EFFECT OF VOLATILE FATTY-ACIDS AND TRIMETHYLAMINE ON DENITRIFICATION IN ACTIVATED-SLUDGE

The effect of volatile fatty acids and trimethylamine on denitrificati on activity of activated sludge was studied in laboratory batch experi ments. Formic acid had no effect on the denitrification rates. Acetic acid, n-butyric acid and trimethylamine all enhanced the rates. Acetat e is the compound with the strongest effect, n-butyric acid has a mode rate effect, while TMA only have a small effect in stimulating the rat es. Propionic, isobutyric, n-valeric, isovaleric and caproic acid inhi bit denitrification, nitrate reduction being more inhibited than nitri te reduction. The inhibitor concentration, K-I, at which activity fall s to 50% of the activity measured when no inhibiting compound were pre sent, were determined by modelling. K-I values for nitrate reduction, in a media not supplemented with an easily metabolised electron donor, were found to be 74 mM for propionic, 30 mM for isobutyric, 36 mM for n-valeric, 18 mM for isovaleric and 105 mM for caproic acid. K-I valu es for nitrite reduction were found to be 196 mM for propionic, 32 mM for isobutyric, 57 mM for n-valeric, 18 mM for isovaleric and 110 mM f or caproic acid. Inhibition of the rate of hydrolysis could not be det ermined. Anaerobically treated wastewaters from fish, potato and onion industries all stimulated denitrification. Reject water from anaerobi c treatment of excess sludge had no significant effect on the denitrif ication processes. For isobutyric, isovaleric and n-valeric acid the u ndissociated compounds appear to act as the inhibitor. For propionic a cid it could not be assessed whether the degree of inhibition were det ermined by the undissociated or the total concentration of the inhibit or.