Thursday, 21st May 2009

Research has shown composted organic mixes of straw and sheep manure could hold the key for the safe disposal of acidic water from deep drains.

Each year, millions of litres of saline acidic water flow through a network of drains in the WA wheatbelt, as farmers try to reclaim land damaged by shallow saline groundwater.

This acidic saline water can pose a threat to aquatic life in naturally occurring lakes and waterways.

Research funded by the Avon Catchment Council and undertaken by the Department of Water, has focused on six different small-scale pilot trials in drains at Beacon and Doodlakine.

The Department’s Dr Degens has spent the past two years trying to find practical and readily available materials as treatment solutions for acidic waters.

“From these trials we found there are a number of ways in which acidity in these drainage waters can be treated, but which one you would use depends on your circumstances,” Dr Degens said.

“The treatment options trialed used a range of materials such as an organic mix of straw and sheep manure, as well as industrial hydrated lime and lime sand, which have neutralizing qualities.

“The most practical treatment option was the use of composted straw and sheep manure in a waterlogged pit, which grew micro organisms that helped lower acidity.

“At a trial of a composting pit at Beacon, the acidic saline water percolated through the compost and was then returned back into an evaporation basin.

“Prior to treatment, the water was similar to weak vinegar and twice as salty as the sea, with a pH of between 3 and 3.5.

“After treatment the pH of the water increased to between 5 and 6 (a drop in acidity). This compares with rainwater pH being about 6.

“Three hundred square metres of the organic mix was treated with about 750 kilolitres of acidic water in the first 12 months.

“There was a drop in the effectiveness of the composting treatment after about six months - highlighting that more work is needed to find a mixture that will continue to work well over the long term.

“We’ve used a simple mix with some success, which suggests that more effective rates of treatment are likely, with better quality materials such as spoilt grain or green waste.”

Dr Degens said the cost of the treatment options ranged from around 15 cents for every 1000 litres of acidic water, to as much as 70 cents for every 1000 litres.

“While there is some promise in treating acidity, the problem of salinity still remains,” he said.

“But we could have more uses for saline groundwater that has been treated for acidity, which is good news.”

The outcomes of this research will be reported in “Guidelines for the Treatment of Acidic Drainage Waters in the Avon Catchment” which is expected to be published later this year.

This work is a follow-up to the Department’s Engineering Evaluation Initiative, which has focused on investigating the effectiveness of engineering solutions to combat salinity in the wheatbelt.

Contact: Dr Brad Degens, Department of Water, 9690 2600 or 0417 917 717