In Bolivia, water seeping from abandoned mines in the Andes is polluting the main water supply of La Paz, the capital city. But a team of researchers is developing a low-cost way to neutralize the acidic, metal-laden water through a highly unusual filter: llama droppings.
In a pilot study, the scientists used llama dung to treat run-off from a tin and silver mine that has killed organisms in an alpine lake and continues to pollute the La Paz water supply.
Their low-tech "bioreactor" system harnesses microbes living in the manure to neutralize the acidic water and remove most of the dissolved metals.
Mine water, which is rich in sulfate and metals such as iron, is particularly damaging to the environment. "Water leaches out of the mine typically bright red from all the iron, and very acidic," said Paul Younger of the University of Newcastle upon Tyne, who led the study in Bolivia.
As the polluted water flows through creeks, the iron and aluminum form solids that coat streambeds in a bright orange-red film. This deadly coating smothers the streams' algae, which are the primary food source for the fish and other smaller aquatic animals. The solid metal particles also kill fish directly by coating their gills and essentially choking them.
After successfully testing a dung-based filtration system in the United Kingdom, Younger and his colleagues tried the method in Bolivia. The mine water is filtered through ponds and lagoons filled with cattle or horse manureor, in the Bolivian case, llama droppings.
The researchers began searching for an effective treatment method because mine water run-off has long been a problem in the region of Newcastle, where Younger is based. "This part of northeast England is the cradle of the Industrial Revolution," he said, "and there has been mining here continuously since the 1600s."
Today, the mining industry in the region has nearly disappeared, leaving a honeycomb of abandoned mines and the burden of dealing with the polluted mine run-off.
In areas where pools of mine water created "dead zones," the researchers developed a system of lagoons and small wetlands containing cow and horse manure. When the mine water flowed through this organic filter, the acidity changed from something equivalent to vinegar to a neutral state close to that of drinking water.
The lagoons and wetlands eventually supported plant life, which helped improve the aesthetics of the affected areas. "They look quite pretty when they are done," said Younger.
In the Bolivian Andes, the extent of the run-off is considerably larger, said Younger. The Andes are particularly arid, but in the case of the mine at Milluri, the excavations hit the underside of a glacier, which is now melting and seeping through the mine and into the surrounding land.