Waste lipids to energy: how to optimize methane production from long-chain fatty acids (LCFA).
Bottom Line: Analyzing existing technologies, applications and problems, it is clear that, until now, wastewaters with high lipids content are not effectively treated by HR-AnWT.Nevertheless, waste lipids are ideal potential substrates for biogas production, since theoretically more methane can be produced, when compared with proteins or carbohydrates.For optimal performance these syntrophic communities need to be clustered in compact aggregates, which is often difficult to achieve with wastewaters that contain fats and lipids.
Affiliation: IBB - Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Braga, Portugal. email@example.comShow MeSH
Mentions: As a consequence of LCFA accumulation onto the sludge, treatment of lipids/LCFAâcontaining wastewaters in conventional upâflow anaerobic reactors can lead to complete sludge washout and process failure, which seems to be more due to particular problems of fluid dynamics than to microbial activity inhibition. In fact, microbial injure due to intensive (high concentration) and extended (long time) contact between anaerobic sludge and LCFA was found to be less severe than could be expected (Alves etâal., 2001; Pereira etâal., 2002a; 2004; 2005). When performing a routine assessment of the specific methanogenic activity of sludge collected from a continuous reactor fed with oleic acid, a surprisingly high methane production was observed in the blank vials, where no external substrate was added (Alves etâal., 2001). The observed methane production resulted from the degradation of substrate that accumulated onto the sludge during the reactor's operation, contradicting the accepted theories of permanent LCFA toxicity and inhibition. This finding led to the development of new concepts and encouraged the study of the microbiology of LCFA degradation in anaerobic bioreactors. The scheme presented in Fig.â1 illustrates the sequence of continuous LCFA feeding, LCFA accumulation and consequent sludge flotation and washout. Subsequent batch incubation of the sludge taken from the reactor, containing biomassâassociated LCFA, results in methane production. The proposed mechanisms of LCFA accumulation onto the biomass are adsorption, entrapment within the flocks structure and precipitation with divalent ions (Pereira etâal., 2005). Fig.â2 shows a microbial aggregate collected from a UASB reactor fed with oleic acid. The whitish matter embedding the cells consisted, in that case, of more than 80% palmitic acid (Pereira etâal., 2005).
Affiliation: IBB - Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Braga, Portugal. firstname.lastname@example.org