Advanced oxidation treatment of pulp mill effluent for TOC and toxicity removals

Pulp mill effluent was treated by different advanced oxidation processes (AOPs) consisting of UV, UV/H2O2, TiO2-assisted photo-catalysis (UV/TiO2) and UV/H2O2/TiO2 in lab-scale reactors for total organic carbon (TOC) and toxicity removals. Effects of some operating parameters such as the initial pH, oxidant and catalyst concentrations on TOC and toxicity removals were investigated. Almost every method resulted in some degree of TOC and toxicity removal from the pulp mill effluent. However, the TiO2-assisted photo-catalysis (UV/TiO2) resulted in the highest TOC and toxicity removals under alkaline conditions when compared with the other AOPs tested. Approximately, 79.6% TOC and 94% toxicity removals were obtained by the TiO2-assisted photo-catalysis (UV/TiO2) with a titanium dioxide concentration of 0.75gl(-1) at pH 11 within 60min.     

Photocatalytic degradation of organic wastes by electrochemically assisted TiO2 photocatalytic system

Photocatalytic degradation of organic wastes with nanosized titanium dioxide particles has been studied for a long time in order to offer an appropriate method for wastewater treatment, but its practical application is greatly limited by the slow process. In this work, an electrochemically assisted TiO2 photocatalytic system was set-up by combining a TiO2 photocatalytic cell with a three-electrode potentiostatic unit. The composite system revealed high photocatalytic activity towards organic wastes mineralization. After continuous treatment for 0.5 h, the maximum absorption of rhodamine 6G (R-6G) was reduced by more than 90%; chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) of textile dye wastewater (TDW) were decreased by 93.9 and 88.7%, respectively. The biodegradability of TDW was also improved because the COD/BOD5 ratio decreased from 2.1 to 1.2. All these results indicated that the composite system could be used for effective organic wastes mineralization or as a feasible detoxification and color removal pretreatment stage for biological post treatment.     

Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater: a short review

In recent years, the application of heterogeneous photocatalytic water purification processes has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible-light spectrum. This paper aims to review and summarize the recent works on the titanium dioxide (TiO(2)) photocatalytic oxidation of pesticides and phenolic compounds, predominant in storm and wastewater effluents. The effects of various operating parameters on the photocatalytic degradation of pesticides and phenols are discussed. Results reported here suggest that the photocatalytic degradation of organic compounds depends on the type and composition of the photocatalyst and, light intensity, initial substrate concentration, amount of catalyst, pH of the reaction medium, ionic components in water, solvent types, oxidizing agents/electron acceptors, catalyst application mode, and calcination temperature in the water environment. A substantial amount of research has focused on the enhancement of TiO(2) photocatalysis by modification with metal, non-metal and ion doping. Recent developments in TiO(2) photocatalysis for the degradation of various pesticides and phenols are also highlighted in this review. It is evident from the literature survey that photocatalysis has good potential to remove a variety of organic pollutants. However, there is still a need to determine the practical utility of this technique on a commercial scale.     

Photocatalytic degradation of disperse blue 1 using UV/TiO2/H2O2 process

The photocatalytic degradation of a dye derivative, C.I. disperse blue 1 (1), has been investigated under UV light irradiation in the presence of TiO2 and H2O2 under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic technique as a function of irradiation time. The degradation was studied under different conditions such as different types of TiO2, reaction pH, catalyst and substrate concentration containing hydrogen peroxide (H2O2), besides molecular oxygen in the presence of TiO2. The degradation of dye was also investigated under sunlight and the efficiency of degradation was compared with that of the artificial light source. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient for the degradation of the dye.     

TiO2光催化氧化的研究进展

概述了TiO2光催化氧化降解水中污染物的原理及TiO2光催化剂的制备，提出了增强其活性的途径。TiO2光催化氧化可应用于印染、农药、造纸等工业废水及饮用水处理中，研制高效的负栽型纳米TiO2光催化剂、解决太阳能利用问题、开发多功能光催化反应器是今后TiO2光催化氧化的发展趋势。     

Degradation of a commercial textile biocide with advanced oxidation processes and ozone

The occurrence of significant amounts of biocidal finishing agents in the environment as a consequence of intensive textile finishing activities has become a subject of major public health concern and scientific interest only recently. In the present study, the treatment efficiency of selected, well-known advanced oxidation processes (Fenton, Photo-Fenton, TiO(2)/UV-A, TiO(2)/UV-A/H(2)O(2)) and ozone was compared for the degradation and detoxification of a commercial textile biocide formulation containing a 2,4,4'-trichloro-2'-hydroxydiphenyl ether as the active ingredient. The aqueous biocide solution was prepared to mimic typical effluent originating from the antimicrobial finishing operation (BOD(5,o) < or =5 mg/L; COD(o)=200 mg/L; DOC(o) (dissolved organic carbon)=58 mg/L; AOX(o) (adsorbable organic halogens)=48 mg/L; LC(50,o) (lethal concentration causing 50% death or immobilization in Daphnia magna)=8% v/v). Ozonation experiments were conducted at different ozone doses (500-900 mg/h) and initial pH (7-12) to assess the effect of ozonation on degradation (COD, DOC removal), dearomatization (UV(280) and UV(254) abatement), dechlorination (AOX removal) and detoxification (changes in LC(50)). For the Fenton experiments, the effect of varying ferrous iron catalyst concentrations and UV-A light irradiation (the Photo-Fenton process) was examined. In the heterogenous photocatalytic experiments, Degussa P25-type TiO(2) was used as the catalyst and the effect of reaction pH (3, 7 and 12) and H(2)O(2) addition on the photocatalytic treatment efficiency was examined. Although in the photochemical (i.e. Photo-Fenton, TiO(2)/UV-A and TiO(2)/UV-A/H(2)O(2)) experiments appreciably higher COD and DOC removal efficiencies were obtained, ozonation appeared to be equally effective to achieve dearomatization (UV(280) abatement) at all studied reaction pH. During ozonation of the textile biocide effluent, AOX abatement proceeded significantly faster than dearomatization and was complete after 20 min ozonation (267 mg O(3)). On the other hand, for complete detoxification, ozonation had to be continued for at least 30 min (corresponding to 400mg O(3)). Effective AOX and acute toxicity removal was also obtained after heterogeneous photocatalytic treatment (TiO(2)/UV-A and TiO(2)/UV-A/H(2)O(2)). The Fenton-based treatment experiments and particularly the dark Fenton reaction resulted in relatively poor degradation, dearomatization, AOX and acute toxicity removals.     

Formaldehyde degradation in the presence of methanol by photo-Fenton process

In this study, the photo-Fenton process for the degradation of formaldehyde was investigated in lab-scale experiments. Results showed that methanol, the additive chemical in a commercial product of formaldehyde, was also decomposed during the formaldehyde oxidation reaction. The oxidation reaction was in three-stages. The first stage was the Fe(2+)/H(2)O(2) reaction in which both formaldehyde and methanol were swiftly decomposed. The second and the third stages exerted a somewhat less rapid degradation of both chemicals. The first stage of the oxidation reaction can be discussed by means of the initial average rate and the third stage or Fe(3+)/H(2)O(2) stage was found to follow the first order reaction rate. The reaction was influenced by the initial pH, the concentration of hydrogen peroxide, the amount of ferrous ions. The initial pH at 2.6 provided the highest removal efficiencies in this system. In addition, the competition between formaldehyde and methanol was investigated and described as r(m)/r(f), where r(m) and r(f) were the initial rates of methanol and formaldehyde, respectively. The addition of methanol exhibited a competitive effect on formaldehyde degradation. The removal of formaldehyde decreased with increasing methanol concentration. At the high concentrations of methanol, the oxidation reaction of formaldehyde was repressed. It appears that all values of r(m)/r(f) obtained from the experiments are lower than the theoretical values.     

Electrocoagulation of vegetable oil refinery wastewater using aluminum electrodes

Electrocoagulation with aluminum electrodes was used to treat the vegetable oil refinery wastewater (VORW) in a batch reactor. The effects of operating parameters such as pH, current density, PAC (poly aluminum chloride) dosage and Na(2)SO(4) dosage on the removal of organics and COD removal efficiency have been investigated. It has been shown that the removal efficiency of COD increased with the increasing applied current density and increasing PAC and Na(2)SO(4) dosage and the most effective removal capacity was achieved at the pH 7. The results indicate that electrocoagulation is very efficient and able to achieve 98.9% COD removal in 90 min at 35 mAcm(-2) with a specific electrical energy consumption of 42 kWh(kgCOD(removed))(-1). The effluent was very clear and its quality exceeded the direct discharge standard.     

用二氧化钛光催化氧化法降低丙烯腈污水中的化学需氧量

在开放的光催化反应器中,以紫外(UV)光为光源,以二氧化钛为催化剂,研究了不同水质条件下对模拟丙烯腈(AN)污水中化学需氧量(COD)的控制效果及主要影响因素。结果表明,UV光-TiO2催化体系对AN污水中COD具有良好的去除效果。当在浓度为300mg/L模拟AN污水中投加浓度为20mg/L的二氧化钛及紫外光照射180min时,污水体系中的COD残存率为7.9%。同时,反应过程中不会对环境产生二次污染。     

电化学氧化处理焚烧厂渗滤液膜浓缩液混凝出水的研究

为了降低城市生活垃圾焚烧厂渗滤液膜浓缩液混凝出水中的有机物浓度,采用电化学氧化对渗滤液膜浓缩液混凝出水进行了处理.同时,考察了阳极材料、电流密度、初始pH值和电解时间对有机物的去除影响,使用三维荧光光谱分析了有机物的去除特性,并通过氯离子的转化探讨了有机物的降解机理.结果 表明,钌铱(Ru-Ir/Ti)阳极对有机物的去...     

Coupled abiotic-biotic mineralization of 2,4,6-trinitrotoluene (TNT)

Munitions wastes such as TNT are widespread contaminants in soils and ground waters. We investigated a coupled abiotic-biotic treatment scheme for remediation of aqueous solutions of TNT. Mineralization of aqueous TNT (0.22 mM) was initially optimized with minimum reactant use (Fe3+ and H2O2) in light-assisted and dark, modified Fenton reactions at acidic and neutral pH. Complete TNT degradation occurred under all reaction conditions within 24 h. Using the optimum reactant concentrations, coupled abiotic-biotic reactions showed an increase in TNT mineralization, from 47 to 80%, after biomass addition to the acidic, dark Fenton-like reaction. Comparable increases of TNT mineralization were observed under neutral pH with similar reaction conditions. In light-assisted Fenton-like reactions at neutral pH, no increase in cumulative TNT mineralization (66%) was seen in coupled abiotic-biotic reactions. Abiotic photo-Fenton-like reactions alone, at acidic pH, produced complete TNT mineralization and required no biotic assistance. While light-enhanced Fenton reactions alone can provide high levels of TNT mineralization, the dark abiotic-biotic reaction scheme has perhaps a wider use due to a similar extent of TNT mineralization in the absence of light, leading to possible applications in soil slurry and in situ processes in the subsurface.     

Comparison of Diuron degradation by direct UV photolysis and advanced oxidation processes

The rates of Diuron elimination by some advanced oxidation processes (AOPs) such as Fe(III)/UV, Ferrioxalate/UV, Fe(III)/H(2)O(2)/UV, Ferrioxalate/UV/H(2)O(2) and Fe(III)/H(2)O(2) have been compared. Experiments have been conducted at pH=2.3+/-0.1 with a batch reactor equipped with a low-pressure mercury lamp emitting mainly at 253.7nm. Data obtained under the following experimental conditions ([H(2)O(2)](0)=10(-3)M, [Diuron](0)=5x10(-5)M and [Fe(III)](0)=10(-3)M) have shown that rates of Diuron oxidation were higher with the systems Fe(III)/H(2)O(2)/UV and Ferrioxalate/UV/H(2)O(2) than with Fe(III)/UV and Fe(III)/H(2)O(2). On the other hand, Fe(III)/UV was found to be very efficient in mineralization of Diuron solution in comparison to direct UV photolysis. The experimental results showed that radical ()OH is the major pathway in the process of Diuron degradation.     

UV-H_2O_2联用工艺去除水中阿特拉津的研究

采用间歇式反应器考察了UV-H2O2高级氧化技术去除水中阿特拉津的效果及其影响因素,并进行了相关的反应动力学研究。结果表明,在pH值6.9,阿特拉津初始浓度500μg/L,紫外辐照强度172μW/cm2时,H2O2投加量50mg/L,反应10min后,阿特拉津的去除率90%。UV-H2O2联用工艺对阿特拉津的降解符合一级反应动力学。H2O2在该联用工艺降解阿特拉津中具有双重作用,一方面,当H2O2投加量较小时,一级反应速率常数随H2O2投加量的增加基本呈现线性增加的趋势;另一方面,当H2O2浓度增加到一定程度(90mg/L)后,阿特拉津的降解速率随H2O2浓度的变化已不明显,而H2O2浓度为102mg/L时,则出现了抑制作用。     

超声-双氧水和亚铁离子体系处理含酚废水研究

在实验装置上对超声-双氧水和亚铁离子体系联合处理含酚废水进行了实验研究。主要考察了废水初始pH值、初始双氧水浓度、超声功率、反应时间等因素对酚去除率的影响。实验结果表明：超声辐射可以在双氧水和亚铁离子体系氧化过程中起加速反应的作用，而且随着超声功率的增大，加速反应的能力增强；实验条件下废水初始pH值为4～6．8，初始双氧水浓度为140mg／L时酚去除效果最佳；超声-双氧水和亚铁离子体系处理含酚废水过程中苯酚的降解规律符合表现一级反应。     

P-25纳米TiO2在含酚废水处理方面的应用

采用室内模拟研究,以P-25纳米TiO2作为光催化剂进行了苯酚水溶液的光催化降解性能探讨,初步考察了溶液的pH、P-25纳米TiO2用量对光催化降解苯酚过程的影响,以获得P-25纳米TiO2光降解含酚废水的较好反应条件.实验结果表明,当溶液pH=8时,降解水体中苯酚效果最佳,强酸和强碱条件均不利于苯酚的降解;在pH 8的反应体系中,当光催化剂用量为0.4g/L时,催化水体中苯酚降解的效果最好.     

光催化氧化处理低浓度含醇废水实验

室内实验了TiO2紫外光催化氧化处理废水中的低浓度甲醇。通过对TiO2催化剂活性及添加方式、溶液pH、紫外光强与催化剂加量等参数优化,在TiO2加入浓度为300mg/L和120 W紫外灯照射条件下,对6.8L甲醇浓度为2.77%的低浓度含醇废水持续处理70min后,废水中的甲醇去除率可达98.31%。该实验为进一步处理低浓度含醇废水提供了方法依据。     

Anaerobic degradation of vinyl chloride in aquifer microcosms

The anaerobic degradation potential at a chloroethene-contaminated site was investigated by operating two anoxic column aquifer microcosms enriched in iron(III). One column was fed with vinyl chloride (VC) only (column A) and one with VC and acetate (column B). In column A, after about 600 pore volume exchanges (PVEs), VC started to disappear and reached almost zero VC recovery in the effluent after 1000 PVEs. No formation of ethene was observed. In column B, effluent VC was almost always only a fraction of influent VC. Formation of ethene was observed after 800 PVEs and started to become an important degradation product after 1550 PVEs. However, ethene was never observed in stoichiometric amounts compared with disappeared VC. The average stable isotope enrichment factor for VC disappearance in column A was determined to be -4.3‰. In column B, the isotope enrichment factor shifted from -10.7 to -18.5‰ concurrent with an increase in ethene production. Batch microcosms inoculated with column material showed similar isotope enrichment factors as the column microcosms. These results indicated that two degradation processes occurred, one in column A and two in parallel in column B with increasing importance of reductive dechlorination with time. This study suggests that in addition to reductive dechlorination, other degradation processes such as anaerobic oxidation should be taken into account when evaluating natural attenuation of VC and that isotope analysis can help to differentiate between different pathways of VC removal.     

光催化氧化法降解有机磷农药的研究

本研究采用负载型TiO2膜作为催化剂降解有机磷农药敌敌畏，探讨了光催化反应时间、溶液的初始浓度对敌敌畏降解率的影响。试验表明，不同初始浓度的敌敌畏在经过90minUV／TiO2处理后，降解率都能达到90％以上，而且降解率随光照时间的增长而增加，随初始浓度的增加而降低。本研究采用毛细管柱气相色谱检测敌敌畏的剩余浓度，检出效果较好，并通过色谱图探讨敌敌畏的降解过程。     

Application of cavitational reactors for water disinfection: current status and path forward

Cavitational reactors are a novel and promising form of multiphase reactors, based on the principle of release of large magnitude of energy due to the violent collapse of the cavities. An overview of cavitational reactors in the specific area of water disinfection, in terms of the basic mechanism, different reactor designs including recommendations for optimum operating parameters and applicability of the cavitation phenomena for disinfection of different micro-organisms have been presented. A design of a pilot scale sonochemical reactor has been presented, which forms the basis for development of industrial scale reactors. Economic analysis for comparison of cavitation phenomena with other conventional techniques of disinfection has been discussed. It appears that though cavitation is quite successful in treatment of water at laboratory scale operations, comparatively higher cost of treatment as compared to the conventional chemical methods is a hindrance in its industrial scale application. Intensification of cavitational activity and efficient design of industrial scale hydrodynamic cavitation reactors is required for ensuring successful application of cavitational reactors at industrial scale operation.     

Microbial remediation of nitro-aromatic compounds: an overview

Nitro-aromatic compounds are produced by incomplete combustion of fossil fuel or nitration reactions and are used as chemical feedstock for synthesis of explosives, pesticides, herbicides, dyes, pharmaceuticals, etc. The indiscriminate use of nitro-aromatics in the past due to wide applications has resulted in inexorable environmental pollution. Hence, nitro-aromatics are recognized as recalcitrant and given Hazardous Rating-3. Although several conventional pump and treat clean up methods are currently in use for the removal of nitro-aromatics, none has proved to be sustainable. Recently, remediation by biological systems has attracted worldwide attention to decontaminate nitro-aromatics polluted sources. The incredible versatility inherited in microbes has rendered these compounds as a part of the biogeochemical cycle. Several microbes catalyze mineralization and/or non-specific transformation of nitro-aromatics either by aerobic or anaerobic processes. Aerobic degradation of nitro-aromatics applies mainly to mono-, dinitro-derivatives and to some extent to poly-nitro-aromatics through oxygenation by: (i) monooxygenase, (ii) dioxygenase catalyzed reactions, (iii) Meisenheimer complex formation, and (iv) partial reduction of aromatic ring. Under anaerobic conditions, nitro-aromatics are reduced to amino-aromatics to facilitate complete mineralization. The nitro-aromatic explosives from contaminated sediments are effectively degraded at field scale using in situ bioremediation strategies, while ex situ techniques using whole cell/enzyme(s) immobilized on a suitable matrix/support are gaining acceptance for decontamination of nitrophenolic pesticides from soils at high chemical loading rates. Presently, the qualitative and quantitative performance of biological approaches of remediation is undergoing improvement due to: (i) knowledge of catabolic pathways of degradation, (ii) optimization of various parameters for accelerated degradation, and (iii) design of microbe(s) through molecular biology tools, capable of detoxifying nitro-aromatic pollutants. Among them, degradative plasmids have provided a major handle in construction of recombinant strains. Although recombinants designed for high performance seem to provide a ray of hope, their true assessment under field conditions is required to address ecological considerations for sustainable bioremediation.