Journal of Hazardous Materials (v.128, #2-3)
Effects of particle size, organic matter and ionic strength on the phosphate sorption in different trophic lake sediments by Shengrui Wang; Xiangcan Jin; Qingyun Bu; Xiaoning Zhou; Fengchang Wu (95-105).
The trophic status and development of lake system is significantly influenced by the phosphate sorption at the sediment–water interface. The effects of organic matter, particle size and ionic strength on the phosphate sorption by sediments were investigated in this study. The results show that maximum phosphate sorption capacity (Q max), equilibrium phosphate concentration (EPC0), phosphate sorption efficiency (k) and phosphate sorption rate decreased as particle size increased for all the studied sediments. But the reliable desorbed phosphorus (RDP) increased. Q max, EPC0, k and RDP of different particle size fractions varied and there were no obvious differences among different trophic lake sediments. Q max, EPC0 increased while k and RDP decreased as the pollution level of lake sediment increased. The phosphate sorption mainly occurred within 0.5 h. Power function and simple Elovich models were the best kinetic models for the phosphate sorption of the different particle size fractions. Q max and phosphate sorption rate decreased with the decreasing of organic matter content of sediments and the increasing of ionic strength. This study suggests that ionic strength and organic matter had similar effects on the phosphate sorption for different trophic lake sediments.
Keywords: Phosphate sorption; Organic matter; Particle size; Ionic strength; Sediment; Lake;
Ambient BTEX and MTBE in the neighborhoods of different industrial parks in Southern Taiwan by Lien-Te Hsieh; Hsi-Hsien Yang; Ho-Wen Chen (106-115).
This study assessed the concentrations of five volatile organic compounds (VOCs), including BTEX (the acronym for benzene, toluene, ethylbenzene, and xylene) and methyl tertiary-butyl ether (MTBE), in six different industrial park neighborhoods in southern Taiwan, including the Nei-Pu, Ping-Tung, Ping-Nan, Ren-Wu, Lin-Yuan and Nan-Zi industrial parks. The concentrations of MTBE and BTEX ranged from undetectable to 145.6 μg/m3. Average MTBE–BTEX ratios of Nei-Pu, Ping-Tung, Ping-Nan, Ren-Wu, Lin-Yuan and Nan-Zi were (13.4:3.6:4.7:1.0:7.4), (2.9:1.0:1.7:1.3:2.9), (3.0:1.0:2.7:1.0:2.7), (5.2:1.0:8.6:1.7:4.9), (3.1:3.1:2.8:1.0:3.3) and (4.3:1.2:3.6:1.0:3.8), respectively. Moreover, average T/B ratios in Nei-Pu, Ping-Tung, Ping-Nan, Ren-Wu, Lin-Yuan and Nan-Zi were 1.3, 1.7, 2.6, 8.6, 0.9 and 2.9, respectively. High T/B ratio (8.6) in the neighborhood of the Ren-Wu industrial park suggested that the emission of large additional sources of toluene from this industrial park, or the existence of major differences in the auxiliary fuels used. Average X/E ratios in Nei-Pu, Ping-Tung, Ping-Nan, Ren-Wu, Lin-Yuan and Nan-Zi were 7.4, 2.2, 2.7, 2.9, 3.3 and 3.8, respectively. The lower X/E ratio (2.2) in the Ping-Tung neighborhood compared to elsewhere indicates an aged air parcel. Furthermore, principal component analysis also confirmed that the dominant influences in the six different industrial park neighborhoods were related to the emissions of MTBE, benzene and toluene.
Keywords: MTBE; BTEX; Industrial park neighborhood; T/B ratio; X/E ratio;
Non-isothermal kinetics of the dehydration reaction of 3-nitro-1,2,4-triazol-5-one rubidium and cesium complexes by Haixia Ma; Jirong Song; Heming Xiao; Rongzu Hu; Huali Wang; Penggang Jin; Yuan Wang (116-121).
3-Nitro-1,2,4-triazol-5-one (NTO) rubidium and cesium complexes were synthesized by mixing the aqueous solution of NTO and their respective metal carbonates. Their thermal decomposition and the non-isothermal kinetics of the dehydration reaction were studied under the non-isothermal condition by DSC and TG-DTG methods. The kinetic parameters were obtained from analysis of the DSC and TG-DTG curves by Kissinger method, Ozawa method, the differential method and the integral method. The most probable mechanism functions for the dehydration reaction of the title complexes were suggested by comparing the kinetic parameters. The dehydration decomposition reaction of RbNTO·H2O and CsNTO·H2O appears to be the same as Avrami–Erofeev equation: f ( α ) = ( 5 / 2 ) ( 1 − α ) [ − ln ( 1 − α ) ] 3 / 5 , G ( α ) = [ − ln ( 1 − α ) ] 2 / 5 , n = 2/5. The critical temperature of thermal explosion is 240.88 °C for RbNTO·H2O and 246.27 °C for CsNTO·H2O.
Keywords: 3-Nitro-1,2,4-triazol-5-one (NTO) rubidium complex; NTO cesium complex; Dehydration; Non-isothermal kinetics;
Synergistic adsorption of phenol from aqueous solution onto polymeric adsorbents by Zhang W. Ming; Chen J. Long; Pan B. Cai; Zhang Q. Xing; B. Zhang (123-129).
Adsorption of phenol from aqueous solution onto a nonpolar adsorbent, aminated adsorbent and weak base adsorbent (Amberlite XAD4, NDA103 and Amberlite IRA96C, respectively) at temperatures from 293 to 313 K was studied for the weak interactions between the phenol molecules and the polymeric adsorbents. Isotherms of Langmuir and Freundlich equation with characteristic parameters for different adsorbents were well fitted to the batch equilibrium adsorption data. The adsorption capacity on NDA103 driven by hydrogen bonding and van der Waals interaction together is higher than that on IRA96C driven by hydrogen bonding interaction only and on XAD4 driven by van der Waals interaction only. For evaluating synergistic adsorption for phenol–water systems onto polymeric adsorbents, the adsorption capacity is normalized to the amounts of specific surface area and amino groups of adsorbents. The synergistic effect with other weak interactions would contribute more to the adsorption as acting simultaneously than that of acting individually.
Keywords: Polymeric adsorbent; Phenol; Adsorption behavior; Synergistic effect;
Oxidation of gas phase trichloroethylene and toluene using composite sol–gel TiO2 photocatalytic coatings by Mehrdad Keshmiri; Tom Troczynski; Madjid Mohseni (130-137).
The previously developed composite sol–gel (CSG) process is proposed for the deposition of thick (10–50 μm) porous films of photocatalytic TiO2. The CSG titania was developed by binding pre-calcined TiO2 particles with TiO2 sol. It had relatively high surface area (15–35 m2/g) and good resistance against mechanical stress and abrasion. Photocatalytic activity tests were carried out on trichloroethylene (TCE) and toluene, and compared with those of standard Degussa P-25 titania. The CSG photocatalyst provided good photo-efficiency in removing both pollutants from contaminated air streams. When compared with P-25 titania, the CSG photocatalyst showed a similar photo-efficiency with first-order kinetic rate constants not significantly different from that of P-25. For both photocatalysts the rate of photocatalytic oxidation of TCE was significantly greater than that obtained for toluene. Overall, the combination of better mechanical integrity, resistance against abrasion, and comparable photocatalytic efficiency of the CSG titania versus that of P-25 titania, make the composite sol–gel (CSG) photocatalyst a viable alternative for industrial applications where long term stability, superior mechanical properties, and good photo-efficiency are of critical value.
Keywords: Photocatalysis; TiO2; Composite sol–gel; Volatile organic compounds; Toluene; Trichloroethylene;
Adsorption of acid dye onto organobentonite by P. Baskaralingam; M. Pulikesi; D. Elango; V. Ramamurthi; S. Sivanesan (138-144).
Removal of Acid Red 151 from aqueous solution at different dye concentrations, adsorbent doses and pH has been studied. The bentonite clay has been modified using cationic surfactants, which has been confirmed using XRD and FT-IR analyses. Experimental result has shown that the acidic pH favours the adsorption. The adsorption isotherms are described by means of Langmuir and Freundlich isotherms. The adsorption capacity has been found to be 357.14 and 416.66 mg g−1 for the cetyldimethylbenzylammonium chloride-bentonite (CDBA-bent) and cetylpyridinium chloride-bentonite (CP-bent), respectively. Kinetic studies show that the adsorption followed second-order kinetics.
Keywords: Adsorption; Acid dye; Organoclay; Isotherms; Kinetics;
TiO2/UV/O3-BAC processes for removing refractory and hazardous pollutants in raw water by Laisheng Li; Wanpeng Zhu; Pengyi Zhang; Qiuyun Zhang; Zulin Zhang (145-149).
TiO2/UV/O3-BAC (biological activated carbon) process was employed to treat raw water and compared to UV/O3-BAC process in its optimum parameters (3 mg/L ozone dosage with 15 min oxidation time and 15 min empty bed contact time in BAC). The results showed that the presence of TiO2 improved ozone utilization and biodegradability of the effluent. For the dissolved organic carbon (DOC) removal, TiO2/UV/O3-BAC was more efficient than UV/O3-BAC and its synergetic effect is more than that in UV/O3-BAC process. It was showed that small molecules with MW < 3000 Da predominated in the raw water accounting for more than 56% DOC, they were increased after oxidation, accounting for more than 64% DOC. GC/MS analysis showed that TiO2/UV/O3-BAC process was effective in removing phthalate esters (PAEs) and persistent organic pollutants (POPs). PAEs’ removal ratio reached more than 94% and reduced with the increase of the length of the alkyl side chains and the alkyl branch chains. TiO2/UV/O3-BAC process was also very effective in removing POPs. Polybromobiphenyls’ removal rate reached more than 89% and decreased with the increase of substitutional bromines except for 2,2′,5,5′-tetrabromobiphenyl, which can be completely removed.
Keywords: Photocatalysis; Titanium dioxide; Ozonation; Biological activated carbon; Dissolved organic carbon; Phthalate esters and persistent organic pollutants;
Adsorption kinetics of malachite green onto activated carbon prepared from Tunçbilek lignite by Y. Önal; C. Akmil-Başar; Didem Eren; Çigdem Sarıcı-Özdemir; Tolga Depci (150-157).
Adsorbent (T3K618) has been prepared from Tunçbilek lignite by chemical activation with KOH. Pore properties of the activated carbon such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by t-plot based on N2 adsorption isotherm. The N2 adsorption isotherm of malachite green on T3K618 is type I. The BET surface area of the adsorbent which was primarily contributed by micropores was determined 1000 m2/g. T3K618 was used to adsorb malachite green (MG) from an aqueous solution in a batch reactor. The effects of initial dye concentration, agitation time, initial pH and adsorption temperature have been studied. It was also found that the adsorption isotherm followed both Freundlich and Dubinin–Radushkevich models. However, the Freundlich gave a better fit to all adsorption isotherms than the Dubinin–Radushkevich. The kinetics of adsorption of MG has been tested using pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Results show that the adsorption of MG from aqueous solution onto micropores T3K618 proceeds according to the pseudo-second-order model. The intraparticle diffusion of MG molecules within the carbon particles was identified to be the rate-limiting step. The adsorption of the MG was endothermic (ΔH° = 6.55–62.37 kJ/mol) and was accompanied by an increase in entropy (ΔS° = 74–223 J/mol K) and a decrease in mean value of Gibbs energy (ΔG° = −6.48 to −10.32 kJ/mol) in the temperature range of 20–50 °C.
Keywords: Activated carbon; Adsorption; Reaction kinetics; Lignite; Malachite green;
Study on photocatalytic degradation of several volatile organic compounds by Guo-Min Zuo; Zhen-Xing Cheng; Hong Chen; Guo-Wen Li; Ting Miao (158-163).
The gas-phase photolytic and photocatalytic reactions of several aromatics and chlorohydrocarbons were investigated. The experimental results revealed that chlorohydrocarbons like trichloroethylene, dichloromethane and chloroform could be degraded through either photolysis or photocatalysis under irradiation of germicidal lamp, and the elimination rate of chlorohydrocarbons through photolysis was quicker than that through photocatalysis. UV light from a germicidal lamp could directly lead to degradation of toluene but could hardly act on benzene. The photodegradation rate for these volatile organic compounds (VOCs) through photolysis followed an order: trichloroethylene > chloroform > dichloromethane > toluene > benzene > carbon tetrachloride, and through photocatalysis followed: trichloroethylene > chloroform > toluene > dichloromethane > benzene > carbon tetrachloride. Besides, a series of modified TiO2 photocatalysts were prepared by depositing noble metal, doping with transition metal ion, recombining with metal oxides and modifying with super strong acid. Activity of these catalysts was examined upon photocatalytic degradation of benzene as a typical compound that was hard to be degraded. It indicated that these modification methods could promote the activity of TiO2 catalyst to different extent. The apparent zero-order reaction rate constant for degrading benzene over SnO2/TiO2 catalyst had the highest value, which was nearly three times as that over P25 TiO2. But it simultaneously had the lowest rate for mineralizing the objective compound. In spite that Fe3+/TiO2 catalyst behaved slightly less active than SnO2/TiO2 for degradation of benzene, the mineralization rate over Fe3+/TiO2 was the highest one among the prepared catalysts.
Keywords: Gas-phase; Photocatalysis; Photolysis; Volatile organic compounds; Titanium dioxide; Catalyst modification;
Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment by Amita D. Apte; Vinod Tare; Purnendu Bose (164-174).
Calculations show that oxidation of chromium oxide (Cr2O3) by oxygen and oxidation of chromium hydroxide (Cr(OH)3) by manganese dioxide (MnO2) are thermodynamically feasible in both aerobic and mildly anoxic environments. Experiments were carried out to determine the rate and extent of chromium oxidation under various conditions, i.e., when Cr2O3 was heated in the presence of oxygen, when Cr(OH)3 and MnO2 mixtures were suspended in aerobic or anoxic aqueous media at various pH values, when Cr(OH)3 and MnO2 mixtures interacted in moist aerobic conditions and when chromium assumed to be Cr(OH)3 and manganese assumed to be MnO2 interacted in the presence of competing electron donors/acceptors, as is the case in chromium-contaminated sludge. Results indicate that trivalent chromium in Cr2O3 could be readily converted to hexavalent chromium at a temperature range of 200–300 °C, with conversion rates of up to 50% in 12 h. In aqueous media, Cr(OH)3 was slowly converted to dissolved Cr(VI) in the presence of MnO2, both in aerobic and anoxic conditions, with conversion rates of up to 1% in 60 days. In moist aerobic conditions and in the presence of MnO2, Cr(OH)3 slowly converted to hexavalent chromium, with up to 0.05% conversion observed in 90 days. Chromium oxidation also occurred in sludge samples, especially under aerobic conditions. However, such transformation was found to be transitory, with the Cr(VI) formed being ultimately reduced back to Cr(III) due to the presence of various reducing agents in the sludge. Nevertheless since up to 17% conversion of Cr(III) to Cr(VI) occurred in sludge under aerobic conditions by 30 days, there is real danger under field conditions of spreading Cr(VI) pollution due to possible intervening rainfall, runoff and percolation.
Keywords: Chromium; Oxidation; Manganese dioxide; Chromium-contaminated sludge; Hexavalent chromium;
Effect of heating temperature on the sintering characteristics of sewage sludge ash by Kae-Long Lin; Kung-Yuh Chiang; Deng-Fong Lin (175-181).
This study investigated and analyzed the effects of the heating temperature on the properties of the sintered sewage sludge ash. The results indicated that the water absorption rate of the sintered sewage sludge ash samples decreased when the firing temperature was increased from 800 to 900 °C. When the heating temperature reached 1000 °C, the absorption rate decreased significantly. The bulk density of the sewage sludge ash samples increased by 2.3 g/cm3 when the heating temperature was increased from 900 to 1000 °C, indicating that the densification was affected by heating. The porosity of the sintered sewage sludge ash samples ranged from 36% to 39% when the heating temperature ranged from 600 to 900 °C. The least porosity occurred at 1000 °C; the sintered samples were well densified. When the temperature was between 900 and 1000 °C, the strength appeared to increase significantly, reaching 2040 kgf/cm2, implying an advance in densification due to sintering. The SEM observations were in general agreement with the trends shown by the density data.
Keywords: Sintering; Porosity; Sewage sludge ash; SEM observation;
Lumped kinetics and acute toxicity of intermediates in the ozonation of phenol in saline media by Eduardo Bessa Azevedo; Francisco Radler de Aquino Neto; Márcia Dezotti (182-191).
This work investigates the feasibility of ozonation for destroying phenol and removing organic matter in saline media. The reaction lumped kinetics was followed using the GLKM (General Lumped Kinetic Model). The main intermediate compounds were: catechol, hydroquinone, 4,4′-dihydroxybiphenyl, and 4-bromophenol. It could be noted no significant differences in phenol degradation, mineralization rates, and toxicity removal up to 2 g L−1 of salt. So, ozonation appears to be a technology that can be used in low salinity media, which is characteristic of waters destined to reuse and recycling programs inside industries.
Keywords: Ozone; Phenol; Saline media; Lumped kinetics; Toxicity; Intermediate;
Decolorization of acid black 24 by the FeGAC/H2O2 process by Huan-Jung Fan; Hung-Yee Shu; Kiyohiko Tajima (192-200).
FeGAC/H2O2 process was developed and employed in this research for the treatment of acid back 24. The removal efficiencies of five treatment processes (GAC, FeGAC, H2O2, GAC/H2O2, and FeGAC/H2O2) were studied in this research. The adsorption capacity of granular activated carbon (GAC) was greatly improved by the coating of iron oxide on GAC surface (FeGAC). The presence of H2O2 significantly improved the removal abilities of FeGAC and GAC. For instance, at solution pH 2, the removal efficiency of FeGAC/H2O2, GAC/H2O2, H2O2, FeGAC, and GAC were 76, 74, 59, 11, and 7%, respectively. The possible removal mechanisms of FeGAC/H2O2 process were proposed in this research. When treating the actual dye contaminated wastewater, the removal efficiencies of FeGAC/H2O2 and GAC/H2O2 were approximately six times greater than that of H2O2 process.
Keywords: Iron oxide coated GAC; Acid black 24; H2O2; Adsorption;
Application of Box–Wilson experimental design method for the photodegradation of bakery's yeast industry with UV/H2O2 and UV/H2O2/Fe(II) process by Ebru Ç. Çatalkaya; Füsun Şengül (201-207).
Decolorization and mineralization of bakery's yeast industry effluent by photochemical advanced oxidation processes (AOPs) utilizing UV with hydrogen peroxide and Photo-Fenton, were investigated in a laboratory scale photo-reactor equipped with a 16 W low-pressure mercury vapor lamp. The Box–Wilson experimental design method was employed to evaluate the effects of major process variables (e.g. pH, oxidant dose, and irradiation time) on the decolorization efficiency. Response function coefficients were determined by regression analysis of the experimental data and prediction results agreed with the experimental results. The optimum hydrogen peroxide concentration and irradiation time were found to be 5 mM and 50 min at pH 3, respectively, for UV/H2O2 process. In the Photo-Fenton process application, maximum decolorization efficiency (96.4%) was obtained at the optimum reaction conditions that were 100 mM H2O2 and 1 mM Fe(II) doses at pH 3, and 10 min of irradiation time.
Keywords: Bakery's yeast industry; Box–Wilson design; Decolorization; Photo-Fenton process; UV/H2O2 process;
On-site mercury-contaminated soils remediation by using thermal desorption technology by T.C. Chang; J.H. Yen (208-217).
In this study, the thermal desorption process was used to treat a mercury-contaminated soils in Taipei. A series of bench or pilot plant experiments were also performed the optimized operation condition. The results showed that the concentrations of residual mercury in all treated soils were below 2 mg/kg, some even lower than 0.05 mg/kg. The supernatant and exhaust gas stream of the condensed desorbed mercury vapor in the remediation site were also met with the effluent standard. The total fee was estimated to be US$ 3,557,000, when treating contaminated soil leading to a unit treatment cost of US$ 834/m3 of soil.
Keywords: Thermal desorption; Mercury; Soil; Remediation; Cost analysis;
Dissolution of a multicomponent DNAPL pool in an experimental aquifer by Kenneth Y. Lee; Constantinos V. Chrysikopoulos (218-226).
This paper presents the results from a well-defined, circular-shaped, multicomponent dense nonaqueous phase liquid (DNAPL) pool dissolution experiment conducted in a three-dimensional, bench scale model aquifer. The multicomponent pool is a mixture of tetrachloroethylene (PCE) and 1,1,2-trichloroethane (1,1,2-TCA); PCE was the major component and 1,1,2-TCA was the minor component. Downgradient plume concentrations were measured at five specific locations over time until the majority of the 1,1,2-TCA was depleted from the DNAPL pool source. The experimental results suggest distinct spatial-temporal plume patterns for minor DNAPL components versus major DNAPL components. The downgradient concentration varied over time for 1,1,2-TCA while a stable plume developed for PCE. A semi-analytical solution for contaminant transport resulting from dissolution of multicomponent nonaqueous phase liquid pools successfully simulated the plume structure and dynamics for both the major and minor DNAPL components.
Keywords: Groundwater pollution; Nonaqueous phase liquids; Dissolution; Contaminant transport; Mathematical models;
A preliminary study on sorption, diffusion and degradation of mustard (HD) in cement by Hairong Tang; Zhenxing Cheng; Min Xu; Shunxiang Huang; Liming Zhou (227-232).
A preliminary study has been done to examine the sorption, diffusion and degradation of mustard (HD) in cement. The sample of dried cement paste is a meso-porous adsorbant with a BET surface area around 40.8 m2/g, which is able to adsorb vapor of HD at room temperature and to result in a multiple-layer isotherm of II type. The molecule of HD seemed to chemically adsorb onto cement surface. Droplet of HD contaminating cement was able to be degraded into less toxic products, but in a very low rate of k = 4.8 × 10−5 min−1 and t 1/2 = 16 × 104 min at room temperature. Droplet of HD is able to penetrate through the layer of cement, but a cement plate of 8 mm can protect against HD droplets over 48 h. A decrease of thickness for cement layer or addition of sand in cement would lead to lower the protection time against HD droplets. The diffusion coefficient of HD molecule in cement was determined, about 1.3 × 10−4 cm2/min and of a typical diffusion in solid.
Keywords: Mustard; Cement; Sorption; Diffusion; Degradation;
Use of hen feathers as potential adsorbent for the removal of a hazardous dye, Brilliant Blue FCF, from wastewater by Alok Mittal (233-239).
Waste material, hen feather, a biosorbent, was successfully utilized in removing a water-soluble hazardous triphenylmethane dye, Brilliant Blue FCF from wastewater. The paper incorporates effect of pH, temperature, amount of adsorbent, contact time, concentration of adsorbate, etc. The adsorption data validates Langmuir and Freundlich adsorption isotherms and on the basis of these isotherms thermodynamic parameters like Gibb's free energy, change in enthalpy and entropy were calculated. Kinetics of the ongoing adsorption was also monitored and specific rate constants for the involved process were calculated at different temperatures. Kinetic measurements suggest a first order adsorption kinetics and adsorption was found to be applicable via film diffusion process in the entire concentration range.
Keywords: Hen feather; Brilliant Blue FCF; Adsorption; Kinetics; Waste material; Biosorbent;
Determination of lead in human saliva by combined cloud point extraction–capillary zone electrophoresis with indirect UV detection by Marta O. Luconi; Roberto A. Olsina; Liliana P. Fernández; M. Fernanda Silva (240-246).
A micelle-mediated phase separation without added chelating agents to preconcentrate trace levels of lead in human saliva as a prior step to its determination by capillary electrophoresis has been developed. The enrichment step is based on the cloud point extraction of lead with the non-ionic surfactant PONPE 7.5 in the absence of chelating agent. The surfactant-rich phase was diluted with acetonitrile and the resultant solution was injected directly into the CE instrument. Factors affecting the combined methodology such as surfactant-rich phase diluting agent, buffer pH and concentration, applied voltage, sample preparation and presence of additives were studied in detail. A BGE of 20 mM imidazole containing 30% acetonitrile, pH 6.20 was found to be optimal for the separation of lead from other saliva constituents. Indirect detection was performed at 205 nm. The detection limit value of lead for the preconcentration of 8 ml of saliva was 11.4 μg l−1. The calibration graph using the preconcentration system was linear with a correlation coefficient of 0.997 at levels near the detection limits up to at least 400 μg l−1. The reproducibility (R.S.D.) on the basis of migration time and peak area were better than 0.68 and 3.6%, respectively. The method was successfully applied to the determination of lead in human saliva.
Keywords: Cloud point extraction; Saliva biomarkers; Lead; Capillary zone electrophoresis;
Removal of Cd(II) from aqueous solution by kaolinite, montmorillonite and their poly(oxo zirconium) and tetrabutylammonium derivatives by Susmita Sen Gupta; Krishna G. Bhattacharyya (247-257).
Kaolinite, montmorillonite and their poly(oxo zirconium) and tetrabutylammonium derivatives have been used in this work for removing Cd(II) from aqueous solution. Batch adsorption studies were carried out under various Cd(II) concentrations, amount of clay adsorbents, pH, interaction time and temperature. The uptake of the metal was initially very fast, but gradually slowed down indicating diffusion into the interior of the adsorbent particles. The adsorption processes were more akin towards second order reaction mechanism. The suitability of the adsorbent was tested by fitting the adsorption data with Langmuir and Freundlich isotherms, which gave good fits with both isotherms. Adsorption was poor in strongly acidic solution but was improved in alkaline medium and continuously increased with rise in pH. The values of the thermodynamic parameters, ΔH, ΔS and ΔG, indicated the interactions to be thermodynamically favourable.
Keywords: Kaolinite; Montmorillonite; Poly(oxo zirconium) clay; Tetrabutylammonium clay; Sorption isotherm;
Effect of biogenic substrate concentration on the performance of sequencing batch reactor treating 4-CP and 2,4-DCP mixtures by Erkan Sahinkaya; Filiz B. Dilek (258-264).
Effect of a biogenic substrate (peptone) concentration on the performance of sequencing batch reactor (SBR) treating 220 mg/l 4-chlorophenol (4-CP) and 110 mg/l 2,4-dichlorophenol (2,4-DCP) mixtures was investigated. In this context, peptone concentration was gradually decreased from 300 mg/l to null in which chlorophenols were fed to the reactor as sole carbon and energy sources. By this way, the effect of peptone concentration on observed yield coefficient (Y), biomass concentration, chlorophenols and COD removal performances were investigated. Decreasing peptone concentration accompanied with lower biomass concentration led to increase in peak chlorophenol and COD concentrations within the reactor during each SBR cycle. This, in turn, caused noteworthy declines in the removal rates as chlorophenol degradations followed Haldane substrate inhibition model. Also, increased peak chlorophenol concentrations led to the accumulation of 5-chloro-2-hydroxymuconic semialdehyde (CHMS), which is -meta cleavage product of 4-CP. Despite the decreased removal rates, complete chlorophenols and CHMS degradation, in addition to high COD removal efficiencies (>90%), were observed for all studied conditions, even chlorophenols were added as sole carbon and energy sources. Another significant point is that 2,4-DCP at slightly elevated concentrations (>20 mg/l) within the reactor caused a strong competitive inhibition on 4-CP degradation. In SBR, feeding the influent to the reactor within a certain period (i.e. filling period) provided dilution of coming wastewater, which decreased the chlorophenols concentrations to which microorganisms were exposed. Therefore, use of SBR may help to avoid both self and competitive inhibitions in the treatment of 4-CP and 2,4-DCP mixture especially in the presence high biogenic substrate concentrations. In addition, isolation and identification studies have indicated that Pseudomonas sp. and Pseudomonas stutzeri were dominant species in the acclimated mixed culture.
Keywords: 4-Chlorophenol; 2,4-Dichlorophenol; SBR; Biodegradation kinetics;
Decolorization of Reactive Red 2 by advanced oxidation processes: Comparative studies of homogeneous and heterogeneous systems by Chung-Hsin Wu; Chung-Liang Chang (265-272).
This study investigated the decolorization of the Reactive Red 2 in water using advanced oxidation processes (AOPs): UV/TiO2, UV/SnO2, UV/TiO2 + SnO2, O3, O3 + MnO2, UV/O3 and UV/O3 + TiO2 + SnO2. Kinetic analyses indicated that the decolorization rates of Reactive Red 2 could be approximated as pseudo-first-order kinetics for both homogeneous and heterogeneous systems. The decolorization rate at pH 7 exceeded pH 4 and 10 in UV/TiO2 and UV/TiO2 + SnO2 systems, respectively. However, the rate constants in the systems (including O3) demonstrated the order of pH 10 > pH 7 > pH 4. The UV/TiO2 + SnO2 and O3 + MnO2 systems exhibited a greater decolorization rate than the UV/TiO2 and O3 systems, respectively. Additionally, the promotion of rate depended on pH. The variation of dye concentration influenced the decolorization efficiency of heterogeneous systems more significant than homogeneous systems. Experimental results verified that decolorization and desulfuration occurred at nearly the same rate. Moreover, the decolorization rate constants at pH 7 in various systems followed the order of UV/O3 ≧ O3 + MnO2 ≧ UV/O3 + TiO2 + SnO2 > O3 > UV/TiO2 + SnO2 ≧ UV/TiO2 > UV/SnO2.
Keywords: Reactive Red 2; Advanced oxidation processes; TiO2; SnO2; O3; MnO2; Decolorization;
Adsorptive removal of phosphate from aqueous solutions using raw and calcinated dolomite by S. Karaca; A. Gürses; M. Ejder; M. Açıkyıldız (273-279).
This study explored the feasibility of utilizing raw and calcinated dolomite under CO2 atmosphere for phosphate removal in laboratory experiments. The experimental work emphasized the evaluation of phosphate adsorption characteristics of this adsorbent material. Studies were conducted to delineate the effect of contact time, initial phosphate concentration, temperature, pH, stirring speed, adsorbent dose and calcination temperature. Phosphate removal decreased with increasing temperature and slightly increased with increasing of pH. The observed decrease in the adsorption capacity with increase of the temperature from 20 to 40 and to 60 °C indicates that the low temperatures favor the phosphate removal by adsorption onto dolomite. Phosphate removal was seen to decrease with increasing calcination temperature due to the structural changes occurring in the structure and pore size distribution of dolomite samples during calcination. The experimental data obtained were applied to the Freundlich, Langmuir, BET, Halsey, Harkins–Jura, Smith and Henderson isotherm equations to test the fit of these equations to raw and calcinated dolomite samples. By considering the experimental results and adsorption models applied in this study, it can be concluded that adsorption of phosphate occurs predominantly through physical interactions, and the dolomite sample has a heteroporous structure. The large values of the constants for Henderson equation and the high value of y m obtained from BET equation indicate the microporous structure is more stable in raw and calcinated dolomite samples.
Keywords: Phosphate adsorption; Dolomite; Calcination; Isotherm models;
Implication of chromium speciation on disposal of discarded CCA-treated wood by Jinkun Song; Brajesh Dubey; Yong-Chul Jang; Timothy Townsend; Helena Solo-Gabriele (280-288).
The wood preservative chromated copper arsenate (CCA) contains hexavalent chromium [Cr(VI)] and the conversion of Cr(VI) to trivalent chromium [Cr(III)] drives fixation of the treatment chemicals to the wood fibers. Since the toxicity of Cr depends on its valence state, an assessment of the Cr species occurring in CCA-treated wood, as well as leachates and ashes from CCA-treated wood, is helpful when assessing implications for disposal. In this study, both new and weathered wood samples of CCA-treated wood and their ashes were evaluated for total Cr and Cr(VI) within the solid matrices and within leachates. Results show that for both new and weathered CCA-treated wood, Cr(VI) occurred in the range of 0.7–4% of the total Cr. Greater Cr leaching occurred at the pH extremes, with Cr(VI) only measured under alkaline pH values (pH > 9.0). Total chromium concentrations from synthetic precipitation leaching procedure (SPLP) leachates from CCA-treated wood were consistently less than 3 mg/L with Cr(VI) below detection limits. The results suggest that leaching of Cr(VI) from discarded CCA-treated wood should not be a concern in most landfill environments. One exception would be disposal in landfills with alkaline leachate; Cr(VI) was observed to leach from CCA-treated wood in the presence of alkaline leachate from crushed concrete. When CCA-treated wood is combusted, chromium becomes concentrated in the ash. Cr(VI) in ash from the combustion of CCA-treated wood was found between 4 and 7% of the total chromium. In ash from the combustion of wood recovered from construction and demolition (C&D) debris (which contained some CCA-treated wood), Cr(VI) accounted for as much as 43% of the total Cr. Nearly, all of the Cr in SPLP leachates produced from the ash was in the Cr(VI) form. The degree of Cr(VI) leaching from the ash was highly dependent upon the alkalinity of the ash, with higher ash leachate pH resulting in greater concentrations of Cr(VI).
Keywords: Chromium; Chromium speciation; Chromated copper arsenate; SPLP; Hexavalent chromium; Trivalent chromium; Treated wood;
Defluoridation of groundwater using brick powder as an adsorbent by Asheesh Kumar Yadav; C.P. Kaushik; Anil Kumar Haritash; Ankur Kansal; Neetu Rani (289-293).
Defluoridation of groundwater using brick powder as an adsorbent was studied in batch process. Different parameters of adsorption, viz. effect of pH, effect of dose and contact time were selected and optimized for the study. Feasible optimum conditions were applied to two groundwater samples of high fluoride concentration to study the suitability of adsorbent in field conditions. Comparison of adsorption by brick powder was made with adsorption by commercially available activated charcoal. In the optimum condition of pH and dose of adsorbents, the percentage defluoridation from synthetic sample, increased from 29.8 to 54.4% for brick powder and from 47.6 to 80.4% for commercially available activated charcoal with increasing the contact time starting from 15 to 120 min. Fluoride removal was found to be 48.73 and 56.4% from groundwater samples having 3.14 and 1.21 mg l−1 fluoride, respectively, under the optimized conditions. Presence of other ions in samples did not significantly affect the deflouridation efficiency of brick powder. The optimum pH range for brick powder was found to be 6.0–8.0 and adsorption equilibrium was found to be 60 min. These conditions make it very suitable for use in drinking water treatment. Deflouridation capacity of brick powder can be explained on the basis of the chemical interaction of fluoride with the metal oxides under suitable pH conditions. The adsorption process was found to follow first order rate mechanism as well as Freundlich isotherm.
Keywords: Defluoridation; Adsorption; Brick powder (BP); Commercially available activated charcoal (CAC);
by G.F. Bennett (294).
by Gary F. Bennett (294-295).
by Gary F. Bennett (295).
by Gary F. Bennett (296).
by Gary F. Bennett (296-297).
by Gary F. Bennett (297-298).
by Gary F. Bennett (297).
volume contents (299-300).