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

Abstract

Oleic acid toxicity and biodegradability were followed during long-term operation of two similar anaerobic fixed-bed units. When treating an oleate based effluent, the sludge from the bioreactor that was acclimated with lipids during the first operation period, showed a higher tolerance to oleic acid toxicity (IC50 = 137 mg/l) compared with the sludge fed with a non-fat substrate (IC50 = 80 mg/l). This sludge showed also the highest biodegradation capacity of oleic acid, achieving maximum methane production rates between 33 and 46 mlCH4(STP)/gVS.day and maximum percentages of methanization between 85 and 98% for the range of concentrations between 500 and 900 mg oleate/l. When oleate was the sole carbon source fed to both digesters, the biomass became encapsulated with organic matter, possibly oleate or an intermediate of its degradation, e.g. stearate that was degraded at a maximum rate of 99 mlCH4(STP)/gVS.day. This suggests the possibility of using adsorption-degradation cycles for the treatment of LCFA based effluents. Both tolerance to toxicity and biodegradability of oleic acid were improved by acclimatization with lipids or oleate below a threshold concentration.

Tratamiento biológico de aguas residuales: Principios, modelación y diseño

“…El proceso de granulación se lleva a cabo adecuadamente en aguas residuales diluidas en un ASBR, inclusive a bajas temperaturas ambientales (Banik et al, 1997). Se observó que los sistemas ASBR eran de particular interés para aguas residuales que contienen AGCL (Alves et al, 2001). Durante el periodo de llenado, los AGCLs son absorbidos en el lodo anaerobio, posteriormente se lleva a cabo un periodo de digestión suave, durante el cual el lodo absorbido se estabiliza y se regenera completamente a biomasa metanogénica altamente activa.…”

A Simple Method for the Detection of Long-Chain Fatty Acids in an Anaerobic Digestate Using a Quartz Crystal Sensor

“…Thus the total mass change during our experiment is a level below 0.1% of the quartz disc weight. In AD, due to the relatively high concentrations of LCFAs (50-3000 mg/L) at inhibition levels [3,4,14], such high sensitivity is not required for the QCM sensor. Meanwhile, selectivity is more important because there are various chemicals similar to LCFAs, such as triglycerides and acetate, in the digestate.…”

“…Since β-oxidation is the rate-limiting step in lipid degradation [3], faster hydrolysis of lipids can lead to LCFA accumulation during the AD of wastes with high oil or fat content. Only a few millimolar of concentration of accumulated LCFAs can strongly inhibit methanogens in an anaerobic process [3][4][5][6] and result in the failure of operation [7]. The toxicity effect is impacted by temperature and the presence of cations such as calcium and magnesium.…”

Methane fermentation process for utilization of organic waste

“…A similar conclusion was also drawn by Massé et al (2000) who studied the effect of antibiotics on psychrophillic anaerobic digestion of swine manure. Aliphatic alcohols exhibit bactericidal effects at different concentrations, starting from 100 mg dm -3 ; the longer their chain, the higher the toxic effect (Alves et al, 2001;Shin et al, 2003). Also unsaturated long-chain fatty acids may evidently inhibit the process of digestion at concentrations of mmol dm -3…”