A Direct Comparison of U.S. Environmental Protection Agency's Method 304B and Batch Tests for Determining Activated-Sludge Biodegradation Rate Constants for Volatile Organic Compounds
Abstract:Biodegradation rate constants for volatile organic compounds (VOCs) in activated-sludge systems are needed to quantify emissions. One current U.S. Environmental Protection Agency method for determining a biodegradation rate constant is Method 304B. In this approach, a specific activated-sludge unit is simulated by a continuous biological treatment system with a sealed headspace. Batch experiments, however, can be alternatives to Method 304B. Two of these batch methods are the batch test that uses oxygen addition (BOX) and the serum bottle test (SBT). In this study, Method 304B was directly compared to BOX and SBT experiments. A pilot-scale laboratory reactor was constructed to serve as the Method 304B unit. Biomass from the unit was also used to conduct BOX and modified SBT experiments (modification involved use of a sealed draft-tube reactor with a headspace recirculation pump instead of a serum bottle) for 1,2-dichloroethane, diisopropyl ether, methyl tertiary butyl ether, and toluene. Three experimental runs - each consisting of one Method 304B experiment, one BOX experiment, and one modified SBT experiment - were completed. The BOX and SBT data for each run were analyzed using a Monod model, and best-fit biodegradation kinetic parameters were determined for each experiment, including a first-order biodegradation rate constant (K 1). Experimental results suggest that for readily biodegradable VOCs (i.e., K 1 > 10 L/g volatile suspended solids [VSS]•h) the two batch techniques can provide improved means of determining biodegradation rate constants compared with Method 304B. In particular, these batch techniques avoid the Method 304B problem associated with steady-state effluent concentrations below analytical detection limits. However, experimental results also suggest that the two batch techniques should not be used to determine biodegradation rate constants for slowly degraded VOCs (i.e., K 1 < 0.1 L/g VSS•h).
Document Type: Research Article
Publication date: November 1, 1999
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