Comparison of methane production rate and coenzyme F₄₂₀ content of methanogenic consortia in anaerobic granular sludge

The coenzyme F₄₂₀ content of granular sludge grown on various substrates and substrate combinations was measured, and the potential of the sludge to form methane (maximum specific methane production rate) from hydrogen, formate, acetate, propionate, and ethanol was determined. The F₄₂₀ content varied between 55 nmol g of volatile suspended solids (VSS)^-1 for sludge grown on acetate and 796 nmol g of VSS^-1 for sludge grown on propionate. The best correlation was found between the F₄₂₀ content and the potential activity for methane formation from formate; almost no correlation, however, was found with acetate as the test substrate. The ratio between the potential methanogenic activities (qCH₄) of sludges grown on various substrates and their F₄₂₀ content was in general highest for formate (48.2 μmol of CH₄ μmol of F₄₂₀^-1 min^-1) and lowest for propionate (6.9 μmol of CH₄ μmol of F₄₂₀^-1 min^-1) as test substrates. However, acetate-grown granular sludge with acetate as test substrate showed the highest ratio, namely, 229 μmol of CH₄ μmol of F₄₂₀^-1 min^-1. The data presented indicate that the F₄₂₀ content of methanogenic consortia can be misleading for the assessment of their potential acetoclastic methanogenic activity.