Propham mineralization in aqueous medium by anodic oxidation using boron-doped diamond anode: influence of experimental parameters on degradation kinetics and mineralization efficiency

This study aims the removal of a carbamate herbicide, propham, from aqueous solution by direct electrochemical advanced oxidation process using a boron-doped diamond (BDD) anode. This electrode produces large quantities of hydroxyl radicals from oxidation of water, which leads to the oxidative degradation of propham up to its total mineralization. Effect of operational parameters such as current, temperature, pH and supporting electrolyte on the degradation and mineralization rate was studied. The applied current and temperature exert a prominent effect on the total organic carbon (TOC) removal rate of the solutions. The mineralization of propham can be performed at any pH value between 3 and 11 without any loss in oxidation efficiency. The propham decay and its overall mineralization reaction follows a pseudo-first-order kinetics. The apparent rate constant value of propham oxidation was determined as 4.8×10⁻⁴ s⁻¹ at 100 mA and 35 °C in the presence of 50 mM Na₂SO₄ in acidic media (pH: 3). A general mineralization sequence was proposed considering the identified oxidation intermediates.     

Causes and consequences of desertification in Kuwait: a case study of land degradation

Desertification in Kuwait is a process of environmental degradation under fragile ecological conditions and intensive human activities and the consequences of Gulf War. In Kuwait, very severe desertification prevails, due to increasing formation of new active sandy bodies, deterioration of many areas of natural vegetation cover to less than 10%, and limited water resources for large-scale forage production. Average annual desertified land in Kuwait is estimated to be 285 km². In Kuwait, three indicators of land degradation are encountered. These are vegetation, soil, and surface hydrological changes. Based on field measurements of soil compaction and vegetation changes, in the west Jahra area in the northern part of the country, degradation levels were assessed. Results of these measurements show that the average infiltration rate in compacted soil decreased by 53.8% in comparison with non-compacted soil, while the average soil penetration resistance in compacted soil increased by 154.1% in comparison with non-compacted soil. The bulk density in open sites was 23.4% higher than that in protected sites. The percentage of litter in open sites decreased by 77.3% in comparison with protected sites, while the percentage of total vegetation in open sites decreased by 6.1% in comparison with protected sites. Electronic Publication     

Toxicity of chlorpyrifos and TCP alone and in combination to Daphnia carinata: the influence of microbial degradation in natural water

The acute toxicity of chlorpyrifos and its principal metabolite 3,5,6-trichloropyridinol (TCP) alone and in combination to a cladoceran, Daphnia carinata, was studied in both cladoceran culture medium and natural water collected from a local suburban stream. TCP was found to be more toxic than its parent chemical chlorpyrifos to Daphnia survival in cladoceran culture medium. However, TCP in natural water was not toxic to D. carinata up to 2 microgL(-1). The LC(50) values for chlorpyrifos, TCP and chlorpyrifos+TCP were 0.24, 0.20 and 0.08 microgL(-1), respectively, in cladoceran culture medium. Although the parent chemicals and their degradation products co-exist in natural waters, the existing guidelines for water quality are based on individual chemicals. The results of this investigation suggest that chlorpyrifos and TCP can interact synergistically, additively or antagonistically, resulting in an increase or decrease in the overall toxicity of the mixture compared to individual compounds. The indigenous microorganisms in natural water could play a significant role in degradation of these compounds thereby influencing their toxicity in receiving waters. This study clearly suggests that the joint action of pesticides and their degradation products should be considered in the development of water quality guidelines. To our knowledge, this is the first study on the interactive effect of chlorpyrifos and TCP to a cladoceran and suggests that these two compounds are non-toxic when present together at concentrations up to 0.12 microgL(-1). However, these compounds together act additively at and above 0.5 microgL(-1) to fresh water invertebrates and therefore pollution with these compounds may adversely affect natural ecosystems.     

Rapid and complete destruction of perchlorate in water and ion-exchange brine using stabilized zero-valent iron nanoparticles

Perchlorate has emerged as a widespread contaminant in groundwater and surface water. Because of the unique chemistry of perchlorate, it has been challenging to destroy perchlorate. This study tested the feasibility of using a new class of stabilized zero-valent iron (ZVI) nanoparticles for complete transformation of perchlorate in water or ion-exchange brine. Batch kinetic tests showed that at an iron dosage of 1.8 g L(-1) and at moderately elevated temperatures (90-95 degrees C), approximately 90% of perchlorate in both fresh water and a simulated ion-exchange brine (NaCl=6% (w/w)) was destroyed within 7h. An activation energy (Ea) of 52.59+/-8.41 kJ mol(-1) was determined for the reaction. Kinetic tests suggested that Cl(VII) in perchlorate was rapidly reduced to chloride without accumulation of any intermediate products. Based on the surface-area-normalized rate constant k(SA), starch- and CMC-stabilized ZVI nanoparticles degraded perchlorate 1.8 and 3.3 times, respectively, faster than non-stabilized ZVI particles. Addition of a metal catalyst (Al, Cu, Co, Ni, Pd, or Re) did not show any reaction improvement. This technology provides an effective method for complete destruction of perchlorate in both contaminated water and brine.     

纳米材料TiO2光催化在IAQ中的应用研究

分析了纳米TiO2光催化处理室内VOC的反应机理，以三种室内常见的探发性有机物为例，分析了单一初始浓度、室内湿度、紫外光强、迎面风速、温度等因素的影响，及其与反应速率的曲线，并与动力学模型L－H进行比较，趋势预测结果满意。     

Effect of nonionic surfactants on the oxidation of carbaryl by anodic Fenton treatment

As a potentially promising technology, anodic Fenton treatment (AFT) has been shown to be very successful in pesticide removal. However, the influence of other constituents in the pesticide formulation, such as nonionic surfactants, has not been addressed. In this study, the effect of Triton X (TX) on the degradation kinetics and pathways of carbaryl undergoing AFT was investigated in an effort to facilitate its practical application. The presence of Triton X-100 was found to slow down the carbaryl degradation rate. This result can be attributed to the consumption of hydroxyl radicals ((*)OH) by surfactants and the formation of a carbaryl...TX...Fe(3+) complex, resulting in the unavailability of carbaryl to (*)OH attack. The modified AFT kinetic model previously developed in this laboratory shows an excellent fit to the carbaryl degradation profile (R(2)>0.998), supporting the formation of a carbaryl...TX...Fe(3+) complex. The carbaryl degradation rate decreased as Triton X-100 concentration increased from 20 to 1000 mg L(-1). Both (*)OH consumption by surfactants and complex formation are responsible for the degradation rate reduction below the critical micelle concentration (CMC), whereas the complex and micelle formation becomes a more dominant factor above the CMC. The effect of ethylene oxide (EO) numbers of a given nonionic surfactant mainly lies in the consumption of hydroxyl radicals, which increases with the length of the EO chain, but does not significantly affect the formation of the carbaryl...TX...Fe(3+) complex. Based on the GC-MS and LC-ESI-MS results, no evidence was found that the carbaryl degradation pathway was affected. Carbaryl was typically oxidized to 1-naphthol and 1,4-naphthoquinone similar to what is observed in the absence of surfactants. Triton X-100 was degraded via the breakdown of EO chains and omega-oxidation of the terminal methyl group, which resulted in the production of a series of ethoxylate oligomers.     

Degradation of phenolic compounds with hydrogen peroxide catalyzed by enzyme from Serratia marcescens AB 90027

In this paper, the degradation of phenolic compounds using hydrogen peroxide as oxidizer and the enzyme extract from Serratia marcescens AB 90027 as catalyst was reported. With such an enzyme/H2O2 combination treatment, a high chemical oxygen demand (COD) removal efficiency was achieved, e.g., degradation of hydroquinone exceeded 96%. From UV-visible and IR spectra, the degradation mechanisms were judged as a process of phenyl ring cleavage. HPLC analysis shows that in the degradation p-benzoquinone, maleic acid and oxalic acid were formed as intermediates and that they were ultimately converted to CO2 and H2O. With the enzyme/H2O2 treatment, vanillin, hydroquinone, catechol, o-aminophenol, p-aminophenol, phloroglucinol and p-hydroxybenzaldehyde were readily degraded, whereas the degradation of phenol, salicylic acid, resorcinol, p-cholorophenol and p-nitrophenol were limited. Their degradability was closely related to the properties and positions of their side chain groups. Electron-donating groups, such as -OH, -NH2 and -OCH3 enhanced the degradation, whereas electron-withdrawing groups, such as -NO2, -Cl and -COOH, had a negative effect on the degradation of these compounds in the presence of enzyme/H2O2. Compounds with -OH at ortho and para positions were more readily degraded than those with -OH at meta positions.     

Degradation of phthalate esters in an activated sludge wastewater treatment plant

Efficient removal of phthalate esters (PE) in wastewater treatment plants (WWTP) is becoming an increasing priority in many countries. In this study, we examined the fate of dimethyl phthalate (DMP), dibutyl phthalate (DBP), butylbenzyl phthalate (BBP), and di-(2-ethylhexyl) phthalate (DEHP) in a full scale activated sludge WWTP with biological removal of nitrogen and phosphorus. The mean concentrations of DMP, DBP, BBP, and DEHP at the WWTP inlet were 1.9, 20.5, 37.9, and 71.9 μg/L, respectively. Less than 0.1%, 42%, 35%, and 96% of DMP, DBP, BBP, and DEHP was associated with suspended solids, respectively. The overall microbial degradation of DMP, DBP, BBP, and DEHP in the WWTP was estimated to be 93%, 91%, 90%, and 81%, respectively. Seven to nine percent of the incoming PE were recovered in the WWTP effluent. Factors affecting microbial degradation of DEHP in activated sludge were studied using [U-¹⁴C-ring] DEHP as tracer. First order rate coefficients for aerobic DEHP degradation were 1.0×10⁻², 1.4×10⁻², and 1.3×10⁻³ at 20, 32, and 43 °C, respectively. Aerobic degradation rates decreased dramatically under aerobic thermophilic conditions (<0.1×10⁻² h⁻¹ at 60 °C). The degradation rate under anoxic denitrifying conditions was 0.3×10⁻² h⁻¹, whereas the rate under alternating conditions (aerobic-anoxic) was 0.8×10⁻² h⁻¹. Aerobic DEHP degradation in activated sludge samples was stimulated 5-9 times by addition of a phthalate degrading bacterium. The phthalate degrading bacterium was isolated from activated sludge, and maintained a capacity for DEHP degradation while growing on vegetable oil. Collectively, the results of the study identified several controls of microbial PE degradation in activated sludge. These controls may be considered to enhance PE degradation in activated sludge WWTP with biological removal of nitrogen and phosphorus.     

Photocatalytic degradation of tetracycline hydrochloride with visible light-responsive bismuth tungstate/conjugated microporous polymer

Conjugated microporous polymer (CMP) is an emerging organic semiconductor with π-conjugated skele-tons,and the bandgap of CMP can be flexibly modulated to harvest visible light.Based on the diversity and adjustability of monomers in CMP,we designed and synthesized donor-accepter (D-A) type BTN-CMP through Sonogashira-Hagihara cross-coupling polymerization,further in-situ constructing series of inorganic/organic Z-scheme BW/BTN-n composite in the presence of Bi2WO6.After optimization,the tetracycline hydrochloride (Co =10 mg·L-1) degradation efficiency reached 84％ with BW/BTN-2 as cata-lyst in 90 min under visible light irradiation,the apparent rate constant k1 is 0.017 min-1,which is 1.7 and 5.7 times higher than bare Bi2WO6 and BTN-CMP.X-ray photoelectron spectra and UV-Vis diffuse spectra showed that the enhanced photocatalytic activity originated from the tight heterojunction between Bi2WO6 and BTN-CMP,which can extend the light absorption range and facilitate the separation and transport of photogenerated charges in the interface of heterojunction.The active species trapping experiments and electron spin resonance technique revealed that h+ was the dominant active species during the photodegradation process of tetracycline hydrochloride (TCH).The present study demon-strated the feasibility to construct inorganic/organic composite for the photocatalytic degradation of environmental pollutants.     

Advanced water treatment with manganese oxide for the removal of 17alpha-ethynylestradiol (EE2)

Municipal wastewater is supposed to be one of the most important sources of endocrine-disrupting compounds (EDCs) in water. Therefore, advanced treatments and cost-efficient techniques should be developed to prevent the spread of this type of pollution into the environment. In this view, experiments were conducted in which the removal of 17alpha-ethynylestradiol (EE2), a synthetic and persistent estrogen, from water was monitored in three upstream bioreactors (UBRs), filled with, respectively, sand, granulated activated carbon (GAC) and MnO(2) granules. Tap water, spiked with 15,000ngEE2/L was filtered through the reactors with a hydraulic retention time of approximately 1h. The removal of EE2 in the sand, GAC and MnO(2) reactors was, respectively, 17.3%,>99.8% and 81.7%. The removal in the GAC reactor was mainly due to adsorption. The MnO(2) reactor, however, removed significantly more EE2 than could be predicted from its adsorption capacity, probably thanks to its catalytic properties. These catalytic properties could make it a cost-efficient technique for the removal of EE2, but further research at more environmentally relevant concentrations is needed.