Effect of vanadium toxicity at its different oxidation states on selected bacterial and protozoan isolates in wastewater systems

Abstract

This study assesses and compares vanadium toxicity in its different oxidation states towards bacterial isolates (Pseudomonas putida and Bacillus licheniformis) and protozoan isolates (Peranema sp. and Trachelophyllum sp.). The isolates were exposed to various concentrations of V in mixed liquors and their tolerance to V was assessed at 30°C at a pH of 4. The results revealed that the increase in V oxidation state increased its toxicity to bacterial isolates, whereas its toxicity decreased for protozoan isolates. Among the bacterial isolates, P. putida was found to be more tolerant to V³⁺(24 h-median lethal concentration (LC₅₀): 390 mg/l), V⁴⁺(24 h-LC₅₀: 230–250 mg/l) and V⁵⁺(24 h-LC₅₀: 180–200 mg/l), whereas for the protozoan isolates, Peranema sp. appeared to be more tolerant to V³⁺(24 h-LC₅₀: 110–120 mg/l), V⁴⁺(24 h-LC₅₀: 160–170 mg/l) and V⁵⁺(24 h-LC₅₀: 160–200 mg/l). A comparison of both groups of organisms revealed Trachelophyllum sp. as the most sensitive organism to V at its various oxidation states. The visual and spectrophotometric methods used to assess V reduction revealed that P. putida was the only isolate able to reduce V⁵⁺, V⁴⁺ and V³⁺ to V²⁺ in mixed liquor media. Vanadium (+2) in concentrations of approximately 46.46 mg/l, 29.57 m mg/l and 38.01 mg/l found in the media was treated with V³⁺, V⁴⁺ and V⁵⁺, respectively, and inoculated with P. putida. This study revealed that the ability of V reduction, adopted with P. putida, can be an effective strategy to remove V from polluted environments. This study also showed that the toxicity of V, in terms of its oxidation states, differs from one species to another and in kingdoms.

Keywords:

• bacteria
• heavy metals
• protozoa
• vanadium
• wastewater
• toxicity

Acknowledgements

The authors are thankful to Anza-vhudziki Mboyi from the TUT-Water Care Unit, for her technical assistance.

Funding

The authors are thankful to the National Research Foundation (NRF) for the funding of this project.