Degradation of parathion and the reduction of acute toxicity in TiO2 photocatalysis.

Photocatalytic degradation of methyl parathion was done using a circulating TiO2/UV and TiO2/solar reactor. Indoor experimental results showed that, under the photocatalysis conditions, parathion was more effectively degraded than under the photolysis and TiO2 only conditions. Parathion (38 microM) was completely degraded under photocatalysis within 90 min, and more than 80% TOC decrease after 150 minutes. The main ionic byproducts during the photocatalysis were measured, and almost complete nitrogen recovery was achieved as mainly NO3- NO2-, and NH4+, and 80% of sulfur as recovered as SO4(2)-. Organic intermediates such as nitrophenol and methyl paraoxon were also identified during the photocatalysis of parathion, and these were further degraded after 90 minutes. Microtox bioassay using Vibrio fischeri was used in evaluating the toxicity of solutions treated by photocatalysis and photolysis of parathion. The results showed that the acute toxicity expressed as EC50 almost reduced after 90 min under the photocatalysis condition whereas only 40% reduction of toxicity as EC50 was achieved in photolysis condition. The outdoor results using a TiO2/solar system were similar to the TiO2 indoor system, indicating the possibility of applying TiO2/solar system for the treatment of parathion-contaminated water.     

Degradation of recalcitrant organic contaminants by solar photocatalysis.

Biological pre-treated landfill leachates of Djebel Chakir contains some macromolecular organic substances that are resistant to biological degradation. The aim of the present work is to assess the feasibility of removing refractory organic pollutants in biological pre-treated landfill leachate by solar photocatalyse process. Leachate pollutant contents are studied to assess their contribution to leachate pollution and their treatability by solar photocatalyse process. Phenol is chosen as model of pollutants, to evaluate its removal and the efficiency of the photocatalytic system. The experiments were carried out in suspended photocatalytic reactor, using TiO2 Degussa P25, under sunlight illumination (UV-A: 15-31 W/cm2). Under optimum operational conditions, applied to single reactant (phenol), the system presents a TOC removal of 90% (the degradation follows a first-order kinetic). Based on the TOC removal, the results shows that the degradation of biological pre-treated leachate follows a zero-order kinetic. After 5 h of sunlight exposure, 74% of COT is removed. The TOC removal is the best without any correction of the pH and at the TiO2 concentration of 2.5 g/L. The photocatalytic degradation of organic contaminants as well as the formation and disappearance of the by-products were followed by GC/MS. The solar photocatalysis processes induce several modifications of the matrix leading to more biodegradable forms: all the remaining and new compounds generated after the biological pre-treatment of leachate are degraded and other types of organics appear, mainly carboxylic acid, aliphatic hydrocarbons and phtalic acids.     

太阳光催化技术在水处理应用中的研究进展

太阳光催化氧化技术是一种具有广谱效应的新型环保节能技术,其较强的化学氧化能力几乎可以降解所有的有机污染物.近二十几年来,该项技术在水处理领域得到了广泛的重视和快速的发展.主要介绍了二氧化钛光催化反应的机理,当前提高太阳光利用效率的方法和太阳光反应器的研究等热点问题,以及一些应用实例,并提出了今后研究的方向和重点.     

纳米TiO2光催化氧化降解水中有机磷农药的研究

用负载在玻璃纤维布上的锐钛型纳米TiO2作为光催化剂,对水中低浓度的有机磷农药敌敌畏(DDVP)的降解进行了研究.结果表明TiO2浸涂面密度和DDVP的降解效果有很大的关系,当TiO2浸涂面密度为17.5 g/m2时,经210 min催化反应,效果最好,其降解率达到85.22%,而通过在纳米TiO2/UV系统中投加氧化剂H2O2 9 mol/L和O32.52 g/L,在60 min内DDVP降解率分别达到73%和67%,比不投加氧化剂时的DDVP降解率有显著提高.说明该方法对降解有机磷农药具有较好的效果.     

Assessment of solar photocatalysis to purify on-site rinse waters from tractor cisterns used in grapevine pest control: field experimentation.

The aim of this study was to assess in a vineyard the effect of purifying by solar photocatalysis the title rinse waters (currently most often rejected) in terms of efficacy and on-site practicality for the wine grower. The on-site, self-functioning, solar purifying unit included a corrugated-steel inclined plate of area S = 1 m2 onto which a TiO2-coated thin material had been slightly pressed, a tank, and an aquarium-type pump powered by a photovoltaic panel (appropriate for isolated locations). For a vineyard of area A = 0.15 km2, the rinse water (about 90 L) corresponding to each of four typical vine treatments in summer was analysed (major pesticides for each treatment, TOC, Microtox test and, in one case, BOD5) by independent laboratories, before and after purification for 8 days. The S/A ratio tested was found insufficient even if the photocatalytic treatment markedly improved the quality of the rinse waters. From the relatively low final organic content reached in one case, it is calculated that a three-time higher S/A ratio might suffice, but new trials are necessary to determine whether it is valid for other typical cases. Inferred contribution of inorganic ions to the post-photocatalytic treatment toxicity points to the need for an additional detoxification. These field experiments have also demonstrated that the purifying prototype is robust, and easy to install and use on site by the wine grower.     

Approach to TiO2-light interaction in heterogeneous photocatalysis.

Photocatalysis can be a useful tool in the treatment of some recalcitrant and toxic pollutants. In fact, it is being applied today in several industrial processes. However some problems arise in the modelling of photocatalytic systems, most of them related to the radiation field. In this work, some methods are presented which can be powerful tools in the evaluation of the radiation absorbed by the photocatalyst, which is the energy really useful in promoting the photocatalytic process. All these methods are based on actinometric procedures carried out in different experimental conditions and using different photoreactors.     

UV/H2O2 degradation of endocrine-disrupting chemicals in water evaluated via toxicity assays.

Due to rising concern regarding the presence of endocrine-disrupting chemicals (EDCs) in surface water and groundwater throughout the United States, Asia and Europe, treatment of these chemicals in drinking water and wastewater to protect human health and the environment is an area of great interest. Many conventional treatment schemes are relatively ineffective in removing EDCs from water and wastewater. This is concerning because these chemicals are biologically active at very low concentrations and effects of mixtures are relatively unknown. 17-alpha-oestradiol (E2) and 17-beta-ethinyl-oestradiol (EE2), suspected EDCs, were degraded significantly by the UV/H2O2 AOP. The UV/H2O2 processes using either low or medium pressure lamps were degraded EDCs by between 80 and 99.3% at a 15 ppm H2O2 concentration and a UV dose of 1,000 mJ/cm2. Significantly greater removal was noted when the removal was based on total oestrogenic activity using a yeast oestrogen screen (YES) assay. These data indicated that a dose of less than 200 mJ/cm2 completely removed oestrogenic activity in lab water. Values for natural waters were slightly higher. A steady state model was developed to determine EDC destruction efficiency in waters of differing quality. The model effectively predicted destruction in water, where concentrations of all scavenging species were known. Based on these results it was concluded than complete destruction of oestrogenic activity was possible under practical advanced oxidation conditions for a variety of water qualities.     

Effects of ultraviolet intensity and wavelength on the photolysis of triclosan.

The effects of ultraviolet (UV) intensity and wavelength on triclosan (TCS) photodegradation kinetic, efficiency, mechanisms and pathway were studied. The TCS photodegradation followed the pseudo-first order kinetic model at all UV intensities examined at the wavelengths of 254 and 365 nm and the photodegradation rate increased with increasing UV intensity. TCS photodegradation efficiencies of 90 to 98% and 79 to 90% were obtained at the wavelengths of 254 and 365 nm, respectively. TCS was degraded mainly by photon induced hydroxyl radicals while the direct photon reaction with TCS played a subordinate role. Chlorophenol, dichlorophenol and phenol were the intermediates detected in all experiments conducted. Dibenzodichloro-p-dioxin and dibenzo-p-dioxin were observed as the intermediates only at lower UV intensities investigated at the wavelength of 365 nm. Based on these intermediates, a complete TCS photolysis pathway was proposed for the first time.     

Effective degradation of para-chloronitrobenzene through a sequential treatment using zero-valent iron reduction and Fenton oxidation

In this study, zero-valent iron (ZVI) was used to pretreat para-chloronitrobenzene (p-CNB), and the major product was para-chloroaniline (p-CAN). By adding H(2)O(2) directly, further p-CAN degradation can be attributed to Fenton oxidation because ferrous ions (Fe(2+)) released during the ZVI corrosion could be used as an activator for H(2)O(2) decomposition. In the reduction process, the reduction efficiency of p-CNB as well as Fe(2+) concentration increased with increasing iron dosage and decreasing solution pH. Under the optimal conditions, 25 mg L(-1) of p-CNB could be transformed in 3 h when initial solution pH was 3.0 and ZVI dosage was 2.0 g L(-1). A sufficient amount of Fe(2+) (50.4 mg L(-1)) was obtained after the above reaction to activate H(2)O(2). In the Fenton process, the oxidization of p-CAN was also more effective in acidic conditions and it increased with increasing H(2)O(2) concentration. The control experiments showed that the sequential treatment was more effective than Fenton oxidation alone in treating p-CNB wastewater since the removal rate of total organic carbon (TOC) was improved by about 34%. It suggested that the amino function group is more susceptible to oxidative radical attack than the nitro function group. Therefore, sequential treatment using zero-valent iron reduction followed by Fenton oxidation is a promising method for p-CNB degradation.     

Membrane chemical reactor (MCR) combining photocatalysis and microfiltration for grey water treatment.

Urban water recycling is now becoming an important issue where water resources are becoming scarce. This paper looks at reusing grey water; the preference is treatment processes based on biological systems to remove the dissolved organic content. Here, an alternative process, photocatalysis is discussed as it is an attractive technology that could be well-suited for treating the recalcitrant organic compounds found in grey water. The photocatalytic process oxidises organic reactants at a catalyst surface in the presence of ultraviolet light. Given enough exposure time, organic compounds will be oxidized into CO2 and water. The best contact is achieved in a slurry reactor but a second step to separate and recover the catalyst is need. This paper discusses a new membrane chemical reactor (MCR) combining photocatalysis and microfiltration for grey water treatment.     

Plasticizers and related toxic degradation products in wastewater sludges.

Plasticizers can persist during the treatment of wastewaters in sewage treatment plants (STPs) and can be discharged in effluents and/or accumulated in sewage sludges. For example, di-2-ethylhexyl phthalate (DEHP) is a common plasticizer that is now considered a priority pollutant and is known to accumulate in sludges. This may add constraints to the exploitation of the beneficial uses of sludges that contain significant quantities of plasticizers. Recently, it was demonstrated in studies with pure cultures that the biodegradation of plasticizers including DEHP and di-ethylhexyl adipate (DEHA) generates toxic metabolites including 2-ethylhexanoic acid, 2-ethylhexanol, and 2-ethylhexanal. However, the environmental impacts and fate of the degradation products arising from plasticizers are unknown. Therefore, this work investigated the concentrations of DEHP and DEHA and their metabolites in the sludges from several STPs in Quebec, Canada. DEHP and DEHA were found in concentrations ranging from 15 to 346 mg kg(-1) and 4 to 743 mg kg(-1), respectively, in primary, secondary, digested, dewatered or dried sludges. Metabolites were detected in almost all sludges, except those that had undergone a drying process at high temperature. It is concluded that sludges can represent significant sources of plasticizers and their toxic metabolites in the environment.     

BTEX degradation in a cold-climate wetland system.

A pilot-scale subsurface vertical-flow wetland system was constructed at the former BP Refinery in Casper, Wyoming in order to determine benzene, toluene, ethylbenzene and xylene (BTEX) degradation rates in a cold-climate application. The pilot system, consisting of 4 cells, each dosed at a nominal flow rate of 5.4 cubic metres per day, was operated between August and December 2002. The pilot tested the effects of wetland mulch and aeration on system performance. Areal rate constants (kA values) were calculated based on an assumed three tanks in series (3TIS). The presence of wetland sod and aeration both improved treatment performance. Mean kA values were 244 m/yr for cells without sod or aeration, and improved to 356 m/yr for cells with sod and aeration. Based on the results of the pilot system, a full-scale wetland system (capable of operating at 6,000 m3/day) was started up in May 2003. The full-scale system achieved permit compliance within one week of startup, but is currently being loaded at only 45% of the design hydraulic load, and 15% of the design BTEX mass load, resulting in a mean kA value of approximately 350 m/yr.     

Improving nitrogen reduction in waste stabilisation ponds.

This paper reviews the performance of two waste stablisation ponds (WSP) systems in the South Island of New Zealand that have been upgraded to multiple ponds-in-series to improve effluent quality. Results of monitoring are provided which show that it is possible to achieve relatively low ammonia (approximately 1 g/m3) and total nitrogen (approximately 10 g/m3) effluent concentrations through the use of nitrification filter beds (rock trickling filters) and sand filters. Evidence suggests that the nitrification and denitrification processes in the extra biofilm surface area provided by the rock filters or rock bank protection is primarily responsible for the improved effluent quality. The paper also compares the WSP results with effluent quality predicted by published formulae. It is concluded that these formulae do not reliably predict the performance of WSP systems and the development of universally applicable design guidelines would be useful.     

Photochemical degradation of naproxen in the aquatic environment.

Naproxen belongs to the group of non-steroidal anti-inflammatory drugs. It is often used to treat pain of rheumatic and non-rheumatic diseases. The photochemical experiments of naproxen degradation were performed in the wastewater effluents from wastewater treatment plant (WWTP) Kloten/Switzerland at its real concentrations (without standard addition) and in drinking water containing naproxen standard, adjusted to pH = 7 and pH = 6. All performed experiments showed that within 5 min of photochemical oxidation, the disappearance of naproxen exceeded 90%. The first-order rate constants of naproxen degradation were determined. The maximal value of rate constant was observed by UV/H2O2 process in water samples at pH = 6 (k = 0.997 min(-1)).     

Probabilistic evaluation of ammonia toxicity in Milwaukee's Outer Harbor.

Water-quality models that are simple yet sound and reliable and that correspond to water-quality criteria that include magnitude, frequency, and duration components are needed. Monte Carlo models are developed on the basis of available flow and water-quality data and a deterministic water-quality model appropriate for the problem at hand and the data available. Monte Carlo models yield time series and probability distributions of constituents of interest in conformance with water-quality criteria. The application of a Monte Carlo model to the probabilistic evaluation of ammonia toxicity in Milwaukee's Outer Harbor is presented here. Under typical operating conditions for the Jones Island Wastewater Treatment Plant, ammonia toxicity was found to not be a problem for the Outer Harbor. The Monte Carlo model then was used to determine effluent limits that would meet the ammonia toxicity criteria.     

Electrolytic degradation of biorefractory organics and ammonia in leachate from bioreactor landfill.

Electrochemical oxidation was applied to treat the effluent from bioreactor landfill with leachate recirculation, characterised as poor biodegradability and high NH3-N concentration. In this study, the effluent was electrolysed in a batch reactor with Ti/TiO2-IrO2-RuO2 anode and stainless steel cathode. The oxidation of dissolved organic matter (DOM) during electrolysis was evaluated based on the evolution of molecular weight grade, hydrophilic fractionation (humic acid, fulvic acid and hydrophilic fractions), specific ultraviolet absorbance (SUVA254) and AOX. The impact of the initial NH3-N concentration on the oxidation was discussed. The results showed that at a current density of 100 mA/cm2, electrolysis time of 1.5 h and electrode gap of 1 cm, NH3-N with an initial concentration of 1.2 g/L could be completely eliminated and 56% of COD with an initial concentration of 1.2 g/L could be removed, which illustrated that the electrolysis-produced chlorine preferentially oxidised ammonia. The electrolysis mainly resulted in the degradation of humic substances and other high molecular DOM, followed by the increase of BOD/COD ratio and decline of SUVA254 of the leachate. The current efficiencies for COD and ammonia oxidation gradually decreased during the electrolysis, with the latter obviously higher than the former. At the optimal electrolysis time of 1.5 h, NH3-N could be totally removed and the BOD/COD ratio could be enhanced to 0.3, which was also favourable to control the AOX at a reasonable level.     

Chromate sorption and reduction kinetics onto an aminated biosorbent.

A novel biosorbent was prepared by chemically grafting of polyethylenimine (PEI) onto the fungal biomass of Penicillium chrysogenum through a two-step reaction. The modified biosorbent is favorable for the removal of anionic Cr(VI) species from aqueous solution due to the protonation of amine groups on the biomass surface. The sorption capacity for Cr(VI) increased by 7.2-fold after surface modification. Sorption kinetics results show that the pseudo-second-order kinetic model described the experimental data well. During the sorption process, X-ray photoelectron spectroscopy (XPS) was used to analyze the chromium species on the biosorbent surface and the results indicate that part of the Cr(VI) ions were reduced to Cr(III) ions which can be chelated with the amine groups on the biomass surface. The reduced Cr(III) ions formed some aggregates on the surface at higher solution pHs.     

Potential of ozonation for the degradation of antibiotics in wastewater.

Increasing concern in recent years over the occurrence and fate of low-level concentrations of pharmaceuticals in the aquatic environment stimulates research on alternative treatment methods. This paper presents a study of the degradation of sulphamethoxazole, an antibiotic used on humans and animals in order to treat various bacterial infections, by ozonation. After 4.5 min of treatment, the concentration of sulphamethoxazole was below the HPLC detection limit of 0.6 mgL(-1), indicating degradation efficiency higher than 99.24%. This value is comparable and in some cases higher than published data on the degradation in drinking water. Kinetic analysis of the data indicated an overall first-order reaction with a rate constant of 1.0594 min(-1) at 20 degrees C. The reaction order differs with the second-order reaction observed by other researchers. This change of reaction order could be explained by the different treatment conditions used. Preliminary analysis using the FT-IR technique was also performed in order to obtain information on the structure of the degradation products. Further analysis using a GC-MS is needed in order to elucidate the structure of the degradation products. Finally, based on the experiments performed, ozonation seems to be a promising technique for the degradation of antibiotics, even in wastewater.     

Characteristics of sludge reduction in an integrated pretreatment and aerobic digestion process.

In this study, integrated pretreatments and aerobic digestion processes were investigated in order to provide a feasible alternative that can achieve effective sludge reduction. An ozone treatment in the presence of ionic manganese, a catalyst, increased the sludge reduction ratio three times higher than that of a single ozonation, presumably due to an increase in OH radical production. The ozone treatment yielded the effective sludge reduction ratio with an increasing ozone dosage, and an effective dosage of the catalyst was found to be 4 mg-Mn/g-TS. When a mechanical pretreatment and an ozone/catalyst were applied in a series, the integrated process, even at a half mechanical intensity and a half level of ozone dosage, showed higher and faster sludge reduction than each single process did. In addition, the integrated pretreatment process showed the highest dewaterability of the treated sludges. A ratio of sludge cake generation, which was newly introduced to quantify overall performance of sludge treatment processes, showed that the integrated pretreatment followed by the aerobic digestion yielded approximately a half of the sludge cake volume compared to the single aerobic digestion. Therefore, the integrated pretreatment can be a feasible method for the effective reduction of total suspended solid and the final volume.