Microbiologically Influenced Corrosion In Water Distribution Systems

Corrosion in drinking water distribution systems has become one of the causes of drinking water pollution and the decrease of durable years of water distribution pipes. Among the processes of corrosion in water pipes, microbiologically influenced corrosion(MIC) is of significant importance. This paper includes the study on the two most characterized corrosion related bacteria, iron bacteria(IRB) and sulfate-reduced bacteria(SRB) in drinking water distribution systems.In this paper, SRB and IRB, which were gained from drinking water distribution pipe in Harbin and purified with solid mediums in the laboratory, there were lots of IRB and a small amount of SRB existing in the corrosion products of water distribution systems. The results indicated that cast iron pipelines without coating had already been corroded after the serving of 10 years. Coupon tests were implemented to compare the growth condition of the two kinds of bacteria. MPN method was applied to measure the growth rates in one experimental period. Using these two kinds of bacteria, the effect of microbiologically influenced corrosion on water supply pipes was studied applying electrochemical techniques and weight-loss method in static coupon tests. Most probable number method was also used to obtain the actual number of SRB and IRB in a corrosion test period. The result showed that the corrosion rate of iron pipe samples decreased in a mixed bacteria environment.Based on the previous research, the disinfection efficacy of bacteria was studied in order to improve the water quality as well as to decrease the corrosion process. The results showed that, the disinfection efficacy could reach 90% after the contact of 100 mins when the concentration of residual chlorine was up to 0.2mg/L. However, it was considered to be effectively disinfected as long as the initial concentration of 1.00mg/L for IRB whereas the initial concentration of 0.20mg/L for SRB. When the residual chlorine was under 0.5mg/L, the growth of SRB and IRB could not be controlled effectively as the actual number of IRB in the corrosion product of water supply system was up to 108cfu/ml, hence high residual chlorine should be maintained in pipe cleaning and repairing techniques.