A Fed-Batch Technique to Evaluate Biodegradation Rates of Inhibitory Compounds with Anaerobic Biofilms Attached to Granular Activated Carbon

Abstract

Adsorption kinetics render measurements of substrate utilization rates in biofilms attached to adsorbing materials difficult. A fed-batch technique which maintains a constant concentration of substrate in the presence of biomass attached to granular activated carbon (GAC) was developed to measure biological kinetics independent of adsorption kinetics. The fed-batch technique used pre-adsorbed substrate on GAC as a source of substrate. During the experiment, the mass of substrate that is biodegraded is negligible when compared to the large mass of adsorbed substrate. Near equilibrium adsorption phenomena maintains the concentration of substrate constant throughout the experiment and eliminates mass transport resistance within the biofilms. Substrate utilization rates were measured at a specific substrate concentration by monitoring methane gas production rates. Samples of GAC with attached biomass were removed from two expanded-bed anaerobic reactors. GAC samples from a 3-ethylphenol (3-ep) fed reactor were used in batch experiments with 3-ep as the substrate and GAC samples from an orthochlorophenol (OCP) fed reactor were used in batch experiments with OCP as the substrate. Data were observed to fit Haldane kinetics and predictions from the Haldane kinetic parameters were in agreement with transient behavior from the 3-ep fed reactor. This technique was useful in predicting threshold inhibitory levels for continuous treatment of inhibitory wastewaters in expanded-bed GAC reactors. The fed-batch technique light also be applied to measure substrate utilization rates of biomass attached to other adsorbable materials such as soils.