Autor(es):
Cavaleiro, A. J. 
; Salvador, A. F. ; Alves, M. M.
Data: 2008
Identificador Persistente: http://hdl.handle.net/1822/8399
Origem: RepositóriUM - Universidade do Minho
Assunto(s): Biogas; LCFA; Organic loading rate; Anaerobic bioreactors
Descrição
Lipids are a group of organic pollutants whose conversion into biogas has been considered
very difficult. During the anaerobic treatment of lipid-rich wastewater this conversion
generally decreases with the increase of the organic loading rate (OLR) applied, due to long
chain fatty acids (LCFA) accumulation. To overcome this problem, correct equilibrium
between LCFA accumulation and degradation should be assured [1, 2, 3], and discontinuous
operation was proposed by Pereira et al. [1] as a strategy to achieve an efficient rate of
methane production. Based on these results, Cavaleiro et al. [4] studied the treatment of an
oleate-rich effluent in an anaerobic reactor operated in cycles, with continuous feeding
phases and batch reaction phases. The results obtained showed that continuous treatment
was possible, with efficient conversion of LCFA to methane, after acclimation of the microbial
consortium through discontinuous operation.
This work aimed the optimization of biogas production in a continuous reactor fed with an
oleate-rich wastewater and inoculated with acclimated anaerobic sludge. Acclimation was
performed through discontinuous operation in a lab scale reactor. During the experiment, the
OLR applied was gradually increased from 5 to 31 kgCOD m-3 day-1, by decreasing the
hydraulic retention time. From 5 to 21 kgCOD m-3 day-1 the increase of the OLR was followed
by a fast increase of the methane production rate, towards an average value that was directly
related with the OLR, showing that there was no inhibition of the anaerobic consortium.
However, when the OLR was increased to 26 kgCOD m-3 day-1, methane production rate
fluctuated around the same average value as in the previous period (16 kgCOD-CH4 m-3 day-
1). For 31 kgCOD m-3 day-1, methane production rate tended to decrease, possibly due to
microbial inhibition or mass transfer limitations. From 21 to 31 kgCOD m-3 day-1 methane
production rate was very instable, indicating that the OLR applied were higher than the
optimum value for the microbial community. Maximum methane yield (100%) was obtained
for the OLR of 12 kgCOD m-3 day-1, but continuous anaerobic treatment of an OLR as high as
21 kgCOD m-3 day-1 was possible with a methane yield of 72% and average COD removal
efficiency of 99%. Nevertheless, 16 kgCOD-CH4 m-3 day-1 is likely the optimum OLR to be
applied, in order to optimize methane production. Oily wastewater can be used as a valuable
source of bioenergy by applying proper anaerobic digestion technology.
