EVALUATION OF THE INHIBITORY EFFECTS OF LITHIUM WHEN USED AS A TRACER FOR ANAEROBIC DIGESTERS

The frequent use of lithium chloride in anaerobic laboratory- and pilot-scale tracer studies called for an investigation into the potential inhibitory effects of the lithium ion on anaerobic sludge. A new method for measuring specific methanogenic activity (SMA) was employed to quantify these effects and results clearly show a relationship between the degree of inhibition and the concentration of lithium. In batch studies, continuous exposure to 0.25 g Li+/l resulted in minor inhibition, while at 2.0 g Li+/l methanogenic activity virtually ceased. Temporary exposure in a continuous plug flow column had no effect at 1.0 g Li+/l, although the activity was reduced at 2.0 g Li+/l. A mechanism for this toxicity is proposed and criteria are given for tracer tests using LiCl. The success of the SMA test indicates its potential in similar fields of research.