Treatment of MTBE by air stripping, carbon adsorption, and advanced oxidation: technical and economic comparison for five groundwaters

An investigation was made of the treatability of methyl tert-butyl ether (MTBE) in five groundwaters with highly varied water quality characteristics. Air stripping, granular activated carbon (GAC) adsorption, and the O(3)/H(2)O(2) and UV/H(2)O(2) advanced oxidation processes were compared in a mobile water treatment pilot plant under a variety of process conditions. Air stripping was shown to have the lower unit treatment costs for higher flowrates (i.e., 3800L/min), although relatively tall towers were required for greater treatment requirements. At low flowrates (i.e., 38L/min), advanced oxidation provided the lowest treatment costs for four of five waters (but was ineffective for a high chemical oxygen demand water). Both the O(3)/H(2)O(2) and UV/H(2)O(2) processes were more efficient at pH 7 versus 9 due in part to increased scavenging at higher pH. GAC was examined using rapid small-scale column tests (RSSCT). GAC was effective at most conditions, although it was also the most costly alternative for most waters. The results of this study can help to provide specific guidance into process selection for treating MTBE in contaminated groundwaters.     

Fenton's oxidation of pentachlorophenol

The combination of H₂O₂ and Fe(II) (Fenton's reaction) has been demonstrated to rapidly degrade many organics via hydroxyl radicals. However, few studies have related hydroxyl radical generation rates with measured organic chemical degradation data. The goals of this work were to investigate the kinetics, stoichiometry, and intermediates of pentachlorophenol (PCP) degradation in the Fenton's reaction and to develop a mathematical model of this reaction system. Batch reaction experiments were performed to assess both initial transients and steady states, and special attention was given to the analysis of intermediates. Solutions of PCP (55 μM) and Fe(II) (200 μM) were treated with variable levels of H₂O₂ (<850 μM), and the concentrations of these reactants and their products were measured. Partial PCP degradation and near stoichiometric dechlorination were observed at low initial H₂O₂ concentrations. Higher H₂O₂ doses achieved at most 70% dechlorination even though nearly all of the PCP was degraded. The reaction intermediates tetrachlorohydroquinone and dichloromaleic acid accounted for up to 5% of the PCP degraded. Organic carbon mineralization (transformation to CO₂) was not observed. The OH scavenging effects of the PCP-by-products mixture were characterized as a lumped parameter in the reaction kinetics model, which provided reasonable predictions of experimental results at different oxidant concentrations and reaction time.     

Assessment of the UV/chlorine process as an advanced oxidation process

Several organic compounds were used as radical scavengers/reagents to investigate the possibility of the UV/chlorine process being used as an advanced oxidation process (AOP) in the treatment of drinking water and wastewater. The UV/H₂O₂ process was selected as a reference, so that the results from the UV/chlorine process could be compared with those of the UV/H₂O₂ process. Methanol was added to active chlorine solutions at both pH 5 and 10 and into hydrogen peroxide samples. The photodegradation quantum yields and the OH radical production yield factors, which are significant in evaluating AOPs, were calculated for both the UV/chlorine and the UV/H₂O₂ processes. The yield factor for the UV/chlorine process at pH 5 was 0.46 ± 0.09, which is much lower than that of the UV/H₂O₂ process, which reached 0.85 ± 0.04. In addition to methanol, para-chlorobenzoic acid (pCBA) and cyclohexanoic acid (CHA) were added to active chlorine solutions and to H₂O₂ solutions, to evaluate the efficiencies of oxidizing these organic compounds. The specific first-order reaction rate constants for the oxidation of pCBA and CHA, using the UV/chlorine process, were lower than those found using the UV/H₂O₂ process.     

A solar-driven UV/Chlorine advanced oxidation process

An overlap of the absorption spectrum of the hypochlorite ion (OCl⁻) and the ultraviolet (UV) end of the solar emission spectrum implies that solar photons can probably initiate the UV/chlorine advanced oxidation process (AOP). The application of this solar process to water and wastewater treatment has been investigated in this study. At the bench-scale, the OCl⁻ photolysis quantum yield at 303 nm (representative of the lower end of the solar UV region) and at concentrations from 0 to 4.23 mM was 0.87 ± 0.01. Also the hydroxyl radical yield factor (for an OCl⁻ concentration of 1.13 mM) was 0.70 ± 0.02. Application of this process, at the bench-scale and under actual sunlight, led to methylene blue (MB) photobleaching and cyclohexanoic acid (CHA) photodegradation. For MB photobleaching, the OCl⁻ concentration was the key factor causing an increase in the pseudo first-order rate constants. The MB photobleaching quantum yield was affected by the MB concentration, but not much by the OCl⁻ concentration. For CHA photodegradation, an optimal OCl⁻ concentration of 1.55 mM was obtained for a 0.23 mM CHA concentration, and a scavenger effect was observed when higher OCl⁻ concentrations were applied. Quantum yields of 0.09 ± 0.01 and 0.89 ± 0.06 were found for CHA photodegradation and OCl⁻ photolysis, respectively. In addition, based on the Air Mass 1.5 reference solar spectrum and experimental quantum yields, a theoretical calculation method was developed to estimate the initial rate for photoreactions under sunlight. The theoretical initial rates agreed well with the experimental rates for both MB photobleaching and CHA photodegradation.     

Degradation of a textile reactive Azo dye by a combined chemical-biological process: Fenton's reagent-yeast

This work presents the results of our studies on the decolorization of aqueous azo dye Reactive black 5 (RB5) solution combining an advanced oxidation process (Fenton's reagent) followed by an aerobic biological process (mediated by the yeast Candida oleophila). Under our conditions, initial experiments showed that Fenton's process alone, as well as aerobic treatment by C. oleophila alone, exhibited the capacity to significantly decolorize azo dye solutions up to 200 mg/L, within about 1 and 24h, respectively. By contrast, neither Fenton's reagent nor C. oleophila sole treatments showed acceptable decolorizing abilities for higher initial dye concentrations (300 and 500 mg/L). However, it was verified that Fenton's reagent process lowered these higher azo dye concentrations to a value less than 230 mg/L, which is apparently compatible with the yeast action. Therefore, to decolorize higher concentrations of RB5 and to reduce process costs the combination between the two processes was evaluated. The final decolorization obtained with Fenton's reagent process as primary treatment, at 1.0 x 10(-3)mol/L H(2)O(2) and 1.0 x 10(-4)mol/L Fe(2+), and growing yeast cells as a secondary treatment, achieves a color removal of about 91% for an initial RB5 concentration of 500 mg/L.     

Effect of oxidant-to-substrate ratios on the degradation of MTBE with Fenton reagent

Prior studies have shown the effectiveness of Fenton reagent (FR) for degrading low concentrations (1.0-2.0mg/L) of methyl tert-butyl ether (MTBE), similar to those found in contaminated groundwater. The present study investigates the effect of increasing FR doses on the extent of degradation and mineralization of a given initial MTBE concentration. The FR to MTBE molar ratio (FMMR) was the operating variable, and was investigated at values between 0.5:1 and 200:1. This approach provided sequential snapshots of the MTBE degradation process, which may help to improve the understanding of MTBE degradation with FR. The initial MTBE concentration (MTBE(0)) was approximately 22.7 microM ( approximately 2.0mg/L), and FR was used in a 1:1 molar ratio of ferrous iron (Fe(2+)) and hydrogen peroxide (H(2)O(2)). The concentrations of MTBE and the following main reaction byproducts: tert-butyl formate (TBF), tert-butyl alcohol (TBA), acetone and methyl acetate were determined from samples collected at specific intervals over a total reaction time of 1h. Total organic carbon (TOC) was monitored to determine MTBE mineralization, and the total concentration of tert-butyl compounds (tBC) was monitored due to the suspected toxicity associated with this functional group. The results showed that the minimum FMMR necessary for achieving complete MTBE degradation was 20:1, but at that FMMR, TOC and tBC reduction were only 45.6% and 24.9%, respectively. Complete MTBE mineralization was not achieved in any case, even at FMMRs as high as 200:1, where only 63.3% of mineralization was observed (although tBC reduction reached 99.6%, since traces of TBA were still detected). These results confirm the relative inability of FR to achieve complete mineralization of a target substrate, even those that are highly reactive with the hydroxyl radical.     

Inactivation of MS2 coliphage by Fenton's reagent

Fenton's reagent (i.e., Fe[II]/H₂O₂) is known to generate strong oxidants capable of oxidizing a broad spectrum of organic compounds in aqueous solution. This study demonstrates the successful inactivation of MS2 coliphage (MS2) by the oxidants produced from Fenton's reagent. The inactivation process of MS2 by Fenton's reagent was found to proceed in two distinct stages. The first stage inactivation, which took place rapidly within 1 min reaction time, was mainly achieved by the reaction of Fe(II) with H₂O₂ (i.e., the Fenton reaction). The second stage, which occurred by the catalytic reactions of Fe(III) with H₂O₂, exhibited much slower inactivation than the first stage. The rate of MS2 inactivation increased as pH decreased from 8.0 to 6.0. The addition of oxalate and humic acids significantly inhibited the MS2 inactivation, whereas 1,10-phenanthroline and bipyridine resulted in a gradual and steady inactivation of MS2. These observations on the effects of pH and iron-chelating agents indicate that oxidants formed on the surface or inside MS2 are responsible for the inactivation.     

Degradation mechanisms and kinetic studies for the treatment of X-ray contrast media compounds by advanced oxidation/reduction processes

The presence of iodinated X-ray contrast media compounds (ICM) in surface and ground waters has been reported. This is likely due to their biological inertness and incomplete removal in wastewater treatment processes. The present study reports partial degradation mechanisms based on elucidating the structures of major reaction by-products using γ-irradiation and LC-MS. Studies conducted at concentrations higher than observed in natural waters is necessary to elucidate the reaction by-product structures and to develop destruction mechanisms. To support these mechanistic studies, the bimolecular rate constants for the reaction of OH and e⁻_aq with one ionic ICM (diatrizoate), four non-ionic ICM (iohexol, iopromide, iopamidol, and iomeprol), and the several analogues of diatrizoate were determined. The absolute bimolecular reaction rate constants for diatrizoate, iohexol, iopromide, iopamidol, and iomeprol with OH were (9.58 ± 0.23)×10⁸, (3.20 ± 0.13)×10⁹, (3.34 ± 0.14)×10⁹, (3.42 ± 0.28)×10⁹, and (2.03 ± 0.13) × 10⁹ M⁻¹ s⁻¹, and with e⁻_aq were (2.13 ± 0.03)×10¹⁰, (3.35 ± 0.03)×10¹⁰, (3.25 ± 0.05)×10¹⁰, (3.37 ± 0.05)×10¹⁰, and (3.47 ± 0.02) × 10¹⁰ M⁻¹ s⁻¹, respectively. Transient spectra for the intermediates formed by the reaction of OH were also measured over the time period of 1-100 μs to better understand the stability of the radicals and for evaluation of reaction rate constants. Degradation efficiencies for the OH and e⁻_aq reactions with the five ICM were determined using steady-state γ-radiolysis. Collectively, these data will form the basis of kinetic models for application of advanced oxidation/reduction processes for treating water containing these compounds.     

Oxidation kinetics and effect of pH on the degradation of MTBE with Fenton reagent

The fundamentals of the Fenton reagent-based degradation of low concentrations of methyl tert-butyl ether (MTBE) in batch reactors under initially anaerobic conditions are discussed in this work. The objective of the study was to quantitatively verify the feasibility of MTBE degradation with Fenton reagent under such conditions. The conclusions may be potentially helpful to further develop an effective in situ treatment of MTBE-contaminated groundwater. Initial MTBE concentrations ([MTBE](0)) of 11.4 and 22.7 microM (approximately 1.0 and 2.0 mg/L, respectively) were treated with Fenton reagent (FR) using a [FR](0):[MTBE](0) molar ratio of 10:1. FR was used in equimolar mixture of Fe(2+)and H(2)O(2) (i.e., [Fe(2+)](0):[H(2)O(2)](0)=1:1). This analysis considers the hydroxyl radicals (OH(*)) produced by FR as the main species responsible for the degradation processes. The effects of [MTBE](0) and pH on the oxidation kinetics were investigated. Under these conditions it was observed that: (i) MTBE was degraded at high extent (90-99%) after 1h of reaction time, (ii) MTBE mineralization was low in all cases and reached only 31.7% at the best conditions, and (iii) In all cases, most of MTBE degradation occurred during the initial 3-5 min of reaction. During this brief initial phase, MTBE transformation followed pseudo-first order kinetics, while the subsequent phase exhibited a sharp drop in degradation rate and had almost negligible contribution to the overall degradation. Experiments performed at acidic pH exhibited the best degradation results, while at neutral pH the degradation rates dropped significantly. Other parameters included in this analysis were: TOC reduction and total concentration of compounds containing the tert-butyl group in their structure (tBC). These compounds were analyzed because of the concerns related to their potential toxicity. Tert-butyl formate (TBF), Tert-butyl alcohol (TBA), acetone and methyl acetate were identified and quantified as major reaction intermediates.     

Oxidative degradation of N-nitrosodimethylamine by conventional ozonation and the advanced oxidation process ozone/hydrogen peroxide

This study investigates the oxidative degradation of N-nitrosodimethylamine (NDMA), a probable human carcinogen, by conventional ozonation and the advanced oxidation process ozone/hydrogen peroxide (AOP O(3)/H(2)O(2)). The rate constants of reactions of NDMA with ozone and hydroxyl radical ((*)OH) were determined to be 0.052+/-0.0016M(-1)s(-1) and (4.5+/-0.21)x10(8)M(-1)s(-1), respectively. The experiments performed with buffered deionized water varying solution pH and employing H(2)O(2) and HCO(3)(-) clearly showed that the reaction with (*)OH dominates the NDMA oxidation during ozonation. Conventional ozonation with up to 160 microM (=7.7 mgL(-1)) ozone led to less than 25% NDMA oxidation in natural waters. The AOP O(3)/H(2)O(2) required 160-320 microM ozone ([O(3)](0)/[H(2)O(2)](0)=2:1) to achieve 50-75% NDMA oxidation. However, multiple injections of ozone of the same overall dose somewhat improved the oxidant utilization efficiency by minimizing (*)OH scavenging contribution of oxidants. Methylamine (MA) was found to be a major amino product from NDMA oxidation initiated by (*)OH. The mechanism of NDMA oxidation to MA is discussed based on the results obtained in this study and the previous literature. Bromate formation may be the limiting factor for NDMA oxidation during ozonation and ozone-based AOPs in bromide-containing waters.     

Effect of inorganic, synthetic and naturally occurring chelating agents on Fe(II) mediated advanced oxidation of chlorophenols

This study examines the feasibility and application of Advanced Oxidation Technologies (AOTs) for the treatment of chlorophenols that are included in US EPA priority pollutant list. A novel class of sulfate/hydroxyl radical-based homogeneous AOTs (Fe(II)/PS, Fe(II)/PMS, Fe(II)/H₂O₂) was successfully tested for the degradation of series of chlorophenols (4-CP, 2,4-CP, 2,4,6-CP, 2,3,4,5-CP). The major objective of the present study was to evaluate the effectiveness of three representative chelating agents (citrate, ethylenediaminedisuccinate (EDDS), and pyrophosphate) on Fe(II)-mediated activation of three common peroxide (peroxymonosulfate (PMS), persulfate (PS), and hydrogen peroxide (H₂O₂)) at neutral pH conditions. Short term (4 h) and long term (7 days) experiments were conducted to evaluate the kinetics and longevity of different oxidative systems for 4-chlorophenol degradation. Results showed that each of the iron-chelating agent couple was superior in activating a particular oxidant and consequently for 4-CP degradation. In case of Fe(II)/PMS system, the inorganic chelating agent pyrophosphate showed effective activation of PMS whereas very fast dissociation of PMS was recorded in the case of EDDS without any apparent 4-CP degradation. In Fe(II)/H₂O₂ system, EDDS was proven to be the most effective whereas pyrophosphate showed negligible activation of H₂O₂. Fe(II)/Citrate system showed moderate activation of all three oxidants. PMS was found to be the most universal oxidant, which was activated by all three iron-chelating agent systems and Fe(II)/Citrate was the most universal chelating agent system, which was able to activate all three oxidants to a certain extent.     

Enhancing Fenton oxidation of TNT and RDX through pretreatment with zero-valent iron

The effect of reductive treatment with elemental iron on the rate and extent of TOC removal by Fenton oxidation was studied for the explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using a completely stirred tank reactor (CSTR). The results support the hypothesis that TNT and RDX are reduced with elemental iron to products that are oxidized more rapidly and completely by Fenton's reagent. Iron pretreatment enhanced the extent of total organic carbon (TOC) removal by approximately 20% and 60% for TNT and RDX, respectively. Complete TOC removal was achieved for TNT and RDX solutions with iron pretreatment under optimal conditions. On the other hand, without iron pretreatment, complete TOC removal of TNT and RDX solutions was not achieved even with much higher H(2)O(2) and Fe(2+) concentrations. Nitrogen was recovered as NH(4)(+) and NO(3)(-) when Fe(0)-treated TNT and RDX solutions were subjected to Fenton oxidation. The bench-scale iron treatment-Fenton oxidation integrated system showed more than 95% TOC removal for TNT and RDX solutions under optimal conditions. These results suggest that the reduction products of TNT and RDX are more rapidly and completely degraded by Fenton oxidation and that a sequential iron treatment-Fenton oxidation process may be a viable technology for pink water treatment.     

Combined toxicity effects of MTBE and pesticides measured with Vibrio fischeri and Daphnia magna bioassays

Methyl-tert-butyl ether (MTBE), a fuel oxygenate that is added to gasoline, commonly contaminates aquatic systems, many of which are already contaminated with pesticides. The toxic effects (EC(50) value) of several pure pesticides (Diuron, Linuron, Dichlofluanid, Sea nine, Irgarol and tributyltin (TBT)) were measured and compared with the EC(50) value of the pesticide mixed with MTBE, using the Vibrio fischeri and Daphnia magna acute toxicity assays. The interaction between chemicals was evaluated in terms of the effects of mixing on the EC(50) value (i.e. the concentration (mg/L) of a compound or mixture that is required to produce a 50% change in a toxic response parameter) and the time required to generate the toxic response. Presence of MTBE enhanced the EC(50) value of several pesticides (Diuron, Dichlofluanid, TBT and Linuron) and/or the toxic response manifested more rapidly than with pure pesticides. Toxicity enhancements were quite substantial in many cases. For example, the presence of MTBE increased the toxicity of Diuron by more than 50% when tested with the V. fischeri assay (5, 15 and 30 min exposure). Also, the toxic response manifested itself within 5 min whereas without the MTBE the same response arose in 30 min. Presence of MTBE increased the toxicity of Dichlofluanid by 30% when measured with the D. magna assay. Toxicities of only two pesticides (Sea nine and Irgarol) were not raised by the presence of MTBE.     

As oxidation by Thiomonas arsenivorans in up-flow fixed-bed reactors coupled to As sequestration onto zero-valent iron-coated sand

The combined processes of biological As^III oxidation and removal of As^III and As^V by zero-valent iron were investigated with synthetic water containing high As^III concentration (10 mg L⁻¹). Two up-flow fixed-bed reactors (R1 and R2) were filled with 2 L of sieved sand (d = 3 ± 1 mm) while zero-valent iron powder (d = 76 μm; 1% (w/w) of sand) was mixed evenly with sand in R2. Thiomonas arsenivorans was inoculated in the two reactors. The pilot unit was studied for 33 days, with HRT of 4 and 1 h. The maximal As^III oxidation rate was 8.36 mg h⁻¹ L⁻¹ in R1 and about 45% of total As was removed in R2 for an HRT of 1 h. A first order model fitted well with the As^III concentration evolution at the different levels in R1. At the end of the pilot monitoring, batch tests were conducted with support collected at different levels in R1. They showed that bacterial As^III oxidation rate was correlated with the axial length of reactor, which could be explained by biomass distribution in reactor or by bacterial activity. In opposition, As^III oxidation rate was not stable in R2 due to the simultaneous bacterial As^III oxidation and chemical removal by zero-valent iron and its oxidant products. However, a durable removal of total As was realized and zero-valent iron was not saturated by As over 33 days in R2. Furthermore, the influence of zero-valent iron and its oxidant corrosion products on the evolution of As^III-oxidizing bacteria diversity was highlighted by the molecular fingerprinting method of PCR-DGGE using aoxB gene as a functional marker of aerobic As^III oxidizers.     

Photocatalytic oxidation of DBP precursors using UV with suspended and fixed TiO2

French River water (Nova Scotia, Canada) was separated into six different natural organic matter (NOM) fractions, including hydrophobic acids, bases and neutrals and hydrophilic acids, bases and neutrals. The raw water, as well as each of the NOM fractions were analysed for disinfection by-product (DBP) formation potential before and after advanced oxidation with UV/TiO₂ to determine the efficacy of this treatment for the removal of DBP precursors. The UV/TiO₂ treatment was carried out with a nanostructured thin film (NSTF), coated with TiO₂ which is compared with the use of a TiO₂ suspension. For the raw river water, removals of total trihalomethane formation potential (TTHMFP) and total haloacetic acid formation potential (THAA₉FP) were found to be approximately 20% and 90%, respectively, with 50 mJ/cm² UV exposure and 1 mg/L TiO₂. For the fractionated samples, approximately 75% of both trihalomethane (THM) and haloacetic acid (HAA) precursors were found to be associated with the hydrophobic acid fraction. For this individual fraction the same UV/TiO₂ treatments exhibited approximately 20-25% removal of both TTHMFP and THAA₉FP, suggesting that the fractionation process may have affected the treatability of HAA precursors or may have altered the results of the oxidation processes.     

Wet peroxide oxidation of chlorophenols

This study evaluates the application of Wet Peroxide Oxidation (WPO) for the treatment of solutions containing 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP). These compounds are of special interest due to their high toxicity and low biodegradability. WPO is included in the Advanced Oxidation Processes, which are technologies based on an initial formation of hydroxyl radicals that further oxidize the organic matter. The influence of some operating conditions such as temperature, dosage of hydrogen peroxide and initial concentration of the chlorophenols was studied in absence of a catalyst. The results of this study prove that 4-CP and 2,4-DCP can be completely removed from wastewaters by means of WPO. Total Organic Carbon (TOC) and 4-CP removals of 72.3% and 100%, respectively, were achieved working at 100 degrees C with 2.5 mL of H(2)O(2) and an initial concentration of 500 ppm of 4-CP after 90 min of reaction. Under the same conditions but with an initial concentration of 500 ppm of 2,4-DCP a TOC removal of 59% and a complete removal of the target compound were achieved.     

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.     

Evaluation of granular activated carbon technology for the removal of methyl tertiary butyl ether (MTBE) from drinking water

This study evaluated granular activated carbons (GACs) using rapid small-scale column tests (RSSCTs) on methyl tert-butyl ether (MTBE) levels from 20 to 2000 microg/L, with or without the presence of tert-butyl alcohol, benzene, toluene, p-xylene (BTX) in two groundwater (South Lake Tahoe Utility District [Lake Tahoe, CA] and Arcadia Well Field [Santa Monica, CA]) and a surface water source (Lake Perris, CA). Direct comparison between two GACs was made for RSSCTs conducted with surface water from Lake Perris. The impact of natural organic matter on GAC performance was investigated and found to correspond with total organic carbon concentration in the three source waters. Significant reduction in GAC performance for MTBE due to competitive adsorption from soluble fuel components (e.g., BTX) was observed. Little or no difference in GAC usage rate or bed life was detected as the empty-bed contact time is changed from 10 to 20 min for RSSCTs conducted in the two groundwater sources, whereas the RSSCTs conducted in the surface water source exhibited significant increase in GAC usage rate as the empty-bed contact time is decreased from 20 to 10 min. This finding suggests that the higher NOM content of the surface water over the groundwater sources caused a greater competitive-adsorption effect that made more sites on the GAC to be unavailable to MTBE, thus decreasing its rate of adsorption and GAC performance for MTBE. Finally, the impact of differential influent MTBE concentration on GAC performance was demonstrated.     

Acute toxicity removal in textile finishing wastewater by Fenton's oxidation, ozone and coagulation-flocculation processes

This study evaluates the effectiveness of Fenton's oxidation (FO) process and ozone (O3) oxidation compared with a coagulation-flocculation (CF) process to remove effluent toxicity as well as colour and COD from a textile industry wastewater. Daphnia magna was used to test acute toxicity in raw and pre-treated wastewater. The operational parameters for each process were determined on the basis of complete toxicity removal. The FO process removed COD at a higher rate (59%) than O3 (33%) while colour removal was similar (89% and 91%, respectively). The CF process removed both COD and colour at rates similar to the FO process. A colour range of 150-250 platin-cobalt (Pt-Co) unit was assessed for toxicity.     

Formation of oxidation byproducts from ozonation of wastewater

Disinfection byproduct (DBP) formation in tertiary wastewater was examined after ozonation (O(3)) and advanced oxidation with O(3) and hydrogen peroxide (O(3)/H(2)O(2)). O(3) and O(3)/H(2)O(2) were applied at multiple dosages to investigate DBP formation during coliform disinfection and trace contaminant oxidation. Results showed O(3) provided superior disinfection of fecal and total coliforms compared to O(3)/H(2)O(2). Color, UV absorbance, and SUVA were reduced by O(3) and O(3)/H(2)O(2), offering wastewater utilities a few potential surrogates to monitor disinfection or trace contaminant oxidation. At equivalent O(3) dosages, O(3)/H(2)O(2) produced greater concentrations of assimilable organic carbon (5-52%), aldehydes (31-47%), and carboxylic acids (12-43%) compared to O(3) alone, indicating that organic DBP formation is largely dependent upon hydroxyl radical exposure. Bromate formation occurred when O(3) dosages exceeded the O(3) demand of the wastewater. Bench-scale tests with free chlorine showed O(3) is capable of reducing total organic halide (TOX) formation potential by at least 20%. In summary, O(3) provided superior disinfection compared to O(3)/H(2)O(2) while minimizing DBP concentrations. These are important considerations for water reuse, aquifer storage and recovery, and advanced wastewater treatment applications.