Responses of the biogas process to pulses of oleate in reactors treating mixtures of cattle and pig manure

Abstract

The effect of oleate on the anaerobic digestion process was investigated. Two thermophilic continuously stirred tank reactors (CSTR) were fed with mixtures of cattle and pig manure with different total solid (TS) and volatile solid (VS) content. The reactors were subjected to increasing pulses of oleate. Following pulses of 0.5 and 1.0 g oleate/L, the most distinct increase in volatile fatty acid (VFA) concentrations were observed in the reactor with the lowest TS/VS content. This suggests a higher adsorption of oleate on the surfaces of biofibers in the reactor with the highest TS/VS and a less pronounced inhibition of the anaerobic digestion process. On the other hand, addition of 2.0 g oleate/L severely inhibited the process in both reactors, and a significant increase in all VFA concentrations combined with an immediate drop in methane production was noticed. However, 20 days after the reactors had been exposed to oleate both reactors showed a lower VFA concentration along with a higher methane production than before the pulses. This indicates that oleate had a stimulating effect on the overall process. The improved acetogenic and methanogenic activity in the reactors was confirmed in batch activity tests. In addition to this, toxicity tests revealed that the oleate pulses induced an increase in the tolerance level of acetotrophic methanogens towards oleate. When evaluating the usability of different process parameters (i.e., VFA and methane production) as indicators of process recovery, following the inhibition by oleate, propionate was found to be most suitable.

Kinetics of Propionate Conversion in Anaerobic Continuously Stirred Tank Reactors

“…The results, together with the literature, also indicates that A max has an upper limit of approximately 30 µmol gVS -1 h -1 in CSTRs treating manure [16]. However, in another study the maximum degradation rate of propionate in CSTRs treating anaerobic sewage sludge at mesophilic and thermophilic temperatures was significantly higher than in all the reactors of the present study [13].…”

Effects of lipid inhibition on biogas production of anaerobic digestion from oily effluents and sludges: An overview

“…Ref. [50] studied oleate pulses onto thermophilic anaerobic reactors and reported the pulses effects on degradation of volatile fatty acids (VFA) and also reducing the lag phase during hydrolysis stage. This agreed with the finding reported by [32] on tolerance of biomass to LCFAs is more achievable by gradually feeding rather than shock feeding at a time.…”

New Steady-State Microbial Community Compositions and Process Performances in Biogas Reactors Induced by Temperature Disturbances

“…Up to now, it is still unknown whether there are different microbial community patterns under the same environmental conditions in biogas reactors if stochastic factors are determining the microbial communities. Although different disturbances (such as temperature and organic loading) on the biogas process have been evaluated before, most of the studies focused only on the reactor performances, and the effect of disturbance on the community assembly was not documented [13][14][15][16]. It is still unknown whether the disturbance in the biogas reactors would lead to different steady-state microbial community compositions and reactor performances.…”