TOXICITY EFFECTS OF PROPIONATE ON 2 MIXED STAGES CULTURE DIGESTERS

Propionate has been found to inhibit methanogenesis at concentrations as low as 20Mm. The objective of this study was to test its toxicity a t various levels on two mixed culture digesters. Propionate acclimatiz ation was performed in an acidogenic digester and in a methanogen enri ched sludge digester. The effect of both pH and organic loading rate i ncreases were observed. It was found that an increase in pH affected t he performance of the acidogenic reactor whereas the methanogenic enri ched sludge was shown to be more sensitive to pH values below neutral. Two propionate-acclimatized mixed stages culture digesters at pH 7.0 and 8.0 were operated with 40 and 50 mu m of propionate. When propiona te was initially added to the digester, hydrogen levels which were ori ginally very low increased and showed a variable pattern. The percenta ge of both COD removal and methane yield were also affected by the pre sence of propionate although they had earlier on been acclimatized (i. e. state conditions had been achieved). pH differences did not show a marked effect on the performance of the digesters.