Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of benzotriazoles

Benzotriazoles (BTs) are high production volume chemicals with broad application in various industrial processes and in households, and have been found to be omnipresent in aquatic environments. We investigated oxidation of five benzotriazoles (BT: 1H-benzotriazole; 5MBT: 5-methyl-1H-benzotriazole; DMBT: 5,6-dimethyl-1H-benzotriazole hydrate; 5CBT: 5-chloro-1H-benzotriazole; HBT: 1-hydroxybenzotriazole) by aqueous ferrate (Fe(VI)) to determine reaction kinetics as a function of pH (6.0-10.0), and interpreted the reaction mechanism of Fe(VI) with BTs by using a linear free-energy relationship. The pK(a) values of BT and DMBT were also determined using UV-Visible spectroscopic method in order to calculate the species-specific rate constants, and they were 8.37 ± 0.0 and 8.98 ± 0.08 respectively. Each of BTs reacted moderately with Fe(VI) with the k(app) ranged from 7.2 to 103.8 M(-1)s(-1) at pH 7.0 and 24 ± 1 °C. When the molar ratio of Fe(VI) and BTs increased up to 30:1, the removal rate of BTs reached about >95% in buffered milli-Q water or secondary wastewater effluent. The electrophilic oxidation mechanism of the above reaction was illustrated by using a linear free-energy relationship between pH-dependence of species-specific rate constants and substituent effects (σ(p)). Fe(VI) reacts initially with BTs by electrophilic attack at the 1,2,3-triazole moiety of BT, 5MBT, DMBT and 5CBT, and at the N-OH bond of HBT. Moreover, for BT, 5MBT, DMBT and 5CBT, the reactions with the species HFeO(4)(-) predominantly controled the reaction rates. For HBT, the species H(2)FeO(4) with dissociated HBT played a major role in the reaction. The results showed that Fe(VI) has the ability to degrade benzotriazoles in water.     

The aqueous degradation of bisphenol A and steroid estrogens by ferrate

The aqueous reactivity of five prominent endocrine disrupting chemicals (EDCs) with potassium ferrate has been studied. The degradation kinetics and reaction pathways for bisphenol A (BPA) have been considered in detail, and the reaction rate constants for 17alpha-ethynylestradiol (EE2), estrone (E1), beta-estradiol (E2), and estriol (E3) have been determined, from tests carried out in the pH range of 8-12 and at different reactant molar ratios. The rate constants were determined by a kinetic model incorporating the various species equilibria for the EDC compounds and ferrate, using observations of the temporal reduction in EDC and ferrate concentrations. In agreement with other studies, the oxidation of the EDCs was found to be greater for mono-protonated ferrate, HFeO(4)(-), than for non-protonated ferrate, FeO(4)(2-). Among the five EDCs, all of which have phenol moieties, the ferrate oxidation of the four steroid estrogens (each incorporating the cyclopentanoperhydrophenanthrene ring) had higher reaction rates than BPA. The by-products of BPA degradation by ferrate were analyzed by liquid chromatography/mass spectrometry-mass spectrometry (LC/MS-MS) and gas chromatography/mass spectrometry-mass spectrometry (GC/MS-MS) and nine specific compounds were identified, including p-isopropylphenol, 4-isopropanolphenol, p-isopropenylphenol, and some dicarboxylic acids, etc. It is concluded that ferrate oxidation could be an effective treatment method for the purification of waters containing these particular EDCs.     

Effect of precursor concentration on the characteristics of nanoscale zerovalent iron and its reactivity of nitrate

Differing precursor concentrations, 1.0, 0.1, and 0.01 M FeCl(3) x 6H(2)O, were performed to produce nanoscale Fe(0) and the results were discussed in terms of the specific surface area, particle size and electrochemical properties. The results indicated that the nanoscale Fe(0) prepared by 0.01 M FeCl(3) had absolutely reduced in size (9-10nm) and possessed the greatest specific surface area (56.67 m(2) g(-1)). These synthesized nanoscale Fe(0) particles were attempted to enhance the removal of 40 mg-NL(-1) unbuffered nitrate solution. The first-order degradation rate constants (k(obs)) increased significantly (5.5-8.6 times) with nanoscale Fe(0) prepared by 0.01 M precursor solution (Fe(0.01 M)(0)). When normalized to iron surface area concentration, the specific rate constant (k(SA)) was increased by a factor of approximately 1.7-2.4 using Fe(0.01 M)(0) (6.84 x 10(-4) L min(-1) m(-2) for Fe(0.01 M)(0), 4.04 x 10(-4) L min(-1) m(-2) for Fe(0.1 M)(0) and 2.80 x 10(-4) L min(-1) m(-2) for Fe(1 M)(0)). The rise of reactivity of the reactive site on the Fe(0.01 M)(0) surface was indicated by the specific rate constant (k(SA)) calculation and the i(0) value of the electrochemical test.     

Degradation of estrone in aqueous solution by photo-Fenton system

Photodegradation of estrone (E1) in aqueous solutions by UV-VIS/Fe(III)/H2O2 system (photo-Fenton system) was preliminarily investigated under a 250-W metal halide lamp (lambda > or = 313 nm). The influences such as initial pH value, initial concentration of Fe(III), H2O2 and E1 on degradation efficiency of E1 were discussed in detail. The results indicated that E1 could be decomposed efficiently in UV-VIS/Fe(III)/H2O2 system. After 160-min irradiation, the photodegradation efficiency of 18.5 micromol L(-1) E1 reached 98.4% in the solution containing 20.8 micromol L(-1) Fe(III), and 1664 micromol L(-1) H2O2 at initial pH value 3.0. The degradation efficiencies of E1 were dependent on initial pH value, Fe (III) concentration and H2O2 concentration. The degradation of four estrogens estrone (E1), estradiol (E2), 17alpha-ethynylestradiol (EE2) and diethylstibestrol (DES) in UV-VIS/Fe(III)/H2O2 system were also conducted. Under the conditions of pH 3.0, the E1 apparent kinetics equation -dC(E1)/dt=0.00093[H2O2]0.47[Fe(III)]0.63[E1]0.24 (r=0.9935, n=11) was obtained. The E1 mineralization efficiency was lower than degradation efficiency under the same conditions, which implied the mineralization occurred probably only at aromatic ring. There are several intermediate products produced during the course of E1 degradation. The comparison of the degradation efficiencies of E1, E2, EE2 and DES degradation in UV-VIS/Fe(III)/H2O2 system were also conducted, and the relative degradability among different estrogens were followed the sequence: DES>E2>EE2>E1.     

Mobilization of Cr(VI) from chromite ore processing residue through acid treatment

Batch leaching studies on chromite ore processing residue (COPR) were performed using acids to investigate leaching of hexavalent chromium, Cr(VI), with respect to particle size, reaction time, and type of acid (HNO(3) and H(2)SO(4)). Aqueous Cr(VI) is maximized at approximately 0.04 mol Cr(VI) per kg of dry COPR at pH 7.6-8.1. Cr(VI) mobilized more slowly for larger particles, and the pH increased with time and increased more rapidly for smaller particles, suggesting that rate limitations occur in the solid phase. With H(2)SO(4), the pH stabilized at a higher value (8.8 for H(2)SO(4) vs. 8.0 for HNO(3)) and more rapidly (16 h vs. 30 h), and the differences in pH for different particle sizes were smaller. The acid neutralization capacity (ANC) of COPR is very large (8 mol HNO(3) per kg of dry COPR for a stable eluate pH of 7.5). Changes to the elemental and mineralogical composition and distribution in COPR particles after mixing with acid indicate that Cr(VI)-bearing solids dissolved. However, concentrations of Cr(VI) >2800 mg kg(-1) (>50% of the pre-treatment concentration) were still found after mixing with acid, regardless of the particle size, reaction time, or type of acid used. The residual Cr(VI) appears to be partially associated with poorly-ordered Fe and Al oxyhydroxides that precipitated in the interstitial areas of COPR particles. Remediation strategies that use HNO(3) or H(2)SO(4) to neutralize COPR or to maximize Cr(VI) in solution are likely to require extensive amounts of acid, may not mobilize all of the Cr(VI), and may require extended contact time, even under well-mixed conditions.     

Inactivation of Escherichia coli O157:H7 during thermophilic anaerobic digestion of manure from dairy cattle

Inactivation of the pathogenic Escherichia coli serotype O157:H7 and a non-pathogenic E. coli strain isolated from dairy cattle manure was evaluated with batch tests at 50 and 55 degrees C in biosolids from a thermophilic anaerobic digester treating the manure. Using differential-selective plating on sorbitol-MacConkey (SMAC) agar to quantify E. coli, the decline in concentrations of both the sorbitol-negative (putative E. coli O157:H7) and sorbitol-positive (putative non-pathogenic E. coli) organisms followed a model that assumed there was a heat-sensitive fraction and a heat-resistant fraction. Inactivation rates of the heat-sensitive fractions were similar for both colony types at each temperature, suggesting that wild-type E. coli can be used as an indicator of inactivation of serotype O157:H7. The decimal reduction time for the heat-sensitive fractions was in the order of 10min at 55 degrees C and ranged from approximately 1-3h at 50 degrees C. Concentrations of heat-resistant organisms at 55 degrees C were 1.4-1.7log(10)cfu/mL. Confirmatory analyses conducted on 30 randomly selected colonies of heat-resistant sorbitol-negative cells from treatment at 55 degrees C indicated that none were serotype O157:H7, nor were they E. coli. Similar analyses on 10 sorbitol-negative isolates from untreated manure indicated that none were serotype O157:H7, although 16S rRNA gene sequence analysis indicated that eight were E. coli or closely related enteric bacteria. These findings suggest that plating on differential-selective media to quantify E. coli, including serotype O157:H7, in effluent samples from thermophilic anaerobic digestion can lead to false positive results. Therefore, more specific methods should be used to evaluate the extent of thermal inactivation of both pathogenic and non-pathogenic E. coli in manure treatment systems.     

Factors affecting removal of selenate in agricultural drainage water utilizing rice straw

Microbial reduction of selenate [Se(VI)] to elemental selenium [Se(0)] is a useful technique for removing Se from agricultural drainage water. A series of batch experiments were conducted in the laboratory to determine the effects of pH (5-10), NO(3)(-) (100-500 mg/l), and SO(4)(2-) (0-5000 mg/l) on the removal of Se(VI) from drainage water with 1000 microg/l of Se(VI) and different amounts (1-4 g) of rice straw. Results showed that rice straw was very effective in creating a reducing environment (Eh=-205 to -355 mV) in the first 3 days of the pH-effect experiments. The optimum conditions for rapid Se(VI) removal from drainage water were a pH range of 6-9, high amounts of SO(4)(2-) (1000-5000 mg/l), low amounts of NO(3)(-) (100 mg/l) and high amounts of rice straw (3-4 g). Under these conditions, it took 5-7 days to reduce 93-95% of the added Se(VI) to Se(0). This study indicates that rice straw may be an inexpensive reducing agent to remediate Se(VI)-dominant San Joaquin Valley drainage water in the field.     

Spectrophotometric determination of ferrate (Fe(VI)) in water by ABTS

A new method for the determination of low concentrations (0.03-35 microM) of the aqueous ferrate (Fe(VI)) was developed. The method is based on the reaction of Fe(VI) with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) which forms a green radical cation (ABTS(+)) that can be measured spectrophotometrically at 415 nm (ABTS method). The reaction of Fe(VI) with ABTS has a stoichiometry of 1 : 1 in excess of ABTS (73 microM). The increase in absorbance at 415 nm for ABTS*+ generation was linear with respect to Fe(VI) added (0.03-35 microM) in buffered solutions (acetate/phosphate buffer at pH = 4.3) and was (3.40+/-0.05) x 10(4) M(-1) cm(-1). The reaction of Fe(VI) with ABTS was very rapid with a half-life time below 0.01 s at pH 4.3 and 73 microM of ABTS. This enables the ABTS method to measure Fe(VI) selectively. The residual absorbance of ABTS*+ was found to be stable in several water matrices (synthetic buffer solution and natural waters) and concentrations of Fe(VI) spiked in natural waters could be determined with high accuracy. The ABTS method can also be used as a tool to determine rate constants of reactions of Fe(VI). The second-order rate constant for the reaction of phenol with Fe(VI) was determined to be 90 M(-1) s(-1) at pH 7.     

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.     

Bio-reduction of soluble chromate using a hydrogen-based membrane biofilm reactor

Hexavalent chromium (Cr(VI)) is a mutagen and carcinogen that is a significant concern in water and wastewater. A simple and non-hazardous means to remove Cr(VI) is bioreduction to Cr(III), which should precipitate as Cr(OH)3(s). Since Cr(VI)-reducing bacteria can use hydrogen (H2) as an electron donor, we tested the potential of the H2-based membrane biofilm reactor (MBfR) for chromate reduction and removal from water and wastewater. When Cr(VI) was added to a denitrifying MBfR, Cr(VI) reduction was immediate and increased over 11 days. Short-term experiments investigated the effects of Cr(VI) loading, H2 pressure, and nitrate loading on Cr(VI) reduction. Increasing the H2 pressure improved Cr(VI) reduction. Cr(VI) reduction also was sensitive to pH, with an optimum near 7.0, a sharp drop off below 7.0, and a gradual decline to 8.2. Cr(III) precipitated after a small upward adjustment of the pH. These experiments confirm that a denitrifying, H2-based MBfR can be used to reduce Cr(VI) to Cr(III) and remove Cr from water. The research shows that critical operational parameters include the H2 concentration, nitrate concentration, and pH.     

Hydroxyapatite-supported Ag-TiO2 as Escherichia coli disinfection photocatalyst

A series of hydroxyapatite (HAP), 1wt% Ag-TiO(2) (AT1), 1wt% Ag-HAP and 5wt% AT1/HAP composite catalysts were prepared by incipient wetness and mechanical mixing methods. They were characterized by X-ray diffraction (XRD), FT-IR, SEM and ESCA analyses and their photocatalytic bactericidal activities were measured in suspension using Escherichia coli (E. coli), a water pollutant indicator. The surface analysis revealed that the Ag/Ti ratio is found to be ca. 0.0273 and also it indicated that the titania is present in the form of Ti(4+) and Ag is present as metallic silver. Both the XRD and ESCA analyses confirmed the phase of metallic Ag particles, which played a significant role on the bactericidal activity of the Ag doped TiO(2) catalysts. The FT-IR analysis of HAP revealed that the peak intensity is due to the absorbance of surface PO(4)(3-) group centered at wave number 1030cm(-1) and is drastically decreased upon exposure to UV for 1h. The HAP displayed high amount of bacteria adsorption, ca. 80% during the dark experiments compared to other catalytic systems tested. The cumulative photocatalytic properties of AT1/HAP catalytic system resulted in 100% E. coli bacteria reduction within 2min.     

Coliform culturability in over- versus undersaturated drinking waters

The culturability of Escherichia coli in undersaturated drinking water with respect to CaCO3 (corrosive water) or in oversaturated water (non-corrosive water) was tested in different reactors: glass flasks (batch, "non-reactive" wall); glass reactors (chemostat, "non-reactive" wall) versus a corroded cast iron Propella reactor (chemostat, "reactive" wall) and a 15-year-old distribution system pilot (chemostat, "reactive" wall with 1% corroded cast iron and 99% cement-lined cast iron). The E. coli in E. coli-spiked drinking water was not able to maintain its culturability and colonize the experimental systems. It appears from our results that the optimal pH for maintaining E. coli culturability was around 8.2 or higher. However, in reactors with a reactive wall (corroded cast iron), the decline in E. coli culturability was slower when the pH was adjusted to 7.9 or 7.7 (i.e. a reactor fed with corrosive water; pHpHs). We tentatively deduce that corrosion products coming from chemical reactions driven by corrosive waters on the pipe wall improve E. coli culturability.     

Evaluation of data from the literature on the transport and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated conditions

Escherichia coli and thermotolerant coliforms are of major importance as indicators of fecal contamination of water. Due to its negative surface charge and relatively low die-off or inactivation rate coefficient, E. coli is able to travel long distances underground and is therefore also a useful indicator of fecal contamination of groundwater. In this review, the major processes known to determine the underground transport of E. coli (attachment, straining and inactivation) are evaluated. The single collector contact efficiency (SCCE), eta0, one of two parameters commonly used to assess the importance of attachment, can be quantified for E. coli using classical colloid filtration theory. The sticking efficiency, alpha, the second parameter frequently used in determining attachment, varies widely (from 0.003 to almost 1) and mainly depends on charge differences between the surface of the collector and E. coli. Straining can be quantified from geometrical considerations; it is proposed to employ a so-called straining correction parameter, alpha(str). Sticking efficiencies determined from field experiments were lower than those determined under laboratory conditions. We hypothesize that this is due to preferential flow mechanisms, E. coli population heterogeneity, and/or the presence of organic and inorganic compounds in wastewater possibly affecting bacterial attachment characteristics. Of equal importance is the inactivation or die-off of E. coli that is affected by factors like type of bacterial strain, temperature, predation, antagonism, light, soil type, pH, toxic substances, and dissolved oxygen. Modeling transport of E. coli can be separated into three steps: (1) attachment rate coefficients and straining rate coefficients can be calculated from Darcy flow velocity fields or pore water flow velocity fields, calculated SCCE fields, realistic sticking efficiency values and straining correction parameters, (2) together with the inactivation rate coefficient, total rate coefficient fields can be generated, and (3) used as input for modeling the transport of E. coli in existing contaminant transport codes. Areas of future research are manifold and include the effects of typical wastewater characteristics, including high concentrations of organic compounds, on the transport of E. coli and thermotolerant coliforms, and the upscaling of experiments to represent typical field conditions, possibly including preferential flow mechanisms and the aspect of population heterogeneity of E. coli.     

Fe2O3有机物光催化降解有机染料的研究进展

探讨了Fe2O3/H2O2体系在可见光下降解有机染料的研究进展,采用Fe2O3/H2O2体系,对大红4BS、甲基橙等染料进行了光氧化降解实验,得出Fe2O3/H2O2/太阳光体系和Fe2O3/H2O2/UV体系在不同pH值条件下的光降解效率。     

Linear correlation between inactivation of E. coli and OH radical concentration in TiO2 photocatalytic disinfection

The biocidal action of the TiO2 photocatalyst has been now well recognized from massive experimental evidences, which demonstrates that the photocatalytic disinfection process could be technically feasible. However, the understanding on the photochemical mechanism of the biocidal action largely remains unclear. In particular, the identity of main acting photooxidants and their roles in the mechanism of killing microorganisms is under active investigation. It is generally accepted that reactive oxygen species (ROS) and OH radicals play the role. The aim of this study is to determine how the OH radical, acting either independently or in collaboration with other ROS, is quantitatively related to the inactivation of E. coli. The steady-state concentrations of OH radicals ([*OH]ss) in UV-illuminated TiO2 suspensions could be quantified from the measured photocatalytic degradation rates of p-chlorobenzoic acid (a probe compound) and its literature bimolecular rate constant with OH radicals. The results demonstrated an excellent linear correlation between [*OH]ss and the rates of E. coli inactivation, which indicates that the OH radical is the primary oxidant species responsible for inactivating E. coli in the UV/TiO2 process. The CT value of OH radical for achieving 2 log E. coli inactivation was initially found to be 0.8x10(-5) mg min/l, as predicted by the delayed Chick-Watson model. Although the primary role of OH radicals in photocatalytic disinfection processes has been frequently assumed, this is the first quantitative demonstration that the concentration of OH radicals and the biocidal activity is linearly correlated.     

Bioaccumulation of nickel from aqueous solutions by genetically engineered Escherichia coli

This study constructed a genetically engineered Escherichia coli JM109 which simultaneously expressed nickel transport system and metallothionein to remove and recover Ni(2+) from aqueous solution. Bioaccumulation process was rapid and followed linearized Langmuir isotherm. A more than six-fold increase of Ni(2+) binding capacity was obtained by genetically engineered E. coli cells compared with original host E. coli cells. A pH assay showed genetically engineered E. coli cells accumulated Ni(2+) effectively over a broad range of pH (4-10). The presence of 1000 mg/L Na(+) and Ca(2+), or 50mg/L Cd(2+) or Pb(2+) did not have a significant effect on Ni(2+) bioaccumulation, while Mg(2+), Hg(2+) and Cu(2+) posed a severe adverse influence on Ni(2+) uptake by genetically engineered E. coli. Furthermore, genetically engineered E. coli cells did not require extra nutrients for Ni(2+) bioaccumulation.     

pH effect on OH radical production in photo/ferrioxalate system

In wastewater treatment using the Fenton and photofenton processes, pH is one of the critical operating parameters, due to the fact that the Fenton reaction can work only under acidic pH conditions. It is hoped that Ferric iron complexed with oxalate (Fe(III)-oxalate; ferrioxalate) will provide an alternative to the traditional Fenton process with its limited range of pH conditions, since its high solubility in aqueous media can broaden the available pH range of the Fenton reaction up to the near neutral pH regime. In this study, we investigated the pH dependency of OH production in the photo/ferrioxalate system, in the presence and absence of externally supplied H(2)O(2), where 2,4--D was used as the probe compound for OH production at a wide range of pH values (1.2--7.4). In the absence of externally supplied H(2)O(2), the 2,4--D degradation was considerably enhanced with increasing pH, whereas it was reduced with increasing pH in the presence of an excess amount of H(2)O(2). These variations in the degradation of 2,4--D were thus found to be precisely related to the formation of H(2)O(2), a factor to which little attention was paid in previous studies. In the absence of H(2)O(2) addition, the in situ formation of H(2)O(2) is facilitated with increasing pH by the reaction of Fe(II) with O(2)(-), which increases with pH, augmenting the production of OH and thereby leading to the faster degradation of 2,4--D. This same reaction can also provide an explanation for the opposite pH dependence of 2,4--D degradation in the presence of H(2)O(2).     

Oxidation of suspected N-nitrosodimethylamine (NDMA) precursors by ferrate (VI): kinetics and effect on the NDMA formation potential of natural waters

The potential of ferrate (Fe(VI)) oxidation to remove N-nitrosodimethylamine (NDMA) precursors during water treatment was assessed. Apparent second-order rate constants (k(app)) for the reactions of NDMA and its suspected precursors (dimethylamine (DMA) and 7 tertiary amines with DMA functional group) with Fe(VI) were determined in the range of pH 6-12. Four model NDMA precursors (dimethyldithiocarbamate, dimethylaminobenzene, 3-(dimethylaminomethyl)indole and 4-dimethylaminoantipyrine) showed high reactivity toward Fe(VI) with k(app) values at pH 7 between 2.6 x 10(2) and 3.2 x 10(5)M(-1)s(-1). The other NDMA precursors (DMA, trimethylamine, dimethylethanolamine, dimethylformamide) and NDMA had k(app) values ranging from 0.55 to 9.1M(-1)s(-1) at pH 7. In the second part of the study, the NDMA formation potentials (NDMA-FP) of the model NDMA precursors and natural waters were measured with and without pre-oxidation by Fe(VI). For most of the NDMA precursors with the exception of DMA, a significant reduction of the NDMA-FP (>95%) was observed after complete transformation of the NDMA precursor. This result was supported by low yields of DMA from the Fe(VI) oxidation of tertiary amine NDMA precursors. Pre-oxidation of several natural waters (rivers Rhine, Neckar and Pfinz) with a high dose of Fe(VI) (0.38 mM = 21 mg L(-1) as Fe) led to removals of the NDMA-FP of 46-84%. This indicates that the NDMA precursors in these waters have a low reactivity toward Fe(VI) because it has been shown that for fast-reacting NDMA precursors Fe(VI) doses of 20 microM (1.1 mg L(-1) as Fe) are sufficient to completely oxidize the precursors.     

Struvite precipitation thermodynamics in source-separated urine

Struvite (MgNH(4)PO(4).6H(2)O) precipitation eliminates phosphate efficiently from urine, a small but highly concentrated stream in the total flux of domestic wastewater. Precipitation experiments with hydrolysed urine evaluated the solubility product of struvite. The stored and fully hydrolysed urine had an ionic strength of between 0.33 and 0.56M and required the estimation of activity coefficients. From our data, we identified the Davies approximation with the two constants A=0.509 and B=0.3 as agreeing best with our laboratory results. The standard solubility product K(s)(0)=f(1)[NH4(+)]f(2)[Mg2+]f(3)[PO(4)(3-)] ([ ]=concentration of the species; f(x)=corresponding activity coefficient) of struvite in urine was found to be 10(-13.26+/-0.057) at 25 degrees C and the enthalpy of struvite formation DeltaH was 22.6(+/-1.1) kJmol(-1). The equilibrium calculations required the following dissolved complexes: [MgCO(3)](aq), [MgHCO(3)](+), [MgPO(4)](-), [NH4HPO4and [NaHPO(4)](-) and to a lesser extent [MgSO(4)](aq) and [NH(4)SO(4)](-). Organic complexes do not seem to influence the solubility product substantially. For practical purposes, a conditional solubility product K(s)(cond)=[Mg(aq)].[NH(4)(+)+NH(3)].[P(ortho)]=10(-7.57)M(3) was derived to calculate struvite solubility in urine at 25 degrees C, pH=9.0 and ionic strength I=0.4M directly from measured concentrations.     

Ferrate(VI) oxidation of glycine and glycylglycine: Kinetics and products

Amino acids and peptides may form potentially harmful disinfection byproducts during the conventional treatment of water and wastewater. Removal of these parent compounds by the use of the environmental-friendly oxidant, ferrate(VI) (Fe^VIO₄²⁻, Fe(VI)) was assessed by studying the kinetics of the oxidation of glycine (NH₃⁺CH₂COOH, Gly) and glycylglycine (NH₃⁺CH₂CONHCH₂COOH, Gly-Gly) as a function of pH (4.0-12.4) at 25 °C. This study with Gly-Gly represents an initial investigation of oxidation of peptides by Fe(VI). Generally, the second-order rate constant (k) increased with decreased pH in the basic pH region, but this trend was reversed in the acidic pH range. Consideration of the reactivity of three oxidants (H₂FeO₄, HFeO₄⁻, and FeO₄²⁻) with three species of Gly and Gly-Gly (positive, neutral, and negative) reasonably explained the pH dependence of the rates. At pH 9.0, the molar consumption of Fe(VI) was nearly equal to that of Gly. The reaction of Fe(VI) with Gly at molar ratios of 1.0 and 2.0 ([Fe(VI)]:[Gly]) produced ammonia, carbon dioxide, and acetate. A reaction scheme is proposed which explains the formation of these products. The values of k for oxidation of iminodiacetate and nitriloacetate at pH 7.0 were also determined in order to compare oxidation of amines by Fe(VI). The calculated half-lives at neutral pH for the oxidation of primary and secondary amines were in seconds while decomposition of tertiary amines would occur in minutes. Overall, the reactivity of Fe(VI) with Gly and Gly-Gly indicates the significant potential of Fe(VI) to remove amine- and peptide-containing pollutants in water and wastewater.