Sulphate reduction optimization in the presence of desulfotomaculum acetoxidans and desulfobacter postgatei species.Application of factorial design and factorial correspondance analysis methods

摘要

The "green acid process" leads to the production of large quantities of phosphogypsum as solid waste.In Morocco,this waste is rejected at sea,contributing to the pollution of the environment.One of the main objectives of the present study is to develop an integrated biological process for the production of sulfur from phosphogypsum,comprising a biological sulfate reduction step.This paper presents the results of sulphate reduction rate optimization studies in the presence of Desulfotomaculum acetoxidans and Desulfobacter postgatei species.The experimental work was carried out according to the method of factorial design,and the results were analysed according to a factorial correspondence analysis technique.Four factors were studied,i.e., the initial sulphate and acetate concentrations ([SO_4]_i,[Act]_i), and the initial pH and incubation temperature (pH_i,T_i).There response-variables were determined: the maximal average sulphate reduction and sulphide production rates and the final pH.These studies show that for Desulfotomaculum acetoxidans (i) optimum bacterial growth and optimum sulphate reductionare obtained for pH_i range from 6.6 to 7.6 and T_i range from 30 deg C to 40 deg C (ii) optimum initial concentrations range from 7.75 to 17.25 mM for sulphate and from 10 to 20 mM for acetate (iii) strong inhibitions occur respectively below pH_i=6.1, above pH_i=8.1 and above T_i=45 deg C (iv) Strong inhibitions are obtained below 3 mM and above 22 mM for sulfate and below 5 mM and above 50 mM for acetate.For Desulfobacter postgatei (i) optimum bacterial growth and optimum sulphate reduction are obtained for pH_i range from 6.2 to 8.4 and Ti range from 25 deg C to 35 deg C (ii) optimum initial concentrations range from 10 to 22 mM for sulphate and from 12.5 to 27.5 mM for acetate.(iii) strong inhibitions are obtainedrespectively above pH_i = 9.5 and Ti= 40 deg C and below pH_i =5.1 and T_i= 20 deg C (iv) strong inhibitions are obtained below 4 mM and above 28 mM for sulfate and below 5 mM and above 45 mM for acetate.