Influence of COM-peptides/proteins on the properties of flocs formed at different shear rates.

Coagulation followed by floc separation is a key process for the removal of algal organic matter (AOM) in water treatment. Besides optimizing coagulation parameters, knowledge of the properties of AOM-flocs is essential to maximizing AOM removal. However, the impact of AOM on the floc properties remains unclear. This study investigated how peptides/proteins derived from the cellular organic matter (COM) of the cyanobacterium Microcystis aeruginosa influenced the size, structure, and shape of flocs formed at different shear rates (G). Flocs formed by kaolinite, COM-peptides/proteins and a mixture of the same were studied, and the effect of intermolecular interactions between floc components on floc properties was assessed. The coagulation experiments were performed in a Taylor-Couette reactor, with aluminum (Al) or ferric sulphate (Fe) utilized as coagulants. Image analysis was performed to gauge floc size and obtain data on fractal dimension. It was found that floc properties were affected by the presence of the COM-peptides/proteins and the coagulant used. COM-peptides/proteins increased floc size and porosity and widened floc size distributions. The Fe coagulant produced larger and less compact flocs than Al coagulant. Moreover, the decrease in floc size that occurred in parallel with increase in shear rate was not smooth in progress. A rapid change for the kaolinite-coagulant suspension and two rapid changes for the suspensions containing COM were observed. These were attributed to various intermolecular interactions between floc components participating in coagulation at different G. Based on the results obtained, shear rates suitable for efficient separation of flocs containing COM were suggested.

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.

Semblanza de Juan Marín Osorio / Remembering Juan Marín Osorio

El 18 de junio del 2010 se cumplieron 9 años de la muerte de un prohombre de la anestesiología latinoamericana, Juan Marín Osorio, médico con una formación autodidacta en la anestesiología y una vocación innata de influir en los demás con su autenticidad. Era ateo, y quizá por esto tuvo tanto problema durante su rotación de anatomía por la Universidad Nacional bajo las riendas del profesor Bermúdez, un teófilo radical y exigente (1). Sin embargo este hombre de fisonomía peculiar, delgado, de baja estatura, con el cabello largo, con una imagen de filósofo y sociólogo desprevenido, era tan humano como la mejor criatura de Dios...