Biological and chemical mineralization of pyridine

A comparison was made between biological and chemical mineralization of pyridine, an N‐heterocyclic pollutant, in a liquid culture and a slurry of ground water and subsurface sediment. A bacterial culture of an Alcaligenes sp. that degrades pyridine was found to be more effective at oxidizing [2,6‐¹⁴C]pyridine to ¹⁴CO₂ than Fenton's reagent. Alcaligenes sp. converted 73.1% of the ¹⁴C‐labeled pyridine to ¹⁴CO₂, whereas the Fenton reagent converted 65.6% of the compound. In the case of bacteria, the remaining chemical was incorporated primarily into biomass (9.2%), whereas the remaining pyridine was converted to unidentified products (16.3%) by the Fenton reagent. However, based on chromatographic analysis, these compounds were not mono‐hydroxylated pyridines. Mineralization of pyridine by Fenton's reagent was affected by the concentration of H₂O₂ and by the concentration and oxidation state of available iron. Maximal mineralization occurred at a concentration of more than 0.15% H₂O₂ (44 mM), 1 mM Fe³⁺, or 2 mM Fe²⁺. Furthermore, the rates of both microbial and chemical mineralization were influenced by the initial pyridine concentration. Maximum specific rates of mineralization were 6.5 μg/h/mg biomass for the bacteria and 2.7 μg/h/mg Fe²⁺ for the Fenton reagent. The feasibility of using Fenton's reagent for treating ground water and subsurface sediments polluted with pyridine was found to be limited, because only 24.5% of the pyridine was converted to CO₂. In contrast, when cultures of the Alcaligenes sp. were used to treat ground water, as much as 54.4% of the labeled compound was mineralized to ¹⁴CO₂.