Álvaro Torres

Performance of an enzymatic extract in Botrycoccus braunii cell wall disruption.

Microalgae can produce and contain lipids, proteins and carbohydrates, which can be extracted and marketed as potential novel added-value bio-products. However, microalgae cell wall disruption is one of the most important challenges involved while processing this type of biomass. In this context, white-rot fungi, responsible for the biodegradation of lignin present in wood due to non-specific extracellular enzymes, could be applied for promoting microalgae cell wall degradation. Therefore, the aim of this study was to evaluate the use of an enzymatic extract produced by the white-rot fungi Anthracophyllum discolor as a biotechnological tool for Botryococcus braunii cell wall disruption. The fungus was inoculated in wheat grains and manganese peroxidase (MnP) activity was monitored while obtaining the enzymatic extract. Then, cell wall disruption trials with different MnP activity were evaluated by the biochemical methane potential (BMP). In relation to cell wall disruption, it was observed that the optimal value was obtained with enzymatic concentration of 1000 U/L with a BMP of 521 mL CH4/g VS. Under these conditions almost 90% of biomass biodegradability was observed, increasing in 62% compared to the microalgae without treatment. Therefore, the results indicate that enzymes secreted by A. discolor promoted the attack of the different cell wall components finally weakening it. Therefore, the application of this treatment could be a promissory biotechnological approach to decrease the energetic input required for the cell wall disruption step.

Challenges for Cost-Effective Microalgae Anaerobic Digestion

1. Microalgae photosynthesis allows biological CO2 fixation, which is expected to mitigate atmospheric CO2 increase (Amin 2009; Brennan & Owende 2010; Mutanda et al. 2011). 2. Microalgae are 10 – 50 times more efficient than plants in terms of CO2 fixation (Wang et al. 2008). Thus, microalgae can fix 1.83 tonnes of CO2 per 1 tonne of produced microalgae (Chisti 2007). 3. Microalgae can be produced on non-arable areas such as lakes, oceans or deserts, thus reducing competition with food production (Mussgnug et al. 2010; Stephens et al. 2010). This advantage is a key factor when energy supply is considered in desert zones near oceans. 4. Some microalgae can grow under saline conditions, which strengthen the use of micro‐ algae as feedstock for biofuel production in desert zones near the ocean when freshwater supply is not feasible.

Use of flocculants for increasing permeate flux in anaerobic membrane bioreactors

Biomass retention, required for high rate anaerobic wastewater treatment, can be accomplished coupling an anaerobic bioreactor with membrane filtration. However, low flux seems to be a common factor when operating anaerobic membrane bioreactors (AnMBRs). Modification of biomass properties may represent a strategy for improving membrane flux. The addition of flocculants was tested as a tool for flux increase. Six different products were tested in dead-end filtration experiments. Based on the results, two products were selected for cross-flow tests. The one presenting better performance (Nalco MPE50) was tested in a laboratory-scale continuous AnMBR. Results show that the flocculant was able to substantially increase flux. Indeed, the flux-increasing effect was observed for several weeks after flocculant addition. Therefore, the use of flocculants seems to be an interesting tool to cope with temporary increases in required flux.