Stoichiometric Analysis of Anaerobic Ethane/Butane Oxidation

Stoichiometric tests were carried out in situ for the biomass of the 1.12 l ethane parent reactor on Days 490, 522, and 559 to investigate nitrogen and electron balances. For stoichiometry determination of nitrate reduction coupled to anaerobic butane oxidation, triplicate batch tests were conducted in 650 ml glass vessels with a subsample of 500 ml biomass anaerobically transferred from the 2.3 l butane parent bioreactor. Total amounts of ethane/butane and N₂ were calculated by considering ethane/butane/N₂ in both the headspace (monitored) and liquid phase (calculated with Henry’s law). Two negative control groups were set up in 600 ml bottles: (i) control groups containing only enriched cultures and nitrate (ethane/butane was removed by flushing the bottles with pure argon gas for 20 min); (ii) abiotic control groups without enriched cultures (only synthetic medium containing ethane/butane and nitrate was provided).