PERTH BIOSOLIDS: Where are they now and how did they get there?

Biosolids reuse in Western Australia has evolved over the decades. Traditional management practices of biosolids derived from Perth Metropolitan wastewater treatment plants included incineration, uncontrolled reuse by market growers, composting and landfilling. With increasing environmental concerns and issues of past practices, a managed reuse program for biosolids was required, aimed at reducing risks to public health and the environment.The community has long recognised the benefits of biosolids reuse as a low-grade fertiliser – for its nutrient and organic composition for enhancing soil quality. The main concern prohibiting the unrestricted reuse classification of biosolids are the heavy metals and pathogens. Reuse of biosolids can be successful if these risks are addressed and managed properly.This report outlines the transition of the management of Perth's biosolids from the state of being minimally managed, to the highly regulated management practices of today.Perth biosolids reuse program commenced in 1996 and has been made possible by the investigations accomplished by Sydney Water. Although the soil and climate issues have not been addressed fully for Perth, there are enough similarities from the Sydney Water study for the Water Corporation to understand the effects of a poorly managed biosolids management program.The release of the Draft Guidelines for Sewerage Systems – Biosolids Management, Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) recommended the areas where biosolids could be reused. The dewatered biosolids cake produced from Perth's wastewater treatment plant are classified as a “restricted use” product. This limits the potential uses to broadacre agriculture, forestry and land rehabilitation. Biosolids are still composted as the end product is classified for “unrestricted use”.The biosolids management plans highlighted that the most likely long term options of reuse will be influenced by factors identified by the market research. The research and development conducted and the cost of reuse will highly influence ultimate fate of biosolids.Currently, most of Perth's biosolids are reused on agricultural land and in composting. Market research conducted in 1997 identified these viable outlets. Additional investigations also identified these markets would pose minimal risks to the public and the environment. The proportion of biosolids to be reused in forestry and land rehabilitation will increase within the next one to two y ears. With the completion of these trials, the optimal application rate and the effect to the direct environment will be determined.For each proposed application, the environmental factors and the risks must be assessed. Each application requires the approval from the Department of Environmental Protection, the Water and Rivers Commission and the Health Department of Western Australia to ensure that the environment and public health risks are minimised.The future for biosolids management and reuse in Perth is seen to be stable as various markets have been identified, and reuse outlets are currently either in full-scale operation or in well progressing trials. The success of Perth's biosolids reuse program will depend on the outcomes of research and development, and understanding the importance of biosolids reuse within a sustainable environment.Liaison with international and interstate wastewater agencies, and continual research is essential in ensuring that biosolids reuse is beneficial without compromising public health and the environment.