Granular Activated Carbon (GAC) biofilter for low strength wastewater treatment

Biofilter can be a cost-effective alternative treatment unit, especially for low strength wastewater. In this study, detailed experimental investigation of a GAC biofilter was carried out in a laboratory-scale unit using low strength synthetic wastewater and biologically treated sewage effluent (BTSE). Performance of the biofilter was evaluated in terms of total organic carbon (TOC) removal. The TOC removal efficiency of the biofilter was found to be stabilized at around 40-45 % after 30 days (even for a short depth of GAC column of 7-15 cm). The maximum biomass retained on the activated carbon was measured to be 44 mg/ g of GAC after 49 days of continuous operation. Filter backwashing provided at 30% bed expansion for 5 minutes on a daily basis to overcome physical clogging of the filter by attached mass, did not have any adverse effect on the active biomass attached to the media and thus the organic removal efficiency of the filter remained unchanged. Molecular size distribution analysis showed that a significant removal of organics of small molecular weight (MW) at the initial stage of operation of biofilter followed by mainly large MW organic matter after one day of operation. This shows that adsorption was the main mechanism at the initial period and biological degradation as the predominating mechanism after one day of operation throughout the rest of the operation. The biofilter was found to remove a majority of hydrophilic organic compounds