Performance of Dual‐Media Expanded Bed Bioreactor

Abstract

AbstractAdsorption and biological treatment are two possible approaches to remove chloro‐organic and organic compounds. Granular activated carbon (GAC) biofilm reactors combine these two features, the adsorptive capacity and irregular shape of GAC particles providing niches for bacterial colonisation protected from high fluid forces, while the variety of functional groups on the surface enhance the attachment of microorganisms. The biofilm process is compact and offers reactions in both aerobic and anoxic states. Studies on removal of nitrogen constituents by a biofilm process were carried out using a dual‐media expanded bed bioreactor, with GAC and plastic media as support media. The plastic media also acts as a filter for the effluent. Experiments were carried out at F:M of about 0.45 and hydraulic residence times (HRT) of 48, 24 and 12 hours. Bed expansion was maintained at 20–30% by recirculation flow. Aerobic condition was maintained at dissolved oxygen (DO) of about 2 mg/l throughout the bed. Chemical oxygen in demand (COD) in feed was 1000 mg/L while the total‐N was 100 mg/L. Analysis showed that the process is able to maintain very stable conditions, achieving substantial COD removal of about 85% and total‐N removal of about 80%. Biofilm biomass measurements showed an increase from 400 mg/l at HRT of 48 hours to 10,100 mg/l at HRT 12 hours, showing that much higher biomass concentrations may be contained in a biofilm process as compared to a conventional suspended biomass process. Bioreactors contain their own ecosystems, the nature of the community and the state of microorganisms define the kinetics and determine reactor performance. Growth kinetic parameters obtained are YH = 0.3421 mg/mg, m̈H = 0.2252 day−1, KH = 319.364 mg/l and bH = 0.046 day−1. The denitrification kinetic parameters obtained are YHD = 0.9409 mg/mg, m̈HD = 0.1612 day−1, KHD = 24.6253 mg/l and bHD = 0.0248 day−1. These parameters enable prediction of required reactor sizes and operational parameters. The plastic media has greatly improved effluent clarification by 98% as compared to single‐media (GAC) only reactor.