A study of microbial population dynamics associated with corrosion rates influenced by corrosion control materials

This research aims to analyze the variations of microbial community structure under anaerobic corrosive conditions, using molecular fingerprinting method. The effect of adding various materials to the environment on the corrosion mechanism has been discussed. In the initial experiment, sulfate-reducing bacteria (SRB) were inoculated in a series of batch culture flasks containing sterile growth media. Several testing coupons of mild steel were placed into the SRB-enriched columns, which contained excess sulfate and lactate. After incubating for 20 days, three materials (MgO2, H2O2 and NaOCl) were added into the flasks so as to observe the effects on biocorrosion rate. Microorganism composition change was observed from the diversity profile using the PCR-DGGE (polymerase chain reaction - denaturing gradient gel electrophoresis) method. The results showed that hydrogen peroxide (H2O2) prompted the microbial community to change quickly and easily and enhanced the corrosion rates of coupons (3-6 times faster than the control run). This fact suggested that adding H2O2 could inhibit biological activities initially; however, it ultimately caused more serious corrosion due to breaking down the protective layer, composed of mainly FeS. When MgO2 was added into the SRB-enriched culture, the corrosion rate on the mild steel test coupons was inhibited to one third of that in the control column. The DGGE profile analysis shows that SRBs were clearly inhibited for a long time (more than 100 days) after adding MgO2. The durability of the MgO2 reaction could be demonstrated by DGGE variations as well as water quality monitoring results.