Microbial analysis of water and biofilm to determine the microbial corrosion rate within a pipeline. From a sample we can extract the DNA to determine the whole microbial population, we then allocated each microbe to a role and can calculate the microbial corrosion rate
Within carbon and nutrient rich sewer systems the importance of aerobic and anaerobic biological degradation and corrosion of pipe walls is receiving increasing attention (Hudon et al. 2011, Eštokov et al. 2012). In contrast biological degradation and corrosion of waste transmission distribution systems transporting source and potable water low in nutrient loads to consumers has received scant attention. Recently, Wang and Cullimore (2010) demonstrated that a complex microbial biofilm within a potable water AC pipe led to enhanced leaching of the free lime and dissolved Ca-bearing minerals in the hydrated cement matrix. The biodegradation leads to softening and weakening of the AC pipe walls that can cause pipe bursts and failures. For CMLM pipes, once the cement lining is lost, microbial induced corrosion (MIB) can occur and rapidly increase the degradation of steel (Melchers and Jeffreys 2008). As both internal and external pipe surfaces are exposed to non-sterile environments, all our pipes are being degraded from both inside and outside but not necessarily by the same microbes or chemical interactions. Our initial filed studies demonstrated that various types of biodeterioration-associated bacteria can be found in raw water pipes, ground water pipes, potable water pipes (inside and outside) and flushed material from potable water pipes. DNA analysis identified diverse functional groups of microorganisms with the potential to cause extensive damage to cement and metal pipe walls. This biodeterioration and biocorrosion is analogous to increased degradation rate of mild steel in marine environments as observed by Melchers and Jefferys (2008). There is a long historic understanding of corrosive gasses such as hydrogen sulphide within sewer systems can attribute to major pipeline failures. Some major causes of H2S build up within pipelines are due to the microbial community present, understanding the microbial community can help determine the potential production rates of H2S. Sewer pipelines experience a wide range of pressure cycles due to the pump stations turning on and off, this combined with the hydrogen sulphide can result in pipeline failure. Understanding the potential production rate of hydrogen sulphide and the concentration present will help determine the high risk locations and the potential corrosion rates that are occurring.
Figure 3 – Biodegradation process on a MSCL pipe showing the interaction between the different types of biodegradation bacteria.