A membrane-based biofilm photobioreactor for enhanced algal growth rates

<p>Biofilm-based algal processes are increasingly used for wastewater treatment, carbon capture, and production of biofuels and other valuable products. They provide high cell densities, are more robust, and are easier to harvest and concentrate than suspended algae. However, algal biofilms are more likely to experience carbon limitation, O<sub>2</sub> inhibition, and pH limitations, especially when thick and exposed to high light intensities. To address these limitations, we studied a novel photobioreactor based on CO<sub>2</sub>-supplying hollow-fiber membranes, where the algal biofilms grow directly on the membranes. We used modelling and experiments to study our membrane biofilm photobioreactor (MB-PBR) system and to compare it to a control with atmospheric CO<sub>2</sub> and bicarbonate supplied in the bulk liquid.</p> <p>Mathematical models of the MB-PBR and the control were developed using COMSOL Multiphysics®. The models included phototrophic growth, diffusion of gases (CO<sub>2</sub>, O<sub>2</sub>, N<sub>2</sub>) across the membrane, nutrient diffusion from the bulk liquid, pH-dependent carbonate speciation, and light attenuation. Experimentally, we compared the MB-PBR and control using bench-scale photobioreactors with hollow-fiber membranes attached to them, 10% BG-11 media and white light from an LED lamp. The MB-PBR membranes were supplied with 5% CO<sub>2</sub> and 95% N<sub>2</sub>.  The control system had sealed membranes, to prevent gas exchange.  We measured the biomass dry weight gravimetrically and the biofilm growth rates by daily measurement of the thicknesses using optical coherence tomography (OCT).</p> <p>Both modeling and experiments suggested that MB-PBR biofilms grow significantly faster than the control. Using our model, we studied the effect of light intensity, pH, buffer concentration and light and oxygen inhibition on MB-PBR behavior. Growth was inhibited by excessively high levels of light and O<sub>2</sub>. By providing CO<sub>2</sub> through the membrane, the carbon limitation was minimized, O<sub>2</sub> was stripped from the biofilm, and pH shifts were attenuated. These results suggest the MB-PBR may provide a more efficient platform for algal biofilm processes.</p>

Effects of Selected Pharmaceuticals on Freshwater Algal Biofilms in Different Organic Loads

The growth pattern of different algal biofilms investigated in the presence of Ibuprofen and Benzoyl Metronidazole in batch reactors at varying organic loads. Study suggests that the inhibition of algal growth is correlated to organic loads in water rather than the concentrations of PhCs (Pharmaceuticals). Mortality of algae was recorded in BG11 media with binary mixtures of PhCs and no growth inhibition was monitored in the activated sludge with PhCs. These outcomes indicate that the presence of PhCs as pollutants in drinking water have severe effect on algal biofilms due to low organic load thus can alter the aquatic ecosystem. Additionally, PhCs might not adversely hinder the growth of microbes in WWTP (Wastewater Treatment Plants) or in waters with high organic loads. Nevertheless, inference of these results to a full-scale WWTP need more evidence through extensive studies using variable organic substrates and PhCs with numerous ranges of organic loads. These findings suggest that PhCs as water contaminant are able to shift microbial ecology in water bodies.

A Test Device for Microalgal Antifouling Using Fluctuating pH Values on Conductive Paints

Due to the current dependence on biocidal antifouling coatings for biofouling control, there is a continuing international challenge to develop more environmentally acceptable antifouling systems. Fluctuating the pH values on paint surfaces is one of these approaches. We developed an antifouling test device to investigate algal biofilms on conductive paints by using a flume with electrochemically working test panels and subsequent confocal laser scanning microscopy (CLSM) of biofilms. By employing a pole reversal of direct current, fluctuating pH values on the paint surface were generated. As a consequence of the resulting pH stress, colonization of the paint surface by diatoms decreased substantially. The density of biofilm algae decreased with increasing pH fluctuations. However, breaks between electrochemical treatments should not exceed one hour. Overall, we established an experimental setup for testing the antifouling capabilities of electrodes based on conductive paints, which could be used for further development of these varnishes.