Simultaneous removal of sulfate and arsenic using immobilized non-traditional SRB mixed culture and alternative low-cost carbon sources

Abstract

This study was designed to obtain simultaneous sulfate (SO42−) and As(III) ions removal by non-traditional sulfate-reducing bacteria (SRB) growing in the presence of a protein biomass (PCF), a solid residual material produced by the poultry industry. Microbial cells and PCF were immobilized into calcium alginate beads to reduce mass losses. Microbial consortium efficiency was tested under different operational conditions: sodium lactate, glycerol and PCF as carbon sources; increasing As(III) content; acidic pH (5.0). Microbial diversity was evaluated by PCR-DGGE. Pantoea agglomerans, Enterobacter sp., Citrobacter sp., Cupriavidus metallidurans, Ralstonia sp. and Burkholderia cepacia were found. With the aim to obtain SO42− and As(III) simultaneous removal, three semi-continuous up-flow reactors were constructed and operated for more than 100 days to prove their feasibility and reliability. Both SO42− and As(III) ions were removed with 74.8% and 80% efficiency, respectively. Solid products were characterized by SEM-EDX, confirming PCF and non-traditional SRB roles during arsenic immobilization. Arsenic/sulfur compounds (possibly As/sulfides) were produced by reaction between As(III) and biogenic sulfide. Microbial consortium proved its ability of growing in an acidic environment without losing its sulfate reductive capacity by using glycerol and PCF as alternative carbon sources and tap water as micronutrients source. The non-traditional SRB culture removed both SO42− and As(III) ions simultaneously, with no prior step needed to guarantee As(III) oxidation to As(V). Two different mechanisms could be involved: (i) precipitation as arsenic sulfide or, (ii) adsorption onto PCF/cells calcium alginate beads.