(427l) Effects of a Biocide and a Biocide Enhancer on Srb Growth and Biocorrosion

Abstract Sulfate reducing-bacteria (SRB) are a notorious group of anaerobic microorganisms that are most commonly involved in Microbiologically Influenced Corrosion (MIC) of various metals such as cast iron, mild steel and stainless steel, copper, aluminum and their alloys. It is important to study not only the planktonic SRB growth behavior, but also more importantly, the sessile cell behavior in biofilms on metal surfaces. To study SRB growth and to find potential mitigation methods for MIC due to SRB, the ATCC 7757 strain of Desulfovibrio desulfuricans was used in this work. It is a common species of SRB. Laboratory experiments were carried out in 100 ml anaerobic vials. A novel biocide enhancer was used in combination with glutaraldehyde that is a commonly used in the field. Glutaraldehyde was found to suppress the planktonic growth of SRB almost completely at a concentration of no more than 50 ppm, if the initial SRB concentration was as low as 100 cells/ml. However, the suppression period lasted only a couple of days when an initial SRB concentration of 10x104 cells/ml and 100 ppm glutaraldehyde was used. A delayed exponential growth phase took off afterwards. When the biocide enhancer was used, the planktonic SRB growth suppression period was prolonged and a lower glutaraldehyde concentration could be used when other experimental conditions were kept the same. It was also observed that the biocide enhancer interfered with the biofilm formation on metal coupon surfaces. Comparing the surfaces of the coupons in the vials with glutaraldehyde and those in the vials with glutaraldehyde plus the biocide enhancer, it was found that the biofilms formed in the absence of the biocide enhancer were thicker and the pits on the coupon surfaces were deeper. The reason may be that the biocide enhancer promoted the penetration of glutaraldehyde into the biofilms, and thus helped the suppression of sessile SRB growth. The biocide enhancer can be potentially used to help mitigate MIC by prolonging the effectiveness of biocides and/or reduce their dosages.