Ecological chemistry of mercury contained in bleached kraft pulp mill effluents

Chemistry of effluents entering natural water bodies is usually ecological chemistry. The object of its study is the influence of effluents on chemical and biological processes of self-purification. Mercury and its compounds are priority pollutants in bleached kraft pulp mill effluents. It is ascertained that Hg enters the effluents from wood and auxiliary reagents: compounds of Na and active Cl and also from H₂SO₄ employed for neutralization of effluents before biological treatment. At the investigated enterprise the effluents have three stages of treatment: biological, physico-chemical and mechanical. This treatment reduces the Hg concentration in effluents from 10 to 30 ppb to 0.3 to 0.5 ppb. No increased Hg accumulation by aquatic organisms and bottom sediments in the area of effluent discharge was found. Moreover, aquatic organisms grown during 1 mo in the effluents medium did not accumulate Hg in comparison with the control animals. It is found that such ecological effect is obtained as a result of inclusion the modern physico-chemical methods into the complex treatment system.