Scientists from Newcastle University are using llama droppings to help combat environmental problems caused by polluted water seeping from abandoned silver and tin mines in the Bolivian Andes.
The project is being spearheaded by Paul Younger, Professor of Hydrogeochemical Engineering at Newcastle University. It has been adapted from a community-based natural regeneration technique which uses waste materials to treat polluted mine waters. Professor Younger pioneered the technique, along with scientists and engineers from the University working in partnership with the residents of former mining communities in North East England, who called him in to help them address the threat to their environment caused by polluted water draining from disused mines.
Mine water has a high acid content and is extremely damaging to the ecology of the surrounding areas. The scientific basis for the regeneration technique, which involves the creation of 'low-tech' bioreactors constructed in the form of wetlands with a substrata of compost and limestone, is called bacterial sulphate reduction. Bacteria living in the compost and limestone use dissolved sulphate, found in abundance in mine water, as an energy source, producing sulphide. The sulphide then reacts with the dissolved iron and traps it, as iron sulphide, in the compost bed. This process also raises the pH in the water and generates alkalinity.
This technique has been so successful in the North East of England that it is now being customised and exported for similar problems in other countries and is helping to make Newcastle University Europe's leading centre for minewater research.
In the Cordillera Real of the Andes, perennial drainage from abandoned tin and silver mines is grossly polluting the main water supply of the capital city, La Paz. Some of this extremely polluted water is used untreated by impoverished local residents for domestic and agricultural purposes, and although the city waterworks efficiently removes iron from the water, unpublished data show that toxic elements such as cadmium have occasionally entered the public water supply in La Paz at concentrations well above the limits specified by the World Health Organisation.
The mine from which the pollution emerges, Mina Milluni, was closed abruptly in 1985 as a consequence of the global slump in tin prices which occurred in that year. Professor Younger explains: 'The former mining company has neither the financial resources nor the legal responsibility to remediate the polluted drainage, so it seems that the problem will continue indefinitely unless some local champions decide to find solutions of their own'. Drawing inspiration from some of the passive treatment systems developed in the UK, Professor Younger has been working with a local engineer, Marcos Arce, on preliminary experiments to assess the feasibility of treating the acid water from Mina Milluni using bacterial sulphate reduction and limestone dissolution.
Professor Younger continues: 'The problems of implementing this technology at Milluni are considerable: lying at about 4400m above sea level, nocturnal freezing is the norm for much of the year, and supplies of compost materials similar to those that have been used successfully in the UK , such as horse and/or cow manure, with composted tree bark mulch, are not readily available in the Bolivian Andes. However, llama droppings are abundant, though it hardly needs stating that no previous data exist on their performance in acid mine drainage remediation systems'.
Professor Younger and his colleagues constructed a series of tanks in which limestone gravel was buried beneath half metre-deep layers of llama droppings. A continuous flow of acid drainage was directed through the tanks for a five-month period between June and November 2000, which is also the coldest period of the year.
'The findings from these experiments are extremely encouraging. As hoped, the llama droppings do promote the activity of sulphate-reducing bacteria (sulphate reduction averaged around 16%), and the average pH of the water rose from 3.2 to 6.3 on passing through the four tanks', said Professor Younger.
'We are currently attempting to identify funding sources which would support Marcos to work with local artesanal miners and other residents to develop larger bioreactors in the field at this and other sites, with the long-term aim of empowering the poverty-stricken communities of indigenous people to reclaim and sustain the water sources which are currently denied to them by the legacy of large scale mining' he concluded. As a result of his research, Professor Younger and his team have been asked to help the European Commission draft its law on the regulation of pollution from mines.
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