Tetradesmus obliquus to treat groundwater contaminated with nitrate towards a semicontinuous process

Nitrate presence in surface and groundwater is an environmental problem because this contaminant in high concentration can cause several healthy risks to the living being. In this sense, the present article aimed to evaluate the microalga Tetradesmus obliquus as an alternative in the remediation of groundwater contaminated by nitrate, mainly. Experiments were carried out in batch and semicontinuous modes with surface and forced aeration, light intensities between 50 and 200 µmol m −2 s −1 , initial nitrate concentration up to 400 mg L −1 and using synthetic and real effluent. The bioreactors were operated between 3 and 15 days. The nitrate and phosphorus removal rate for the real effluent (containing 100–150 mg L −1 of nitrate and supplemented with 20 mg L −1 of phosphorus) reached 100 and 94%, respectively. In semicontinuous mode, volumetric replacement rates (v/v) of 20, 40, 60, and 80% were tested in 3 days cycles of volumetric replacement time and obtaining, until the third cycle, stability of the process for the replacement rates of 40 and 60% (considering the maximum limits of legislation for nitrate and phosphorus and biomass production). Graphical abstract