Underground barriers to stop toxic waste from contaminating water

January 7th, 2009 - 4:30 pm ICT by IANS  

Sydney, Jan 7 (IANS) Thousands of garbage dumps are quietly leaking a toxic brew of old and sometimes deadly chemicals into the water consumed or used by millions of people. Researchers are developing a solution to one of the most urgent problems faced worldwide — the poisonous fluids which leach out of old rubbish dumps and enter the groundwater.

“The contamination depends on what was in the garbage placed in the tip (dump). It usually contains old industrial and household chemicals, solvents and oils, antibiotics and endocrine disruptors, medical drugs, personal care products, biological pollutants and heavy metals,” explained ‘Vigi’ Vigneswaran.

Vigneswaran who is a professor at the University of Technology Sydney said the solution to this assault on good health is the ‘permeable reactive barrier’, an underground wall that filters and cleanses the toxic flow before it can enter the aquifers which are used by communities for drinking, domestic, stock or industrial water.

While modern dumps are designed to prevent the flow of toxic leachate from reaching groundwater, older ones were not, and many are still quietly and insidiously feeding the pollution from decades ago back into the community of today.

Ravi Naidu, managing director of The Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC-CARE) said Vigi’s barrier can be buried 20 metres and be up to two metres thick.

“It is a sophisticated sandwich of materials which adsorb, break down or otherwise render harmless the contaminants in the leaching tip water,” Naidu explained.

Traditionally permeable reactive barriers have consisted of iron particles or slag which helped remediate the contaminated leachate. Vigi’s design tailors the barrier precisely to the particular pollutants in the leachate and subjects them to a series of processes which ensure they are destroyed or rendered harmless.

“For example, first we use biosorption to remove and neutralise biodegradable hydrocarbon compounds. This uses a material on which biofilm forms - and these do the job of breaking down the pollutants,” Vigi explained.

The barrier’s second layer subjects POPs or persistent organic pollutants to fierce oxygen free radicals which break down the poisons into harmless by-products such as water, CO2 and nitrogen.

The third layer is designed to deal with toxic heavy metals such as arsenic or the lead and mercury left by the millions of discarded batteries and other poisonous metals from old consumer electronics, said a CRC-CARE release.

Depending on the type of contaminants in the leachate, these layers may be arranged in different sequences to obtain the best results.

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