Systematic review and meta-analysis of the application of microorganisms for the Cr(VI) removal from tannery effluents

Abstract

The application of microorganisms as bioadsorbents for the treatment of industrial effluents is shown to be an efficient and environmentally viable technology, since it does not generate toxic products. In the present systematic review and meta-analysis, information was gathered about the capacity of microorganisms to remove hexavalent chromium (Cr(VI)) from tannery effluents. In addition, the different variables of the bioadsorption process such as pH, microorganism dose, incubation time, initial metal concentration and final metal concentration were investigated. These parameters were considered according to each species studied in the included investigations. For the meta-analysis, Review Manager 4.0 (RevMan) software was used through the fixed effect model with a 95% confidence interval. The results revealed that the included investigations showed a considerable statistical heterogeneity (I² = 87%) and that the application of microorganisms for the Cr(VI) removal from tannery effluents showed greater efficiency at lower initial concentrations of the metal. It was also observed that the microorganisms used in the included investigations showed percentages of Cr(VI) removal higher than 70% for the treatment of tannery effluents.