Evaluation of combined activated sludge - microalgae system for wastewater treatment

The biotechnological principle of using combined microalgae – activated sludge system for wastewater treatment consists in bidirectional metabolic fluxes that can be established between the photoautotrophic microalgae and heterotrophic bacteria. Thereby, the oxygen released during the photosynthesis process by the microalgae species is used by bacteria to degrade organic matter, the resulted degradation products (mainly CO2) being used in turn as nutrients by the microalgae for cell development. Since the microalgae biotechnology has been recognized as a viable solution for wastewater treatment, it was used mainly in tertiary treatment processes. However, during the last decade, several researchers focused their studies on using the microalgae for secondary wastewater treatment, high treatment performances for domestic and industrial wastewater being attained. The main drawback of this biotechnology is represented by the poor microalgae cells recovery. The currently applied methods (centrifugation, filtration, flocculation/coagulation etc.) are involving high costs, contamination with heavy metals, filter clogging etc. In order to solve this problem, several researches were conducted in this field and, until now, bio-flocculation method seems to be the most feasible solution.