Modeling of photosynthesis and respiration rate for microalgae–bacteria consortia

Abstract

In this article, the influence of culture conditions (irradiance, temperature, pH, and dissolved oxygen) on the photosynthesis and the respiration rates of microalgae–bacteria consortia in wastewater treatment was analyzed. Specifically, some short photo‐respirometric experiments, simulating outdoor raceway reactors, were performed to evaluate the response of microalgae, heterotrophic bacteria, and nitrifying bacteria to variations in environmental parameters. Results demonstrate that irradiance is the most dominant variable to determine microalgae photosynthesis rates. However, reduction in microalgae activity was not observed at higher irradiance, ruling out the existence of photoinhibition phenomena. Related to heterotrophic and nitrifying bacteria, their activities were strongly affected by the influence of temperature and pH. Moreover, the effect of dissolved oxygen concentrations on microalgae, and bacteria activities was studied, displaying a reduced photosynthetic rate at dissolved oxygen concentrations above 20 mg/L. Data have been used to develop an integrated model for each population (microalgae, heterotrophic bacteria, and nitrifying bacteria) based on considering the simultaneous influence of irradiance, temperature, pH, and dissolved oxygen. The models fit the experimental results in the range of culture conditions tested, and they were validated using data obtained by the simultaneous modifications of the variables. These individual models serve as a basis for developing a global biologic microalgae–bacteria model for wastewater treatment to improve the optimal design and management of microalgae‐based processes, especially outdoors, where the cultures are subject to variable daily culture conditions.

ABACO: A New Model of Microalgae-Bacteria Consortia for Biological Treatment of Wastewaters

“…The model has been developed considering the main microalgal and bacterial processes that simultaneously occur in the microalgae-based wastewater treatment. An initial dynamic model considering the influence of main environmental variables (irradiance, temperature, pH and dissolved oxygen) on microalgae and bacteria growth was developed by [20]. The model equations were inspired in the BIOALGAE model [17], and it was already validated, the model allowing one to simulate the effect of environmental conditions on the photosynthesis and respiration rate of microalgae-bacteria consortia.…”

“…However, information on microalgae parameters in wastewater treatment systems is scarce. Therefore, in this work, a new microalgae-bacteria mathematical model named ABACO is proposed; the characteristic parameters of microalgae in it were obtained experimentally in previous works [20,21]. Thus, the main purpose of this study was to develop, calibrate, and validate the whole microalgae and bacteria model with experimental data from duplicate laboratory-scale photobioreactors using pig slurry as a nutrient source.…”

Variables Governing Photosynthesis and Growth in Microalgae Mass Cultures

“…Recently, a photo-respirometry technique for quantifying the rates of the main metabolic processes in microalgae-bacteria consortia has been developed and tested [170]. When studying microalgae-bacteria consortia, for example whether wastewater used as a nutrient source, it is beneficial to distinguish between the contribution to oxygen balance by both groups.…”

An Interactive Tool for Simulation of Biological Models Into the Wastewater Treatment With Microalgae

“…As a result, and through oxygen production, it is possible to obtain models to predict the biomass productivity in these complex systems. -Zurano et al (2021a) developed a dynamic model considering several important environmental parameters (light intensity, temperature, pH, and dissolved oxygen) on microalgae and bacteria growth (Sánchez Zurano et al, 2021b). The model equations were built using experimental data related to the influence of the environmental parameters on the photosynthesis rate and the respiration rate of microalgaebacteria consortium, distinguishing between microalgae activity, heterotrophic activity, and nitrifying activity and by considering the methodology proposed by (Sánchez-Zurano et al, 2020a).…”

“…when only solar radiation is considered. This simplification of the model described by Sánchez-Zurano et al (2021a) allows to offer an idea of the maximal productivity obtaining in a wastewater bioreactor in which microalgae are the only microbial population and the rest of the operational and environmental parameters do not affect the process.…”