Land and Water Link

November 2003

Most of the water reserves in Western Australia lie underground, so the city of Perth relies on groundwater for about 50% of all water needs. But groundwater is vulnerable to contamination by fertilisers, pesticides, industrial waste and all of the other pollutants generated by urban, commercial and industrial activities.

The conventional approach to remediation is complicated and expensive, but now there is an alternative – thanks to an innovative team of scientists from CSIRO Land and Water and the University of Western Australia, and a select group of naturally occurring microbes.

In this new system, microbes are encouraged to multiply and gobble up pollution. As Dr Bradley Patterson from CSIRO Land and Water explains, ‘We provide the microbes with their chemical needs, and they convert the contaminants into less harmful substances, free of charge!’

‘For example, in large-scale trials on groundwater contaminated with fertiliser, sequential delivery of oxygen and then ethanol induced bacteria to convert ammonium-based fertiliser residues into harmless nitrogen gas, which simply bubbles off – leaving clean water.’

The cost-effective and reliable technique is being applied to the clean-up of an ever increasing range of pollutants, in groundwater and soils. Field trials have been successful.

‘Our system removed 90% of the ammonium from the treated underground plume of badly polluted water at a site in Perth’, observes Dr Patterson. ‘This entailed burying, by vibration, a 20m long barrier system in saturated sand to a depth of seven metres and letting the bugs do their work. We are confident that the technique can be further scaled-up by the use of many such modules.’

Similarly, ethanol was supplied to stimulate indigenous sulfate reducing bacteria for the remediation of metal-contaminated groundwater, with greater than 95% reduction in zinc and copper concentrations.

The team has also demonstrated that the system can deal with contamination by the herbicide atrazine. And a number of useful microbial species have been identified that could potentially work against other pollutants.

Dr Patterson believes the polymer mat system will be most useful in the remediation of point source contamination that might arise from accidents or industrial spills. In this situation, current practice involves pumping large volumes of dirty water to the surface for prolonged treatment and then returning the clean water to the ground.

‘Our new technique will provide a competitive alternative to the pump, clean and reinject system that’s now the standard way of dealing with contamination.’

As Dr Patterson explains, ‘This system has tremendous potential because it can decontaminate water while it is still in the ground. And once the barrier is in place, the system is low cost and low maintenance.’

Natural hydraulic gradients push water through permeable cleansing barriers, so there is no need for pumping at all – even below ground. This approach should be cheaper and better for the environment.

For example, at one of the test sites, contaminated water is flowing out to the ocean – with associated risks including the formation of blue green algae. ‘But our system promises to be safer, because we can control the movement of the plume of contamination,’ says Dr Patterson.

The innovative permeable reactive barrier system will soon be ready for commercial application. ‘The key to this remediation strategy is the fundamental understanding of the natural biochemical processes, coupled with the ability to deliver selected amendments in a long-term, cost-effective way’, says Dr Patterson.

The team is refining the system in further trials and is looking for industry leaders interested in taking up the new bioremediation technology.

Diagram shows the permeable reactive biobarrier system at work.

CSIRO contact:

Dr Bradley Patterson
Ph: +61-8-9333 6276