Bacterial Reduction of Sulfates as Suitable Method for Removal of Sulfates from Acid Mine Drainage

Abstract

The aim of this work was to investigate of the sulfates removal from acid mine drainage (AMD) by biological method using sulfate-reducing bacteria (SRB). A sample of AMD out-flowing from the Pech shaft of the abandoned and flooded Smolník deposit in Slovak Republic was studied. The untreated AMD (with contents metals) and treated AMD i.e. after of the metals removing by the synthetic sorbent Slovakite were used. The base of the biological sulfates elimination was the sulfates bacterial reduction under influence of SRB genera Desulfovibrio. These bacteria realize the sulfates reduction to hydrogen sulfide at the simultaneously oxidation of energetic substrate. Standard selective nutrient medium DSM-63 and modified selective nutrient medium DSM-63 (without sulfates contents) with standard amount of sodium lactate (as energetic substrate) were used in the experiments with untreated AMD. Standard selective nutrient medium DSM-63 and modified selective nutrient medium DSM-63 with standard, double and triple amount of sodium lactate were used in the experiments with treated AMD. In the case of untreated AMD has been reached low removing of sulfates - 20% efficiency (standard medium) and 26% (modified medium). The formation of heterogeneous precipitates containing metals pointed to the need for treatment of AMD by the initial removal of metals by sorption on Slovakite sorbent and subsequent removal of sulfates by bacterial reduction. The results of experiments with AMD treated in this way showed 49%, 70% and 88% efficiency of sulfate removal when using sodium lactate in standard, double and triple amounts. The results of this work suggest that ratio of substrate quantity and sulfate concentration is one of the key parameter of sulfate reducing condition. However, the price of the energy substrate is also an important factor. Therefore, subsequent experiments will be focused on the use of the more affordable substrates (e.g. whey) or mixed bacterial culture of SRB, which will also be able to use the products of decomposition of basic energetic substrates.