Reduction of Mercury in
WasteWaters from Chlorine Plants
HANS 0. BOUVENG, Director
P. ULLMAN, Engineer
Swedish Water and Air Pollution Research Laboratory
Stockholm, Sweden
INTRODUCTION
The Swedish nature conservancy authorities require today that all industrial
discharges of mercury to the environment should be prevented to the extent technically and economically possible. This standpoint is a consequence of the recent
findings that any form of mercury will at least partly be converted into organism-
bound methylmercuric complexes in an aquatic system and, further, that these,
under some conditions, highly toxic complexes become enriched in organisms such
as fish representing the higher levels of an ecosystem (1).
Neither the exact routes which the mercuric ion is transferred into a methyl-
mercuric complex nor the exact nature of this complex are well known. The information concerning the ecological properties of methylmercuric ion in the form
of biological complexes is, on the other hand, steadily increasing. It is, for instance,
known that the initial methylation is induced by bacteria, species of which have been
isolated from bottom sediments and other sources (2).
The property of methylmercuric complexes to become enriched when transported upwards through a food chain has been of prime importance for considering
mercury of any form as a pollutant. It is true that the ultimate concentration of
methylmercury in fish very much depends on the form (metallic, inorganic oxidized
or organic) in which it is discharged and on the characteristics of the receiving
ecosystem. The effect of large discharges of inorganic mercury in some places, therefore, has been rather insignificant. ■ However, concentrations of methylmercury as
high as five - ten mg/1 in non-migrating species of fish in some inland waters have
rightly been decisive for the authorities when characterizing any discharge of mercury
to the environment as involving a hygienic risk. The banning of phenylmercurials for
use as slimicides in paper mills was one consequence of this decision. Another was the
demand that the chlorine industry — at the time producing about 250,000 tons of
chlorine per year — should undertake such technical measures that the present
discharges of mercury — or, from a technical point of view, losses — were drastically
reduced.
SOURCES OF MERCURY DISCHARGED FROM CHLORINE PLANTS
When the Swedish nature conservancy authorities in late 1966 officially required that the chlorine industry should in future efficiently prevent discharges of
mercury to the environment, the industry and our Institute had already agreed upon
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