Land and Water Link

April 2003

Waste Makes a Comeback

A common source of waste is now a sustainable agricultural resource in South Australia (SA), thanks to an award-winning CSIRO Land and Water research team, and their collaborators from SA Water and United Water.

Dr Mike McLaughlin, who leads the CSIRO team, explains: 'These days, biosolids management is becoming increasingly difficult, as regulatory and environmental pressures encourage wastewater treatment plants to investigate sustainable management practices. This has triggered the realisation that re-using stockpiles of biosolids from treatment plants can be both sustainable and economical.'

The value of using organic waste to enrich soil for agriculture is familiar to all of us. Extending this tradition, the accumulated biosolids from wastewater treatment plants could provide an additional source of beneficial nutrients and organic material.

'Unfortunately', as Dr McLaughlin points out, 'biosolids may also contain contaminants that are detrimental to soils, food quality and human health. So it is important to understand these risks, as well as any potential benefits, if we are to manage the sustainable use of biosolids in agriculture.'

The initial challenge was to ensure that the Australian guidelines for biosolids re-use are suitable for South Australian soils. A trial project for biosolids from the Bolivar Wastewater Treatment Plant (in Adelaide) was established with two South Australian field sites at Avon and Kapunda. The trials have been conducted for four years so far, and three new sites will continue for at least another four years.

'We knew that a scientific basis for the re-use of biosolids was needed', says Dr McLaughlin. 'Our objectives were to establish the benefits that nutrients, trace elements and organic matter in biosolids would have for dryland crops. We also needed to determine the long-term sustainability of using biosolids in accordance with the Biosolids Guidelines of the Environmental Protection Authority.'

The researchers scrutinised the key pathways through which contaminants would appear. They also recognised that another potential concern with biosolids re-use was that the trace metal cadmium might pose a risk to food quality.

According to Dr McLaughlin, 'Our research has been instrumental in revising precautionary maximum permitted values for cadmium in South Australian soils to which biosolids are applied, to ensure that long-term sustainability of biosolids re-use will not be compromised'.

Based on their work, the guidelines for re-use of biosolids were amended to reduce the maximum concentration of cadmium in soils to which biosolids can be applied from 3 mg/kg to 1 mg/kg.

Cadmium was only one of the contaminants taken into account. A key feature of the research is the breadth of the effects studied. These included both adverse and beneficial effects on soil structure, plant growth, soil microbial activity and food quality.

The project provides data crucial for developing a sound scientific basis for protecting soil resources from irreversible degradation from salt, heavy metals and metalloids. At the same time it ensures that soils benefit from biosolids as a source of organic matter and nutrients.

This innovative research into a scientific framework for agricultural re-use of biosolids has placed South Australia in the lead with respect to the sustainable re-use of solid waste in Australia.

'Having a sound scientific framework in place has underpinned the acceptance and rapid increase in safe biosolids re-use in South Australia', says Dr McLaughlin. 'Levels of biosolids re-used now exceed annual production, so the stockpile of waste stored at the Bolivar Wastewater Treatment Plant is being reduced.'

The importance of this work has recently been recognised by water corporations around Australia, with its extension into a National Biosolid Research Program, which aims to provide data to underpin regulations for biosolid re-use at state and national levels.

'We are also studying the benefits of nutrients and organic matter in biosolids and quantifying their economic benefit', says Dr McLaughlin.

'Field experiments have already begun in Queensland, New South Wales, Victoria and Western Australia, and are continuing in South Australia. We hope that we will be able to fine-tune regulations for Australian conditions so that in the future one of our most common sources of waste will be transformed into a valuable, sustainable agricultural resource.'

The efforts of the CSIRO Land and Water biosolids re-use research team – Mike McLaughlin, Daryl Stevens, Michelle Smart, Bogumila Tomczak and Bernie Zarcinas, along with their collaborators from SA Water and United Water – were recognised with the Australian Water Association 2002 Award for excellence in Research and Development (SA).

For further information

Contact

Dr Mike McLaughlin
Ph: 08 8303 8433