Bran filters arsenic from water
A portable filtering system made from chemically modified bran offers a cheaper way to filter arsenic and hexachlorocyclahexane (HCH) from water.
The Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) developed the mobile HCH and arsenic treatment system for a large chemicals company. The system uses bio-adsorbers made from chemically modified bran. “You can get bran from grain mills for a few Euros per metric hundredweight,” says Dr. Manfred Kühn of the Institute. “We modify it chemically and use its hydrophobic properties, so that it can bind the toxic substances.”
In tests, the bio-filters were found to bind almost all of the arsenic and HCH in water, leaving residues of 0.004 milligrams per litre and 0.13 micrograms per litre respectively, well below statutory limits. The bio-filters could also be re-used by desorbing the pollutants, although this process was more expensive than combusting and composting the filters. Similar bio-adsorption systems developed by the Institute are already being used for copper, lead, cadmium, zinc and chromium.
Arsenic-polluted drinking water is pervasive in countries like Bangladesh. Arsenic is also used by the semiconductor and glass industries, whose wastewaters must be treated to remove the arsenic. HCHs are present in some pesticides, although their use has been banned in Germany since the 1980s.
A head of a new US research centre for water treatment recently claimed that many water systems are outdated, inefficient and expensive (see related story). With impending water crises in the developing world, there is an urgent need for new methods of water recovery.