Volume 9, Issue 1

This study describes the combined chemical, i.e. modified Fenton’s reaction, and aerobic biological removal of polycyclic aromatic hydrocarbons (PAHs) in creosote oil contaminated soil. The initial concentration of eight selected PAHs (acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene and chrysene) was 4 g/kg soil. The soil was rich in iron (16.4 g Fe/kg soil) and slightly acidic (pH 5-6). Therefore, no pH adjustment or iron addition was performed. Aged contaminated soil was treated with 30% H 2 O 2 in laboratory-scale, packed soil columns. The chemical treatment removed up to 52% of the total PAHs in the soil. The effect of the chemical treatment on indigenous PAH-degrading bacteria was studied by incubating untreated and H 2 O 2 treated soil. Biodegradation of untreated soil removed up to 36% of the total PAHs. The indigenous PAH-degrading bacteria were able to survive aggressive chemical soil treatment with concentrated H 2 O 2 and the combined chemical-biological treatment decreased the PAH-concentration by 55%.

In this work the kinetics of Wet Oxidation reactions are taken under investigation. Two different types of wastewater were chosen, pulp and paper mill wastewater and model solutions containing 4-chlorophenol. Concerning Wet Oxidation of pulp and paper mill wastewater, two kinetic models were tested, the “Generalized Kinetic Model for Wet Oxidation of Organic Compounds” from Li, and the “Lumped Kinetic Model for Wastewater Organic Burden Biodegradability Prediction” proposed by Verenich and Kallas. The first model was found to be suitable to predict the COD (Chemical Oxygen Demand) removal throughout the reaction when working at the lowest temperatures i.e., 433-443 K. On the other hand, the kinetic model of Verenich and Kallas was able to predict the biodegradability of the wastewater throughout the reaction in all ranges of temperatures studied (433-473 K). Regarding the kinetics of Wet Oxidation reactions of solutions containing 4-chlorophenol, a model was suggested taking into account the existence of an induction period previous to the oxidation in which the hydroxyl radicals are generated. This model showed good performance when predicting the 4-chlorophenol (4-CP) concentration during the reaction.

The aim of the present work is to study the biodegradability enhancement of a wastewater containing a non-biodegradable compound, 4-chlorophenol (4-CP), using a so-called Advanced Oxidation Process (AOP) named Photo-Fenton (Ph-F). The location of this study is in a more complex project the aim of which is the connection of this AOP with a biological treatment. The parameters to be studied are the initial concentrations of Fe 2+ and H 2 O 2 and the operating temperature. The work was planned using an experimental design named Central Composite Design (CCD), in order to observe the effect of each factor on different responses, such as 4-CP removal, Total Organic Carbon (TOC) removal, Chemical Oxygen Demand (COD) removal, Biochemical Oxygen Demand (BOD 5 )/COD ratio evolution and total time until the total consumption of hydrogen peroxide. The operating conditions are optimized taking into account the operating costs. The results showed that Fe 2+ and temperature do not affect the degradation and biodegradability enhancement results, but they affect significantly the time of the experiment, and consequently the operating costs.

The Electro-Fenton is one of the processes based on the Fenton reaction, which have been investigated to improve the efficiency of classical Fenton treatment. The Electro-Fenton has been shown to be efficient in the degradation of many organic compounds. However, generally there is no true estimation of its efficiency compared to that of the classical Fenton process. This study aimed to compare the two processes using an experimental approach and modelling. First of all, degradation of hydrogen peroxide (externally applied) was studied. It was shown that the Electro-Fenton process needs smaller quantities of iron (5 times less) than the Fenton to decompose the same quantity of hydrogen peroxide. The Electro-Fenton process may also produce hydrogen peroxide in situ (oxygen reduction). This leads to an important reduction in the consumption of chemicals (hydrogen peroxide, small quantities of iron salt). Finally, a study of the degradation of phenol, when hydrogen peroxide was electrogenerated has shown the greater efficiency of Electro-Fenton compared to the Fenton process.

The new photocatalysts were prepared from the commercial metatitanic acid (TiO(OH) 2 ) by ethanol treatment. The photocatalytic activity of catalysts thus prepared was studied by degradation of phenol and dyes (Reactive Red (monoazo dye) Direct Green (polyazo dye) in water under artificial solar light irradiation. Introduction of carbon-containing species to the TiO 2 was identified from the FTIR/DRS spectra (new bands in the regions 3100-2800 cm -1 and 1750-1400 cm -1 ). With increasing temperature through ethanol carbonisation, the rate of photodegradation of phenol under artificial solar light irradiation increased and the turbidity of the solution insignificantly decreased. On the UV-Vis/DR spectra of the TiO 2 /C photocatalysts, the decrease in reflectance in the visible light region was observed. Absorption of visible light by TiO 2 /C photocatalysts thus prepared can enhance their activity under solar light.

Starting materials such as Ti 4 O 7 were mixed with PVA powders in various mass ratios and then heated up to different temperatures from 900 °C in Ar. Fine particles of photocatalytic Ti 4 O 7 were coated by carbon, and reduced phases, such as Ti 5 O 9 were formed through interaction between Ti 4 O 7 and coated carbon. The photocatalytic activity was evaluated from the decomposition of iminoctadine triacetae (IT) in aqueous solution under visible light or UV irradiation. Commercial grades of anatase (ST-01), and commercially available Ti 4 O 7 were employed as reference materials. Under UV irradiation, the carbon-coated Ti 4 O 7 and Ti 5 O 9 were confirmed to have photocatalytic activity, though a little lower than that of anatase (ST-01). However, carbon-coated Ti 4 O 7 and Ti 5 O 9 were photoactive even under visible light, whereas anatase ST-01 was inactive. On comparison of Ti 4 O 7 and Ti 5 O 9 with and without carbon coating under irradiation of visible light, it was confirmed that Ti 4 O 7 and Ti 5 O 9 with carbon-coating had a higher photocatalytic activity than uncoated oxides.

Non-thermal plasmas are innovative and promising tools with respect to end-of-pipe treatment of waste gases. Among other features, they allow decomposition of low concentrations of volatile organic compounds in air streams at atmospheric pressure. In this paper, a plasma-catalytic hybrid system for the removal of trichloroethylene (TCE) in dry air is discussed. A pin-to-mesh electrode concept is used to obtain a positive corona discharge. A packed bed of TiO 2 photocatalyst partially fills the gap between the pin(s) and the mesh. TCE destruction performances of the system with and without the photocatalyst are compared. It is shown that the presence of the catalyst enhances the TCE decomposition with a maximum removal fraction of 85% at an energy density of 600 J/l for a total air flow rate of 1.5 slm with 100 ppm TCE at the inlet.

The rates and products of photooxidation of ibuprofen, clofibric acid, diclofenac and naproxen, pharmaceuticals emerging as contaminants in wastewater, were examined in UV-irradiated TiO 2 suspensions. Emphasis was on ibuprofen absorption on TiO 2 and its oxidation rate and pathways. Both absorption and oxidation of ibuprofen decreased with increasing pH above 3, consistent with preadsorption of ibuprofen on TiO 2 as an essential step in the oxidation process. Sec-butylacetophenone and sec-butylphenethyl alcohol were identified as products indicating that part of the oxidation proceeds via electron transfer from the carboxylate group to valence band holes on TiO 2 . Ring oxidation products were not found. Oxidation half lives of 0.1 mM naproxen, ibuprofen, clofibric acid, and diclofenac in 0.4% TiO 2 were 7, 14, 16 and 20 min, respectively; kinetics follow Langmuir-Hinshelwood rate laws.

The non-biodegradability of textile wastewaters is mainly due to the presence of synthetic dyes. We have studied the photocatalytic degradation of four commercial (i.e. containing additives) azo dyes (viz. Yellow Cibacron FN-2R, Red Cibacron FN-R, Navy Erionyl R 180%, Everdirect Black VSF) in aqueous suspensions of TiO 2 Degussa P25 under irradiation at 365 nm. Measurements performed were: the extent of dark adsorption; the kinetic variations in absorption, TOC and pH; the temporal formations of inorganic ions and carboxylates. In some cases, the effects of initial pH, TiO 2 loading and dye concentration were determined. Aside from considerations regarding the practical outcomes, the results are exploited to revisit the photocatalytic degradation pathways of these types of dyes, particularly on the basis of organic chemistry fundamental mechanisms.

This paper compares the photocatalytic and photoelectrocatalytic decolouration of dilute solutions of two dyes, one, methylene blue, cationic and one, reactive orange, anionic. For both methylene blue and reactive orange there is evidence that, as in photocatalytic decolouration, the initial stage in photoelectrocatalytic degradation is the destruction of the chromophore responsible for absorption in the visible region of the spectrum. For both dyes, both photoelectrocatalysis and photocatalysis were more efficient at pH > 9 than at pH 4. For the cationic dye, methylene blue, photoelectrocatalytic degradation was slower than photocatalytic degradation - indeed even though photocatalytic decolouration of 0.2 mM methylene blue solutions could be achieved photoelectrocatalytic degradation was negligible under the conditions used by us. However, photoelectrocatalytic decolouration of 0.1 mM methylene blue solution was achieved. The reduced efficiency of photoelectrocatalysis probably occurs because adsorption of the dye molecules on the TiO 2 surface is a necessary first step in photocatalysis and because the positive potential on the photanode reduces adsorption of the cationic methylene blue. For the anionic dye, reactive orange, photoelectrocatalytic degradation was more effective, under the conditions of our experiment. However, the rate of decolouration was approximately the same as that of photocatalytic degradation by a TiO 2 immobilized on a non-woven paper. The rate of both photocatalytic and photoelectrocatalytic degradation of the negatively charged Reactive Orange was faster at pH 10 than at pH 7, even though at the higher pH the surface of the TiO 2 may be expected to be more negatively charged.

Treatment of an aged raw landfill leachate with H 2 O 2 /UV was performed to find an effective way to cope with large refractory organic compounds. A 2 3 factorial design experiment, using leachate pH, H 2 O 2 dose and UV fluence as factors, and COD, BOD 5 and color as measured responses, showed that UV fluence was significant factor for COD and color reduction and BOD 5 improvement; H 2 O 2 dose was important for both COD and color reduction; and leachate pH was only significant to COD reduction. Then, the aged raw leachate and the membrane fractionated leachate samples were oxidized with H 2 O 2 /UV, and COD, BOD 5 , color and molecular size distribution were monitored. The COD removal efficiency of H 2 O 2 /UV on the fractionated samples varied from 12% to 33% depending on the sample initial quality. H 2 O 2 /UV reduced color effectively for the particle-free samples. After H 2 O 2 /UV treatment, BOD 5 increase of the particle-free samples seemed to be only dependent on UV fluence. Molecular size distribution analysis demonstrated that no new peaks were observed after treatment except the sample of 0.45 μm to 10k Da. Particles larger than 0.45 μm seemed to hinder the reduction of COD and large molecule peaks .

The wide pollution of Endocrine Disrupting Chemicals (EDCs) in the aquatic environment is of great concern to aquatic organisms and human health. Previous researches indicated that the main sources of the EDCs were sewage treatment plants (STPs). In this paper, we reported treatment results of synthetic wastewater containing several EDCs by a three-dimensional electrode system. Pt/Ti granular electrodes were used to enlarge the effective surface area of the anode. Concentrations of EDCs were prepared in the range of 1-1000 μg/l. In batch and continuous treatments, EDCs were successfully removed by the present system. Electric current and recycling flow rate played important roles for removal efficiency and reactor design. Energy consumptions were in the range of 0.1-10 Wh/m 3 . Furthermore, a selective removal of EDCs was demonstrated. From these results, we concluded that electrochemical oxidation process using the system has a potential for the treatment of trace EDCs.

The photocatalysed degradation of a pesticide derivative, acetylphosphoramidothioic acid O,S-dimethyl ester, (Acephate, 1) has been investigated in aqueous suspensions of titanium dioxide (TiO 2 ) by monitoring the depletion in total organic carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation kinetics were studied using different parameters such as pH, substrate and photocatalyst concentration, different kind of titanium dioxide and in the presence of electron acceptors such as H 2 O 2 and KBrO 3 besides molecular oxygen. The photocatalytic activity was found to be better for Degussa P25 as compared to other photocatalysts. From the obtained data a detailed account of the influence of various parameters on the mineralization rate have been discussed. The degradation products were analyzed by GC/MS technique and the probable pathways for the formation of different products have been proposed.

Previously, the authors have developed the concept of in-situ reduction of hexavalent chromium in contaminated groundwater, using various forms of active reagent delivery, based on site geohydrological conditions. While these approaches are highly successful and cost effective, in some cases, such active approaches may not be appropriate. Rather, it may be appropriate to limit the spread of chromium contamination by formation of permeable reactive barriers or reactive zones through the borehole placement of aqueous reductants. A passive approach, utilizing bore-hole placed reactive barriers and Monitored Natural Attenuation (MNA), offers real advantages for groundwater remediation, especially in situations involving groundwater in fractured or cavernous bedrock, where the water table is at great depth, or where on-going activities in the source area limit access for more active approaches. A geochemical reactive barrier was used at a South Australian timber preservation facility sited over a cavernous limestone. After remedial activities within the plume achieved significant reduction of the mobile chromium mass, the applicable regulatory agency authorized MNA for control of residual contamination. A phased approach has been utilized at a Central Valley, California timber preservation site, to develop data on the radial spread of reductant injection through diffusion, and the longevity of the effect of such injection, and a full-scale remedial approach designed, recognizing limitations on injection imposed by limited access. The paper discusses the requirements to demonstrate the effectiveness of MNA. Case histories of successful application of the integrated approach of passive reduction and MNA are presented, as a cost-effective and environmentally-protective means of accomplishing remediation of hexavalent chromium in groundwater.