Removing Mercury from Water

Mercury is a well-known highly toxic pollutant. To remove it from industrial waste-water, US scientists have developed an efficient method by using an easy-to-grow bacterial strain engineered in bioreactors to produce a mercury-binding protein. An EU-funded FP5 demonstration project (Biotechnology Programme) aims to prove the feasibility and profitability of this approach under real-time conditions. Within this framework, a bioremediation plant installed at Usti-nad-Labem (Czech Republic) has been operating since July 2000.

Health-threatening pollution

Industrial production sometimes emits pollutants into the environment. Among them, heavy metals are of major environmental and health concern. Mercury, for example, is a highly toxic metal which, once released into rivers, accumulates in the food chain, damaging fish, shrimps and the people who eat them. The famous Minamata affair (called after a town on the Japanese island of Kyushu where the inhabitants suffered the toxic effects of fish poisoned by mercury-rich industrial effluents) is an example of the devastating effects mercury can have on the nervous system.

The biological way to decontamination

Mercury removal from industrial waste water, therefore, is obligatory and should be strictly controlled by any environmental legislation. However, existing techniques, such as precipitation or ion-exchange, are expensive and not sufficiently efficient: small but significant amounts of mercury still remain in the water. The solution to this problem has been found in the realm of microbials. Researchers have discovered that many bacteria have developed an astonishing tolerance towards heavy metals. This ability gives them a competitive advantage over other micro-organisms with whom they share a metal-rich environment. The secret of this resistance to toxic metals lies in the production of proteins able to bind metals into harmless compounds – for example, metallo-thionein that binds mercury. Similar microbial help in decontamination can be found for other metals, too: copper, silver, nickel, zinc, cadmium, lead, and even uranium.

The bioremediation process

Unfortunately, naturally thriving mercury-tolerant bacteria are rare and cannot be grown easily in culture. Hence, researchers at Cornell University (New York) inserted the metallo-thionein gene into the well-known laboratory workhorse Escherichia coli. A sufficiently large number of bacteria are now continuously treating mercury-polluted water inside a bioreactor. The bacteria finally die and can then be incinerated to recuperate the accumulated pure mercury. The efficiency of the procedure is incredibly high, with the bacteria removing mercury from polluted water down to a few nanograms per litre.

A European demonstration

Mercury emissions are predicted to increase by 30% throughout Europe between 1990 and 2010. European researchers have a strong incentive to follow the same path as their American homologues. Under the Fourth Framework Programme, the European Commission funded a demonstration project (BIO4-CT98-0168) to show the feasibility and profitability of the microbial remediation technology under real-time conditions. The plant has been installed at Usti-nad-Labem, in the Czech Republic, and has been operating since July 2000. The rationale of EU-funded demonstration projects is to show the cost-effectiveness of new technologies and to disseminate relevant information in order to transfer results out of the laboratories to scientists and managers in the private sector.

CO-ORDINATOR
Irene Wagner-Döbler
Gesellschaft für Biotechnologische Forschung
Mascheroder Weg 1
D-38124 Braunschweig
Tel: +49 531 61 81 408
E-mail: iwg@gbf.de