Pseudo-first Order Degradation Rate Constants Research Articles

Hydrogen peroxide and persulfate activation using UVA-UVB radiation: Degradation of estrogenic compounds and application in sewage treatment plant waters

In the present work, the degradation of three estrogens (17β-estradiol (E2), estrone (E1) and 17α-ethinylestradiol (EE2)) was investigated under photoactivation of hydrogen peroxide and persulfate. Lab-scale irradiation experiments showed that both UVA and UVB radiations are able to photoactivate the oxidant precursors, although UVB is more efficient to generate radicals and therefore to degrade the targets. The efficiency of both oxidant precursors was investigated showing higher efficiency in the system with persulfate. The pseudo-first order degradation rate constants and the second order rate constants between the hydroxyl or the sulfate radicals and estrogens were measured. In order to evaluate the process efficiency in real treatment conditions, the degradation of the estrogens spiked into sewage treatment plant effluent was studied. Measurements of second order rate constants between the radical and the effluent organic matter by laser flash photolysis allowed to understand the involved quenching mechanisms. A Yeast Estrogen Screen (YES) assay was used to follow the decrease in estrogenic activity during the estrogen degradation. This assay permitted to ensure that the studied processes are not only able to degrade the estrogens but also to remove their estrogenic activity.

Coupling of nanofiltration and UV, UV/TiO2 and UV/H2O2 processes for the removal of anti-cancer drugs from real secondary wastewater effluent

The detection of anti-cancer drugs in surface waters at ng/L indicates that most wastewater treatment processes currently applied are not effective enough to remove these resilient compounds from wastewater. Therefore alternative treatment processes should be tested to avoid discharges in the environment of drugs that have been linked to genotoxic effects. The innovative contribution of this study stands in coupling nanofiltration with advanced oxidation processes to treat real secondary wastewater effluents spiked with 4 widely consumed anti-cancer drugs. Direct photolysis was found to be extremely effective to degrade etoposide and paclitaxel from the secondary effluent as well as from the highly concentrated retentate produced by nanofiltration. The two drugs were not detected after 10 min of exposure that corresponds to higher than 98% removals given the method detection limits by direct injection. This is equivalent to pseudo-first order degradation rate constants higher than 0.46 min−1, which, to the best of the author's knowledge, has not yet been reported for paclitaxel in the literature. However, none of the tested oxidation processes (UV, UV/TiO2 and UV/H2O2) using the reactor setup, exposure times and concentrations of TiO2 and H2O2 tested, were able to degrade cyclophosphamide or ifosfamide effectively. Compared to literature data, this is probably related to the low amount of photons received by the treated media. Finally important aggregation of catalyst particles was observed in secondary effluent, and photocatalysis had no advantage compared to the other two processes tested.

Field demonstration of N-Nitrosodimethylamine (NDMA) treatment in groundwater using propane biosparging

N-Nitrosodimethylamine (NDMA) is found in groundwater and drinking water from industrial, agricultural, water treatment, and military/aerospace sources, and it must often be treated to part-per-trillion (ng/L) concentrations. The most effective remedial technology for NDMA in groundwater is pump-and-treat with ultraviolet irradiation (UV), but this approach is expensive because it requires ex situ infrastructure and high energy input. The objective of this project was to evaluate an in situ biological treatment approach for NDMA. Previous laboratory studies have revealed that propane-oxidizing bacteria are capable of biodegrading NDMA from μg/L to low ng/L concentrations (Fournier et al., 2009; Webster et al., 2013). During this field study, air and propane gas were sparged into an NDMA-contaminated aquifer for more than 1 year. Groundwater samples were collected throughout the study from a series of monitoring wells within, downgradient, and sidegradient of the zone of influence of the biosparge system. Over the course of the study, NDMA concentrations declined by 99.7% to >99.9% in the four monitoring wells within the zone of influence of the biosparge system, reaching low ng/L concentrations whereas the control well declined by only 14%. Pseudo first-order degradation rate constants for NDMA in system monitoring wells ranged from ∼0.019 day −1 to 0.037 day −1 equating to half-lives ranging from 19 to 36 days. Native propanotrophs increased by more than one order of magnitude in the propane-impacted wells but not in the control well. The field data show for the first time that propane biosparging can be an effective in situ approach to reduce the concentrations of NDMA in a groundwater to ng/L concentrations.

Destruction of phenicol antibiotics using the UV/H2O2 process: Kinetics, byproducts, toxicity evaluation and trichloromethane formation potential

Phenicol antibiotics (PABs) degradation by UV/H2O2 is important because we need to determine the reduction in toxicity and disinfection byproducts for post-chlorine. In this study, the degradation of PABs, including florfenicol (FLO), chloramphenicol (CAP) and thiamphenicol (THA), was examined. The pseudo-first order degradation rate constants of PABs were 3 times higher in ultrapure water (UW) than that in synthetic wastewater (SW) for these conditions: [PABs]0 = 1 μM, [H2O2] = 0.1 mM, and I0 = 1.985 × 10−6 E L−1 s−1. Fulvic acid (FA) and HCO3– inhibited PABs degradation, Cl− and NO3– concentrations of up to 5 mM and 10 mM had a negligible impact. The impact of water matrix on PABs degradation was successfully predicted using pseudo-steady-state kinetic model. The degradation of PABs was triggered via hydroxylation and/or hydrogen abstraction. The treatment of PABs via UV/H2O2 could decrease their antimicrobial properties, while the byproducts of FLO and THA showed higher acute toxicity in Vibrio fischeri. In addition, two identification products (TP-276 and TP-354) of FLO had higher ecotoxicity toxicity (using ECOSAR) in fish, daphnid and green algae. The trichloromethane formation potential (TCMFP) for PABs with post-chlorination in UW and SW can be reduced after UV/H2O2 compared to UV, and is related to the corresponding decrease of dissolved organic carbon (DOC).

Effect of field site hydrogeochemical conditions on the corrosion of milled zerovalent iron particles and their dechlorination efficiency

Milled zerovalent iron (milled ZVI) particles have been recognized as a promising agent for groundwater remediation because of (1) their high reactivity with chlorinated aliphatic hydrocarbons, organochlorine pesticides, organic dyes, and a number of inorganic contaminants, and (2) a possible greater persistance than the more extensively investigated nanoscale zerovalent iron. We have used laboratory-scale batch degradation experiments to investigate the effect that hydrogeochemical conditions have on the corrosion of milled ZVI and on its ability to degrade trichloroethene (TCE). The observed pseudo first-order degradation rate constants indicated that the degradation of TCE by milled ZVI is affected by groundwater chemistry. The apparent corrosion rates of milled ZVI particles were of the same order of magnitude for hydrogeochemical conditions representative for two contaminated field sites (133–140mmolkg−1day−1, indicating a milled ZVI life-time of 128–135days). Sulfate enhances milled ZVI reactivity by removing passivating iron oxides and hydroxides from the Fe0 surface, thus increasing the number of reactive sites available. The organic matter content of 1.69% in the aquifer material tends to suppress the formation of iron corrosion precipitates. Results from scanning electron microscopy, X-ray diffraction, and iron K-edge X-ray adsorption spectroscopy suggest that the corrosion mechanisms involve the partial dissolution of particles followed by the formation and surface precipitation of magnetite and/or maghemite. Numerical corrosion modeling revealed that fitting iron corrosion rates and hydrogen inhibitory terms to hydrogen and pH measurements in batch reactors can reduce the life-time of milled ZVI particles by a factor of 1.2 to 1.7.

Effect of boron on reactivity and apparent corrosion rate of microscale zerovalent irons

The reactivity and apparent corrosion rate of newly produced boron-alloyed microscale zerovalent iron (mZVI) particles toward a variety of chlorinated aliphatic hydrocarbons (CAHs) were assessed in laboratory-scale batch reactors. For comparison, commercially available nanoscale zerovalent irons (nZVIs) were also included in the study. Based on mass normalized (kM) pseudo first-order degradation rate constants, the reactivity of boron-alloyed mZVIs appeared to be one order of magnitude lower than most reactive nZVI. However, specific surface area normalized reaction rate constants (kSA) were 1–2 orders of magnitude higher than for nZVIs showing that boron-alloyed mZVIs can compete with nZVIs. The high reactivity of boron-alloyed mZVIs was attributed to (1) the prevented iron surface passivation during anaerobic corrosion due to the simultaneous iron and boron dissolution kinetics preventing the formation of insoluble oxidized iron species, (2) the involvement of boron in facilitating electron transfer by inducing β-elimination followed by hydrogenation to ethane and/or (3) involvement of boron in improved particle size reduction during milling process leading to increased active surface areas of the particles. Results of this study suggest that boron-alloyed mZVIs could be an efficient alternative to nZVIs for in situ groundwater remediation of different CAHs in terms of their reactivity and apparent corrosion rate.

Catalytic ozonation of an industrial textile wastewater in a heterogeneous continuous reactor

Textile wastewaters (WWs) are highly colored and non-biodegradable having variable compositions of colored dyes, surfactants and toxic chemicals. Discharge of these WWs to the environment is very detrimental for ecosystems, therefore new methods have been investigated in order to meet the quality criteria of water and the discharge standards of the partly treated WWs. Recently, catalytic ozonation being one of the advanced oxidation processes (AOPs), is considered as an effective method that can be used in the treatment of industrial WWs. In this study, catalytic ozonation of industrial textile WW obtained from AKSA Textile Plant in Yalova/Turkey has been examined in a three phase reactor where the solid catalyst phase was fluidized at different experimental conditions. The effects of inlet chemical oxygen demand (COD) value, pH, different catalyst types [perfluorooctylalumina (PFOA) and alumina] and gas to liquid flow rate ratios (QG/QL) have been determined. Pseudo-first order degradation rate constants for the dyes in the real industrial textile WW were determined in terms of COD, by taking samples at different heights along the reactor during an experimental run at steady state. Moreover, “absorbance vs. concentration” calibration correlations were developed to estimate the concentrations of colored dyes in the sample. This provided the opportunity to measure the dye concentrations and estimate the percent removals of each dye in the samples, separately. Besides COD removals, also total organic carbon (TOC) removals and ozone consumptions were measured and discussed by comparing the results obtained in both sole and catalytic ozonation experiments.

Effect of phenolic compounds on photodegradation of anthracene and benzo[a]anthracene in media of different polarity

Abstract The photodegradation of anthracene (Ant) and benz[a]anthracene (BaA) were studied in air-equilibrated hexane, methanol and pure water solutions in the absence and presence of phenolic compounds (4-methylcatechol, guaiacol and syringol). In the absence of phenolic compound, the pseudo first-order degradation rate constants of Ant and BaA increased with the polarity of solvent, demonstrating the influence of solvent effects on the photoreactivity. The differences can be attributed to factors such as the proton donating potential of the solvent, and the formation potentials of PAH radical cation and hydroxyl radical in solvent. In the presence of phenolic compound, Ant and BaA photodegradation rates were accelerated in hexane and methanol while inhibited in water solutions. Photodegradation kinetics of the phenolic compounds were also measured; and visible colored products were observed in all three solvents. The observed accelerations of Ant and BaA photodecay in the presence of the phenolic compounds can be explained by energy transfer from the phenolic compound to PAH, phenolic hydrogen abstraction by excited PAH and more reactive radical formation from the phenolic compound. However, the inhibition effects of Ant and BaA photodecay in water were more influenced by the quenching of photo-produced reactive oxygen species (ROS) by the phenolic compound and/or its photoproducts. The results indicate that the photodegradation of PAHs will be highly dependent on the aerosol water content. i.e., the chemical composition of the environmental aerosols.

자외선과 초음파를 동시에 조사하는 연계 공정의 시너지 효과에 관한 연구

본 연구는 UV와 US를 함께 조사하는 UV/US 연계 공정을 통해 발생하는 시너지 효과를 조사하고, 이를 효과적으로 오염물질 처리 공정에 적용 가능한지에 대하여 연구하였다. US를 조사하는 경우에는 <TEX>$H_2O_2$</TEX>의 농도가 지속적으로 증가하지만, UV/US를 동시에 조사한 경우 <TEX>$H_2O_2$</TEX>의 농도가 증가하는 속도가 점점 감소하여 일정 농도로 수렴하는 포화속도곡선의 경향을 보였으며, US가 단독으로 조사되었을 때 생성된 <TEX>$H_2O_2$</TEX>와 UV/US 연계 공정을 통해 생성된 <TEX>$H_2O_2$</TEX>와의 차이가 오염물질 제거율 향상에 시너지 효과를 일으킨다고 판단된다. 시너지 효과를 검증하기 위해 인체에 유해한 영향을 미치는 가소제 중 하나인 bis(2-ethylhexyl) phthalate(DEHP)를 이용하여 제거실험을 실시하였다. UV와 US를 동시에 조사하는 UV/US 연계 공정의 경우 DEHP의 제거 유사 일차반응 속도상수(k1)가 <TEX>$14.81{\times}10^{-3}min^{-1}$</TEX>로 UV만 조사하는 경우의 <TEX>$2.60{\times}10^{-3}min^{-1}$</TEX>과 US만 조사하는 경우의 <TEX>$10.34{\times}10^{-3}min^{-1}$</TEX>보다 더 큰 것을 확인하였다. 이를 통해 UV/US 연계 공정에서 DEHP의 제거가 더 활발하게 일어남을 확인하였으며, 이는 시너지 효과에 의한 것이라 판단된다. 또한 DEHP 제거 유사 일차반응 속도상수 값을 이용하여 시너지 효과를 이론적으로 계산한 결과 시너지 효과 값은 1.15로 나타나 기준값인 1보다 큰 값을 가지므로 시너지 효과가 발생했다고 판단된다. Both ultraviolet (UV) and ultrasound (US) systems are used in degrading of organic contaminants and they can thus be applicable simultaneously as an UV/US hybrid system in attempts further to increase the degradation efficiency. The pseudo-first order degradation rate constants with the UV, US and UV/US hybrid irradiation were 2.60, 10.34, and <TEX>$14.81{\times}10^{-3}min^{-1}$</TEX>, respectively. It was observed that the synergistic effect of UV/US hybrid system for degrading the bis (2-ethylhexyl) phthalate (DEHP). The highest rate of DEHP degradation was found during UV/US hybrid irradiation and the synergistic effect factor (SEF) was calculated to be 1.15 based on the pseudo-first order degradation rate constants. Results indicate that synergistic effect of UV/US hybrid system is closely correlated to the enhancement of sonochemical reactivity with the UV-US interaction of increasing the formation rate of OHby providing additional <TEX>$H_2O_2$</TEX> production through the pyrolysis of water molecules during UV/US hybrid irradiation.

초음파 (US)와 다양한 파장범위의 자외선 (UV) 조사에 따른 DEP 분해특성에 관한 연구

Diethyl phthalate (DEP) is widely spread in the natural environment as an endocrine disruption chemicals (EDs). Therefore, in this study, ultrasound (US) and ultraviolet (UVC), including various applied power density (10-40 W/L), UV wavelengths (365 nm, 254 nm and 185 nm) and frequencies (283 kHz, 935 kHz) were applied to a DEP contaminated solution. The pseudo-first order degradation rate constants were in the order of <TEX>$10^{-1}$</TEX> to <TEX>$10^{-4}\;min^{-1}$</TEX> depending on the processes. Photolytic and sonophotolytic DEP degradation rate also were high at shortest UV wavelength (VUV) due to the higher energy of photons, higher molar absorption coefficient of DEP and increased hydroxyl radical generation from homolysis of water. Sonolytic DEP degradation rate increased with increase of applied input power and the dominant reaction mechanism of DEP in sonolysis was estimated as hydroxyl radical reaction by the addition of t-BuOH, which is a common hydroxyl radical scavenger. Moreover, synergistic effect of were also observed for sonophotolytic degradation with various UV irradiation.

Sonophotolytic Degradation of Estriol at Various Ultraviolet Wavelength in Aqueous Solution

This study investigated degradation of the hormone estriol by sonolysis, photolysis and sonophotolysis at various UV wavelengths. Degradation was determined with UVA (365 nm), UVC (254 nm), or VUV (185 nm) irradiation and/or ultrasound exposure (283 kHz). The pseudo-first order degradation rate constants were in the order of 10-1 to 10-4 min-1 depending on the processes. The dominant reaction mechanism of estriol in sonolysis was estimated as hydroxyl radical reaction by the addition of tert-butanol (t-BuOH), which is a common hydroxyl radical scavenger. Photolytic and sonophotolytic estriol degradation rate also were high at shortest UV wavelength (VUV) due to the higher energy of photons, higher molar absorption coefficient of estriol and increased hydroxyl radical generation from the homolysis of water. Small synergistic effects were observed for sonophotolytic degradation with UVA and UVC irradiation. No synergy was observed for sonophotolysis with VUV irradiation.

광촉매 공정에 따른 이부프로펜의 분해 특성

In this study, Ibuprofen (IBP) degradation by the photo catalytic process was investigated under various parameters, such as UV intensity, optimum dosage of <TEX>$TiO_2$</TEX>, alkalinity, temperature and pH of bulk solution. The pseudo-first order degradation rate constants were in the order of <TEX>$10^{-1}$</TEX> to <TEX>$10^{-4}min^{-1}$</TEX> depending on each condition. The Photocatalytic IBP degradation rate increased with an increase in the applied UV power. At high UV intensity a high rate of tri-iodide (<TEX>$I_3{^-}$</TEX>) ion formation was also observed. Moreover, in order to avoid the use of an excess catalyst, the optimum dosage of catalyst under the various UV intensities (30 and 40 W/L) was examined and ranged from approximately 0.1 <TEX>$gL^{-1}$</TEX>. The photo catalytic IBP degradation rate was changed depending on the alkalinity and temperature and pH in the aqueous solution. This study demonstrated the potential of photo catalytic IBP degradation under different conditions.

Decomposition of cyclohexanoic acid by the UV/H2O2 process under various conditions

Naphthenic acids (NAs) are a broad range of alicyclic and aliphatic compounds that are persistent and contribute to the toxicity of oil sands process affected water (OSPW). In this investigation, cyclohexanoic acid (CHA) was selected as a model naphthenic acid, and its oxidation was investigated using advanced oxidation employing a low-pressure ultraviolet light in the presence of hydrogen peroxide (UV/H2O2 process). The effects of two pHs and common OSPW constituents, such as chloride (Cl−) and carbonate (CO32−) were investigated in ultrapure water. The optimal molar ratio of H2O2 to CHA in the treatment process was also investigated. The pH had no significant effect on the degradation, nor on the formation and degradation of byproducts in ultrapure water. The presence of CO32− or Cl− significantly decreased the CHA degradation rate. The presence of 700mg/L CO32− or 500mg/L Cl−, typical concentrations in OSPW, caused a 55% and 23% decrease in the pseudo-first order degradation rate constants for CHA, respectively. However, no change in byproducts or in the degradation trend of byproducts, in the presence of scavengers was observed. A real OSPW matrix also had a significant impact by decreasing the CHA degradation rate, such that by spiking CHA into the OSPW, the degradation rate decreased up to 82% relative to that in ultrapure water. The results of this study show that UV/H2O2 AOP is capable of degrading CHA as a model NA in ultrapure water. However, in the real applications, the effect of radical scavengers should be taken into consideration for the achievement of best performance of the process.

Significant diethyl phthalate (DEP) degradation by combined advanced oxidation process in aqueous solution

Ultrasound (US) combined with ultraviolet (UV) irradiation and a titanium dioxide (TiO(2)) catalyst was used to effectively remove diethyl phthalate (DEP) from aqueous solutions. Single (sonolysis, photolysis, photocatalysis) and combined (sonophotolysis, sonophotocatalysis) processes were performed to confirm the synergistic effects and DEP degradation mechanism. Using only US, the optimum frequency for DEP degradation was 283kHz. At this frequency a high rate of hydrogen peroxide (H(2)O(2)) formation was observed of approximately 0.32mMmin(-1). The pseudo-first order degradation rate constants were 10(-2)-10(-4)min(-1) depending on the process. Significant degradation and mineralization (TOC) of DEP were observed with the sonophotolytic and sonophotocatalytic processes. Moreover, synergistic effects of 1.29 and 1.95 were exhibited at the sonophotocatalytic and sonophotolytic DEP degradation, respectively. Furthermore, additional advantageous reactions may occur in the heterogeneous sonophotocatalytic process due to interactions between US, UV, and the photocatalyst.

Sonophotolytic diethyl phthalate (DEP) degradation with UVC or VUV irradiation

This study investigated the degradation of diethyl phthalate (DEP) by sonolytic, photolytic and sonophotolytic processes. Two types of UV lamps, UVC (254nm) and VUV (185nm+254nm), were combined with ultrasound (283kHz). The pseudo-first order degradation rate constants were in the order of 10−1–10−3min−1 depending on the processes. The sonolytic DEP degradation rate increased with increasing applied power. Photolytic or sonophotolytic degradation of DEP when using a VUV lamp appeared to be effective because the photo ІІ (UVC/VUV) resulted in a significantly faster degradation than the photo І (UVC) processes due to the higher photon energy and higher hydroxyl radical generation by homolysis of water by VUV. Significant degradation and mineralization (TOC) of DEP were observed with the combined sonophotolytic processes. Moreover, synergistic effects of 1.68 and 1.23 were exhibited at DEP degradation of the sonophoto I and sonophoto II processes, respectively. This was attributed to the UV-induced dissociation of hydrogen peroxide (H2O2) generated by the application of US to hydroxyl radicals. Therefore, US in sonophotolytic processes can play an important role in enhancing DEP degradation. Moreover, the sonophoto ІІ process is more effective on the mineralization and biodegradability of DEP.

Comparative efficiencies of the decolourisation of Methylene Blue using Fenton’s and photo-Fenton’s reactions

The decolourisation and mineralization of Methylene Blue azo dye (MB) under Fenton's and photo-Fenton's conditions have been studied. Some parameters, such as initial concentrations of iron (Fe(2+)) and fixed hydrogen peroxide (H(2)O(2)), were evaluated to find the optimal conditions for the efficient degradation of azo dye. The experimental assays showed better efficiency for the photo-Fenton's system. Pseudo-first order degradation rate constants were obtained from batch experimental set up. It is suggested that photo-Fenton's reactions are viable processes for treatment of azo dye MB, according to the high levels of colour (UV(665)) and total organic carbon (TOC) removal.

Study of kinetic parameters related to the decolourization and mineralization of reactive dyes from textile dyeing using Fenton and photo-Fenton processes

The decolourization and mineralization of two reactive azo dyes, Procion Red H-E7B (CI Reactive Red 141) and Cibacron Red FN-R (CI Reactive Red 238), under Fenton's and photo-Fenton's conditions have been investigated. Some parameters, like temperature, initial concentrations of Fe(II) and H 2O 2 and the use of natural or artificial light were evaluated aiming to find the optimal conditions to promote the efficient degradation of the dyes. The experimental results showed that the Fenton's process run under solar light was the most effective. Pseudo-first order degradation rate constants were obtained from batch experimental data. It is suggested that Fenton's and photo-Fenton's type reactions are viable techniques for the treatment of such types of reactive dyes, according to the high levels of colour, aromatic content (UV 254) and DOC removal.

Kinetic modeling of the radiolytic degradation of Acid Orange 7 in aqueous solutions

The degradation of Acid Orange 7 (AO7) in aqueous solutions induced by gamma-ray irradiation was investigated in terms of both the disappearance of parent molecule (decoloration) and the degree of mineralization. The disappearance of AO7 followed pseudo first-order kinetics, whereas its mineralization could be described by zero-order kinetics. The pseudo first-order degradation rate constants were found to be proportional to irradiation dose rates and the reciprocals of initial AO7 concentrations. Based on the experimental results and a reaction analysis on the steady-state radiolysis of aerated aqueous solutions, a kinetic model was developed for describing the radiolytic degradation of AO7. Moreover, with this kinetic model, the reaction rate constants of e(aq)(-) and H. with AO7 were estimated as 3.0 x 10(9) and 8.4 x 10(9) x L mol(-1) s(-1), respectively. Taking the relative contributions of oxidative and reductive species to AO7 degradation into account, oxidative radiolysis proved to be a better approach for the degradation of AO7.

Comparison treatment of various chlorophenols by electro-Fenton method: relationship between chlorine content and degradation

This study describes a comparative degradation of various chlorophenols by electro-Fenton method. Chloride released and reaction intermediate products were determined by ionic chromatography (IC) and gas chromatography/mass spectrometry (GC/MS). Using pentachlorophenol (PCP) as the model compound, we investigated the effects of cell voltage, electrolyte concentration and pH to optimize the degradation conditions. It was noted that the addition of small quantities of Fe 3+ or Fe 2+ significantly accelerated the degradation rate. Under the optimal conditions, electro-Fenton method was used to treat various chlorophenols including PCP, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and their mixture aqueous solutions. Their pseudo first-order degradation rate constants at the first stages were calculated and compared, which gave the following sequence: 2,4-DCP > 2,4,6-TCP > PCP > 4-CP. The relationship between the chlorine content and degradation rate was discussed and compared with other advanced oxidation processes. Finally, we proposed the degradation pathways of different chlorophenols.

Ultimate biodegradation of alkylphenol ethoxylate surfactants and their biodegradation intermediates

The ultimate biodegradation of the commercial products nonylphenol ethoxylates (NPE9), octylphenol ethoxylates (OPE9), and their biodegradation intermediates, NPE1.5, OPE1.5, NP, and OP, was measured using conventional methods. The extent of biodegradation was also determined by gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography (HPLC) analysis of metabolites and measurement of dissolved organic carbon. Optimized pseudo-first order degradation rate constants and half-lives were calculated from these data and from previously published data, using Larson's equation for surfactant degradation kinetics. Ultimate aerobic biodegradation of alkylphenol ethoxylates and their biodegradation intermediates has now been examined using acclimated wastewater treatment plant sludge as the microbial seed, household wastewater treatment systems, and unacclimated fresh water, seawater, and soil. Ultimate biodegradation half-lives ranged from about one to four weeks and provide definitive evidence for the extensive biodegradability of alkyphenol ethoxylates (APE) surfactants and their metabolites and their lack of persistence in the environment.