Operação sequencial de um sistema batch para biosorção e mineralização anaeróbia de efluentes de lacticínios

Um efluente lácteo real enriquecido em gordura foi mineralizado a metano num processo em reactor fechado. Realizaram-se três ciclos de adição/degradação, tendo-se monitorizado em cada ciclo a CQO solúvel, os AGV e a produção de metano em diferentes intervalos de tempo. O consórcio anaeróbio tinha sido previamente aclimatado a ácido oleico. A eficiência de remoção da CQO solúvel aumentou ao longo da operação, os AGV totais diminuíram sucessivamente e a produção cumulativa de metano aumentou significativamente do primeiro para o terceiro ciclo. Estes resultados vêm confirmar que a chave para a degradação de efluentes com elevado conteúdo em lípidos reside na sequenciação das fases de acumulação na biomassa e degradação

Biosorption and mineralization of a dairy wastewater under sequential operation mode

This work aimed to apply a sequential batch operation mode to promote the biomethanation of a real dairy wastewater enriched in fat. Three cycles were conducted with biomass previously acclimated to oleic acid. Soluble COD, VFA and methane content were analyzed in each cycle at different time intervals. The soluble COD removal efficiency improved slightly in each new feed and the total VFA levels detected decreased successively. The maximum cumulative methane production also improved from cycle 1 to cycle 3. These results contribute to support the idea that the key for the degradation of effluents with high lipid content is to sequence adsorption and degradation steps during the treatment process

The role of interfaces and morphology on silver diffusion in hard coatings

One of the main approaches to increase the tool lifetime during dry machining of “hard-to-machine” aerospace alloys is self-lubrication by the incorporation of noble metals in hard matrixes with good mechanical and diffusion barrier properties. In this paper, the diffusion of an Ag-rich layer sandwiched between two layers of either TiN or TiSiN is studied by transmission electron microscopy and in situ Rutherford backscattering spectrometry. The layer stacks were subjected to annealing treatments at 600 ◦C and 800 ◦C for 2 hours. Three processes were found to control the diffusion of silver: the morphology of the “sandwich” layers, the formation of small voids in the involved interfaces and the sublimation of Ag in the surface at temperatures near the melting point. The study revealed that the dense TiSiN matrix allowed a significantly better control of Ag diffusion than the more open TiN matrix.info:eu-repo/semantics/publishedVersio

Enhancement of methane production from long chain fatty acid based effluents

Two anaerobic sludges previously loaded with oleate and palmitate accumulated 4570 ± 257 and 5200 ± 9 mgCOD-LCFA gVSS−1, respectively. These sludges were incubated in batch assays and methane production was recorded after addition of 100–900 mg L−1 of oleate and palmitate, respectively. The batch assays were conducted before and after allowing the depletion of the biomass-associated LCFA. The presence of biomass-associated LCFA decreased the capacity of both sludges to convert the added LCFA to methane. After the degradation of biomass-associated LCFA, the lag phases observed before the onset of methane production were significantly reduced, evidencing an increase in the tolerance of the acetotrophic methanogens to the presence of LCFA. In another experiment, three recurrent pulses were performed with a real dairy wastewater containing 3.6 gCOD L−1, from which 53% was fat. Methane yields of 0.45 ± 0.01, 0.88 ± 0.02 and 1.29 ± 0.08 gCOD- CH4 gCODfed-1 were achieved in the first, second and third pulses, respectively, evidencing an increasing capacity of the sludge to convert substrate accumulated in previous additions.Fundo Social Europeu (FSE)Fundação para a Ciência e a Tecnologia (FC

Development of a novel reactor for high-rate anaerobic treatment of LCFA containing wastewater

treatment. More than 2,000 full-scale installations are running worldwide (Van Lier, 2007) and mainly treat wastewaters containing readily degradable organic pollutants such as volatile fatty acids and carbohydrates. Lipids do not belong to this group, since their hydrolysis results in the production of long chain fatty acids (LCFA). Until recently these were considered toxic to anaerobic bacteria and a nuisance because they induce floatation of biomass (Hwu, 1997). Since the success of conventional anaerobic treatment systems is based on optimisation of biomass sedimentation, floatation leads to washout and subsequent process disruption. Therefore, lipids are normally removed from wastewater prior to anaerobic treatment using e.g. dissolved air floatation. Pereira et al. (2002) showed that lipids are not toxic and can be converted to biogas. As to prevent washout induced by LCFA adsorption, a sequential process including at least a feeding and reaction phase was proposed as the preferred technology for anaerobic LCFA removal from wastewater (Pereira et al., 2005). It was further postulated that the specific contact area between bacteria and LCFA should be maximised as to maximise LCFA adsorption and minimise mass transfer limitations. The sequential process was applied at la

Innovative start-up strategies for optimal methane production from lipids in anaerobic bioreactors

Lipids and long-chain fatty acids (LCFA) are energy-rich compounds that can be used as carbon and energy source by anaerobic microbial communities. Theoretically, large amounts of methane, a valuable energy carrier, may be generated during this process. However, operational problems, mainly associated with LCFA accumulation onto the sludge, have limited the use of anaerobic technology to produce methane from LCFA. In this work, two novel start-up strategies were tested for optimal methane production from LCFA: (i) bioreactor start-up using a intermittent feeding strategy, and (ii) bioreactor bioaugmentation with a LCFA-degrading bacterium. Intermittent feeding start-up resulted in efficient continuous methane production from high LCFA loads (up to 21 kgCOD m-3 day-1, 50% COD as oleate (unsaturated LCFA, C18:1)). Alternating continuous bioreactor feeding and batch degradation periods, during bioreactor start-up, was crucial for sludge acclimation and contributed to the development of a metabolically specialized anaerobic microbial community that was able to efficiently convert oleate to methane. After intermittent feeding bioreactor start-up, methane yields higher than 70% were achieved, and neither LCFA nor VFA accumulated in the system. Bioaugmentation experiments were performed using Syntrophomonas zehnderi, a bacterium able to degrade saturated and unsaturated LCFA [1]. Anaerobic sludge amended with active and inactive S. zehnderi was incubated with 1 mM oleate as sole carbon and energy source. Methane production from oleate in bioaugmented batches was faster and high methane yields (89±5%) were achieved. This work highlights the importance of the start-up strategy for the development of balanced syntrophic communities specialized in methane production from LCFA. Intermittent feeding and bioaugmentation with LCFA-degrading bacteria may be applied as alternative or complementary strategies.Fundação para a Ciência e a Tecnologia (FCT) - FCOMP-01-0124-FEDER-014784, SFRH/BD/24256/2005.FEDER - COMPETE programEuropean Social Fund (ESF

New perspectives for methane production from oleate : bioaugmentation of anaerobic sludge with Syntrophomonas zehnderi

Biogas production from waste lipids is a promising technology for sustainable energy production. In anaerobic bioreactors, lipids and long-chain fatty acids (LCFA) are easily removed from the liquid medium, mainly by adsorption. However, further LCFA degradation is rate-limiting and possible dependent on the development of syntrophic communities. Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA genes was used to follow the changes in bacterial communities during continuous and fed-batch reactors operation with oleate, an unsaturated LCFA. A specific dominant DGGE-band corresponding to bacteria deeply clustering with Syntrophomonas zehnderi (99% identity) was found in all the sludges that could degrade oleate, thus suggesting the involvement of this bacterium in unsaturated LCFA catabolism. Therefore, the potential of S. zehnderi as bioaugmenting strain for improving methane production from oleate was further studied in batch assays. Oleate was added to the medium at a final concentration of 1 mM and the assays were performed with and without the solid microcarrier sepiolite. Methane production was faster in the bioaugmented assays, and this effect was more pronounced in the presence of sepiolite. The positive effects of sepiolite can be related to a decrease in oleate toxicity towards the acetoclastic methanogens, or to an improvement of the syntrophic relationships. Bioaugmentation with S. zehnderi might be a suitable strategy for accelerating LCFA conversion to methane in anaerobic bioreactors, shortening the start-up period of high rate continuous processes or recover LCFA-inhibited sludge

Enhancing methane production from fat by bioaugmenting Syntrophomonas zehnderi to anaerobic sludge

Fundação para a Ciência e a Tecnologia (FCT) - bolsa SFRH/BD/24256/200

Fed-batch anaerobic degradation of long chain fatty acids

Efficient mineralization of effluents with high lipid content is possible in anaerobic digesters when a sequential operation mode is applied, favoring the adsorption of LCFA onto the sludge and then allowing the adsorbed substrate to be biodegraded1-3. The study of adsorption along time can help to optimize the process. Five batch assays were conducted in 160mL vials inoculated with flocculent biomass and fed with sodium oleate (1g CQO/gVSS). Feeding was applied during 10min (0.8ml/min), after which (t=0) a vial was immediately sacrificed and analyzed for soluble COD, VSS and biomass-associated LCFA. After 0.5, 1, 24 and 1000 hours of incubation at 37±1°C, 150rpm, one vial was sacrificed and analyzed for the parameters stated before. Two additional vials prepared and fed in a similar way and two blank controls (without substrate) were incubated in the same conditions to follow cumulative methane production. At the end of the feeding period, soluble COD removal efficiency was 73%, corresponding exclusively to LCFA accumulation onto the sludge. During the first 24 hours, methane or VFA production were negligible probably due to residual substrate degradation. Palmitic acid accounted for 46 to 54% of the biomass-associated LCFA and oleic acid for 31 to 40%. After 1000 hours of incubation soluble COD removal was 86% and palmitic acid accounted for 100% of the biomass-associated LCFA (45mg COD-LCFA/g VSS)

Methane production from oleate : assessing the bioaugmentation potential of Syntrophomonas zehnderi

The potential for improving long-chain fatty acids (LCFA) conversion to methane was evaluated by bioaugmenting a non-acclimated anaerobic granular sludge with Syntrophomonas zehnderi. Batch bioaugmentation assays were performed with and without the solid microcarrier sepiolite, using 1 mM oleate as sole carbon and energy source. When S. zehnderi was added to the anaerobic sludge methane production from oleate was faster. High methane yields, i.e. 89 ± 5% and 72 ± 1%, were observed in bioaugmented assays in the absence and presence of sepiolite, respectively. Sepiolite stimulated a faster methane production from oleate and prevented the accumulation of acetate. Acetoclastic activity was affected by oleate in the absence of sepiolite, where methane production rate was 26% lower than in assays with microcarrier.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/24256/200