Microalgae and bacteria team up against arsenic-poisoned water

Australian scientists have developed a new type of water filter that combines microalgae with bacteria taken from soil contaminated with heavy metals. The technology could prove an effective, cheap and safe way to clean up the potentially deadly arsenic that pollutes the drinking water of tens of millions of people around the world.

Mezbaul Bahar, of the CRC for Contamination Assessment and Remediation of the Environment (CRC CARE) and the University of South Australia, said the “king of poisons” has harmed more humans than any other toxic chemical in history. Arsenic poisoning causes vomiting and diarrhoea, and long-term exposure can lead to cancer, diabetes, heart disease and death.

Bahar said arsenic is an ever-present threat, contaminating groundwater “in more than 70 countries, including Bangladesh, India, the USA, South America, China, Thailand and Taiwan” and is difficult and expensive to remove. “Around 137 million people are poisoned daily by arsenic in their drinking water and food,” he said.

The principal supervisor of the CRC CARE research, Professor Megh Mallavarapu, explained that two forms of arsenic are commonly found in the environment: arsenic (III) and arsenic (V).

“Arsenic (III) is 60 times more toxic than the other form and is highly soluble, which makes it more difficult to remove, as it travels everywhere … The solution then is to convert arsenic (III) into the less toxic and less soluble form, making it easier to extract from the water.”

Previous techniques using chemicals and bacteria have attempted such a conversion, said Professor Mallavarapu - but the use of chemicals was an expensive process which brought unwanted side effects; and the bacteria required constant feeding as they required carbon to grow.

The CRC CARE team recently discovered “bacteria in soil that has been contaminated with heavy metals”, said Bahar, which developed the ability to convert arsenic into its less harmful form in order to survive.

The scientists also found a type of microalgae which could provide food for the bacteria. Professor Mallavarapu said the microalgae only need sunlight to sustain themselves and to generate energy, “and together with water, they’ll grow and produce carbon and oxygen to support the bacteria”.

“However, when the bacteria break down the organic matter produced by the microalgae as well as from contaminated water, they produce carbon dioxide, which in turn can be used to feed the microalgae.”

Once the arsenic has been converted, said Professor Mallavarapu, it can be easily absorbed and removed using material such as coir pith made from coconut husks.

Bahar said the technology will be tested in the laboratory to determine whether it can be used in individual households or villages.

Bahar is this week presenting a poster on the technology at the CleanUp 2013 conference, hosted by CRC CARE and taking place at the Crown Conference Centre in Melbourne from 15-18 September. Further details can found at www.cleanupconference.com.