Modelling treated waste disposal in Port Phillip Bay and bass strait biogeochemical and physical removal

Large cities, such as Melbourne, generate substantial quantities of sewage, which, after treatment, must be disposed. Melbourne's sewage is disposed v ia two routes, that treated at the Western Treatment Plant (WTP) is dischar ged in enclosed Port Phillip Bay, while the Boags Rock outfall empties into the exposed Bass Strait. In Port Phillip Bay biogeochemical processes cont rol the fate of waste, while in the Bass Strait physical mixing rapidly dis perses the waste. These different processes require very different ecosyste m models. Port Phillip Bay requires detailed modelling of water-column and in-sediment processes, in particular detailed models of recycling processes , and also modelling of benthos-water-column interactions. Interaction of t hese components gives the model a nonlinear response to change in load. The Bass Strait ecosystem model is simple with no modelling of the sediment an d limited modelling of water-column recycling. This model's behaviour is la rgely controlled by the physical environment. (C) 2001 Elsevier Science Ltd . All rights reserved.