TERTIARY-TREATMENT OF SECONDARILY TREATED URBAN WASTE-WATER BY INTENSIVE CULTURE OF PHORMIDIUM-BOHNERI

Phormidium bohneri, a self-flocculating cyanobacterium, was grown outd oors in a 75 1 intensive culture basin (semi-continuous system) and us ed for the tertiary treatment of domestic wastewater. The behavior, gr owth and purification potential of P. bohneri were studied. The nutrie nt removal efficiency (max.: Ni = 83%, 12.5 mg N l-1 d-1; Pi = 81%, 1. 3 mg P l-1 d-1) of this process allows a quite rapid treatment of the secondary effluent (hydraulic retention time = 1d). Stripping account for about 62% of nitrogen (NH3) removal while 38% is assimilated by P. bohneri. Inorganic phosphorus is removed mainly by precipitation (57% ) and to a lesser extent is taken-up by Phormidium (43%). The cyanobac terial biomass (P: 1.1%, N: 8.6%, protein: 53.5%, dry weight basis) ca n be easily harvested after the treatment by settling.