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The effect of ORP (oxidation–reduction potential) on the bacterial community and corrosion rate was investigated in this study. A continuous sulfate-reducing bacteria (SRB)-enriched reactor equipped with an ORP controller was operated from anaerobic to anoxic condition in this bio-corrosion experiment for over 200 days. Testing mild steel coupons were placed into the reactor for immersion test which was used to compare with the result of electrochemical corrosion current density. The results showed that as the ORP increased, the sulfide, corrosion current density and the proportion of SRB in microbial community would decrease. This study employed oxygen to change the microbial communities, which successfully enabled heterotrophs to inhibit SRB even under excessive TOC and sulfate inflow conditions. However, from the results of corrosion weight loss it could be discovered that the fact of higher control of ORP leading to better corrosion inhibition was not certain. Once the ORP was controlled to −250 mV, the same result could be achieved as well as the ORP being controlled to −180 mV. In addition to the advantage of energy-saving, controlling ORP at −250 mV can also prevent more corrosion reactions from possibly being caused by other microorganisms in the continuous rising of ORP. [ABSTRACT FROM AUTHOR]

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 (MgO 2 , H 2 O 2 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 (H 2 O 2 ) 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 H 2 O 2 could inhibit biological activities initially; however, it ultimately caused more serious corrosion due to breaking down the protective layer, composed of mainly FeS. When MgO 2 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 MgO 2 . The durability of the MgO 2 reaction could be demonstrated by DGGE variations as well as water quality monitoring results. [ABSTRACT FROM AUTHOR]