The objective of this study was to combine coagulation and mechanically induced air flotation in order to determine the optimum operational condition for the removal of total petroleum hydrocarbons (TPHs) from oily wastewater. A mixture of water, gas oil, and emulsifier was used to generate a stable emulsion as the simulated wastewater. Aluminum sulfate, ferric chloride, and polyaluminum chloride were employed as coagulants to destabilize the emulsions, and the subsequent separation of hydrocarbons was carried out in a mechanical flotation cell. Considering the multiplicity of factors in both stages of coagulation and flotation, the effects of each factor were studied using Taguchi design of experiments technique, and the optimum conditions were revealed. The results showed that at the optimal conditions, about 93% TPH removal was achieved by addition of 50 mg/l aluminum sulfate at pH 4, flotation time of 10 min, impeller speed of 1,000 rpm, and airflow rate of 4.5 l/min.

Adsorption kinetics and loading capacity of Zn(II) onto a coconut shell-based activated carbon (AC) was investigated at different solution concentrations, pH values, and temperatures. Characterization of the AC was performed by using scanning electron microscopy, N₂ adsorption and desorption isotherms, pore size distribution, surface area determination, determination of point of zero charge (pH_PZC), and Boehm titration. The equilibrium studies showed that the Zn(II) adsorption onto the AC increases from 1.98 to 4.24 mg/g by increasing the initial Zn(II) concentration from 23 to 148 mg/L. The kinetic experiments revealed that the initial adsorption rate of Zn(II) is rapid and decreased afterwards. The adsorption rate significantly increased with raising the temperature from 25 to 45°C. The activation energy for the adsorption of Zn(II) ions onto the AC was 54.23 kJ/mol. Both of the adsorption kinetics and loading capacity decreased with increasing the acidity of solution. The results of Boehm titrations, determination of pH_PZC, and the time course of the system pH during the sorption process showed that the adsorption of Zn(II) ions onto the AC takes place through cation-exchange mechanism with acidic surface functional groups. The results of linear and nonlinear regression methods showed that the equilibrium data among different two- and three-parameter isotherm models closely obey from a three-parameter isotherm model, namely Koble–Corrigan. The results of linear regression method revealed that the kinetic data among different kinetic models closely obey from Elovich model. The rate-limiting step in the adsorption of Zn(II) onto the AC was assessed through the Webber and Morris plots.

In this study, natural hematite was used for the removal of zinc(II) from aqueous solutions due to its lower cost and high adsorption capacity. Variables of batch experiments including solution pH, contact time, initial concentration, and the amount of adsorbent were studied. The results indicated that the adsorption capacities are strongly affected by the parameters mentioned above. The optimum pH and amount of adsorbent was obtained 6 and 5 g, respectively. The isothermal data were fitted with Freundlich equation. The intraparticle diffusion model was the best for describing the kinetic data. It was revealed that natural hematite can be used as an effective adsorbent for removing Zn(II) from aqueous solutions.