Microbial Analyses of Granulated Activated Carbon Biofilter for the Treatment of Secondary Effluent

Ahn, Y.^*, H. Shon¹, R. Tatavarty², S. Vigneswaran¹, J.-W Yang³, and I.S. Kim²

¹ Department of Environ. Eng., Univ. of Technology, Sydney, Australia

² Department of Environ. Sci. and Eng., Gwangju Inst. of Sci. and Technology, Korea

³ Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea

Abstract

            Granular activated carbon (GAC) biofilter process is used as an advanced treatment technique for the reuse of treated domestic wastewater. Adsorption of organics and biological degradation of the organics adsorbed onto the activated carbon can be the two major mechanisms for the consistent removal of organics by the GAC biofiltration. However, information on microorganisms associated with the process is limited. In this study, we analyzed microorganisms in biofilters that were packed with different amounts of GAC. The objectives of the study were (i) to evaluate DOC removal activities of biofilters, (ii) to assess biomass in influent, biofilter bed, and effluent, (iii) to analyze microbial profiles at different heights of GAC bed, and (iv) to estimate biomass lost by daily backwashing.

            Three filter columns (each with a diameter of 2 cm and a height of 50 cm) were employed. The columns were packed with 10, 20, and 40 g (bed depth 3.5, 7, and 14 cm) of GAC, respectively. The GAC beds were fed with secondary effluent from Gwangju wastewater treatment plant, Korea at a constant filtration rate of 1 m/h. The biofilters were backwashed at 30% bed expansion for 5 min on a daily basis to avoid physical clogging of the filter by attached mass. Microbial analyses were conducted on day 25 of biofilter operation.

            The biofilter containing 40 g GAC showed the highest TOC removal efficiency during the initial 11 days of operation. However, all 3 biofilters showed similar and constant efficiency (65-70%) afterward. Sorption was initially dominant as judged by MW distribution of the biofilter effluents sampled with time.