Comparing the Tolerance Limits of Selected Bacterial and Protozoan Species to Vanadium in Wastewater Systems

Abstract

This study compared the tolerance limits of selected bacterial (Bacillus licheniformis, Brevibacillus lactosporus and Pseudomonas putida) and protozoan (Aspidisca, Trachelophyllum and Peranema) species to V5+ in wastewater systems. The isolates were exposed to various concentrations of V5+ (from 10 to 240 ppm), and their tolerance limits to this heavy metal were assessed at different temperatures (25, 30, 35 and 40°C) and pHs (4, 6, 7, 8 and 10) for 5 days. Chemical oxygen demand (COD), dissolved oxygen (DO) and die-off rate of the isolates were measured using standard methods. The results indicated that test isolates were tolerant to V5+, with a gradual decrease in their colony/cell counts when V5+ concentration gradually increased. Bacterial species were found to be more significantly tolerant (MIC: 110–230 ppm V5+) to V5+ than protozoan species which showed an earlier total inhibition/die-off rate (100%) at 60–100 ppm V5+ (MIC) (p < 0.001). P. putida was the most tolerant bacterial species (MIC: 230 ppm V5+) and Aspidisca sp. the most sensitive protozoan species (MIC: 60 ppm V5+). An increase in COD and DO removal was observed throughout the experimental period. The highest COD increase (up to 237.11%) and DO removal (almost 100%) were observed in mixed liquor inoculated with P. putida after exposure to 10 ppm V5+. Changes in pH and temperature affected the tolerance limits of all isolates. This study suggests the use of these tolerant bacterial and protozoan species in the bioremediation of V5+ from domestic and industrial wastewater under the control of pH and temperature.