TiO2 photocatalyst for water treatment applications

Recently, many water treatment technologies, such as biological treatment, coagulation/precipitation techniques, Fenton oxidation treatments, and advanced oxidation techniques, have been assessed to address the worsening clean water shortage. This review summarizes these technologies and provides the background and principle of photocatalysis for advanced oxidation technology. In particular, this paper focuses on semiconductor TiO₂ photocatalysts as well as the latest modifications of TiO₂ photocatalyst, such as the introduction of metals or heteroatoms onto TiO₂, physical modification of TiO₂ for a variety of morphologies, and hybrid TiO₂/nanocarbon composites, to improve the photocataytic activities for an advanced oxidation process. This review provides useful information to scientists and engineers in this field.     

Advanced oxidation of raw and biotreated textile industry wastewater with O3, H2O2 /UV‐C and their sequential application

The advanced chemical oxidation of raw and biologically pretreated textile wastewater by (1) ozonation, (2) H₂O₂ /UV − C oxidation and (3) sequential application of ozonation followed by H₂O₂ /UV − C oxidation was investigated at the natural pH values (8 and 11) of the textile effluents for 1 h. Analysis of the reduction in the pollution load was followed by total environmental parameters such as TOC, COD, UV–VIS absorption kinetics and the biodegradability factor, f_B. The successive treatment combination, where a preliminary ozonation step was carried out prior to H₂O₂ /UV − C oxidation without changing the total treatment time, enhanced the COD and TOC removal efficiency of the H₂O₂ /UV − C oxidation by a factor of 13 and 4, respectively, for the raw wastewater. In the case of biotreated textile effluent, a preliminary ozonation step increased COD removal of the H₂O₂ /UV − C treatment system from 15% to 62%, and TOC removal from 0% to 34%. However, the sequential process did not appear to be more effective than applying a single ozonation step in terms of TOC abatement rates. Enhancement of the biodegradability factor (f_B) was more pronounced for the biologically pretreated wastewater with an almost two‐fold increase for the optimized Advanced Oxidation Technologies (AOTs). For H₂O₂ /UV − C oxidation of raw textile wastewater, apparent zero order COD removal rate constants (k_app), and the second order OH· formation rates (r_i) have been calculated. © 2001 Society of Chemical Industry     

Monitoring the Physicochemical and Chemical Treatment of Textile Wastewater using GC/MS,LC/MS and ‐MS/MS Techniques

Abstract

Conventional biological wastewater treatment processes often fail in the elimination of finishing agents contained in textile wastewater such as dyes, surfactants, and softeners. Therefore, discharges from the textile industry are known as a major source of water pollution reaching groundwater and even drinking water treatment. Physicochemical treatment and advanced treatment processes (AOP) were applied to eliminate the pollutants prior to discharge. Ozone (O₃), O₃/UV, hydrogen peroxide/UV (H₂O₂/UV), Fenton's reagent (Fe²⁺/H₂O₂) were applied to eliminate by oxidation while ultrasonication (US) alone, US/UV or powdered activated carbon (PAC) were used for the physicochemical treatment. Elimination was monitored by a conventional sum parameter analyses (COD, BOD, DOC) while gas chromatography/mass spectrometry (GC/MS) and liquid chromatography coupled with MS and tandem mass spectrometry (LC/MS and ‐MS/MS) was applied for follow‐up of pollutants and their degradation products. The application of PAC, Fenton, and O₃/UV resulted in the highest dissolved organic carbon elimination. A complete or partial elimination and/or degradation of non‐polar or polar pollutants was observed by GC/MS or flow injection analysis/MS (FIA/MS) respectively. LC/MS and MS/MS analyses confirmed that ethoxylated surfactants (AEO) present in the original wastewater could be oxidized or destroyed resulting in carboxylated AEO and polyethylene glycol (PEG) or even carboxylated PEG.     

Electrochemical oxidation of polyvinyl alcohol using a RuO2/Ti anode

Polyvinyl alcohol (PVA), known as the dominant contributor of chemical oxygen demand (COD) in textile wastewater, is very difficult to decompose by conventional treatment technologies. In this study, electrochemical oxidation using a RuO₂/Ti anode was applied to treat a PVA solution. The mechanisms of PVA degradation and COD destruction were investigated, while the operating parameters affecting the mechanisms were also studied. The parameters investigated included current density, PVA concentration in waste stream, the rate of electrolyte consumption of sodium chloride, and the feed rate of wastewater. The overall mass transport behavior of electrochemical oxidation of PVA was explained by the mathematical relationship of dimensionless numbers such as the Reynolds, Schmidt and Sherwood numbers.     

Combination of chemical oxidation‐membrane filtration processes for the elimination of phenyl‐ureas in water matrices

BACKGROUND: Phenyl‐urea herbicides are found in surface waters and wastewaters as a consequence of their extensive use in agriculture. Due to their pollutant power, the removal of phenyl‐ureas is a priority objective in water treatment technologies. RESULTS: Four selected phenyl‐ureas herbicides (linuron, diuron, chlortoluron and isoproturon), dissolved in two water matrices (a groundwater and and a reservoir water), were subjected to sequential combinations of chemical treatments and membrane filtration processes. Two specific sequences were conducted: first, a chemical oxidation stage (where UV radiation, ozone and ozone plus hydrogen peroxide were used) followed by a nanofiltration process; and second, a membrane filtration stage (using UF and NF membranes) followed by an ozonation stage. Values for the herbicide removals in the oxidation stages and for the rejection coefficients in the filtration stages are provided, and the partial contribution of the different stages is established for each combined treatment. CONCLUSIONS: High removals (over 80%) were reached for phenyl‐ureas elimination by most of the combined processes tested. In the combined chemical oxidation/nanofiltration processes, the most effective was an ozonation pretreatment ([O₃]₀ = 1.5 mg L^?1)) followed by a NF step. In the opposite sequence filtration/chemical oxidation, the most effective was a NF pretreatment followed by the ozonation ([O₃]₀ = 2 mg L^?1). Copyright © 2009 Society of Chemical Industry     

Towards a cleaner natural gas production: recent developments on purification technologies

ABSTRACT

The development of new, efficient and cost-effective technologies for acid gases (CO₂ and H₂S) removal from natural gas is pertinent for cleaner energy productions. The removal of acid gases from natural gas can be carried out using different techniques (chemical, physical or hybrid). Although the widely employed techniques are generally effective, they have some ascribed drawbacks such as process efficiency and high-energy cost. Emerging techniques are being considered to reduce or eliminate these limitations but their deployment on an industrial scale may require that certain scientific and technological criteria, such as higher selectivity and gas separation kinetics, be met. Unprecedented and lacking in previous appraisals, this review has focused on the emerging and sustainable developments on acid gases removal from natural gas, but not without a critical evaluation of the existing technologies to provide a better background on the subject, ascertain the status-quo and identify gaps for further improvements. Efficiency of these emerging technologies are analysed with focus on ionic liquids and their blends, binding organic liquids, enzyme-based separation technologies and others. This review also features the brief contribution of the authors towards the development of low-cost materials for CO₂/natural gas separation. This article is expected to serve as an in-depth requisite background for further research on carbon capture processes with respect to natural gas purification.     

The optimization of the photo-oxidation parameters to remediate wastewater from the textile dyeing industry in a continuous stirred tank reactor

The remediation of textile dying wastewater was carried out at ambient temperatures in a pilot-scale continuous stirred tank reactor by using the photo-Fenton oxidation process. The preliminary results suggest that the treatment system reached a steady state condition within 5–10 min after it was started up. By using a 2 ^k factorial design, the effects of various parameters on the removal efficiency of color, BOD and COD were identified under steady state conditions. The removal efficiencies of color and BOD were affected by the feed rate of H₂O₂ and Fe²⁺, whereas none of the parameters in the investigated ranges affected the removal efficiency of COD. Consequently, using univariate analysis to investigate higher parameter range values, the optimum conditions for treating textile wastewater were found to be 25 ml H₂O₂/min, 5 ml Fe²⁺/min and 90 W UV-A power for 20 min. In addition, the removal of all pollutants was enhanced within the acidic pH range. Approximately 69.2, 99.4 and 48.5% of color, BOD and COD were removed, respectively. However, the concentration of TDS increased slightly during the treatment period due to the formation of new species or intermediate oxidation products. Nevertheless, all values of pollutants in the treated wastewater except COD were in the range of the standard values permitted for discharge into the environment.     

TOC Destruction of a Phenol/Water Azeotrope by “Photoreactive Distillation” Through an Incoherent Vacuum-UV Excimer Lamp

The simultaneous treatment of a phenol/water azeotrope by distillation and by vacuum-UV(VUV) oxidation with a Xenon excimer flow-through photoreactor (emission maximum λ_max of 172 nm) is demonstrated on a laboratory scale. The so-called “photoreactive distillation” of the phenol/water mixture led to a TOC-free distillate. Therefore, this combined process of distillation and VUV oxidation has unprecedented potentials in water recycling technologies. Furthermore, this novel concept of “photoreactive distillation” by using excimer VUV or UV lamps as flow-through photoreactors may open new fields of photochemical research.     

Degradation of Aqueous Pharmaceuticals by Ozonation and Advanced Oxidation Processes: A Review

A vast number of pharmaceuticals have been detected in surface water and drinking water around the world, which indicates their ineffective removal from water and wastewater using conventional treatment technologies. Concerns have been raised over the potential adverse effects of pharmaceuticals on public health and aquatic environment. Among the different treatment options, ozonation and advanced oxidation processes are likely promising for efficient degradation of pharmaceuticals in water and wastewater. Recent progress of advanced oxidation of aqueous pharmaceuticals is reviewed in this paper. The pharmaceuticals and non-therapeutic medical agent of interest include antibiotics, anticonvulsants, antipyretics, beta-blockers, cytostatic drugs, H₂ antagonists, estrogenic hormone and contraceptives, blood lipid regulators, and X-ray contrast media.     

Electrochemical Single‐Cell Reactor for Treatment of Industrial Wastewater Composed of a Spent Textile Bath

Abstract

In the paper the electro‐oxidation of a spent dyeing bath, mediated by the Cl^?/Cl₂ redox couple, was studied and proposed for the treatment of textile wastewater as a technology alternative to hypochlorite oxidation. The work focused on the optimization of the electrochemical reactor. Particular attention was paid to the dependence of transport mechanisms and reaction rates on temperature, applied current, and hydrodynamic conditions in the reactor. The simultaneous production of H₂O₂ from the cathodic reduction of O₂, which could also react with the dye, was also assessed. The regime which controlled the reaction was determined from the Hatta number.     

State‐of‐the‐Art Adsorption and Membrane Separation Processes for Hydrogen Production in the Chemical and Petrochemical Industries

Abstract

This review on the use of adsorption and membrane technologies in H₂ production is directed toward the chemical and petrochemical industries. The growing requirements for H₂ in chemical manufacturing, petroleum refining, and the newly emerging clean energy concepts will place greater demands on sourcing, production capacity and supplies of H₂. Currently, about 41 MM tons/yr of H₂ is produced worldwide, with 80% of it being produced from natural gas by steam reforming, partial oxidation and autothermal reforming. H₂ is used commercially to produce CO, syngas, ammonia, methanol, and higher alcohols, urea and hydrochloric acid. It is also used in Fischer Tropsch reactions, as a reducing agent (metallurgy), and to upgrade petroleum products and oils (hydrogenation).

It has been estimated that the reforming of natural gas to produce H₂ consumes about 31,800 Btu/lb of H₂ produced at 331 psig based on 35.5 MM tons/yr production. It is further estimated that 450 trillion Btu/yr could be saved with a 20% improvement in just the H₂ separation and purification train after the H₂ reformer. Clearly, with the judicious and further use of adsorption or membrane technology, which are both classified as low energy separation processes, energy savings could be readily achieved in a reasonable time frame.

To assist in this endeavor of fostering the development of new adsorption and membrane technologies suitable for H₂, CO and syngas production, the current industrial practice is summarized in terms of the key reforming and shift reactions and reactor conditions, along with the four most widely used separation techniques, i.e., absorption, adsorption, membrane, and cryogenic, to expose the typical conditions and unit processes involved in the reforming of methane. Since all of the reactions are reversible, the H₂ or CO productivity in each one of them is limited by equilibrium, which certainly provides for process improvement. Hence, the goal of this review is to foster the development of adsorption and membrane technologies that will economically augment in the near term and completely revamp in the far term a typical H₂, CO or syngas production plant that produces these gases from natural gas and hydrocarbon feedstocks.

A review of the emerging literature concepts on evolving adsorption and membrane separations applicable to H₂ production is provided, with an emphasis placed on where the state‐of‐the‐art is and where it needs to go. Recommendations for future research and development needs in adsorbent and membrane materials are discussed, and detailed performance requirements are provided. An emphasis is also placed on flow sheet design modification with adsorption or membrane units being added to existing plants for near term impact, and on new designs with complete flow sheet modification for new adsorption or membrane reactor/separators replacing current reactor and separator units in an existing plant for a longer term sustainable impact.     

Catalytic processes and catalysts for production of elemental sulfur from sulfur-containing gases

The modern technologies for production of elemental sulfur are considered. It is demonstrated that along with the further wide application of the conventional Claus process with conventional alumina catalyst in the observable future some new trends which may significantly influence the technological picture of recovered sulfur manufacturing may be formulated: active development of Claus tail gas cleanup processes with the stress on replacement of subdewpoint Sulfreen-type processes by processes of hydrogen sulfide selective oxidation by oxygen; development of novel highly-efficient technologies for hydrogen sulfide decomposition to sulfur and hydrogen; application of new catalysts forms, first of all — at microfiber supports for Claus and H₂S oxidation processes; wider application of titania and vanadia catalysts at the newly constructed Claus units; development of technologies and catalysts for direct purification of H₂S-containing gases and for catalytic reduction of SO₂ for sulfur recovery from smelter gases. All these prospective routes are actively developed by Russian science and some of them are completely based on domestic developments in this area.     

煤气化技术在中国:回顾与展望

系统回顾了煤气化技术在中国150多年的发展历史,从新中国建立前、新中国建立到改革开放前、改革开放后3个阶段,分别介绍了我国引进各类煤气化技术的过程及其应用情况;以改革开放前和改革开放后2个阶段,重点概括了我国煤气化技术领域的艰难探索、系统深入研究和技术示范与应用过程中取得的重要进展与成果;对我国自主开发的主要煤气化技术的研发历程、技术特点、应用情况及最新进展进行概要阐述,并对地下气化、催化气化、加氢气化、超临界水气化、等离子体气化等新型气化技术的国内研发进展进行简要述评;总结了我国煤气化技术引进、自主研究与工程应用经验,从降低装置投资、提高系统效率、实现环境友好、协同处理液/固有机废物、融合信息化技术、开发新技术、保护知识产权等方面对煤气化技术的未来发展进行了展望。     

A novel Ni doped BaTiO3/h-BN nanocomposite for visible light assisted enhanced photocatalytic degradation of textile effluent and phytotoxicity evaluation

The objective of this research is to synthesize novel Ni–BaTiO₃/h-BN nanocomposites. XRD, UV–Vis, PL, FT-IR, SEM, TEM, Zeta potential, XPS, BET, EIS, Mott- Schottky and LC-MS analyses were used to analyze the nanocomposite phase structure, band gap, electron-hole recombination rate, vibrational modes, morphology, elemental analysis stability, oxidation state, pore size distribution, and electron distribution. The nanocomposites have an average particle size of 32 nm, as measured using HR-TEM microscopy. The band gap of synthesized h-BN was found to be 3.82 eV, whereas the Ni–BaTiO₃/h-BN binary nanocomposite shifts it to 2.43 eV. The nanocomposite photocatalytic efficiency was used to degrade textile effluent, followed by a phytotoxicity assessment of real textile effluent. Furthermore, the photocatalytic treatment analysis revealed that the 40 mg Ni–BaTiO₃/h-BN catalyst degraded up to 81.4% and 86% against textile effluent and crystal violet (CV) dye within 120 min under visible light, respectively, and the concentrations of numerous Physico-chemical parameters of textile effluent have significantly decreased in deteriorated textile effluent. According to a pot study, the toxicity of the degraded textile effluent was reduced following photocatalytic treatment. To examine the mechanism, the photodegradation effectiveness of the catalyst was investigated utilizing various scavengers. From the scavenger study, it is found that the holes (h⁺) contribute more to the degradation process. In real textile dye wastewater, the Ni–BaTiO₃/h-BN nanocatalyst was proved to be an excellent and low-cost degrading technique.     

Treatment and reuse of dyeing effluents by potassium ferrate

The use of potassium ferrate, K₂FeO₄, an environmentally-friendly chemical reagent containing iron in the + 6 oxidation state, has been investigated as a new approach for dyeing wastewater purification.The performance of this product, alone or in combination with a cationic organic polymer and/or power ultrasound, was compared to the traditional biological activated sludge process and a tertiary treatment featuring ozonation.Experimental tests showed that, thanks to its unique properties (high redox potential and simultaneous generation of ferric coagulating species), potassium ferrate can be successfully used in dyeing wastewater treatment. In fact, treatment with ferrate at the optimal dose of 70 mg/L as Fe(VI) was found to allow a high removal efficiency of relevant parameters such as turbidity, total suspended solids and chemical oxygen demand (COD).Whilst potassium ferrate alone had a minor effect on colour, the combination of ferrate with the organic polymer allowed a good decolourisation: this suggested the eventual application of this combined process for reuse of dyeing wastewater, resulting in environmental and economic benefits. The possibility of reusing the purified effluent in textile processes that do not require softened water was demonstrated through dyeing tests.     

Electrochemical waste water treatment using high overvoltage anodes Part II: Anode performance and applications

The performance of highly doped SnO₂ anodes for the oxidative treatment of biologically refractory waste water was compared with PbO₂ and Pt. The oxidation of a wide range of organic compounds proceeds with an efficiency which is about 5 times higher than with platinum anodes. The oxidation efficiency was found to be independent of the pH of the water. In chloride containing media, SnO₂ anodes produce less chlorine gas than platinum anodes and hence show less potential to form hazardous chlorinated organic by-products. The design of a simple plate-and-frame reactor with undivided cells for waste water treatment using SnO₂ anodes was based on two experimental findings: (a) no interference of the cathode with the oxidation has been found: (b) the rate of oxidation is not limited by mass transfer, indicating the participation of homogeneous reactions in the overall oxidation. The new anode material reduces the specific energy requirement of electrochemical oxidation of organics in waste water to 30 to 50 kWh kg^–1 of COD removed. This makes the process an interesting alternative to chemical oxidation using oxidants such as ozone and hydrogen peroxide, or wet oxidation using oxygen at elevated temperature and pressure.     

An Optimal Usage of NOx in a Combined Pt/Ceramic Foam and a Wall-Flow Monolith Filter for an Effective NOx-Assisted Soot Oxidation

An NO₂-assisted soot oxidation based filter candidate consists of Pt-coated ceramic foam in combination with a wall-flow monolith is proposed to acquire for an optimal usage of exhaust NO _x . The configuration is designed to operate as deep bed filtration on Pt/ceramic foam and surface filtration on the wall-flow monolith. The oxidation of soot by NO₂ takes place by multi-cycle reaction in Pt/ceramic foam and by the normal CRT on the wall-flow monolith. The filter performs with a higher oxidation rate and a lower NO₂-slip.     

EVALUATION OF UV/O3 AND UV/H2O2 PROCESSES FOR NONBIODEGRADABLE COMPOUNDS: IMPLICATIONS FOR INTEGRATION WITH BIOLOGICAL PROCESSES FOR EFFLUENT TREATMENT

Poorly biodegradable compounds reduce the efficiency of biological effluent treatment processes. These are often encountered in pharmaceutical and speciality chemical industries. Advanced oxidation technologies (AOT) are appropriate for the conversion of such compounds into biodegradable entities. Tetrahydrofuran, 1,4-dioxane, and pyridine are heterocyclic compounds that are known to be recalcitrant and nonbiodegradable. AOT were investigated for the destruction of these model compounds. Two forms of AOT, UV-O₃ and UV-H₂O₂, were studied. UV-H₂O₂ treatment resulted in higher biodegradability for tetrahydrofuran; UV-O₃ treatment resulted in higher biodegradability for 1,4-dioxane. For pyridine, neither treatment improved biodegradability. For efficient integration of AOT with biological processes for effluent treatment, it is necessary to evaluate the AOT with multiple objectives, such as level of destruction of target compound, level of reduction in COD, and enhancement of biodegradability. Due to the presence of multiple pollutants in real effluents and in AOT, kinetics of oxidation elucidated with single compounds is unlikely to be useful.     

Anodic oxidation of phenol in the presence of NaCl for wastewater treatment

The electrochemical oxidation of phenol in the presence of NaCl for wastewater treatment was studied at Ti/SnO₂ and Ti/IrO₂ anodes. The experimental results have shown that the presence of NaCl catalyses the anodic oxidation of phenol only at Ti/IrO₂ anodes due to the participation of electro-generated ClO^– in the oxidation. Analysis of the oxidation products has shown that initially organo-chlorinated compounds are formed in the electrolyte which are further oxidized to volatile organics (CHCl₃).     

Engineering arrangement of nanoparticles within nanocomposite membranes matrix: a suggested way to enhance water flux

ABSTRACT

In this research, with the aim of engineering arrangement of nanoparticles within membrane pores, ZrO₂ nanoparticles was modified by sulfate and carboxylate functional groups. Thereafter, the filtration performance of PSf/ZrO₂, PSf/Zr-COOH, and PSf/Zr-SO₄ nanocomposites in treating textile wastewater were compared. SEM, EDX and AFM analysis showed that the functional groups manipulate surface and structural properties of the membranes. Therefore, water flux of ¹³PSf/^2.68Zr-SO₄ and ¹³PSf/^2.68Zr-COOH were 42% and 32% more than those of ¹³PSf/^2.68ZrO₂. Moreover, dye rejection of ¹³PSf/^2.68Zr-SO₄,¹³PSf/^2.68Zr-COOH and ¹³PSf/^2.68ZrO₂ was about 99% and 97% and 95%, which is 14%, 12% and 10% higher than raw membrane.