Experimental Study of Dynamic Effects of Iron Bacteria–Formed Biofilms on Pipeline Head Loss and Roughness

Abstract

This research investigated the dynamic effects of iron bacteria–formed biofilms and associated material accumulation on pipeline head loss and roughness for the Salt Interception Scheme (SIS) in South Australia. Two case studies were conducted in high-density polyethylene (HDPE) pipelines pumped with ground water that contained iron bacteria. The friction factor and equivalent pipe roughness were calibrated using the measured head loss and flow. The topological and microstructure of the material accumulation were studied, and deoxyribonucleic acid (DNA) analysis was used to reveal the bacteria that contributed to the material accumulation. The results showed that, for pipelines with various diameters but at similar initial flow velocity (Case study 1), the material accumulated faster and imposed more significant head loss in smaller pipes. For pipelines with the same size (Case study 2), the material accumulated faster and introduced higher head loss in pipes in which the flow velocities were higher. The conventional calibration approach that assumes a constant pipe diameter is not appropriate for pipes with excessive biofilm growth (as the case in this study). The approach that considers a 2-mm reduction in pipe effective diameter with every 1-mm increase in equivalent roughness produced friction factor and roughness results in reasonable physical ranges, and the calibrated equivalent roughness was generally consistent with the observed thickness of the accumulated material. The material accumulation was highly nonuniform, and comprised microbial iron nanowires. The nanowire had a helically coiled structure which was different from that of common brown compounds of oxidized iron. The bacteria Mariprofundus ferrooxydans were the producers of the iron nanowires. Overall, to limit the growth of iron biofilms and material accumulation in pipes used in the SIS, smaller pipes should be avoided, and use of the largest pipe diameter practical to achieve low flow velocity is recommended.