Anaerobic biodegradation of oleic and palmitic acids: Evidence of mass transfer limitations caused by long chain fatty acid accumulation onto the anaerobic sludge

Abstract

Palmitic acid was the main long chain fatty acids (LCFA) that accumulated onto the anaerobic sludge when oleic acid was fed to an EGSB reactor. The conversion between oleic and palmitic acid was linked to the biological activity. When palmitic acid was fed to an EGSB reactor it represented also the main LCFA that accumulated onto the sludge. The way of palmitic acid accumulation was different in the oleic and in the palmitic acid fed reactors. When oleic acid was fed, the biomass-associated LCFA (83% as palmitic acid) were mainly adsorbed and entrapped in the sludge that became "encapsulated" by an LCFA layer. However, when palmitic acid was fed, the biomass-associated LCFA (the totality as palmitic acid) was mainly precipitated in white spots like precipitates in between the sludge, which remained "non-encapsulated." The two sludges were compared in terms of the specific methanogenic activity (SMA) in the presence of acetate, propionate, butyrate, and H(2)CO(2), before and after the mineralization of similar amounts of biomass-associated LCFA (4.6 and 5.2 g COD-LCFA/g of volatile suspended solids (VSS), for the oleic and palmitic acid fed sludge, respectively). The "non-encapsulated," sludge exhibited a considerable initial methanogenic activity on all the tested substrates, with the single exception of butyrate. However, with the "encapsulated" sludge only methane production from ethanol and H(2)/CO(2) was detected, after a lag phase of about 50 h. After mineralization of the biomass-associated LCFA, both sludges exhibited activities of similar order of magnitude in the presence of the same individual substrates and significantly higher than before. The results evidenced that LCFA accumulation onto the sludge can create a physical barrier and hinder the transfer of substrates and products, inducing a delay on the initial methane production. Whatever the mechanism, metabolic or physical, that is behind this inhibition, it is reversible, being eliminated after the depletion of the biomass-associated LCFA.

Two-phase anaerobic co-digestion of used vegetable oils’ wastes and pig manure

“…In this case, the lag phase extended to 400 h, but the process recovered. This phenomenon agrees with Pereira et al (2005) that demonstrated that inhibition by LCFA accumulation was a reversible phenomenon more likely to be related to physical transport limitations, than to metabolic functions.…”

Assessing amendment properties of digestate by studying the organic matter composition and the degree of biological stability during the anaerobic digestion of the organic fraction of MSW

“…volatile fatty acid and steroid-like molecules) (Réveillé et al, 2003) (0-28 ppm); (ii) long chain aliphatic carbon (e.g. plant aliphatic biopolymers) (Pereira et al, 2005) and proteins (Dignac et al, 2000) (28-47 ppm); (iii) O-alkyl carbon (e.g. polysaccharides) (Kögel-Knabner, 2002) (47-113 ppm); (iv) aromatic carbon (e.g.…”

Codigestion of Untreated and Treated Sewage Sludge with the Organic Fraction of Municipal Solid Wastes

“…During the AD of a co-substrate microorganisms utilize carbon from 25 to 30 times faster than nitrogen [20] and the nitrogen content in WAS compensates a possible lack of nutrients in OFMSW while their content of lipids increases biogas yield [21]. On the other hand a lipid-rich substrate leads to an increase in Long Chain Fatty Acids (LCFAs) which may form a hydrophobic layer that destabilizes the digestion process [22], affecting bacteria transport and reducing contact between the substrate and the encapsulated bacteria. LCFAs entrapment causes the flotation and inhibition of methanogenic bacteria leading to cellular membrane damage [23].…”