Removal heavy metals and sulphate from waste waters by sulphate-reducing bacteria

This article is devoted to the process of bacterial sulphate reduction, which is used to removal of heavy metals and sulphate ions from waste waters.The life of animals and plants depends on the existence of microscopic organisms – microorganisms (MO), which play an important role in cycle changes of biogenic elements on the earth. The sulphur cycle in the nature is considered as one of the oldest and most significant biological systems (Fig. 1). The sulphate-reducing bacteria (SRB) miss the assimilatory part of the cycle and produce sulphides. The microbial population of this dissimilatory part is called “sulfuretum”. The SRB can be found in anaerobic mud and sediments of freshwater, thermal or non-thermal sulphur springs, mining waters from sulphide deposits, oil deposits, sea and ocean beds, and in the gastrointestinal tract of man and animals. The SRB represent a group of chemoorganotrophic, strictly anaerobic and gramnegative bacteria, which exhibit a great morphological and physiological diversity. Despite of their considerable morphological variety, they have one property in common, which is the ability to utilise preferentially sulphates (occasionally sulphites, thiosulphates, tetrathionates) as electron acceptors, which are reduced to sulphides, during anaerobic respiration. The electron donors in these processes are simple organic compounds as lactate, malate, etc.,(heterotrophically reduction) or gaseous hydrogen (autotrophically reduction). SRB can produce a considerable amount of hydrogen sulphide, which reacts easily in aqueous solution with the cations of heavy metals, forming metal sulphides that have low solubility. The bacterial sulphate reduction can be used for the treatment of acid mine drainage waters, which is considered to be the major problem associated with mining activities.In order to remove heavy metals from waste waters, e.g., from galvanizing plants, mine waters (Smolnik, Šobov locality) and metallurgic plants (works Krompachy) by use of the activity of SRB, mixed strains were isolated, cultivated, and their production of hydrogen sulphide was assessed. The cultures were then tested for the ability to precipitate copper and sulphates from a model solution.The bacteria were isolated from water samples from two localities: Východoslovenské železiarne (works) – VSŽ and spring Gajdovka – Gj. Isolation, cultivation and eliminating Cu2+ and SO42- was carried out under following conditions: statically, temperature 30 oC, pH 7,5, nutrient medium by J. Postgate (medium B, C and D) and anaerobic conditions. Residual copper in the solution was measured by atomic absorption photometry. The concentracion of sulphates in the solution was measured by the nefelometric method.Our findings from the isolation of SRB from two Slovak water samples and testing the cultures for their ability to remove copper permit the following conclusions: SRB occur in sufficient numbers in sulphur mineral water from natural sources and in industrial waste waters reservoirs, the sulphate-reducing activity can be harnessed for the purification of some industrial waste waters.The nature possesses a great biological potential that can be exploited under certain conditions in the cleanup of environmental pollution resulting from the industrial activity in the past and present.