Conditions Favouring Growth of Freshwater Biofouling in Hydraulic Canals and the Impact of Biofouling on Pipe Flows

The objective of the Master Thesis titled “Conditions Favouring Growth of Freshwater Biofouling in Hydraulic Canals and the Impact of Biofouling on Pipe Flows” is to present the details on investigations into the effect of colour and water quality on the growth of biofouling in open channels and the impact of biofouling in pipes and penstocks. It is well known that biofouling causes significant problems in engineered structures, mostly related to reductions in efficiency, since it can change the wall roughness properties and associated frictional drag. A biofilm is a layer of biological growth that attaches itself to the internal walls and forms an interface with the water. It may any combination of bacteria, algae, protozoa, fungi, mosses and invertebrate organisms. Its composition can have significant impact on roughness and friction properties of the biofouled conduit. The study aimed to develop a better understanding of the effect of colour and water quality on the growth of biofouling in open channel flow and pipes and of the relationship between the biofouling and friction effects on turbulent flow in pipes. It follows previous studies undertaken about this important topic at the University of Tasmania. It encompasses field and laboratory studies and a statistical analysis of water quality data collected in several lakes in Tasmania. The effect of colour on the growth of biofouling was studied by submerging mild steel plates painted with four different coloured epoxy coatings in two different locations (Transition n.4 and Pond n.1) in the Tarraleah Power Scheme. These locations are characterized by different average flow velocity. The plates were placed in a concrete lined canal for a period of time to allow biofouling to grow. Results showed that the amount of biofouling increased progressively from the white to the black plates However, the effect of colour on the growth of biofouling became less significant when the biofouling was fully developed. This field study included UV light measurements. It was found that the amount of light also affected the biofouling growth. Under full sunlight and lower velocity conditions, plates with lower total light intensity and lower UV light exhibited higher levels of biofouling. The second part of the study was addressed to a statistical analysis of a number of water quality data from eight Tasmanian Lake used to hydroelectric power generation. Several water quality parameters, such as pH, turbidity, conductivity, temperature, dissolved oxygen, total iron, total manganese, total nitrate, total aluminium and others, were considered in this analysis. It was found that power station with less biofouling use water with higher pH value and dissolved oxygen level and with lower conductivity, turbidity, iron, manganese, aluminium and nutrients. Despite it was not possible to establish a direct relationship between biofouling and water quality and further studies on the ecology of biofouling causing organisms are required, these results provided a useful reference for ongoing research in this field. Finally, a new pipe rig was designed and built to investigate the impact of biofouling on pipe flows. The rig, located in the Laboratory of Hydraulics of the University of Tasmania, consisted of a removable test section that was placed in a purpose built rig test installed in the Pond n.1 in the Tarraleah Power Scheme. The pressure drop between the test section and velocity profile at the end of the test section were measured for both clean and biofouled conditions under different Reynolds numbers. Results showed that biofouling increased the head losses along the test section and changed the shape of the velocity profiles, Furthermore, due to biofouling the Darcy-Weisbach friction factor f increased with the Reynolds number Re up to a peak value where biofouling detachment started. After that, f decreased with the progressive detachment of the biofouling. Hence, to fit the velocity profiles of the biofouled pipes, it was proposed to apply a log-law with modified values of both the Von Kármán constant and the B parameter. Finally, the modified Colebrook-White equation proposed by Lambert et al. (2009) was applied to the experimental data.