a Sand-GAC Filter to Achieve High-Rate Biological Filtration

A single dual-layer filter, combining sand and granular activated carbon (GAC) and maintaining the mechanisms of biological treatment, was studied in France as a possible means o i achieving high-rate filtration. Initial results attest that the dual layer far outperforms a single-layer sand unit, particularly with respect to the removal of suspended solids and ammonia. Using GAC for the top layer of the double filter ensures the removal of appreciable quantities of assimilable carbon and consequently has a positive effect on final chlorination and the palatability of the water. The dual-layer filtration technique is