Biosolids: Black gold in Western Australia

Abstract

Of the three major wastewater treatment plants in the capital city of Perth, Western Australia, two produce dewatered biosolids cake (DBC) and the third produces lime-amended biosolids (LAB). The total production of both DBC and LAB in the 2004/2005-year was approximately 20,000 tonnes dry solids (t DS) and is increasing at a growth rate of 4% yr-1. The demand for Perth's biosolids as a low-grade fertiliser has outweighed supply and has achieved an average of 94% beneficial use for the past four years. The use of biosolids in Western Australia is strictly regulated by the 'Western Australian Guidelines for Direct Land Application of Biosolids and Biosolids Products 2002' (DEP et al. 2002). The three major users of biosolids in Western Australia include agriculture, forestry and composting accounting for 74%, 5% and 17% of the total biosolids production, respectively. Within the agricultural sector, the application of DBC commenced in 1996, mostly to wheat and canola crops in a dryland farming system. Local farmers have often referred to the biosolids as 'black gold' due to improvement in their crop yield and income following application. In forestry, biosolids research was commenced in 1998 on a 17 year-old pine plantation on the Swan Coastal Plain. Tree growth has improved significantly following the application of biosolids compared with inorganic fertiliser application, with no detrimental impact on groundwater quality. The composting of biosolids with other materials for domestic use and bagging has been practiced for more than 17 years.This paper summarises the evolution and current use of biosolids in Western Australia and highlights the main research programs instigated by the Water Corporation to ensure that Perth's biosolids are used beneficially and safely in the environment. Research has concentrated mostly on plant and tree nutrient uptake, particularly nitrogen and phosphorus, heavy metals, composting of biosolids, flies and pathogens. Much of the research data has been collected within the Australian National Biosolids Research Project (NBRP).