The potential of membrane-assisted microalgae-bacteria consortia for the treatment of real municipal sewage

Microalgae-bacteria consortia are considered a promising alternative for wastewater treatment. Photosynthesis performed by microalgae induces a self-oxygenation of the culture, eliminating the requirements for mechanical aeration. However, systems have limitations, such as high hydraulic retention times and difficulties associated with effluent clarification. Biomass retention by membranes has been explored as an alternative to overcome such problems. This work evaluated the application of a membrane-enhanced bioreactor, containing microalgae-bacteria consortia, as an alternative to provide sanitation services (sewage treatment). Two 50 L raceway reactors were operated, one provided with an external microfiltration membrane module. Both reactors were fed with real sewage, at two different hydraulic retention times, 7 and 4 h. Comparative evaluation of both systems showed a superior performance of membrane-based system, in terms of nitrogen, COD and phosphorus removal. Application of membrane filtration, as expected, provided an effluent free of solids and faecal coliforms, which is relevant when water reuse in of interest. Under the conditions of this study critical flux in the range 10–15 L m⁻² h⁻¹ were observed. As is the case of other membrane bioreactors, biomass concentration showed to be a key factor determining particle deposition, defining critical flux and fouling rate when critical flux is surpassed.