Adsorption Characterization Of Cu～(2+) And Cd～(2+) By Spirulina Platensis

In order to search for locally available biomaterials with high removal capacity of heavy metals from waste water, biosorption of 9 strains in 4 genera to heavy metal ions Cu²⁺, Cd²⁺ was investigated. Spirulina platens is 439 was screened with relatively strong ability of absorbing Cu²⁺ and Cd²⁺. The characteristics of Spirulina platensis 439 were studied such as the growth curve and the surface characteristics. It is fundamental for the bioremediation of waste water and associated envionments with heavy metal pollutant and the construction of genetically engineered bacteria. The researches are useful for further understanding the mechanisms of heavy metal-microorganism interactions. The main results were outlined as following:1. The screened bacteria Spirulina platensis 439 has relatively strong ability of absorbing Cu²⁺ and Cd²⁺, with the maximum adsorption amount 1992 mmol Cu²⁺ / Kg dry biomass, 2347 mmol Cd²⁺ / Kg dry biomass, respectively. The adsorption isotherm of Cu and Cd on the tested bacteria fitted to the Langmuir equation well (r>0.91, p<0.05). As compared with some other bacteria, the tested stain had higher absorbability to Cu²⁺ ion and Cd²⁺ ion.2. Results of the determination of the growth curve indicated that S. platensis 439 grew into the logarithmic phase at 4 or 5 days when they were inoculated into BG-11 medium. The surface area of S. platensis 439 was 214.4m²/g measured by the methylene blue adsorption method. Within the tested pH range, the surface charge density was -2.05 umol/m²ï½ž9.19umol/m², and the isoelectric point was 5.0.3. The pH had significant effects on the Cu²⁺ and Cd²⁺ adsorption on the tested bacteria among several environmental conditions. A marked increase in the adsorption of Cu²⁺ and Cd²⁺on S. platensis 439 was observed with the increase of pH from 1.5 to 5.0, while an adsorption plateau was found with the increase of pH from 5.0 to 6.0, then a increase of adsorption amount of Cu²⁺ and Cd²⁺ occurred because of precipitation. Adsorbability of dead cells is obviously lower than that of live cells to the two heavy metals, with the decrease of the maximum adsorption amount 634.3 mmol Cu²⁺ / Kg dry biomass, 749.4 mmol Cd²⁺ / Kg dry biomass.4. The adsorption process may be divided into the following phases: fast biosorption phase, slow phase and equilibrium phase. The adsorption equlibrium of copper was reached in 2h, and cadmium in 4h, and the kinetics of Cu and Cd adsorption could be described well with the Power equation.5. The copper and cadmium adsorbed could be desorbed electively by HNO₃, EDTA and NH₄NO₃, but HNO₃ could influence the repeated using of the bacteria.