REDUCTION OF Cr(VI) COMPOUNDS BY THE IMMOBILIZED CELLS OF SULFATE-REDUCING BACTERIA DESULFOMICROBIUM SP. CrR3

Abstract

Immobilization of microorganisms is an effective method of intensification of wastewater purification form chromate-containing compounds. This paper presents a method of sulfate-reducing bacteria immobilization in agar developed in order to determine the effectiveness of water purification from toxic hexavalent chromium compounds. Dependence of the influence of different factors on the reduction of hexavalent chromium compounds by immobilized cells of sulfate-reducing bacteria Desulfomicrobium sp. CrR3 has been studied. Both free and agar-immobilized Desulfomicrobium sp. CrR3 cells almost completely reduced Cr(VI) at the initial concentration of 1 mM. Immobilized cells reduced over 90 % of Cr(VI) in 4 days, and non-immobilized ones – in 6 days. Cr(III) content increased with the decrease of hexavalent chromium concentration. A possibility of multiple usage of agar-immobilized Desulfomicrobium sp. CrR3 cells for the purification of the model solution from Cr(VI) at the concentration of 0.5 mM and 1 mM during 60 h was confirmed. After three-time usage of the immobilized cells (1g/L), effectiveness of Cr(VI) reduction is 68 % at their initial concentration of 0.5 mM and 50  % – at 1 mM; at cells concentration 3 g/L – 87 % and 77 %; 5 g/L – 94 % and 92 %, and at cells concentration 8 g/L – 98 % and 96 %, respectively. As a result of the regression analysis of the influence of different factors on the purification of the model solution from Cr(VI) by agar-immobilized Desulfomicrobium sp. CrR3 cells a reliable dependence of the studied parameter change on time, initial content of hexavalent chromium and cells concentration was found. Determination indices have been calculated and the equation of the dependence of change of hexavalent chromium concentration per unit of time on the three analysed factors has been derived. Immobilization of Desulfomicrobium sp. CrR3 cells is the promising way of water purification from hexavalent chromium compounds. Effectiveness and duration of the process of water purification from Cr(VI) by the immobilized Desulfomicrobium sp. CrR3 bacteria depend on the initial hexavalent chromium content and cell concentration.