Conditions favouring growth of fresh water biofouling in hydraulic canals and the impact of biofouling on pipe flows

摘要

Biofouling increases frictional resistance and slows the water flow in fresh water canals andudpipes. It results in up to 10% reduction in the flow carrying capacity in hydropower canals inudTasmania, Australia. This project investigated the effect of colour on the growth of biofouling inudopen channels and the impact of biofouling in pipes and penstocks.udThe effect of substratum colour on the growth of biofouling was studied by submerging mildudsteel plates painted with four different coloured epoxy coatings in fresh water. The plates wereudplaced in a concrete lined canal for a period of time to allow biofouling to grow. Results showudthat black was the favoured colour for the growth of biofouling whereas the white platesuddeveloped the least amount. The amount of biofouling increases progressively from white toudgrey to black at the settlement stage of biofouling. However, the effect of colour on the growth ofudbiofouling became less significant when the biofouling was fully developed. It was found that theudamount of light also affected the growth of biofouling. Under full sunlight and slow flowudconditions(1 m/s), plates with lower total light intensity and lower UV light exhibited higher levelsudof biofouling.udIn addition to open channels, biofouling also causes head losses in cooling water pipes andudpenstocks in hydroelectric power stations. The influence of water quality on the growth ofudbiofouling was investigated by analysing water quality data of eight lakes used for hydroelectricudpower generation. It was found that power stations with fewer biofouling problems in theirudcooling pipes use water with a higher pH value and dissolved oxygen level, while having lowerudwater conductivity, water turbidity, iron, manganese, aluminium and nutrients.udA new pipe rig was designed and built to investigate the impact of biofouling on pipe flows.udLocated in the hydraulics laboratory at the University of Tasmania, this consisted of audremovable test section that was placed in a purpose built field test rig installed in a hydropowerudstation canal. The pressure drop across the test section and velocity profiles under different flowudrates were measured for both clean and fouled conditions. Results show that biofoulingudincreased the head loss along the test section and changed the shape of the velocity profiles.udThis data did not fit the widely used Colebrook-White equation.