Effects of lipids and oleic acid on biomass development in anaerobic fixed-bed reactors. Part II: Oleic acid toxicity and biodegradability

Oleic acid toxicity and biodegradability were followed during long-term ope ration of two similar anaerobic fixed-bed units. When treating an oleate ba sed effluent, the sludge from the bioreactor that was acclimated with Lipid s during the first operation period, show ed a higher tolerance to oleic ac id toxicity (IC50 = 137 mg/l) compared with the sludge fed with a non-fat s ubstrate (IC50 = 80 mg/l). This sludge showed also the highest biodegradati on capacity of oleic acid, achieving maximum methane production rates betwe en 33 and 46 mlCH(4(STP))/gVS.day and maximum percentages of methanization between 85 and 98% a for the rang of concentrations between 500 and 900 mg oleate/l. When oleate nas the sole carbon source fed to both digesters, the biomass became encapsulated with organic matter, possibly oleate or an int ermediate of its degradation, e.g. stearate that was degraded at a maximum rate of 99 mlCH(4(STP))/gVS.day. This suggests the possibility of using ads orption-degradation cycles for the treatment of LCFA based effluents. Both tolerance to toxicity and biodegradability of oleic acid were improved by a cclimatization with lipids or oleate below a threshold concentration. (C) 2 000 Elsevier Science Ltd. All rights reserved.