Lignite versus bituminous GAC for biofiltration— a case study: Fid-Bau Portal

Lignite versus bituminous GAC for biofiltration— a case study

Najm, Issam / Kennedy, Michael / Naylor, William

The city of Wilmington, N.C., initiated a study to compare lignite granular activated carbon (GAC) to bituminous GAC for biofiltration at the city's surface water treatment plant. The plant uses conventional filtration with preozonation and intermediate ozonation to treat water from the Cape Fear River. For this study, the existing GAC media in two of the plant's full‐scale dual‐media filters was replaced—one with lignite GAC and the other with bituminous GAC. The two new filters and one control filter containing the original GAC were operated and monitored for 13 months. The first three months were used to exhaust the adsorptive capacity of the new GAC and biologically acclimate it. During the subsequent 10 months, water quality samples were collected from various points throughout the treatment plant and from the effluent of each of the three filters. The samples were analyzed for various physical, chemical, and biological constituents. Quarterly GAC samples were also collected from each filter and analyzed for biomass content. The results indicated that the two types of GAC performed equally well in terms of removing turbidity, dissolved organic matter, color, assimilable organic carbon, and total aldehydes. The bacterial counts in the effluent of the two filters and on the GAC were also similar.