A Case Study of the Improvements Gained in Conduit Efficiency by Cleaning a Biofouled Pipeline

The hydraulic performance of pipelines can be significantly affected by the presence of biological growth on internal surfaces. The change in wall roughness brought about by biofilms has been studied by the use of headloss tests, pre- and post-cleaning, of a low pressure hilltop pipeline of a Hydro Tasmanian hydroelectric scheme. Results of the headloss tests show that improvements to hydraulic efficiency can be achieved from the cleaning of biofouling material, and that identifying the flow velocities at which hydraulically smooth, transitional or rough conditions occur can aid in optimising the operating characteristics of the conduit. Results show both reductions in headloss and improvements in power output at the powerstation at given flow rates. The data when plotted in the style of a Moody diagram shows that the friction law, roughened by biological growth, is observed to deviate from the Colebrook-White relationship, although the results are too narrow in Reynolds number to be conclusive. It was found that bacteria made up the majority of the biofilm biomass in the pipeline studied. Based on molecular analysis, members of the class Alphaproteobacteria were the most frequently detected followed by members of the phylum Chloroflexi. Chemical analyses found high levels of iron, manganese and aluminium in the biofilm. © 2008 Institution of Engineers Australia.