Cristina T. Matos

Effect of light on the production of bioelectricity and added-value microalgae biomass in a Photosynthetic Alga Microbial Fuel Cell

This study demonstrates the simultaneous production of bioelectricity and added-value pigments in a Photosynthetic Alga Microbial Fuel Cell (PAMFC). A PAMFC was operated using Chlorella vulgaris in the cathode compartment and a bacterial consortium in the anode. The system was studied at two different light intensities and the maximum power produced was 62.7 mW/m(2) with a light intensity of 96 μE/(m(2)s). The results showed that increasing light intensity from 26 to 96 μE/(m(2)s) leads to an increase of about 6-folds in the power produced. Additionally, the pigments produced by the microalga were analysed and the results showed that the light intensity and PAMFC operation potentiated the carotenogenesis in the cathode compartment. The demonstrated possibility of producing added-value microalgae biomass in microbial fuel cell cathodes will increase the economic feasibility of these bioelectrochemical systems, allowing the development of energy efficient systems for wastewater treatment and carbon fixation.

Nannochloropsis sp. biomass recovery by Electro-Coagulation for biodiesel and pigment production.

Biofuel production from microalgal biomass could be an alternative solution to conventional biofuels typically dependent on food and high land/water demanding crops. However, the economic and energetic viability of microalgal biofuels is limited by their harvesting processes. The finding of innovative, low cost and efficient harvesting method(s) is imperative. In this study, the Electro-Coagulation (EC) was studied as a process to harvest the marine Nannochloropsis sp. microalga. Several EC operational conditions were studied and the best EC recovery efficiency (>97%) was achieved using a current density of 8.3 mA cm(-2) for 10 min. The quality of the recovered microalgal biomass was evaluated in terms of total lipids, fatty acid and pigment profile where no significant differences were observed after EC treatment. The energy requirements of the harvesting process were estimated and the combination of EC and centrifugation processes proved to decrease significantly the energy demand when compared with the individual process.

Life cycle assessment of advanced bioethanol production from pulp and paper sludge

This work evaluates the environmental performance of using pulp and paper sludge as feedstock for the production of second generation ethanol. An ethanol plant for converting 5400 tons of dry sludge/year was modelled and evaluated using a cradle-to-gate life cycle assessment approach. The sludge is a burden for pulp and paper mills that is mainly disposed in landfilling. The studied system allows for the valorisation of the waste, which due to its high polysaccharide content is a valuable feedstock for bioethanol production. Eleven impact categories were analysed and the results showed that enzymatic hydrolysis and neutralisation of the CaCO3 are the environmental hotspots of the system contributing up to 85% to the overall impacts. Two optimisation scenarios were evaluated: (1) using a reduced HCl amount in the neutralisation stage and (2) co-fermentation of xylose and glucose, for maximal ethanol yield. Both scenarios displayed significant environmental impact improvements.

Green metrics evaluation of isoprene production by microalgae and bacteria

Isoprene is a key intermediate compound for the production of synthetic rubber and adhesives and is also used as a building block in the chemical industry. Traditionally, isoprene is obtained from crude oil during the refinery process. Nevertheless, plants and animals are also able to synthesize this important compound. This work compares two renewable approaches for isoprene production: by photosynthetic organisms (autotrophic microalgae/cyanobacteria) and by heterotrophic organisms (bacteria). These are two alternative pathways for the conventional isoprene production obtained from the petrochemical-based refinery process, which were assessed in this work using green metrics. Their performance was evaluated in terms of: material efficiency, energy efficiency, economic evaluation and land use. A 10-tonne scale was chosen to perform the green metrics evaluation for both biological processes leading to isoprene. For each process, a comparison was made between a scenario considering the highest isoprene produced reported in the literature and a scenario considering the maximum theoretical stoichiometric isoprene productivity.

Correction: Green metrics evaluation of isoprene production by microalgae and bacteria

Correction for ‘Green metrics evaluation of isoprene production by microalgae and bacteria’ by Cristina T. Matos et al., Green Chem., 2013, 15, 2854–2864.