Tertiary Treatment by Flocculation and Filtration

The conventional water treatment processes of flocculation, sedimentation, and rapid-sand filtration were studied in a 0.5 mgd pilot plant to demonstrate their applicability in tertiary treatment following high-rate trickling filtration. The quality of effluent from a large municipal wastewater plant utilizing high rate trickling filter secondary treatment can be improved by employing water supply treatment principles in tertiary treatment. Lime and alum have been used as primary coagulants assisted in settling by activated silica, ferric sulfate, and an organic polyelectrolyte. Suspended solids, BOD, and phosphates have been significantly reduced. Cost estimates have been prepared for construction and operation of a full scale plant and costs have been compared to levels of BOD₅ and phosphate removals attainable. Problems experienced in pilot scale operation that could affect full scale operation are described.