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ABSTRACT: Both an optimization statistical model and a chemical thermodynamic equilibrium computer model were proposed to develop, improve, and optimize struvite precipitation process.
The NH(4)-N in synthetically prepared wastewater was removed using struvite precipitation technology. A quadratic statistical modeling, response surface methodology (RSM), was applied to investigate the improvement availability for high-level removal of ammonium-nitrogen by struvite precipitation. Then, a chemical equilibrium model, Visual MINTEQ, was used to calculate the equilibrium speciation and saturation index in aqueous solution and solid phases. In addition, the availability of Mg(2+), NH(4)(+), and PO(4)(3-) ions as a function of pH was modeled. The predicted and experimental data indicated that the two models might describe the experiments well. The results showed that pH was an important parameter in ammonium-nitrogen removals at low initial NH(4)-N concentration. P/N molar ratio was a limiting factor on struvite precipitation at high initial NH(4)-N concentration.
Within the ranges of the investigated factors, Visual MINTEQ program can be proposed to predetermine the concentration of ammonium precipitated by struvite, and RSM can be used to predict total NH(4)-N removal by both struvite precipitation and ammonia volatilization from our investigated system operated at high pH and opened to the atmosphere.
Environmental Science and Pollution Research 07/2011; 19(2):347-60. · 2.65 Impact Factor
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ABSTRACT: Landfill leachate was treated by a combined sequential batch reactor (SBR), coagulation, Fenton oxidation and biological aerated filter (BAF) technology. The metals in treatment process were fractionated into three fractions: particulate and colloidal (size charge filtration), free ion/labile (cation exchange) and non-labile fractions. Fifty percent to 66% Cu, Ni, Zn, Mn, Pb and Cd were present as particulate/colloidal matter in raw leachate, whereas Cr was present 94.9% as non-labile complexes. The free ion/labile fractions of Ni, Zn, Mg, Mn, Pb and Cd increased significantly after treatment except Cr. Fifty-nine percent to 100% of Al was present mainly as particulate/colloidal matter >0.45 μm and the remaining portions were predicted as non-labile complexes except in coagulation effluent. The speciation of Fe varied significantly in various individual processes. Visual MINTEQ simulation showed that 95-100% colloidal species for Cu, Cd and Pb were present as metal-humic complexes even with the lower dissolved organic carbon. Optimum agreements for the free ion/labile species were within acidic solution, whereas under-estimated in alkaline effluents. Overestimated particulate/colloidal fraction consisted with the hypothesis that a portion of colloids in fraction <0.45 μm were considered as dissolved.
Science of The Total Environment 02/2011; 409(9):1613-20. · 3.29 Impact Factor
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ABSTRACT: The treatment of concentrated landfill leachate rejected from reverse osmosis (RO) with Fenton process was studied, and the system model was developed through the examination of reaction kinetics. The leachate is typically non-biodegradable with low BOD(5)/COD ratio 0.01. The oxidation reactions of Fenton process was found to be a two-stage process, where a fast initial reaction (H(2)O(2)/Fe(2+)) was followed by a much slower one (H(2)O(2)/Fe(3+)). A simple and more accurate mathematics model based on COD and TOC removals has been derived successfully to describe the two-stage reaction kinetics. The two corresponding parameters involved in this model have been identified as the initial reaction rate and the maximum oxidation removal efficiency, respectively. It was found to be very useful for evaluating the performance of Fenton system and/or for process design using the two parameters under different experimental conditions.
Waste Management 10/2010; 31(3):468-74. · 2.43 Impact Factor
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ABSTRACT: In this study, the Fenton process was found to be successful to treat landfill leachate rejected after reverses osmose treatment. Central composite design (CCD) and response surface method (RSM) were applied to evaluate and optimize the interactive effects of three operating variables, initial pH and dosages of H(2)O(2) and Fe(2+) on physical and oxidative performances of Fenton process. Six dependent parameters such as overall chemical oxygen demand (COD) removal, COD removals of oxidation and coagulation, mineralization, humic substances (HS) removal and sludge volume ratio (SVR) were either directly measured or calculated as responses. According to analysis of variances (ANOVA) results, six proposed models could be used to navigate the design space with high regression coefficient R(2) varied from 0.9489 to 0.9988. It was found that initial pH, H(2)O(2) and Fe(2+) dosage had significant effects on the overall COD removal, mineralization and HS removal due to their respective effects on the oxidation and coagulation removals. Synergies effect of oxidation and coagulation during Fenton process controlled the treatment. The visual search of overlaying critical response contours plot was demonstrated. The results indicated the optimum conditions to be 3.64 of initial pH, 100 mM of Fe(2+) and 240 mM of H(2)O(2) dosage, respectively. The experimental data and model predictions agreed well. The overall COD removal, COD removals of oxidation and coagulation, mineralization, HS removal and SVR of 71.81%, 46.22%, 25.80%, 63.81%, 91.53% and 3.50 ml/mM were demonstrated.
Journal of hazardous materials 08/2010; 180(1-3):456-65. · 4.14 Impact Factor
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ABSTRACT: The degradation of humic acid (HA) was carried out in the presence of the Fenton reagent. The experiments demonstrated that HA was removed by oxidation and coagulation. Moreover, the oxidation occurred mainly at the first 60 min and predominated the HA removal efficiency. A new kinetic model was established according to the generally accepted mechanism of high active OH oxidation in order to well describe the Fenton oxidation reaction in HA aqueous solution. The model embraced two key operating factors affecting the HA degradation in Fenton process, including the dosages of hydrogen peroxide and ferrous ion. The experimental data were fitted by using the most commonly used first- and the second-order reaction models and the new model, respectively. The goodness of fittings demonstrated that the new model could better fit the experimental data than the other two models, which indicated that this analytical model could better describe the kinetics of Fenton reaction mathematically and chemically. Results indicated that the oxidation rate and removal efficiency were strongly dependent on initial pH, initial concentration of Fenton reagents, initial HA concentration and reaction temperature. The experiments demonstrated that hydrogen peroxide and ferrous ion would approach their saturated value with increasing dosage.
Journal of hazardous materials 03/2010; 179(1-3):533-9. · 4.14 Impact Factor
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ABSTRACT: To study the correlation between stinging and skin barrier and to make the lactic acid stinging test much safer.
The modified lactic acid stinging test with 3% and/or 5% aqueous solution of lactic acid combined with transepidermal water loss (TEWL) and capacitance (CAP) was used. The amount of 50 microL-test material was applied on test areas, the skin of both sides nasolabial fold of 50 healthy subjects. Subjects assessed stinging basing on a 4-point scale at 0, 2.5, 5.0 and 8 min TEWL and CAP were measured at baseline and 8 min.
The results show that the tendency of decrease in baseline CAP and increase in baseline TEWL are proportional with the increase of the sum of clinical scores (CSS). In 5% lactic acid test, negative correlation between changing ratio of TEWL (PTEWL) and clinical score at 5 min (CS5 min), and negative correlation between changing ratio of capacitance (PCAP) and CS5 min are registered.
Our data indicate that there is certain relationship between the degree of stinging and the skin barrier. The stinging test method modified by lower concentration aqueous lactic acid and the assessment combined with PTEWL and PCAP is suitable for Chinese to evaluate the skin susceptibility.
Skin Research and Technology 06/2003; 9(2):90-3. · 1.71 Impact Factor
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ABSTRACT: The treatment of humic acid (HA) in water with Fenton reagents was carried out and the roles of oxidation and coagulation in removing HA during treatment were investigated. The removal efficiencies of HA by oxidation and coagulation were tested under various operating conditions: reaction time, initial pH, dosages of Fenton reagents, [H2O2]/[Fe2+] molar ratio, initial HA concentration and reaction temperature. It is demonstrated that Fenton process can effectively remove HA. The values of 27.6% mineralization of HA and 78.9% reduction of UV absorbance at 254 nm (UV254) by oxidation after 120 min reaction time indicated that HA was not completely oxidized to carbon dioxide but rather transformed to some organic intermediates. Moreover, the oxidation occurred mainly at the first 60 min and predominated the HA removal efficiency. Under the most favorable conditions (initial pH 4.0, H2O2 160 mM, Fe2+ 40 mM, reaction time 120 min, reaction temperature 30 °C), 93.3% of UV254 was reduced, the reduction of UV254 by oxidation and coagulation were 78.9% and 14.4%, respectively. Results highlighted the synergistic roles of oxidation and coagulation in Fenton treatment of HA.
Colloids and Surfaces A Physicochemical and Engineering Aspects 379:151-156. · 2.24 Impact Factor
