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The present paper focuses on the treatment of indigo blue dye from an industrial wastewater using coagulation--flocculation process and explains removal mechanisms through the density functional theory. The conducted study analyzed the effect of different factors, including the dose and concentration of the coagulant AlCl3, flocculant dose, and pH and their influence on coloration removal, chemical oxygen demand (COD) reduction, and sludge amount, and seeks the optimization of these factors using the design of experiment. The optimal removal efficiencies were found to be 96.42% for COD, 98.21% for absorbance, and 10.40 mL for sludge volume under optimal operational parameters, 11.25, 4.07 mL, 3.23 g/L, and 0.94 mL for pH, coagulant dose, concentration dose, and flocculant dose with a total cost of 0.0826 USD/m³, respectively. Analysis of the global reactivity descriptors for reagents indicated that AlCl3 (ω = 6.156 eV) acts as an electrophile and the indigo blue dye (ω = 7.174 eV) as a nucleophile. The Parr's index analysis Pk + and Pk -- of indigo blue revealed that the vulnerable location for the nucleophilic attack is sited on the -C8=O10 and -C11=O19 bonding area. Finally, the developed model may emphasize the process engineering aspects of industrial wastewater treatment, and the linking with theoretical data could explain the involved removal mechanisms. [ABSTRACT FROM AUTHOR]

Activated carbon from grape seed was prepared using the chemical activation method, which consisted of treatment by potassium hydroxide (KOH). Factors influencing the activated carbon preparation were particle size, impregnation ratio, final temperature, heating rate, and the activating agent concentration were studied by using a central composite design. The methodology chosen in this paper is based on the use of a polynomial model to express the responses, yield of activated carbon synthesized, and adsorbed amount of methylene blue as a function of the five influencing factors. The significance of the factors was studied by analysis of variance using the Fisher test, linear effects diagram, response surface curves, and iso-response curves. According to the Response Surface Methodology, optimal conditions for the preparation of activated carbon have been identified to be a particle size of 300 μm, an impregnation ratio of 0.15, a final temperature of 650°C, a heating rate of 10°C/min and an activating agent concentration of 35%. Under these conditions, the synthesis yield of AC and 40%, while the adsorption capacity of methylene blue was 492 mg/g. The characteristics of activated carbon obtained under these experimental conditions were by FTIR analysis indicate the presence of a variety of functional groups on the surface of activated carbon. These results demonstrated that the grape seeds are a suitable precursor for the production of activated carbon. [ABSTRACT FROM AUTHOR]

Geopolymers are considered as an alternative solution of portland cement. The setting of these materials depends on the gelling reaction of sodium silicate, which can lead to the formation of three types of gels; irreversible gel that has interest and no interest gels (reversible and a non-gelling solution). Obtaining an irreversible gel depends on several parameters. In order to control the influence of these parameters on the development of irreversible gel, a central composite design with 23 experiments is employed to improve the irreversibility (Irr) and the variation of the gelling time according to the following parameters (concentration of sodium silicate, concentration of hydrochloric acid and the volume of hydrochloric acid added), while considering their square and rectangular interactions. Optimization of the model by reports to the factors shows that in order to obtain an irreversible gel, the optimal gelling time should be between 10 and 45 min with an acid concentration varying between 1.20 and 1.40 mol/L and a concentration of sodium silicate between 1.70 and 1.80 mol/L with addition of 12.5 mL of hydrochloric acid to the alkaline solution. [ABSTRACT FROM AUTHOR]