Preparation of Immobilized Sulfate-Reducing Bacteria-Microalgae Beads for Effective Bioremediation of Copper-Containing Wastewater

A strain of Desulfovibrio sp. sulfate-reducing bacteria (SRB) was isolated from a sludge sample. Novel immobilized SRB beads with microalgae (Chlorella vulgaris, Scenedesmus obliquus, Selenastrum capricornutum, and Anabaena spiroides) as the carbon source were prepared and then used to treat wastewater containing 60 mg/L Cu(II) and 600 mg/L sulfate in batch experiments. The microalgae were first degraded by co-existing fermentative bacteria into fatty acids, which then served as a carbon source for SRB. The solution chemical oxygen demand was significantly lower with microalgae substrates than with ethanol as a substrate. Different immobilization methods were evaluated with an orthogonal design, which indicated that the compositional parameters for preparing immobilized beads with an optimal sulfate reduction rate were polyvinyl alcohol (2%), sodium alginate (1%), calcium chloride (6%), silica sand (1%), and a 50-mL volume of SRB suspension. SRB activity in the immobilized beads was distinctly enhanced compared with that of suspended SRB. At an initial pH of 5.5, 72.4-74.4% of sulfate and over 91.7% of Cu(II) were removed, indicating that immobilized SRB beads with plentiful low-cost microalgae as a nutrient source may be an efficient method for acid mine drainage treatment.