Single and combined inhibition of Methanosaeta concilii by ammonia, sodium ion and hydrogen sulfide.

Single and combined inhibition of lag time λ and specific methanogenic activity RCH4 of Methanosaeta concilii by NH3, Na+ and H2S were investigated using inhibition tests with a single inhibitor and a 33 full-factorial experiment of NH3, Na+ and H2S concentrations (1.5 ≤ total ammonia nitrogen (TAN)/L ≤ 4.5 g, 1 ≤ Na+/L ≤ 4.3 g, 14.2 ≤ total hydrogen sulfide sulfur (THSS)/L ≤ 836 mg). All three inhibitors significantly increased λ and reduced RCH4 of M. concilii. The half-maximal inhibitory concentrations of NH3, Na+ and H2S for M. concilii were 6.4 g TAN/L, 5.2 g Na+/L and 1.6 g THSS/L. Partial cubic models adequately approximated the corresponding response surfaces of λ and RCH4 from the 33 full-factorial experiment. The inhibitors inhibited RCH4 synergistically, but inhibited λ in a complex manner. The combination of NH3 and Na+ showed the strongest synergistic inhibition of both λ and RCH4.