Melbourne Water's Western Treatment Plant at Werribee, Victoria treats raw sewage that is a mixture of domestic and industrial output. The processing plant has been in operation for more than 100 years and in that time over 0.87 million tons of dried sludge (biosolids) has been stockpiled. The high organic and nutrient contents of biosolids make them a valuable resource for improving the fertility of soils in agriculture, forestry and mine sites restoration. Melbourne Water aims to use beneficially all the annual production of biosolids from the WTP by the year 2010.

The existing biosolids stockpile is contaminated with heavy metals including arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc. The degree of contamination exceeds the current EPA (Vic) guidelines for the reuse of biosolids. This study is investigating the bioavailability of heavy metals in the biosolids stockpile and the ability of plants such as willows (Salix spp.), poplars (Populus spp.), and mustards (Brassica spp.) to take up heavy metals. The potential for Australian native species as metal accumulators is largely unknown. Phytoremediation will provide more options to reuse the biosolids and reduce the existing stockpile. This is a challenging research area requiring the development of an innovative and cost effective solution to the problem of metal contamination.