Self-purification processes in Estonian rivers receiving sewage from oil shale processing industry.
Truu, Jaak; Talpsep, E.; Heinaru, E.; Heinaru, A.
Rivers in the northeastern part of Estonia have been for decades under constant input of phenolic leachate water from semi-coke mounds formed as by-product of oil-shale processing. The dynamics of chemical and microbiological parameters were studied along river system polluted by ash-dump leachate in May-September 1995. The structure of the bacterial community was characterized by general microbial functional groups (heterotrophic bacteria), by biodegradative bacterial groups (phenol, m-toluate, benzoate, salicylate, camphor, naphtalene and heptane degrading bacteria), and by community-level physiological profile (Biolog microplates). The taxonomic diversity of the isolated phenol-utilizing bacterial strains was studied using commercial identification systems (Biolog and API). Multivariate statistical techniques were applied to relate different aspects of bacterial community structure to environmental parameters, and to assess the relationships between different estimates of community structure. Pollution markedly altered all aspects of the studied microbial diversity. The structure and functioning of the bacterial communities changed significantly along the river and revealed remarkable adaptation to phenolic compounds in environment. Based on the data observed the concentration of volatile phenols decreased as an average 85 % along the river system, and the most significant process involved in selfpurification is biodegradation of these compounds.