Experimental and modeling studies on membrane-aerated granular activated carbon-sequencing batch biofilm reactors for wastewater treatment

The Granular Activated Carbon-Sequencing Batch Biofilm Reactor (GAC-SBBR) is a novel unsteady-state periodic hybrid wastewater treatment system that combines operating advantages of the Sequencing Batch Reactor, membrane aeration, fixed-film biodegradation and GAC adsorption technologies. The reactor employs a gas-permeable silicone tubing pressurized with oxygen to support the biofilm and provide bubble-free oxygenation. This work sought to obtain an understanding of the operation of the various technologies employed in the GAC-SBBR with operating time and conditions and to identify potential interactions among them using a combination of fundamental experimental and modeling studies.; This objective was pursued in two phases. The first phase investigated the operation of the GAC bed in a series of experimental and modeling studies using toluene and F-300 activated carbon as a model solute/GAC system. The internal and external GAC structure characteristics were determined using several characterization techniques. Equilibrium studies were conducted to obtain the adsorption/desorption isotherms and to quantify the extent of irreversible adsorption. The toluene adsorption and desorption dynamics were determined experimentally under a wide range of operating conditions in batch and fixed-bed GAC adsorbers and were described successfully using a model which accounted for external mass transfer and intraparticle surface diffusion with a surface diffusion coefficient which increased with surface coverage.; The second phase addressed the development of a mathematical model for the GAC-SBBR process and its use for investigating the operation of the system with time and operating conditions. The model considered the various system components (membrane, biofilm, liquid bulk, GAC bed) and accounted for important transport and biological processes in them under dynamic conditions. Substrate biodegradation in the biofilm and the liquid bulk, permeation across the silicone membrane and GAC adsorption/desorption were considered. Oxygen diffusion in the membrane/biofilm system, biological consumption and adsorption/desorption were also accounted for. The model was verified using experimental results from previous bench-scale studies on the treatment of synthetic toluene wastewaters in SBBRs and was subsequently used to conduct an extensive operation analysis for the GAC-SBBR through model simulations.