Influence of culture media composition on the rheology of microalgae concentrates on a large scale.

The role of microalgae in the production of bioproducts and biofuels, along with their ability to provide a sustainable pathway for wastewater treatment, makes them promising alternatives to conventional processes. Nevertheless, large-scale downstream processing requires an understanding of biomass rheology that needs to be addressed further. This study aimed to characterize microalgal concentrates rheologically in different culture media. The presence of bacteria was quantified by photorespirometry and plate counting techniques. The culture medium was found to significantly influence viscosity, with primary wastewater exhibiting the highest viscosity and seawater plus pig slurry the lowest. The concentration of heterotrophic bacteria was directly related to the viscosity. Extracellular polysaccharides (EPS) in supernatant exhibited an inverse viscosity trend compared to biomass concentrates, with pig slurry cultures having higher concentrations. These findings emphasize the profound influence of culture medium and EPS on the rheology of microalgal biomass, underscoring the need for continued research aimed at facilitating and optimizing large-scale downstream processes within the framework of a circular economy and the attainment of the Sustainable Development Goals (6,8, and 12).

Reduction of natural radioactivity in groundwater with different salinity through adsorption of uranium and radium in filter materials.

In many small communities in the Mediterranean area, groundwater is usually the only water body available. Depending mainly on the surrounding geology, their concentration of naturally occurring radionuclides may pose a radiological hazard. Removal of uranium and radium from drinking water is the best way to avoid it, i.e., reverse osmosis (RO), but consuming a lot of energy. Thus, two modified drinking water treatment plants (DWTPs) using zeolites coated with manganese dioxide as adsorbent material were analyzed as an alternative to RO. Groundwater salinity can negatively affect this process. Radium removal decreased as water salinity increased; but it had a major impact on uranium, rendering the adsorption effectless in one DWTP. Waste management and how to avoid it from becoming radioactive are of major concern. Radium and uranium were associated to the reducible fraction in the filter material and also to the carbonate fraction in the case of uranium. Regeneration of the filter material using KCl solutions was able to remove 81% and 63% of uranium and radium, respectively.

Rheology of microalgae concentrates and its influence on the power consumption of enzymatic hydrolysis processing.

The optimization of downstream processing is a critical step in any microalgae-related process. The microalgal biomass is separated from the initial diluted cultures to form a concentrated slurry, the properties of which greatly influence the design and performance of further processing steps, such as enzymatic hydrolysis. In this work, the rheological behaviour of two microalgal concentrates produced both in freshwater (Scenedesmus almeriensis) and seawater (Nannochloropsis gaditana) were studied. Measurements were performed on the entire range of biomass concentrations, from 0.5 g/L to 264 g/L. Non-Newtonian behaviour was observed whatever the water type and biomass concentration used, especially at high biomass concentrations above 10 g/L. The rheological data were adjusted to the Power Law model, and the consistency and flow behaviour indexes were correlated with the biomass concentration. The results show that the freshwater and seawater biomasses exhibited different behaviours, with freshwater slurries being more viscous than seawater ones. The high viscosity of freshwater slurries requires increased energy consumption for mixing, with an estimated cost increase of 60% when using them under the non-Newtonian conditions considered. These findings highlight the considerable effect of algal biomass rheology on the mixing power required during microalgal biomass processing.