太阳光Fenton氧化-混凝联合处理含酚废水

研究了煤气含酚废水和模拟苯酚废水的太阳光Fenton氧化-混凝联合处理技术,比较了混凝法、太阳光Fenton氧化法及其联合技术对含酚废水的处理效果。结果表明,太阳光Fenton体系可有效地氧化降解含酚废水,但废水完全矿化所需的H2O2用量较大,导致处理成本较高。含酚废水直接采用混凝处理的效果不理想,CODCr和挥发酚去除率较低(6.5%～28.7%)。采用太阳光Fenton氧化-混凝联合技术处理中等浓度的煤气含酚废水,使其CODCr和挥发酚浓度达到国家二级排放标准,只需投加700mg/L的H2O2,而单纯采用太阳光Fenton氧化所需消耗的H2O2大于2800mg/L,即联合技术可节约H2O2用量3倍以上。结果还表明晴天下太阳光Fenton氧化反应45min与人工电紫外光Fenton氧化反应30min对含酚废水的处理效果相当。太阳光Fenton氧化-混凝联合技术具有能耗低、处理效率高、处理量大等特点,在环境治理领域具有更广阔的应用前景。     

Decolorization and mineralization of commercial reactive dyes under solar light assisted photo-Fenton conditions

The degradation of different commercial reactive dyes: a monoreactive dye (Procion Red H-E7B), an hetero-bireactive dye (Red Cibacron FN-R) and a Standard Trichromatic System, by using solar light assisted Fenton and photo-Fenton reaction is investigated. The reaction efficiencies have been compared with the ones obtained for the same system in the dark or under the assistance of an artificial light source. The use of solar light is clearly beneficial for the removal of color, aromatic compounds (UV₂₅₄), total organic carbon (TOC), and the increase of the BOD₅/COD ratio. The possibility of a combined advanced oxidation process (AOP)/biological treatment based on the use of sunlight is suggested.     

Solar photo-Fenton treatment of chip board production waste water

In a joint project the Universidade Federal de Uberlândia and the German Aerospace Center are developing solar water treatment technologies for industrial applications. Wastewater from chip-board production is difficult to detoxify by standard processes. Different advanced oxidation processes using solar light were tested on this effluent. In opposition to TiO₂ treatment, the application of the photo-Fenton process using a compound parabolic collector (CPC) type solar reactor shows excellent results, with a reduction in the COD higher than 70% with the application of about 800 kJ m⁻² of UVA radiation. HPLC analysis shows an efficient degradation of the organic matter present in the effluent (formaldehyde, melamine, urea, wood extractives, lignin and urea/formaldehyde and melamine/formaldehyde resins fragments) prior to their complete disappearance.     

Enhanced remediation of simulated wastewaters contaminated with 2-chlorophenol and other aquatic pollutants by TiO2-photoassisted ozonation in a sunlight-driven pilot-plant scale photoreactor

Solar photoassisted remediation of a simulated wastewater contaminated with 2-chlorophenol (2-CP) was carried out by various advanced oxidation processes in a pilot-plant-scale Pyrex glass tubular-type photoreactor using solar cell derived electricity to drive the whole setup. The UV-assisted degradation and mineralization (loss of total organic carbon, TOC) of 2-CP in the co-presence of TiO₂ and ozone (UV/TiO₂/O₃) was enhanced significantly compared with ozonation alone (UV/O₃) and conventional TiO₂ photocatalysis in oxygenated dispersions (UV/TiO₂/O₂). The mineralization process was monitored by TOC assays and chloride ion analyzes. The utilization of immobilized TiO₂ was also examined with a TiO₂-coated glass photoreactor and compared with dispersed TiO₂ in aqueous media. In addition, simulated wastewaters contaminated with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), the endocrine disruptor bisphenol-A (BPA), the anionic surfactants sodium dodecylbenzenesulfonate (DBS) and sodium butylnaphthalenesulfonate (BNS), together with the cationic benzyldodecyldimethyl- ammonium bromide (BDDAB) surfactant were also efficiently remediated under otherwise identical conditions. The TiO₂-photoassisted ozonation of organic wastewater contaminants is a promising synergistic methodology to accelerate the remediation of such wastewaters, even when the TiO₂ is immobilized which can lead to reduced costs of operation.     

Optimization of the heterogeneous Fenton-oxidation of the model pollutant 2,4-xylidine using the optimal experimental design methodology

Among advanced oxidation processes (AOP), the photochemically enhanced Fenton reaction (photo-Fenton) may be particularly effective for the treatment of industrial waste water, and the possibility to use solar light is an additional advantage of this process. In the present work, a Fe³⁺-exchanged zeolite Y was tested as a heterogeneous photo-Fenton catalyst for the degradation of the model organic pollutant, 2,4-xylidine. The performance of the catalyst was investigated using a bench photochemical reactor as well as solar reactors. The incident solar radiant powers (determined by ferrioxalate actinometry) showed linear correlations with the outputs of a Si-photodiode and a bolometer mounted on the solar unit, and could therefore be easily estimated from the on-line observation of the sensor outputs. The experimental design methodology was used for planning the experiments under normalized conditions and for modeling the rates of 2,4-xylidine oxidation as a function of the concentrations of the additives (Fe³⁺-exchanged zeolite catalyst and hydrogen peroxide). Although a direct quantitative comparison between both reactors is difficult (different geometries and volumes, different spectral distribution of the radiation sources), the performance of the solar reactor appears to compare favorably with that of the bench photochemical reactor.     

Solar wastewater treatment plant for aqueous solution of pesticide

A pesticide (Vydine) considered priority substances by the Jordanian environment ministry and dissolved in water at 25 mg L⁻¹ (or at maximum water solubility) has been degraded at solar pilot plant scale using direct solar UV-light, solar UV combined with H₂O₂ or Fe(II) and solar photo-Fenton. Two different solar irradiation conditions (med day irradiation under clear sky and late hour irradiation under clear sky) have been tested and discussed, using mainly pesticide concentration, TOC mineralization, COD removal and BOD for comparison of treatment effectiveness. A cute toxicity assays were also employed for evaluating the photocatalytic treatments, and comparison between these results. Direct solar UV photolysis is less efficient in term of pesticide degradation than other AOP’s. In contrast, solar photo-Fenton reaction produced higher pesticide degradation in a shorter time (40 min was sufficient for 88% pesticide removal with 20 mg L⁻¹ H₂O₂ and 20 mg L⁻¹ Fe (II)). In these conditions, the BOD₅ was increased from zero for pure pesticide solution to 54 mg O₂/L and acute toxicity was decreased from 19 to 6 toxicity unit.     

Evaluation of solar photo-Fenton parameters on the pre-oxidation of leachates from a sanitary landfill

The main purpose of this work is to study the treatment of a leachate after preliminary aerated lagooning by a solar photo-Fenton process, using a photocatalytic reactor with compound parabolic collectors (CPCs). The influence of different process parameters in the reaction rate was evaluated, such as, the type of acid used in the acidification step (H₂SO₄, HCl, H₂SO₄ + HCl); type of iron salt (FeSO₄, FeCl₃) and respective iron concentration (60, 80, 100 and 140 mg Fe²⁺/L); temperature; and ratio of illuminated to total volume (25 L/35 L; 25 L/72 L). DOC abatement in the acidification procedure is independent of the type of acid used and temperature, and is related principally with the precipitation of humic acids. The use of HCl alone or in combination with H₂SO₄ leads to a substantially increase of the chloride ions, leading to the formation of less reactive chloride radicals when compared with sulfate radicals, decreasing the photo-Fenton reaction rate. The use of ferrous ions instead of ferric ions influenced positively the photo-Fenton reaction. Meteorological conditions favoring higher temperature of the leachate enhance the photo-Fenton reaction. Alternating dark and illumination intervals has shown a negligible effect on the illumination time needed to achieve the same mineralization, indicating that the Fenton process that takes place in dark zones is not efficient, even in the degradation of intermediate compounds resulting from the light-enhanced reaction. According to biodegradability tests, the optimum energy dose, necessary to obtain a biodegradable effluent, is 57.4 kJ_UV/L, consuming 120 mM of H₂O₂ and leading to a final DOC of 284 mg/L which corresponds to approximately 66% of mineralization.     

Highly solar active Fe(III) immobilised alumina for the degradation of Acid Violet 7

The hetero-Fenton catalyst Fe(III)-Al₂O₃ was prepared and characterised by ICP-AES, FT-IR and SEM-EDX. A detailed investigation of photocatalytic degradation of Acid Violet 7 (AV 7) using this Fenton immobilised Al₂O₃ catalyst was carried out. The optimal reaction conditions for the photodegradation of AV 7 with this catalyst are reported. Higher efficiency of the catalyst in solar light than in UV light makes this heterophoto-Fenton degradation, a green technological process. The catalyst is found to be stable and reusable. The completion of degradation has also been confirmed by chemical oxygen demand (COD) measurements.     

Hydrogen-based sono-hybrid catalytic degradation and mitigation of industrially-originated dye-based pollutants

Hazardous pollutants in water bodies have increased global concern due to their considerable toxicity and threat to the environmental matrices. Conventional remediation approaches are futile for eliminating various toxic dyes and other related pollutants. Regulations compliances for wastewater expulsion have forced scientists to either introduce new methods or upgrade present technologies to attain operative deprivation and mineralization of pollutants. Advanced oxidation processes (AOPs) relying on the generation of highly reactive oxidizing radicals, like ^?O, and ^?OH are considered efficient to attain high mineralization of a large number of dye pollutants and many other organic contaminants. Compared to conventional AOPs, including photocatalysis, Fenton, photo-ferrioxalate, ozone/UV, ozonation, H₂O₂/UV, etc., sonolysis is a comparatively newer AOP that implicates the use of ultrasound irradiation for generating oxidizing radicals, leading to the degradation of recalcitrant dyes. Due to no chemical catalyst requirement and being executed at ambient pressure and temperature, ultrasound-assisted AOPs have become robust hybrid AOPs to degrade environmental contaminants. Ultrasound treatments to mitigate pollutants are important because of the cavitation phenomenon. This review focuses on the degradation of dyes through ultrasound-based advanced oxidation processes. Firstly, we have described the ecotoxicity and health hazards of dye pollutants, then different sono-based methods such as sono-hybrid Fenton (US + Fe⁺²/H₂O₂), Fenton like (Fe⁺³/H₂O₂) process, sono-hybrid photo-Fenton process (US + Fe²⁺/H₂O₂/UV system, sono-hybrid hydrogen peroxide (US + H₂O₂), sono-hybrid catalytic (photo/electro) processes have been examined in details for their efficacy for degradation of dyes in wastewater. Future perspectives of ultrasound-assisted AOPs for dyes removal have also been discussed.     

Optimizing the solar photo-Fenton process in the treatment of contaminated water. Determination of intrinsic kinetic constants for scale-up

The elimination of aromatic compounds present in surface water by photo-Fenton with sunlight as the source of radiation was studied. The concentrations of Fe³⁺ and H₂O₂ are key factors for this process. A solar simulator and a prototype parabolic collector were used as laboratory-scale reactors to find the parameters of those key factors to be used in the CPC (compound parabolic collector) pilot plant reactor. The initial mineralization rate constant (k_obs) was determined and evaluated at different Fe³⁺ and H₂O₂ concentrations to find the best values for maximum efficiency. In all the experiments the mineralization of an aqueous phenol solution was described by assuming a pseudo-first-order reaction. The intrinsic kinetic constants not dependent on the lighting conditions were also estimated for scale-up.     

Photocatalytic colour and COD removal in the distillery effluent by solar radiation

The photodegradation of distillery effluent has been studied for removal of colour and COD reduction in the presence of solar radiation. The influence of experimental parameters such as H₂O₂ concentration dosage, effluent COD concentration, TiO₂ catalyst and pH on colour and COD removal efficiency through solar photochemical process has been investigated. Maximum colour removal of the distillery effluent achieved was 79% at an H₂O₂ concentration of 0.3 M, pH 6, effluent COD concentration of 500 ppm and catalyst dosage of 0.1 g/L. The TiO₂/H₂O₂ system seems to be more efficient in comparison to the synergetic action that appears when using H₂O₂ and TiO₂. The photocatalytic degradation process using solar light as an irradiation source showed potential application for the colour removal of the distillery effluent treatment. Solar radiation can be an considered as an alternative, effective and economic energy carrier for the treatment of industrial effluent.     

Fe supported on ceria as effective catalyst for the heterogeneous photo-oxidation of basic orange 2 in aqueous solution with sunlight

Fe^III supported on ceria as an effective catalyst for oxidation was prepared and used for the degradation of basic orange 2 azo textile dye (BO2). BO2 was chosen as a model pollutant and the catalytic oxidation was carried out in a batch reactor using hydrogen peroxide as the oxidant at pH 3. The influent factors on BO2 oxidation, such as catalyst dosage, H₂O₂ concentration, and BO2 concentration were studied by considering the BO2 conversion and chemical oxygen demand (COD) removal. The Fe^III-ceria catalyst showed a high catalytic activity for the oxidation of BO2 in aqueous solution. It was observed that the solution became colorless after 5 h of oxidation and over 90% COD removal was achieved with all the Fe^III-ceria catalysts used under dark conditions in the catalytic oxidation system. The catalytic removal of BO2 during BO2 oxidation was improved under solar radiation, which notably increased the BO2 degradation rate. Consecutive BO2 oxidation cycles carried out with the same Fe^III-ceria catalyst and untreated fresh dyestuff solution showed that the catalyst had good stability and good degradation performance, thus evidencing the possibility of being used in continuous processes. This study showed that the Fe^III-ceria catalytic oxidation process is an efficient method for the treatment of BO2 aqueous solutions.     

Decoration of Pt on the metal free RGO-TiO2 composite photocatalyst for the enhanced photocatalytic hydrogen evolution and photocatalytic degradation of pharmaceutical pollutant β blocker

Easy synthesis of graphene based composite photocatalyst with the incorporation of minimal quantity of noble metals for the enhanced photocatalytic hydrogen evolution as well as photocatalytic degradation and mineralization of recalcitrant pollutants under solar irradiation is an urgent requirement from the clean energy and environment point of view all over the globe. Herein, we demonstrate the decoration of Pt by photodeposition method on the hydrothermally synthesized RGO-TiO₂ nanocomposite. The various photocatalysts synthesized were successfully characterized by XRD, FTIR, Raman, UV–visible absorption spectra, XPS, SEM and TEM techniques. The well characterized photocatalysts were further investigated for the photocatalytic hydrogen evolution studies of methanol water mixtures under UV as well as simulated solar light irradiation. The optimized Pt-RGO-TiO₂ (1 wt % Pt and 10 wt % RGO) composite was found to show 14 fold increase in the photocatalytic hydrogen evolution efficiency under UV light irradiation and 20 fold increase under simulated solar light irradiation as compared to bare TiO₂ under UV light irradiation. The ternary photocatalyst showed very good recycle and reuse capability up to 4 cycles. The optimized Pt-RGO-TiO₂ was further tested for the enhanced photocatalytic degradation and mineralization of pharmaceutical pollutant namely β blocker Propranolol under UV as well as simulated solar light irradiation. The obtained results showed 79% and 94% reduction in COD of Propranolol under UV and simulated solar light irradiation respectively. The appreciable enhancement in the photocatalytic activity of the Pt decorated RGO-TiO₂ photocatalyst as compared to bare TiO₂ under UV and simulated solar light can be attributed to the use of maximum range of solar spectrum along with their excellent properties of charge separation by RGO and Pt.     

Treatment of dairy wastewater using anaerobic and solar photocatalytic methods

The present study was aimed to treat the dairy wastewater by using anaerobic and solar photocatalytic oxidation methods. The anaerobic treatment was carried out in a laboratory scale hybrid upflow anaerobic sludge blanket reactor (HUASB) with a working volume of 5.9 L. It was operated at organic loading rate (OLR) varying from 8 to 20 kg COD/m³ day for a period of 110 days. The maximum loading rate of the anaerobic reactor was found to be 19.2 kg COD/m³ day and the corresponding chemical oxygen demand (COD) removal at this OLR was 84%. The anaerobically treated wastewater at an OLR of 19.2 kg COD/m³ day was subjected to secondary solar photocatalytic oxidation treatment. The optimum pH and catalyst loading for the solar photochemical oxidation was found to be 5 and 300 mg/L, respectively. The secondary solar photocatalytic oxidation using TiO₂ removed 62% of the COD from primary anaerobic treatment. Integration of anaerobic and solar photocatalytic treatment resulted in 95% removal of COD from the dairy wastewater. The findings suggest that anaerobic treatment followed by solar photo catalytic oxidation would be a promising alternative for the treatment of dairy wastewater.     

Solar photo-catalysis to remove paper mill wastewater pollutants

Solar degradation of effluents in board paper industries has been studied using different photo-catalysts: Fenton reagent and TiO₂. p-Toluenesulfonic acid was chosen as a model compound for sulfonated pollutants already present in the incoming waters. The abatement of a 0.005 M solution of this pollutant after 6 h was found to be 47% for photo-Fenton and 27% for TiO₂ (pseudo-first-order rate constants 0.002 and 0.001 min⁻¹, respectively). Eugenol and guaiacol were chosen as models for lignin degradation products. They were efficiently degraded by both photo-catalysts, and reaction rates were higher for eugenol (0.0024 min⁻¹) than for guaiacol (0.0018 min⁻¹). A solution of sodium acetate, sodium butyrate and d-glucose was chosen to study the effect of photo-catalysis towards volatile fatty acids and saccharides arising from starch degradation. In this case a clearly worse performance was observed: only 20% degradation was observed after 7 h of treatment. When the real wastewater was treated with photo-catalytic methods, the best performance was obtained in closed circuits, when the COD values were higher. This fact can be explained by taking into account that closure of the circuits results in an accumulation of reluctant phenolic pollutants, while starch derivatives are continuously degraded by microorganisms in the circuits; as phenolic compounds are more easily degraded by photo-catalytic means, these methods are suitable for closed circuits. Finally, changes in the BOD_st were determined by means of active sludges respirometry. A noticeable BOD_st increase (30-50%) was observed in all cases, attributable to chemical oxidation of biodegradable species.     

Photocatalytic treatment of water soluble pesticide by advanced oxidation technologies using UV light and solar energy

Advanced oxidation technologies (AOTs) using UV lamps and solar radiation were investigated for treating aqueous solutions of pesticide (Vydine). One group of experiments was conducted using UV light irradiated at wavelengths of 254 nm (UV₂₅₄) and 350 nm (UV₃₅₀). Another similar group was conducted using solar radiation incident during the months of March (Sol-Mar) and June (Sol-Jun). Experimental measurements of pesticide concentration, TOC mineralization, COD and BOD were monitored and recorded.Results showed that AOTs with (UV₂₅₄) irradiation or (Sol-Jun) solar radiation were more efficient than those with (UV₃₅₀) or (Sol-Mar) irradiations. Pesticide eliminations achieved by using UV₂₅₄ and Sol-Jun were 50% and 32%, respectively, while the maximum Vydine elimination achieved by UV₃₅₀ or Sol-Mar was 20%. The use UV₂₅₄ with photo-Fenton increased the pesticide elimination to more than 95%.Photo-degradation rates of Vydine in the presence of TiO₂ followed the order of UV₂₅₄ > Sol-Jun > Sol-Mar > UV₃₅₀. The photo-catalytic reactions of pesticide followed pseudo first-order kinetics. The calculated rate constants were 0.015, 0.012, 0.009 and 0.0065 min⁻¹ when using UV₂₅₄, Sol-Jun, Sol-Mar and UV₃₅₀, respectively. Degradation processes examined under the conditions of the present work were able to mineralize the pesticide (Vydine) totally and/or to improve the treated solution biodegradability. Photo-Fenton and TiO₂ mineralized all the organic matter content from the solution in 230 min. Moreover, BOD₅ was increased from 0 to 9 mg O₂/L when UV₂₅₄ irradiation was only used and increased to 50 mg O₂/L following the use of photo-Fenton treatment.     

Advance electrochemical oxidation of fipronil contaminated wastewater by graphite anodes and sorbent nano hydroxyapatite

Degradation of C₁₂H₄Cl₂F₆N₄OS phenylpyrazole insecticide (Fipronil) by advance electrochemical oxidation in aqueous water solution was studied. The process efficiency was figured based on the COD, chloride, and fluoride reduction from fipronil. Further, we tried to highlight the importance of nano-hydroxyapatite (n-Hap) as a cost-effective nano sorbent for removal of fluoride from fipronil. From the advance electrochemical oxidation experiment, it was found that the COD removal was 79%, chloride 52%, and fluoride 80%. The intermediate of fipronil compounds was examined by GC-MS. The final results conclude that advance electrochemical oxidation process was effective for removal of fipronil synthetic wastewater.     

Decontamination of industrial cyanide-containing water in a solar CPC pilot plant

The aim of this work was to improve the quality of wastewater effluent coming from an Integrated Gasification Combined-Cycle (IGCC) power station to meet with future environmental legislation. This study examined a homogeneous photocatalytic oxidation process using concentrated solar UV energy (UV/Fe(II)/H₂O₂) in a Solar Compound Parabolic Collector (CPC) pilot plant. The efficiency of the process was evaluated by analysis of the oxidation of cyanides and Total Organic Carbon (TOC). A factorial experimental design allowed the determination of the influences of operating variables (initial concentration of H₂O₂, oxalic acid and Fe(II) and pH) on the degradation kinetics. Temperature and UV-A solar power were also included in the Neural Network fittings. The pH was maintained at a value >9.5 during cyanide oxidation to avoid the formation of gaseous HCN and later lowered to enhance mineralization. Under the optimum conditions ([H₂O₂] = 2000 ppm, [Fe(II)] = 8 ppm, pH = 3.3 after cyanide oxidation, and [(COOH)₂] = 60 ppm), it was possible to degrade 100% of the cyanides and up to 92% of Total Organic Carbon.     

Solar photoassisted advanced oxidation of synthetic phenolic wastewaters using ferrioxalate complexes

In this work, the performance of advanced oxidation solar assisted photochemical treatments of synthetic phenolic type wastewaters was studied at natural pH conditions, and with phenol concentrations in the range of 180-733 mg/L. The photochemical treatment was mediated with ferrioxalate and peroxide in two CPC (compound parabolic collector) photoreactors of different volumes and operation conditions (batch and with closed flow). Phenol transformation efficiencies of 100% and total COD reduction percentages of 85% were reached within the first hour of phototreatment, having as final product an aromatics free effluent, in both types of reactors. The ferrioxalate type complexes using mass ratios of oxalate/phenol = 1.5, oxalate/Fe³⁺ = 15 and H₂O₂/phenol > 5.0 showed to be very effective in the treatment of these effluents, even at pH conditions close to neutrality, pH region in which the Fenton type processes begin to lose efficiency due to the precipitation of iron as a hydroxide.     

Solar photocatalytic degradation of real textile effluents by associated titanium dioxide and hydrogen peroxide

The present work investigated the photodegradation of real textile effluents by advanced oxidative process (AOP) using TiO₂/H₂O₂/sunlight system. The procedures were carried out at ambient conditions in March 2005. The results were evaluated by COD reduction concomitant to the increase in inorganic ion concentration (mineralization) and the analysis of the effluent characteristic spectral wavelengths: 228, 254, and 284 nm (simple aromatic compounds), 310 nm (conjugated aromatic compounds), and 390, 450, and 530 (color). As this study is not restricted to the decolorization process, it allows a more reliable evaluation of effluent mineralization. The results indicate that solar radiation is as efficient as or even more efficient than artificial radiation was in previous studies and that it also allows a reduction in effluent treatment operational costs.