Research On The Pipe Corrosion Caused By Iron Bacteria In Water Distribution Systems

The security of drinking water quality directly affects the development ofpeople’s life and the development of national economy. How to ensure thedrinking water quality attained the standard is the main research field. However,after the drinking water is purified by water treatment plant process and reachesthe water quality standard, the drinking water needs to go through a huge waterdistribution system before it can be used by comsumers. Because the waterdistribution system are made of metal materials in most cases, metal in the mediaof drinking water that contains a variety of electrolyte and microorganisms areeasy to be rusted. The corrosion will release some elements from the waterdistribution system to drinking water, thus leading to various changes of index indrinking water, causing the secondary pollution of drinking water. As themicroorganisms is the main factor causing water supply pipeline corrosion,studying the microbial corrosion regularity is important to enhance the waterquality and solve the problem of secondary pollution.To understand the mechanism of microbial corrosion, this study focused oniron bacteria, one of the two major bacteria that caused pipeline corrosion (theother is sulfate reducing bacteria). A pure strain of iron bacteria was isolated fromtap water, and then observed its phenotype and analyzed the factors that affect itsgrowth. Colonies of iron bacteria were round, smooth, dark brown, with a metallicluster and a slight sour smell. Number of bacteria in the pipeline was determinedin winter and in summer, and the result showed bacteria number in summer(1.4x105cfu/ml) was much higher than that in winter (230cfu/ml), suggested thatgrowth of iron bacteria was largely affected by temperature.The isolated stain of iron bacteria was used to test single-bacteria staticcorrosion of a cast iron block. During the short-term corrosion process, the growthcurve of iron bacteria, corrosion rate and corrosion potential of the iron block wererecorded. The results showed that, during the corrosion process, since it was an enclosed static environment, the iron bacteria showed typical lag phase, log phase,stationary phase and death phase. Under sterile conditions, the corrosion rate ofiron was about0.010g/(m2h), and the corrosion potential was stably between-0.620mV and-0.690mV. When the iron bacteria participated and reachedstationary phase (number of bacteria kept stable at around106cfu/ml), corrosionrate increased to0.025g/(m2h), and corrosion potential steadily decreased from-730mV to-763mV; then when the bacteria went into death phase, number ofbacteria decreased to around4x105cfu/ml, while corrosion rate increased to0.040/(m2h) at the highest, and corrosion potential surged from-0.763mV to-610mV.Corrosion of cast iron pipes by iron bacteria was not only affected by number ofbacteria, but also by the growth phase of the bacteria in.Finally, using the sodium hypochlorite as a disinfectant for inactivation testof iron bacteria and sulfate reducing bacteria, the results show that using sodiumhypochlorite as the the disinfectant and guaranteeing the residual chlorineconcentration of0.2mg/L, can remove90%of the iron bacteria and sulfatereducing bacteria. It will provides the theoretical basis for designing the residualchlorine concentration in the water distribution network and controlling themicrobial corrosion.