Denitrification by New Strains of Thiobacillus Denitrificans under Non-Standard Physicochemical Conditions. Effect of Temperature, pH, and Sulphur Source

Abstract

Nitrates removal from waters can be achieved by physicochemical or by biological means. The use of ion exchange processes can be applied in both superficial and ground waters. The biological technologies are restricted nowadays to groundwater, because the heterotrophic microorganisms implied in such processes in the case of superficial waters generally have a weak efficiency during winter time leading to troubles such as the release of nitrites, which are intermediary products of the reduction procedure. Biological autotrophic processes using Thiobacillus denitrificans have been elaborated at least at a pilot scale, and with a good efficiency. Until now no work had been done upon the ability of this bacterium to denitrify under non standard conditions, including low temperatures. The purpose of this work was to isolate environmental Thiobacillus denitrificans strains able to remove nitrates under unusual temperature and pH conditions. We isolated several psychrophilic strains, some of them removing nitrates at 5°C in fixed cultures, and at pH ranging from 6 to 8, in batch conditions. The sulphur sources influenced nitrates removal and were classified as S₂O₃ ²⁻ > FeS > FeS₂ > S°, according to the affinity of Thiobacillus denitrificans for the source.

Keywords:

• Nitrates
• denitrification
• Thiobacillus denitrificans
• low temperatures
• fixed cultures on pouzzolane