Sustainable Treatment of Boron from Geothermal Water by Recycled Mussel Shell Waste
Project no. 22246 · Status: Kapanmış (Yayın bekleniyor) · 2020
Summary
<p>In this thesis, the removal of boron, which adversely affects life in high concentration, from thermally and chemically polluted geothermal water sources using recycled mussel shells was investigated. Geothermal fluids are seen as valued sources. However, excess boron in geothermal water, which is used as irrigation water in agricultural lands, reduces crop yields due to its toxic effects, and therefore causes concern among farmers. The boron concentration in groundwater reaches up to 100 mg/L. Boron, which is one of the most common pollutants in Turkey, causes environmental problems by negatively affecting plant growth and human health when taken in excess. For this reason, World Health Organization is made a recommendation that boron content in drinking water should be below 2.4 mg/L. Although there are many methods for boron removal, the adsorption method is among the best methods in terms of low cost and high efficiency. In the study, mussel shell waste, which is predicted to be a successful biosorbent thanks to its 96% calcium carbonate content, was used to develop an environmentally friendly and sustainable sorbent.</p><p>The thesis consists of four parts which are recycling, modification and characterization of mussel shell wastes, equilibrium tests, kinetic tests and finally the column-mode tests. The calcination temperature and time were analyzed to observe modification effect on sorption capacity. The characterization of unmodified and modified biosorbents under optimum conditions was investigated by FTIR, TGA, SEM XRD and BET analyzes. Within the scope of the research, biosorbent dosage, pH, temperature, concentration, selectivity and regeneration in equilibrium studies, temperature and mixing rate in kinetic studies, and column bed height and flowrate parameters in column studies were investigated.</p><p>Optimum modification conditions were obtained with calcined mussel shells at 800 °C for 4 hours. When the FTIR results were examined, it was determined that the modified and unmodified biosorbents contained C-H, C=C, Ca-O bonds and OH- group. By TGA analysis, the mass loss of unmodified biosorbent, modified biosorbents before and after adsorption was calculated as 36.535%, 17.999% and 34.059%, respectively. When the surface morphology of biosorbents were analyzed with SEM, it was observed that the mussel shells, which were observed as rough, thin and long plate-like crystals, turned into more circular-like structures such as oval or spherical after the modification process. In addition, EDAX results showed that unmodified and modified biosorbents are composed of Ca, C and O. XRD analysis, on the other hand, indicates CaO content with high-intensity diffraction peaks at 32.3, 37.4 and 54.0 after modification. Finally, the increased surface area, pore size and volume of the biosorbent after modification were determined by BET analysis.</p><p>As a result of the equilibrium tests, it was observed that the optimum amount of sorbent was 2 g biosorbent/25 mL geothermal water. When the pH effect was examined, it was found that pH ineffective on boron removal, so the tests were performed at the original pH of the geothermal water (7.68). In addition, the highest efficiency was obtained at 25 °C for the temperature parameter investigated in the temperature-controlled water bath shaker. When thermodynamic analysis was performed, negative ∆H° values showed that the adsorption process was exothermic and low temperatures favored adsorption. Negative ∆S° values indicated a decrease in the concentration adsorbed at the solute-solution interface and an increase in the concentration adsorbed in the solid phase. On the other hand, it was understood that the reaction was non-spontaneous and need an input of energy in order to take place since the ∆G° values were positive. As a result of the studies examining the effect of other ions other than boron, it was observed that the adsorption efficiency was negatively affected in the presence of Na+ and Mg2+ ions. In regeneration studies, the highest yield was determined as 72.33% with 1 mol/L nitric acid solution. In order to examine the effect of ions in geothermal water, the effects of concentration were studied separately with geothermal water and aqueous solution, and the results were compared. Langmuir, Freundlich, DKR, Temkin and Redlich-Peterson isotherm models were applied with the obtained data. In both studies, it was observed that the adsorption of boron to the mussel shell better fit the Freundlich isotherm model.</p><p>The data obtained in the kinetic studies were evaluated by pseudo-first-order, pseudo-second-order, intraparticle diffusion and Elovich kinetic models, and the pseudo-second-order kinetic model was fitted better than the other models.</p><p>In the column studies, Thomas and Yoon-Nelson models were applied and the model predictions showed similarity with the experimental data. In this thesis, the highest boron removal efficiency obtained under the determined optimum conditions was determined as 30.26%.</p>