The occurrence of priority PAHs, nonylphenol and octylphenol in inland and coastal waters of Central Greece and the Island of Lesvos

Polycyclic aromatic hydrocarbons (PAHs) as well as nonylphenol (NP) and octylphenol (OP) are substances of major environmental concern because of their adverse health effects on organisms, including endocrine disrupting activity. Seven PAHs, NP and OP have been included in the priority list of substances regulated by 2000/60/EC Water Framework Directive. The present work concerns the investigation of the occurrence of the seven priority PAHs, NP and OP in surface and coastal waters in Central Greece and the Island of Lesvos. Samples were collected and analyzed seasonally for one year from the four reservoirs that supply water to Athens: Mornos, Marathonas, Yliki and Evinos. Samples were also collected from inland waters of the Lesvos Island (the rivers Mylopotamos and Evergetoulas), and from coastal waters (five sampling points) of the Mytilene area, which is the capital city of the Island of Lesvos. The results have shown that in most cases the water samples that were analyzed are free from PAHs, possibly because of lack of PAHs release sources nearby the particular areas, or due to the adsorption of PAHs on sediments. NP occurred at low levels in several cases, while OP was detected only in one sample.     

Validation of a FT-IR method for the determination of oils and grease in water using tetrachloroethylene as the extraction solvent

The term “Oils and Grease” (OG) encompasses a broad family of chemical compounds such as fatty material of biogenic origin, or petroleum hydrocarbon constituents. These compounds can cause environmental degradation and induce related public health risks when discharged in surface or ground waters. Consequently, OG is regulated by both European and National legislation for drinking water and wastewater. The development of methods for OG determination presents several difficulties and challenges for the analytical laboratory, since this parameter is methoddefined, i.e. the method establishes the measurand. Among several alternative methods that have been proposed in the literature, FT-IR determination after liquid–liquid extraction is known to be an easy, low-cost alternative for monitoring of OG at the ppm level. However, established FT-IR methods are based on Freon 113 extraction, a solvent which has been banned as an ozone depleting agent. This paper presents the development and validation of an in-house FT-IR method for the determination of OG in water that uses tetrachloroethylene as a Freon 113 substitute. The method was developed in EYDAP’s laboratories for the monitoring and control of OG in surface and drinking waters. Results regarding the calibration, linearity, OG recovery, precision, detection — quantitation limits and robustness are presented and discussed. Tetrachloroethylene proved to be a suitable alternative to Freon 113 and the method was deemed appropriate for monitoring oil spills or discharges in surface waters or in the drinking water network, at levels > 0.1 ppm.     

A Survey of Occurrence and Risk Assessment of Pharmaceutical Substances in the Great Lakes Basin

The present study is an overview of the literature on the occurrence and potential risks of pharmaceutical substances in the wastewater treatment plants (WWTP), natural waters and drinking water treatment plants served by the Great Lakes Basin (Canada and the USA) between the years of 2007–2012. Large number of pharmaceutical substances, including anti-inflammatories, lipid regulators, antidepressants, antibiotics, beta blockers, anti-epileptics, anti-hypertensions and stimulants, in high ng/L concentrations, has been reported in the WWTP influents. Most of these compounds have also been detected in the WWTP effluents at comparable concentrations with the exception of caffeine, cotinine and salicylic acid suggesting the inefficiency of conventional treatment processes in the degradation of pharmaceutical compounds. Decreasing surface water concentrations have been observed with the distance downstream of the discharge point due to the dilution effect. Surface waters located around septic systems and agricultural areas have also been found to be contaminated with pharmaceutical substances. Carbamazepine, caffeine, its metabolite paraxanthine, ibuprofen, gemfibrozil and sulfamethoxazole have been frequently detected in the surface waters. The number of occurrences of carbamazepine, ibuprofen, naproxen, gemfibrozil, bezafibrate, sulfamethoxazole and macrolide antibiotics in drinking water sources, at ng/L concentration ranges, has been quite high. Although the detection frequencies in treated drinking waters were relatively low, the concentrations of the above mentioned pharmaceutical substances were at the same range as the source water concentrations.

Six of the detected pharmaceutical substances, namely, fluoxetine, sulfamethoxazole, clarithromycin, erythromycin, carbamazepine and esterone exhibit a high environmental risk in Great Lakes WWTP effluents and surface waters, while none of the pharmaceutical substances seem to pose a risk for human health at their highest reported concentrations in the drinking water sources from the Great Lakes.     

Effect of silicates on the structure of Ni-containing catalysts obtained from hydrotalcite-type precursors

New nickel hydrotalcite-like compounds with silicates as interlayer anions used as catalyst precursors in the catalytic partial oxidation of methane were prepared by the coprecipitation method. The properties of these materials were compared with those of compounds obtained from carbonate-containing materials. The precursors and calcined samples were characterized by powder X-ray diffraction, FT-IR and Vis/UV/NIR spectroscopies, thermal analyses (DTA and TG), temperature programmed reduction (TPR) and N₂ adsorption/desorption at −196 °C. The results show that the incorporation of silicates in the lamellar compounds modifies the structural and textural properties of the precursors. After calcination, silicates – which are non-volatile anions – contribute to the final structure of the catalysts, which form a new forsterite-like phase, increasing their specific surface area but not altering the reducibility of the nickel species.     

Solar still an appropriate technology for potable water need of remote villages of desert state of India — Rajasthan

Rajasthan, the largest state of the India faces a grim scenario in relation to water availability resources. Rajasthan has two-third of its area as desert and it faces scanty rainfall, recurring droughts in 3–4 years in a cycle of 5 years. It would be seen from the present status of drinking water detailed out of 237 blocks in Rajasthan that only 49 are safe in terms of ground water while 101 are critical and semi critical and 86 are over exploited. It is a hard reality that state dependence on ground water is 91% for drinking water. About 21,190 villages/habitations suffer from the problem of excessive salinity, 23,297 villages/habitations suffer from excess fluoride problem and 20,659 villages/habitations suffer from excess nitrate problem. Based on the WHO guidelines for drinking-water quality about 56% of the water sources are un-potable.

But on other hand Rajasthan is blessed with ample amount of solar radiation. The arid parts of Rajasthan receive average maximum solar radiation of about 7.5 kW h/m² in the month of May and minimum of about 4.6 kW h/m² in the month of Dec & Jan. Part of this energy may be utilized to meet out drinking water need of remote area dwellers of Rajasthan.

Solar distillation and desalination unit is most appropriate for remote area dwellers because it is economical, easy to construct and maintain. Most parts of Rajasthan have enough solar radiation available which is the prime input for the system.

A low cost high efficiency solar still with porous evaporating surface is fabricated for the purpose and cost analysis is done to calculate the cost of water in this paper [Bassam et al., Experimental study of a solar still with sponge cubes in the basin, Energy Conserv. Manage., 44 (9) (2003) 1411–1418; Bouchekima et al., Performance study of the capillary film solar distiller, Desalination, 116 (1999) 185–192; Bassam et al., Water film cooling over the glass cover of a solar still including evaporation effect, Energy, 22 (1) (1997) 43–48].

Water samples are collected from a remote village of state and analyzed to find the quality of drinking water. The working habits and medical history of the villagers is also investigated to work out cost analysis more realistically.     

Structural investigations of aquatic humic substances from different watersheds

Aquatic humic substances are amorphous organic macromolecules and precursors of mutagens formed on chlorination of raw water. Their isolation from River Mornos and Lake Yliki (primary reservoirs of Athens Water Supply and Sewerage Company) using columns of XAD-8 and IR-120 resins is performed in order to study their structural differences among reservoirs. Fractionation into humic and fulvic acids (HA and FA respectively) and spectroscopic examinations with FTIR technique is applied. In addition, THMFP is determined in every fraction of the reservoirs mentioned above. The presence of carboxylic acids and other functional groups such as alcohols, aromatic rings and aliphatic chains is indicated. Chloroform and chloropropanones detected can be considered to be products of humic acid, as they can be formed during chlorination of hydroxy-benzoic acid and β-keto-carboxylic acid. The chlorosubstituted acetonitriles detected are attributed to the reaction between chlorine and aminoacid.     

Characterization of Pd-based FCC CO/NOx control additives by in situ FTIR and extended X-ray absorption fine structure spectroscopies

Pdⁿ⁺/Ceⁿ⁺/Na⁺/γ-Al₂O₃-type materials used as FCC additives for CO/NO_x control were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and in situ FTIR. The EXAFS data indicate that in freshly prepared samples palladium is present in the form of highly dispersed PdO species. Reduction with H₂ at 500 °C leads to the formation of small Pd clusters incorporating on average approximately six to eight metal atoms at a Pd−Pd bond distance of 2.76 Å. All components of these materials can interact with NO and promote the formation of nitrate/nitrite species, essentially “trapping” NO_x species on the catalyst surface. However, the Na⁺ species dominate the surface chemistry and readily form sodium nitrates with a characteristic IR band at 1370–1385 cm⁻¹. Finally, hydroxyls from the support are also actively participating in the formation of HNO_x type compounds with characteristic stretching vibrations in the 3500–3572 cm⁻¹ region.     

Effect of Ozonation on the Chlorine Demand of a Treated Surface Water and Some Macromolecular Compounds

The study described in this paper was conducted to examine the effects of ozonation and ozone-GAC filtration treatment steps on chlorine consumption of the Seine river water treated in the Choisy-le-Roi drinking water works. Ozone-GAC combined treatment was found to significantly reduce both the initial chlorine demand and the long-term chlorine demand of waters, excepting for waters sampled during cold months of the year. The removal of the chlorine demand potential by ozonation alone was found to be limited for the studied waters and for solutions of macromolecular compounds even in the presence of carbonate species. Ozonation carried out in the absence of bicarbonate ion was found to increase reactive sites with chlorine treatment of an aquatic fulvic extracted from the Seine river water.     

In situ FTIR characterization of the adsorption of CO and its reaction with NO on Pd-based FCC low NOx combustion promoters

The adsorption of CO and its reaction with NO in the 400–600 °C temperature range on Ceⁿ⁺/Na⁺/γ-Al₂O₃ and Pdⁿ⁺/Ceⁿ⁺/Na⁺/γ-Al₂O₃ type materials used commercially as FCC additives were monitored by FTIR spectroscopy. Exposure of both types of samples to CO leads to the formation of carboxylates and carbonates. The concentration of these species was higher in samples containing Pd, indicating that palladium catalyzes their formation. The Pdⁿ⁺ cations initially present in these samples undergo partial reduction to form metallic Pd in the presence of CO even at room temperature. More complete reduction of Pd, along with some aggregation, was observed after exposure to CO at elevated temperatures. Exposure of both types of samples to NO/CO mixtures in the 400–600 °C temperature range leads to the formation of surface isocyanate species. Both Na⁺ and Ceⁿ⁺ promote the formation of such NCO species. However, surface isocyanate species were formed with substantially higher rates in the presence of palladium. The formation of the isocyanate species strongly correlates with changes observed in the ν_OH region, indicating that hydroxyls actively participate in the surface chemistry involved and are capable of protonating the NCO species. The isocyanates are also reactive towards O₂ and NO yielding CO₂ and N₂. These results suggest that isocyanates are possibly involved as intermediates in the CO–NO reaction over the materials examined.     

Solid catalysts for wet oxidation of nitrogen-containing organic compounds

Several solid catalysts (Co₃O₄/γ-Al₂O₃, Fe₂O₃/γ-Al₂O₃, Mn₂O₃/γ-Al₂O₃, Zn–Fe–Mn–Al–O, Pt/γ-Al₂O₃, Ru/CeO₂, Ru/C) have been prepared and used to remove N-containing organic contaminants while processing toxic and hazardous industrial waste waters using wet oxidation by air (WAO). The autoclave tests of catalysts were done to reveal the main advantages of catalysts in water presence at high pressures and temperatures. Catalyst activity was determined with regard to oxygen interaction with model mixtures (water–organic contaminant: acetonitrile, carbamide, dimethyl formamide, or multi-component mixture of aliphatic alcohols). Activity tests were done in a static reactor under ideal mixing regime. Reagents and products were monitored using gas chromatograph Cvet-560, Millichrom-1 HPLC, and routine chemical analysis. Optimum process conditions for the best catalyst (Ru/graphite-like carbon) are as follows: partial oxygen pressure – 1.0 MPa, temperature – 473–513 K. At 0.5–5.0 MPa total pressure and 433–523 K catalysts show high water-resistance and high activity level (residual content of toxic compounds is less than 1%, and no NO_x and NH₃ are detected). There are no legal restrictions on catalysts operation, since they are harmless to environment.     

Catalysis of the isocyanate-hydroxyl reaction by non-tin catalysts

Tin compounds, especially dibutyltin dilaurate, are in widespread use in coatings as catalysts for the isocyanate/hydroxyl reaction. Because of the high aquatic toxicity of some organotin compounds, there has been an attempt to ban organotin compounds from all coating applications. As a general rule organotin catalysts are not selective, they catalyze the reaction of isocyanates with both hydroxyl groups and water and also catalyze the hydrolysis of ester groups. We are interested in finding alternatives to these catalysts and in developing compounds which exhibit increased selectivity for the isocyanate/hydroxyl reaction. In addition, we are interested in developing materials which give a longer potlife and enhanced reaction rates. We will report on various metal salts and chelates we have investigated, the mechanism of catalysis and application characteristics in both high solids and water-borne applications. We found zirconium chelates activates the hydroxyl groups and catalyze the isocyanate-hydroxyl reaction by an insertion mechanism. This reaction is selective and preferred over the isocyanate-water reaction. This permits the use of this catalyst in waterborne isocyanate crosslinked two component coatings. In addition this catalyst permits very high reaction rate which suggests is use in plural component gun applications.     

Dissolved and particulate trace metal levels in the Saronikos Gulf, Greece, in 2004. The impact of the primary Wastewater Treatment Plant of Psittalia

The present study examines the concentrations of Cd, Cu, Mn, Ni, Pb and Zn in 2004 in the Saronikos Gulf, an embayment affected by anthropogenic inputs from the nearby metropolitan area of Athens. We investigated in particular the impact of the operation for a decade of the primary Wastewater Treatment Plant of Athens, which is located at Psittalia Island, on the levels of these metals in the marine environment of the gulf, few months before the inauguration of the secondary treatment. Therefore, the present work represents the needed baseline for any future comparisons and assessment of the impact of the secondary treatment. For two samplings carried out in May and September 2004 in a grid of fifteen stations, dissolved and particulate metal concentrations are, respectively, in the range 5.0–63 and 0.22–3.6 ng/L for Cd, 0.03–0.72 and 0.03–0.23 μg/L for Cu, 0.11–1.2 and 0.02–0.55 μg/L for Mn, 0.19–1.5 and 0.01–0.11 μg/L for Ni, 0.05–0.60 and 0.02–0.59 μg/L for Pb and 0.13–5.8 and 0.06–1.0 μg/L for Zn. The concentrations of the majority of the studied metals obtained in 2004 are comparable to those of the year 2000 and among the lowest detected in the Saronikos Gulf ever since the beginning of the MED-POL program twenty years ago. This stabilization is attributed to the operation of the wastewater treatment plant and offers an indication that the levels of trace metal pollution of the marine environment of the gulf are possibly reaching a steady state.     

A comparative investigation on the properties of Cr-SBA-15 and CrOx/SBA-15

High-surface area and well-ordered mesoporous Cr-incorporated SBA-15 (Cr-SBA-15) and SBA-15-supported chromia (CrO_x/SBA-15) with Cr surface density = 0.05–1.11 Cr-atom/nm² have been prepared, respectively, using the one-step synthesis and incipient wetness impregnation method, and characterized by AAS, XRD, BET, ESEM, TEM, XPS, laser Raman, UV-Vis, FT-IR, and H₂-TPR. It is observed that the Cr-SBA-15 and CrO_x/SBA-15 samples showed an evolution of surface morphology from long chain-shaped to short rod-like and further to an irregularly spherical architecture at elevated Cr content, which might arise from the interaction of Cr ions or CrO_x domains with SBA-15. There were co-presence of tetrahedrally coordinated mono- and poly-chromate (Cr⁶⁺) as well as octahedrally coordinated Cr³⁺ species in Cr-SBA-15 and CrO_x/SBA-15, with the Cr⁶⁺ species being dominant at Cr surface density ≤0.22 Cr-atom/nm² in Cr-SBA-15 and Cr ≤0.54 Cr-atom/nm² in CrO_x/SBA-15, whereas the amount of the Cr³⁺ species increased markedly at Cr surface density ≥0.53 Cr-atom/nm² due to the formation of crystal Cr₂O₃ phase. Maximal Cr incorporation into Cr-SBA-15 and one monolayer surface CrO_x coverage on CrO_x/SBA-15 occurred at Cr surface density ≤0.53 Cr-atom/nm² and <1.11 Cr-atom/nm², respectively. The CrO_x/SBA-15 samples exhibited better reducibility than the Cr-SBA-15 samples, with the best reducibility exhibited at Cr surface densities of 0.54 and 0.12 Cr-atom/nm², respectively.     

Cu-ZSM-5 zeolite highly active in reduction of NO with decane under water vapor presence: Comparison of decane, propane and propene by in situ FTIR

Selective catalytic reduction of NO_x (SCR-NO_x) with decane, and for comparison with propane and propene over Cu-ZSM-5 zeolite (Cu/Al 0.49, Si/Al 13.2) was investigated under presence and absence of water vapor. Decane behaves in SCR-NO_x like propene, i.e. the Cu-zeolite activity increased under increasing concentration of water vapor, as demonstrated by a shift of the NO_x–N₂ conversion to lower temperatures, in contrast to propane, where the NO_x–N₂ conversion is highly suppressed. In situ FTIR spectra of sorbed intermediates revealed similar spectral features for C₁₀H₂₂– and C₃H₆–SCR-NO_x, where –CH_x, R–NO₂, –NO₃⁻, Cu⁺–CO, –CN, –NCO and –NH species were found. On contrary, with propane –CH_x, R–NO₂, NO₃⁻, Cu⁺–CO represented prevailing species. A comparison of the in situ FTIR spectra (T–O–T and intermediate vibrations) recorded at pulses of propene and propane, moreover, under presence and absence of water vapor in the reaction mixture, revealed that the Cu²⁺–Cu⁺ redox cycle operates with the C₃H₆–SCR-NO_x reactions in both presence/absence of water vapor, while with C₃H₈–SCR-NO_x, the redox cycle is suppressed by water vapor. It is concluded that decane cracks to low-chain olefins and paraffins, the former ones, more reactive, preferably take part in SCR-NO_x. It is concluded that formation of olefinic compounds at C₁₀H₂₂–SCR-NO_x is decisive for the high activity in the presence of water vapor, while water molecules block propane activation. The increase in NO_x–N₂ conversion due to water vapor in C₁₀H₂₂–SCR-NO_x should be connected with the increased reactivity of intermediates. These are suggested to pass from R–NO_x → –CN → –NCO → NH₃; the latter reacts with another activated NO_x molecule to molecular nitrogen. The positive effect of water vapor on the NO_x–N₂ conversion is attributed to increased hydrolysis of –NCO intermediates.     

Oxidation of H2S on activated carbon KAU and influence of the surface state

Properties of the oxidized activated carbon KAU treated at different temperatures in inert atmosphere were studied by means of DTA, Boehm titration, XPS and AFM methods and their catalytic activity in H₂S oxidation by air was determined. XPS analysis has shown the existence of three types of oxygen species on carbon catalysts surface. The content of oxygen containing groups determined by Boehm titration is correlated with their amount obtained by XPS. Catalytic activity of the KAU catalysts in selective oxidation of hydrogen sulfide is connected with chemisorbed charged oxygen species (O_3.1 oxygen type with BE 536.8–537.7 eV) present on the carbons surface.

Formation of dense sulfur layer (islands of sulfur) on the carbons surface and removal of active oxygen species are the reason of the catalysts deactivation in H₂S selective oxidation. The treatment of deactivated catalyst in inert atmosphere at 300 °C gives full regeneration of the catalyst activity at low temperature reaction but only its partial reducing at high reaction temperature. The last case is connected with transformation of chemisorbed charged oxygen species into CO groups.

The KAU samples treated in flow of inert gas at 900–1000 °C were very active in H₂S oxidation to elemental sulfur transforming up to 51–57 mmol H₂S/g catalyst at 180 °C with formation of 1.7–1.9 g S_x/g catalyst.     

Removal of manganese from water supplies intended for human consumption: a case study

In the Volcano Etna area (Sicily) a substantial part of groundwater, used for potable purpose, has concentrations of metals (vanadium, iron and manganese) higher than the maximum contaminant levels (MCLs) set by European and National regulations (European Directive 98/83 and D.Lgs. 31/2001). Specifically, high levels of manganese, up to 1810 μg/l, significantly exceeding the maximum contaminant level (MCL = 50 μg/l), were detected in groundwaters currently used as drinking water supply upwelled from the Etna Volcano aquifer. The paper presents the results of the manganese removal process by potassium permanganate oxidation followed by flocculation, settling and filtration. Batch tests were carried out varying pH, oxidant doses and polyelectrolytes. Two different filters (35 μm and 0.45 μm mesh) were tested as a final step of the treatment. Significant removal (up to 95%) was achieved by addition of polyelectrolytes at pH 8.5, with a 0.5 stoichiometric dose of oxidant and final filtration through 35 μm mesh filter.     

Propane partial oxidation over M-substituted vanadyl phosphates dispersed on titania and silica

Mono-substituted M³⁺ compounds of vanadyl phosphate dihydrate VOPO₄·2H₂O, with formula [M(H₂O)]_xVO_1−xPO₄·nH₂O (M=Al, Fe, Cr, x=0.15–0.20, n=2–2.40), and a di-substituted compound with formula Fe_0.08Cr_0.08(H₂O)_0.16VO_0.84PO₄·2.9H₂O, either pure or supported, were characterised by XRD, EDAX, TG/DTA, physisorption and chemisorption measurements, and tested as catalysts in the partial oxidation of propane. Incorporation of the M³⁺ cation into VOPO₄ produces a marked increase in surface area, pore volume, and reducibility, with subsequent enhancement of the catalytic activity. Upon adsorption of these compounds on titania, a homogeneous distribution of highly dispersed species is obtained, whereas on silica small conglomerates of crystalline phases of VOP and FeVOP are formed, presumably by polymerisation on the acidic surface sites of the support. The titania-supported samples exhibit higher catalytic activity and better selectivity to partial oxidation products (acetic acid and propene), compared to silica-based materials; these effects are attributed to the higher dispersion and reducibility of the surface species. Propane oxidation over the supported materials undergoes transition to the ignited state, in which surface temperatures up to 900 K are attained, and homogenous reactions yield mainly propene and CO.     

Evaluation of cure temperature effects in cataphoretic automotive primers by electrochemical techniques

The temperature dependences of dc electrical conductivity, σ, and Seebeck coefficient, S, for six recently synthesized quaternary salts of bipyridine and indolizine pyridine (GAL compounds) in thin films, have been investigated. The thin-film samples (d = 0.06–0.60 μm) were deposited by spin-coating using dimethylformamide solutions, onto glass.

XRD was used for structure investigations, while AFM technique, corroborated to optical microscopy, was used for the examination of surface morphology of samples.

The present compounds behave as typical n-type polycrystalline semiconductors.

The activation energy of electrical conduction, ΔE, ranged between 1.61 and 1.73 eV, while the ratio of charge carrier mobilities, b, laid in the range 1.08–1.14.

By studying optical absorption direct band gaps ranged between 3.78 and 4.00 eV have been found.

Some correlations between semiconducting parameters and molecular structure of the compounds were established. The model based on band gap representation can be conveniently used for the explanation of electronic transport in investigated compounds.

The investigated compounds are also suitable for applications in thermistor manufacture.     

Copper-impregnated Al–Ce-pillared clay for selective catalytic reduction of NO by C3H6

The selective catalytic reduction (SCR) of NO by hydrocarbon is an efficient way to remove NO emission from lean-burn gasoline and diesel exhaust. In this paper, a thermally and hydrothermally stable Al–Ce-pillared clay (Al–Ce-PILC) was synthesized and then modified by SO₄²⁻, whose surface area and average pore diameter calcined at 773 K were 161 m²/g and 12.15 nm, respectively. Copper-impregnated Al–Ce-pillared clay catalyst (Cu/SO₄²⁻/Al–Ce-PILC) was applied for the SCR of NO by C₃H₆ in the presence of oxygen. The catalyst 2 wt% Cu/SO₄²⁻/Al–Ce-PILC showed good performance over a broad range of temperature, its maximum conversion of NO was 56% at 623 K and remained as high as 22% at 973 K. Furthermore, the presence of 10% water slightly decreased its activity, and this effect was reversible following the removal of water from the feed. Py-IR results showed SO₄²⁻ modification greatly enhanced the number and strength of Brönsted acidity on the surface of Cu/SO₄²⁻/Al–Ce-PILC, which played a vital role in the improvement of NO conversion. TPR and XPS results indicated that both Cu⁺ and isolated Cu²⁺ species existed on the optimal catalyst, mainly Cu⁺, as Cu content increased to 5 wt%, another species CuO aggregates which facilitated the combustion of C₃H₆ were formed.     

Modeling remineralization of desalinated water by limestone dissolution

Desalted waters or highly soft waters produced by desalination plants cannot be directly used as they are unpalatable, corrosive and unhealthy. Remineralization is necessary in order to overcome these problems. A commonly used operation in the remineralization process is to contact CO₂ acidified desalinated water with a bed of domestic limestone. Limestone dissolution provides two essential ingredients to the water—bicarbonate alkalinity and calcium content: CaCO₃ + CO₂ + H₂O = Ca²⁺ + 2HCO₃^–. Limestone dissolution is a slow rate-controlling step. Prediction of the limestone rate of dissolution as a function of the water composition is essential for reliable design and operation of the limestone contactor. A critical comparison of various kinetic expressions proposed in the literature carried out in this study reveals major differences in results evaluated from different dissolution models. An experimental study was conducted in order to identify the most reliable kinetic dissolution model. Two series of experiments were carried out—one involving remineralization of distilled water containing low initial CO₂ concentrations (0.5–2 mM) and the other, remineralization of soft water, having high initial CO₂ concentrations (1.5–15 mM). The CO₂ acidified water was contacted in a 2 m high vertical column (32 mm I.D.), packed with 2.85 mm calcite particles. The change in water composition along the column was monitored to provide both differential and integral dissolution data. Analysis of the data showed that none of the available models fitted the experimental results. The closest agreement was with the rather complex model of Plummer et al but this agreement was rather mediocre. In the high CO₂ content range, the model predicted dissolution rates higher by a factor of 2–4 in the high CO₂ range and by a factor of 10–20 in the low CO₂ range. Based on the experimental results, two models were developed for the design of limestone dissolution column contactors. When the final composition of the remineralized water has a CO₂ content above 2 mM, the limestone bed can be designed by a very simple integral expression. However, if the dissolution depletes the CO₂ concentration to low values, well below 2 mM, the bed design requires numerical integration of the more general dissolution rate expression derived in this work.