Influence of high NaCl and NH4Cl salt levels on methanogenic associations

Abstract The effect of high levels of NaCl and NH 4 Cl on the activity and attachment of methanogenic associations in semi-continuous flow-through reactor systems has been evaluated. Two well-functioning reactors received shock concentrations of NaCl and NH 4 Cl while two other reactors were adapted to increasing levels of the salts during a period of 45 days. The methanogenic associations, grown on a medium containing mainly acetate and ethanol, were found to be more resistant to NaCl and NH 4 Cl than previously reported. Initial inhibition occurred at shock treatments of 30 gl −1 for both salts. The reactors which were gradually exposed to increasing levels of the salts, adapted well and their tolerance levels surpassed those of the non-trained counterparts. Initial inhibition and fifty percent inhibition was observed at 65 and 95 gl −1 respectively for adaptation to NaCl. Initial inhibition for the reactor adapting to NH 4 Cl occurred at 30 gl −1 and a 50% inhibition was observed at 45 gl −1 of NH 4 Cl. For the reactors receiving NH 4 Cl, the free ammonia-N should be kept below a concentration of 80–100 mg l −1 for optimal performance. The bacterial populations in the reactors consisted mostly out of Methanosarcina (> 99% of the biomass)