Efflorescence algale

Une efflorescence algale (parfois décrite avec un emprunt à l'anglais bloom algal ou bloom phytoplanctonique) est une augmentation relativement rapide de la concentration d'une (ou de plusieurs) espèce(s) d'algues (ou de bactéries, les cyanobactéries, anciennement appelées « algues bleues »), appartenant généralement au phytoplancton, dans un système aquatique d'eau douce, saumâtre ou salée. Cette prolifération se traduit généralement par une coloration de l'eau (en rouge, brun, brun-jaune ou vert). Ces couleurs sont dues aux pigments photosynthétiques dominants des cellules algales en cause. Le phénomène peut être naturel ou favorisé par des pollutions terrigènes (nitrates, phosphates). Dans ces derniers cas, des proliférations intenses et longues peuvent conduire à des « zones mortes », en raison d'une consommation de la totalité de l'oxygène dissous dans l'eau la nuit ou d'émissions de toxines par certaines espèces de plancton (cyanophycées, notamment). En général, seule une ou q

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Bacteria-induced mixing in natural waters

Oscar Rodrigo Sepúlveda Steiner, Talia Ekin Tokyay Sinha, Alfred Johny Wüest

Swimming organisms can enhance mixing in their natural environments by creating eddies in their wake and by dragging water along. However, these mixing mechanisms are inefficient for microorganisms, because swimming-induced variations in velocity, temperature, and dissolved substances are evened out before they can be advected. In bioconvection, however, microorganisms induce water movement not by propulsion directly but by locally changing the fluid density, which drives convection. Observations of bioconvection have so far mainly been limited to laboratory settings. We report the first observation and quantification of bioconvection within a stratified natural water body. Using in situ measurements, laboratory experiments, and numerical simulations, we demonstrate that the bacterium Chromatium okenii is capable of mixing 0.3 to 1.2 m thick water layers at around 12 m water depth in the Alpine Lake Cadagno (Switzerland). As many species are capable of driving bioconvection, this phenomenon potentially plays a role in species distributions and influences large-scale phenomena like algal blooms.

2017

Chargement

Monitoring particulate fouling of North Sea water with SDI and new ASTM MFI0.45 test

Margot Ninon Lauren Olive

For assessing the particulate fouling of water, the modified fouling index (MFI0.45) is a superior test to the silt density index (SDI). There is a need to compare both tests in terms of sensitivity, how they are affected by the filter material and the type of support plate and also illustrate their use for monitoring of seawater quality over time. In this work, we studied seven different filter holders with different filter support plates and three different 0.45 mu m filter materials, and we applied the tests for monitoring of North Sea water quality. The results illustrated that the type of support plate of the filter holder greatly influences the measured MFI0.45 values and thus, a correction for the effective membrane area may be needed when carrying out an MFI0.45 test. An attempt to normalize differences in MFI0.45 due to filter material with a Formazin solution was tested but proven not successful. When monitoring the seawater, the MFI0.45 was much more sensitive than SDI to water quality variations in particular during algal growth. As the SDI and MFI0.45 tests can be measured with help of the same equipment, more alignment in the ASTM protocols for both methods is recommended.

2019

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A sustainable production of algal biomass integrating wastewater treatment and bioenergy generation

Mariluz Bagnoud, Christian Ludwig, Céline Terrettaz

This project aims to demonstrate the feasibility of producing renewable microalgae biomass using as a main nutrient source a secondary wastewater stream. It is planned to purify the wastewater by the growth of algal biomass while producing a feedstock that can be used for the bioenergy sector. If important biomass density is achieved, this strategy will be adopted in a novel process named SunCHem (proposed at the EPFL-PSI SWT group) using hydrothermal treatment of microalgae to produce methane. Wastewater treatment coupled with algal biomass production is particularly suitable for an implementation in Colombia as it requires low capital investment and it allows the generation of added-value through the valorization of the biomass. In addition, the climatic conditions in Colombia (high annual solar irradiance) are favorable to the installation of this highly ecological sound process. This concept may be interesting to municipal utilities, industrial companies and agricultural firms, since it helps to solve many of their pollution issues. In a preliminary study it was demonstrated the efficient nutrient removal by Dunaliella salina microalgae using a primary treated wastewater effluent1. This microalgae strain reduced the nitrate and phosphate load in the wastewater at 84% and 90% respectively and its specific growth rate of 0.46 d-1 was comparable with that achieved using a standard nutrient media (0.47 d-1). We are currently comparing the ability of three microalgae (Chlorella, Scenedesmus and Ankistrodesmus) strains to remove nitrogen and phosphorus in a conventional media. These three microalgae were selected due to an appropriate carbon balance for their future hydrothermal conversion into methane.

2012

Chargement

Eutrophisation

thumb|upright=1.6|Les fertilisants utilisés pour les cultures (phosphore et azote) dopent la croissance des plantes et des algues dans le ru jouxtant le champ cultivé. En France et en Europe, la mise

Cyanobacteriota

Les Cyanobacteriota sont des bactéries photosynthétiques. Longtemps appelées Cyanobacteria, ce nom n'a jamais été officiellement validé malgré son usage très courant. Le nom validé Cyanobacteriota a

Algue

Les algues sont des organismes vivants capables de produire de la photosynthèse oxygénique et dont le cycle de vie se déroule généralement en milieu aquatique. Elles constituent une part très impor

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