PHOSPHORUS REMOVAL FROM WASTE-WATER BY HALF-BURNED DOLOMITE

The possibility of phosphorus removal from wastewater by fixation with half-burned dolomite grains was investigated. The results obtained showed the formation of a non-stochiometric calcium phosphate on the surface of the grains, undoubtedly of an amorphous nature as structure identification could not be made when X-ray diffraction techniques were employed. Identification by ESCA technique indicated a structure having a (Ca + Mg)/P ratio of 1.4. Equilibria experiments carried out at 25-degrees-C between the solid and a phosphate-containing solution showed that the fixation could be modelled following a Freundlich type isotherm. The fixation capacity of grains with a 0.5 mm mean particule size was 10 mg PO4-P g-1 solid. The influences of hydraulic conditions and grain specific area on the fixation capacity were investigated. Acid regeneration of the spent material seemed to be of no practical interest. From an engineering point of view, this treatment could serve as a tertiary step after biological treatment of a wastewater. Finely pulverized powder (diameter < 100-mu-m) should be directly added at the outlet of a poor axial mix aeration basin, in order that the powder incorporates into the biological floc which will enhance separation of the sludge in the sedimentation tank.