Autor(es):
Pereira, M. A. 
; Pires, O. C. ; Mota, M. ; Alves, M. M.
Data: 2005
Identificador Persistente: http://hdl.handle.net/1822/3488
Origem: RepositóriUM - Universidade do Minho
Assunto(s): LCFA; Methanogenic activity; Transport limitations
Descrição
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.Whenoleic 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 H2CO2, before and after the mineralization of similar amounts of biomassassociated 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 andH2/CO2
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.
