Humic acid (HA) was used as a model organic compound and its removal was monitored by total organic carbon (TOC) measurements using 410 nm (color) and 254 nm (UV₂₅₄) wavelengths. Trihalomethanes (THMs) were measured for the evaluation of DBPs formation during PEC treatment of chloride and HA mixture. It was found that unlike photocatalytic treatment, THMs might form in the PEC system. To investigate the effects of anions on the PEC treatment, chloride (Cl⁻), sulfate (SO₄²⁻), phosphoric acid (H₂PO₄⁻)/hydrogen phosphate (HPO₄²⁻) and bicarbonate (HCO₃⁻) ions were added separately to the HA and bacterial suspensions. Presence of H₂PO₄⁻/HPO₄²⁻ and HCO₃⁻ ions resulted in inhibitory effects on both HA degradation and E. coli inactivation, which were also examined in the photoanode. It was observed that the presence of HA had a strong inhibitory effect on the disinfection of E. coli.     

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.     

Simultaneous degradation of disinfection byproducts and earthy-musty odorants by the UV/H2O2 advanced oxidation process

Advanced treatment technologies that control multiple contaminants are beneficial to drinking water treatment. This research applied UV/H₂O₂ for the simultaneous degradation of geosmin, 2-methylisoborneol, four trihalomethanes and six haloacetic acids. Experiments were conducted in de-ionized water at 24 ± 1.0 °C with ng/L amounts of odorants and μg/L amounts of disinfection byproducts. UV was applied with and without 6 mg/L H₂O_2. The results demonstrated that brominated trihalomethanes and brominated haloacetic acids were degraded to a greater extent than geosmin and 2-methylisoborneol. Tribromomethane and dibromochloromethane were degraded by 99% and 80% respectively at the UV dose of 1200 mJ/cm² with 6 mg/L H₂O₂, whereas 90% of the geosmin and 60% of the 2-methylisoborneol were removed. Tribromoacetic acid and dibromoacetic acid were degraded by 99% and 80% respectively under the same conditions. Concentrations of trichloromethane and chlorinated haloacetic acids were not substantially reduced under these conditions and were not effectively removed at doses designed to remove geosmin and 2-methylisoborneol. Brominated compounds were degraded primarily by direct photolysis and cleavage of the C-Br bond with pseudo first order rate constants ranging from 10⁻³ to 10⁻² s⁻¹. Geosmin and 2-methylisoborneol were primarily degraded by reaction with hydroxyl radical with direct photolysis as a minor factor. Perchlorinated disinfection byproducts were degraded by reaction with hydroxyl radicals. These results indicate that the UV/H₂O₂ can be applied to effectively control both odorants and brominated disinfection byproducts.