Beatrice Smyth

The impacts of replacing air bubbles with microspheres for the clarification of algae from low cell-density culture

Dissolved Air Flotation (DAF) is a well-known coagulation-flotation system applied at large scale for microalgae harvesting. Compared to conventional harvesting technologies DAF allows high cell recovery at lower energy demand. By replacing microbubbles with microspheres, the innovative Ballasted Dissolved Air Flotation (BDAF) technique has been reported to achieve the same algae cell removal efficiency, while saving up to 80% of the energy required for the conventional DAF unit. Using three different algae cultures (Scenedesmus obliquus, Chlorella vulgaris and Arthrospira maxima), the present work investigated the practical, economic and environmental advantages of the BDAF system compared to the DAF system. 99% cells separation was achieved with both systems, nevertheless, the BDAF technology allowed up to 95% coagulant reduction depending on the algae species and the pH conditions adopted. In terms of floc structure and strength, the inclusion of microspheres in the algae floc generated a looser aggregate, showing a more compact structure within single cell alga, than large and filamentous cells. Overall, BDAF appeared to be a more reliable and sustainable harvesting system than DAF, as it allowed equal cells recovery reducing energy inputs, coagulant demand and carbon emissions.

Grass Biomethane for Agriculture and Energy

Many factors enforce the intensification of grassland utilization which is associated with significant environmental impacts subjected to various legislative constraints. Nevertheless, the need for diversification in agricultural production and the sustainability in energy within the European Union have advanced the role of grassland as a renewable source of energy in grass biomethane production with various environmental and socio-economic benefits. Here it is underlined that the essential question whether the gaseous biofuel meets the EU sustainability criteria of 60% greenhouse gas emission savings by 2020 can be met since savings up to 89.4% under various scenarios can be achieved. Grass biomethane production is very promising compared to other liquid biofuels either when these are produced by indigenous or imported feedstocks. Grass biomethane, given the mature and well known technology in agronomy and anaerobic digestion sectors and the need for rural development and sustainable energy production, is an attractive solution that fulfils many legislative, agronomic and environmental requirements.