Traitement tertiaere d'un effluent domestique secondaire par culture intensive de la cyanobactériePhormidium bohneri

Phormidium bohneri, a self‐flocculating cyanobacterium, was grown outdoors in a 75 1 intensive culture basin (semi‐continuous system) and used for the tertiary treatment of domestic wastewater. The behavior, growth and purification potential of P. bohneri were studied. The nutrient removal efficiency (max.: Ni = 83%, 12.5 mgN 1‐1 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 cyanobacterial biomass (P: 1.1%, N: 8.6%, protein: 53.5%, dry weight basis) can be easily harvested after the treatment by settling.