A Comparative Study Of Microbiologically Influenced Corrosion Of Stainless Steel In Reclaimed Water

In this paper the growth characteristics of SRB in real reclaimed water and the influence of ionic strength are studied. And a strain of sulfate-reducing bacteria was isolated from the sludge at the bottom of cooling-water tower. The result showed that this strain of SRB could grow in reclaimed water under experimental condition. The sulfate was reduced in this process and the rate of sulfate reduction reach to 58.8% at the end. And the increase of ionic strength by concentrating the reclaimed water can promote the growth of SRB.In present work, the formation process of bio-film formed by SRB in real reclaimed water and local corrosion on the surfaces of stainless steels (SS304, SS316L, and SS317L) were studied. The results showed that the process of SRB adhesion to surfaces of stainless steels was relation to the content of some composition of these three stainless steels. After removing the bio-film, the corrosion pits were observed on the surface of SS304 sample, and it was 541.24nm deep, while no significant pits were found on the surface of SS316L and SS317L samples.The SEM/EDS experiments showed that the bio-film formed by SRB on the surfaces of stainless steels consisted of SRB, metabolism substance and corrosion products (FeS_X). And the bio-film on the surface of SS304 sample was more thick and solid than the others. While there were less corrosion products in the bio-film on the surfaces of SS316L and SS317L samples, and the structure of biofilm were more loose and porous than SS304. It was proved that SS316L and SS317L had better characteristic of corrosion resistant than SS304 against SRB in real reclaimed water.The corrosion behaviors of SS304,SS316L and SS317L stainless steel were investigated by measuring EIS. The results showed that the electrochemical characters of the corrosion due to biofilms, corrosion product films and metabolism substance were different on the different steels. The changes of polarization resistance and electric capacity value of SS304 dued to the breaking of passive film by the corrosion products, and the localized corrosion was accelerated. While there were no significant changes of electric capacity of electric capacity, and the decrease of polarization resistance value were less than SS304. It proved that the corrosion to SS316L and SS317 were less than SS304 by the bio-film due to SRB, and the bio-film on the surfaces played a role of inhibiting corrtion to some degree.