Binary removal of heavy metals cadmium and nickel by bacteria isolated from the wastewater of steel industry factory and investigation of effective parameters in their removal and study of RSM response surface methodology

In the last two decades, environmental pollution by heavy metals has increased, and the accumulation of these pollutants in aquatic ecosystems has brought many risks to the health of humans, animals, plants, and the environment. Cadmium and nickel can be mentioned as metals that have very toxic and carcinogenic properties. In this research, the isolation of bacteria from the steel industry factory in Sari, the effluent of the sausage factory in Golestan province, and the Lavij hot spring in Mazandaran, which have the ability to uptake heavy metals cadmium and nickel, were investigated. In the following, the optimization process of biological adsorption (the effect of parameters such as: temperature, concentration of metals, dosage of bacteria, pH...) was investigated. Based on the above results, the best isolate was used to remove these metals. Biochemical, morphological, and molecular findings have shown the closeness of the selected isolate to the genus Bacillus. According to the minimum inhibitory concentration test of the selected Bacillus bacteria, this isolate was resistant to a concentration of 1500 ppm of cadmium and 2200 ppm of nickel. The optimum pH for the removal of cadmium and nickel metals by the selected bacteria was 6.5 and 5.5, respectively, and the adsorption efficiency of cadmium and nickel metals was 0.72 and 0.63 mmol/g, respectively. The temperature for the removal of cadmium and nickel by Bacillus bacteria was about 45 degrees Celsius. The adsorption isotherm for both metals is similar to the Langmuir isotherm, which shows that the surface adsorption process is single-layer, and its kinetics is according to the second-order kinetic model, and the optimal amount of Bacillus bacteria biomass is about 1.5 g/liter. The selected isolate has suitable characteristics for use in real and industrial scale containing the mentioned metals.