Annual assessment of the wastewater treatment capacity of the microalga Scenedesmus almeriensis and optimisation of operational conditions

Abstract

The depth of the culture and the dilution rate have a striking effect on the biomass productivity and the nutrient recovery capacity of microalgal cultures. The combination of culture depth and dilution rate that allows to maximise the performance of the system depends on environmental conditions. In the current study, a response surface methodology was used to explore the relationship between the two most relevant operational conditions and the biomass productivity achieved in 8.3 m2 pilot-scale raceways operated using urban wastewater. Four polynomial models were developed, one for each season of the year. The software predicted biomass productivities of 12.3, 25.6, 32.7, and 18.9 g·m−2·day−1 in winter, spring, summer, and autumn, respectively. The models were further validated at pilot-scale with R2 values ranging within 0.81 and 0.91, depending on the season. Lower culture depths had the advantage of minimising nitrification and stripping but allow to process a lower volume of wastewater per surface area. Biomass productivity was higher at culture depths of 0.05 m, when compared to 0.12 and 0.20 m, while the optimal dilution rate was season-dependent. Results reported herein are useful for optimising the biomass productivity of raceway reactors located outdoors throughout the year.

Production of Scenedesmus almeriensis Using Pilot-Scale Raceway Reactors Located inside a Greenhouse

“…Fv/Fm values were comparable in both seasons and around 0.6, which is the optimum for S. almeriensis produced in raceway reactors. The biomass productivity values were compared to those obtained using a model that predicts biomass productivities as a function of culture depth and the dilution rate [25]. The comparison between the experimental and predicted biomass productivity values is shown in Figure 4.…”

“…Overall, no major differences were observed between the composition of the biomass produced in spring or in summer. The protein content of the biomass was on average The biomass productivity values were compared to those obtained using a model that predicts biomass productivities as a function of culture depth and the dilution rate [25]. The comparison between the experimental and predicted biomass productivity values is shown in Figure 4.…”

“…In the present study, the biomass productivity obtained when operating the reactors in spring and summer was compared with that predicted using a recently published model based on a response surface methodology [25]. A response surface methodology explores the relationship between several explanatory variables and one or more response variables.…”

“…Experimental results were compared to those predicted by a recently published model developed following a surface response methodology [25]. The model allows predicting biomass productivity in raceway reactors as a function of the dilution rate and the depth of the culture.…”

Microalgae based wastewater treatment coupled to the production of high value agricultural products: Current needs and challenges

“…Raceway reactors can be operated at depths of 0.10-0.15 m (Acién Fernández et al, 2013). However, higher depths of up to 1 m have also been evaluated as a strategy to avoid freezing and minimise heat loss during cold time (Sawant et al, 2018) and lower depths (0.05 m) have been used to increase light availability (Sánchez-Zurano et al, 2021b). Light availability is the most important factor in the growth and productivity of photosynthetic microorganisms and current raceway designs do not allow to optimise light utilisation (Barceló-Villalobos et al, 2019).…”