Sodium Toxicity control by the use of Magnesium in an Anaerobic Reactor

Abstract

This study investigated the effectiveness of magnesium in reducing sodium toxicity in mesophilic (35ºC) completely mixed anaerobic digesters (CMADs). The CMADs were operated at a chemical oxygen demand (COD) loading of 0.5 g/l/day initially which was gradually increased to 1.8 g/l/day. To evaluate the effect of sodium concentration on methanogens, the biomass in one of the CMADs was acclimated to an increasing concentration of sodium while the feed to the second CMAD was not supplemented with any additional sodium. The COD removal efficiency and methane production decreased by nearly 30% and 20% respectively at a sodium concentration of 9.0 g/l. Similarly, the total volatile fatty acids (VFAs) concentration increased from a mere 200 mg/l to 3000 mg/l. At this point, magnesium was added gradually to one of the reactors. The COD removal efficiency and methane production returned to the original level of 92% and 62% respectively, and the VFA concentration became negligible. It can be concluded that magnesium is very effective in reducing sodium toxicity to methanogens.


Journal of Applied Sciences and Environmental Management Vol. 8 (1) 2004: 17 - 21