Melbourne Water Project

Project outline

Many cities treat domestic and industrial waste waters in large, open-air, maturation ponds. As the wastewaters move through a series of interconnected ponds, natural consortia of bacteria remove much of the reactive organic matter, diminishing its impact on the environment. In the early stages of the digestion process, large amounts of plant nutrients such as ammonia, nitrate, and phosphate are also released. Consequently, the initial ponds in the sequence are highly eutrophic. The extra nutrients fuel the growth of luxury crops of phytoplankton primarily (blue green algae or cyanobacteria). Some of these organisms produce harmful water-soluble toxins. To ensure that toxin-laden waters are not released to the natural environment or enter the recycling stream, waste water treatment plants are tightly regulated with strict limits to the toxin concentration in waters released to the environment or sent for recycling.

Direct measurement of the toxin concentration is time consuming and requires highly specialized laboratory equipment. Consequently, indirect indicators of toxin concentration such as Chlorophyll are used as the principal control variables for the day to day operations of the plant. These are imperfect measures of potential toxin concentration at the best of times. They are subject to the uncertainties of relying on point measurements to characterize a very large, and non-uniform, pond. Wind-driven mixing and the buoyancy of the cyanobacteria produce further fluctuations in the amount surface cyanobacteria at the surface.

This collaborative project with the scientific staff of Melbourne Water aims to integrate satellite remote sensing data of the distribution of chlorophyll and other characteristic molecules in ponds (the individual ponds are large enough to be easily visible from space), with local sensors of surface phytoplankton concentration, and the aquatic modelling capabilities of our colleagues in CSIRO Land and Water. The intended outcome is the capability of predict the likely incidence of high concentrations of cyanobacteria up to a week in advance as well as the capability to identify in real time surface blooms (very high concentrations of cyanobacteria).

Our approach to this problem uses many of the same experimental techniques deployed in the Lake Hume project, but modified to take account of the much higher concentrations of cyanobacteria and chlorophyll in the waste water ponds at the Werribee Waste water treatment plant which requiring specific characterization of the bio-optical properties of the waters.