Towards sustainable microalgal biomass production by phycoremediation of a synthetic wastewater: A kinetic study

Abstract

Microalgae are considered as one of the most promising sources of biomass for energy production. However, bioenergy production by microalgal culture is still not economically viable and it has high environmental impact (requirement of high amount of freshwater). These drawbacks can be surpassed by coupling microalgal biomass production with phycoremediation of wastewater. In this context, this study evaluates the kinetics of biomass production and nutrient removal by two microalgal species (Chlorella vulgaris and Pseudokirchneriella subcapitata) cultivated in different medium compositions. The potential of microalgae for biomass production and their high efficiency on nutrients removal from medium, particularly nitrogen and phosphorus, was demonstrated. Maximum biomass productivity was observed for C. vulgaris (0.106 +/- 0.004 g L-1 d(-1)), while P. subcapitata reached a maximum of 0.050 +/- 0.001 g L-1 d(-1). The value of N: P molar ratio that favoured microalgal growth was 8: 1 for C. vulgaris and 16: 1 for P. subcapitata. A complete removal (100%) of ammonium was measured and high removal efficiencies were observed for nitrate (above 95%) and phosphate (above 97%). Microalgae were also able to efficiently remove sulphates, presenting removal efficiencies from 54 to 100%. The removal kinetics for all the nutrients have been determined through application of pseudo-first-order kinetic model and modified Gompertz model. In conclusion, this work gives relevant data for culturing microalgae in wastewater, contributing to the bioprocess design of a sustainable and low-cost production of microalgal biomass.