Biotechnologic remediation of uranium in water

In the current work, the remediation of uranium-contaminated water, which is a very dangerous radioactive and heavy metal in terms of human and environmental health, was investigated by different biotechnological methods. The first part of the studies carried out as two sections investigated the uranium removal with bacteria (mixed anaerobic / sulfate-reducing), while biosorption with microalgae was investigated in the second part. Prior to making the uranium removal in water with URMM (uranium resistant mixed microorganisms) in anaerobic conditions, uranium-resistant microorganisms were obtained by growing in the medium containing different uranium concentrations and making several transfers to the new medium containing uranium, in approximately 1 year period. The 3 different uranium removal experiments were performed by URMM. In the first experiment, the removal of uranium in water was conducted at pH 7 and with low uranium concentrations (5mg/L, 25mg/L, 50mg/L) with live and heat-killed URMM. In the samples with the heat killed URMM uranium removal of 24-78% and with the living URMM 40-79% have been obtained. In a second experiment uranium (100 mg/L) removal anaerobic Batch experiments in water in different ORP (100mV, 50mV, -50mv, -100mv) and pH values (4-10) were held. As a result, 78.1% to 96.3% uranium removal was obtained in 3 days. Most removals were obtained at -50 ORP and pH 7. In the third experiment was tried the removal of different uranium concentrations and in ultrapure water. As a result of this experiments, the uranium removal was between 0.33 - 53%. All the experiments were repeated 4 times. The uranium removal experiments by SRB (sulfate reducing bacteria) at different redox potential (50mV, 100mV, -50mv and -100mv) and pH (4; 7; 10) conditions were performed in anaerobic Batch reactors. It took 3-10 days for uranium removal in all reactors. The high uranium removal percentages of 95.36% to 99.9% have been achieved. The highest removal was in the negative redox potentials (-50mv and -100mv). Here the uranium concentration decreased from initial 100 mg/L to 0,777mg/L (for -50mv) and 0,115mg L (for -100mv). The experiments were repeated 4 times. The U (VI) reducing the rate with SRB determination, thermodynamic and visualMINTEQ program calculations were made and the results were analyzed. viii In the second part, uranium removal was investigated by using microalgae. In these studies, Scenedesmus sp. and Chlorella sp. microalgae species were used. Uranium removal from water with Scenedesmus sp. microalgae has been investigated. The uranium concentrations of 5mg/L, 10mg/L, 15mg/L and different microalgae concentrations (41.54 mg / L and 115.94 mg / L) were used in the experiments. The uranium removal in the water was carried out under different physical-chemical conditions (pH, temperature) and for 2 hours. The obtained results were analyzed by plotting the adsorption effects of different parameters. Also, the three-dimensional graphs were analyzed with the help of the Box-Behnken program and the optimal conditions of the variable parameters were found. Optimal conditions were as follows: pH 6-8, temperature 45⁰C, algae alive, high algae concentration, duration 55-62,4 minutes. When such optimal conditions are met, the yield is as high as 90-100%. With the help of statistical calculation ANOVA, it also revealed that pH, the first concentration of uranium and the concentration of algae, are important parameters affecting the removal of uranium. Studies with Chlorella have investigated uranium removal in two different microalgae concentrations (71.61 mg / L and 282.42 mg / L). Here too, the experiments with Chlorella sp. microalgaes have been carried out in the same way as with Scenedesmus sp. macroalgae. Here, pH, the initial concentration of uranium and the duration were determined as the most important parameters affecting the removal of uranium. Optimal conditions were the same as those in the experiments with Scenedesmus sp. macroalgae. When optimal conditions were met, it was gotten over 95% of uranium removal. In order to determine whether or not the reduction of uranium with anaerobic bacteria has been accomplished with 'Cytochrome C' protein as mentioned in some studies, this protein was firstly synthesized from bread yeast in laboratory conditions for the removal of uranium in the Batch reactors by this protein. The concentration changes of the reduced and oxidized 'Cytochrome C' during the experiments were measured daily. As a result, it was observed that the increase of the degree of oxidation of 'Cytochrome C' protein was almost the same with the decrease of the degree of its reduction. Thus, the reduction of uranium is accomplished by the oxidation of Cytochrome C, which is the result of electrons transferring from the protein to uranium.