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Cadmium biosoption by immobilized dead yeast cells from bioethanol industries



 There are many reports about effluent discharges that bring hazardous materials and metals poured into aqueous environments and soils that end-up in the food-chain threatening natural and human population health. The toxic and carcinogenic cadmium is released by industrial processes at 20,000 tons per year with no efficient removal or ameliorating system to protect from its negative effects. The first report on cadmium toxicity appeared in 1946 in Japan and was described as the “Itai-Itai Syndrome” related bone problems. Presently cadmium is wide used in the automobile industry, telecommunications, on the dying and ink processes, PVC and other plastics, phosphate fertilizers, batteries, fungicides, leather industry, etc and it was found in large amounts in urban waste and metallurgy industrial discharges. Dead yeast cells are an abundant residue of the Brazilian ethanol industry and the industries still don’t have a proper or desirable destiny for all these cells, which means tons of vitamins and proteins that have not a major end. In the other hand, heavy metal residues are a problem, especially for leather industry, where Brazil is also a great producer. In this work, dead yeast cells were used to evaluate cadmium biosorption samples. Yeast cells from sugar-cane bioethanol fermentation process 80% concentrated were obtained from COSAN Group, at Piracicaba, SP, Brazil. The yeast cell suspension was spread on trays, frozen at –80 0C, 24 h and lyophilized for 48 h and then killed by heat and pressure at 120 0C 30 minutes, 1 atm. Na-alginate 0.5 % and 20% (W/V) of dead yeast cells were added to 100 mL of deionized water at 9.5 pH. This suspension was mixed homogenized and droplets poured into Calcium Chloride 4% using a peristaltic pump for the micro spheres production. The same procedure was done with alginate solution without adding dead yeast cells. Samples were collected each hour and analyzed in atomic absorption spectrophotometer Varian AA-175. Biosorption was measured using a two double draft tube fluidized acrylic bioreactors were built (15 cm height) with 40 mL of internal volume and 100 mL of external volume dimensions. Each internal column was filled with 28 g of micro spheres connected to a peristaltic pump calibrated to sustain a flow of 2 mL per minute of cadmium synthetic solution at a concentration of CdCl2 of 250 mg Cd/L. Suspension desorption were measured also. Results have shown that dried dead yeast cells at 20 % (W/V) immobilized in Na-alginate beads 0.5 % can be an efficient alternative for the capture of cadmium. The average biosorption rate was 122.10 mg Cd/g of dry biomass in comparison to the control using only the Na-alginate beads 0.5 % where the biosorption rate achieved 57.29 mgCd/g of dry biomass. For countries as Brazil, the yeast cells residue from fuel industry represents large amounts of such biomass. The research represented by the use of yeast cells from ethanol industry in a stable and efficient process demands future studies with the purpose of effluent treatment other than cadmium and other heavy metals to develop large scale processes using immobilized yeast cells, in order to minimizes the heavy metal impact on environment as well as using the yeast cells residues from ethanol industry.
Financial support: FAPESP

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