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Prawn pond pollution slashed

CSIRO : 03 March, 2000  (Technical Article)
CSIRO researchers have come up with a way to prevent prawn farm effluent from polluting the local environment. Effluent from prawn farms has damaged the industry in a number of countries. Concerns about potential environmental impacts of these effluents has prompted the search for ways of re-capturing waste nutrients before discharge into receiving waters or re-circulation into production ponds.
Speaking at the Outlook 2000 conference in Canberra CSIRO's Dr Nigel Preston revealed a simple system that permits farmers to achieve this objective.

This is the result of a three-year study involving CSIRO Marine Research and the prawn farming industry. The study was funded by the Cooperative Research Centre for Aquaculture.

'We found that by using a sedimentation pond to treat pond water prior to discharge or recirculation we could achieve effective reduction of nutrients,' says project leader Dr Nigel Preston. 'This system is based on natural physical, chemical and biological processes that occur in a sedimentation pond designed to maximise nutrient removal.'

The $700,000 study also examined the use of treatment ponds containing oyster beds and marine plants to remove excess nutrients.

In addition to obvious improvements in water clarity, the scientists found that by including treatment ponds and partial recirculation as well as a sedimentation pond, nitrogen levels could be reduced by a total of 75 percent.

If necessary, additional reductions in nitrogen can be achieved by increasing the area devoted to treatment, says Dr Preston.

'An added bonus is gained by harvesting the nutrient-rich algae and selling it either as fertiliser for land crops, or as a source of valuable compounds for use in food and medical products.'

'One plant being trialled is the red algae Gracillaria edulis which is a valuable source of plant gelatine.'

The CRC for Aquaculture experiments have demonstrated impressive plant growth rates with over one tonne of plant material removed from a 0.3 hectare pond in just three weeks.

Prawn farming in Australia has developed only relatively slowly compared with most other prawn farming regions, such as those in south-east Asia. Only 350 ha of prawn ponds are currently in production from farms distributed over 2,000 km of coastline.

In addition, Australia has strict environmental regulations to ensure good water quality.

According to prawn farmers who have trialled the system as part of the study, the research will help farmers meet these strict environmental regulations, which in turn will protect our reputation as suppliers of high-value aquaculture product.

Overall, government and industry groups are spending about $1 million a year over five years on research aimed at achieving environmentally sustainable production. As a result, Australia is fast establishing itself as a world leader in waste treatment technology for prawn ponds, says Dr Preston.
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