title: The ACCEL model for accelerating the detoxification kinetics of hydrocarbons requiring initial monooxygenation reactions.
abstract: The two-tank accelerator/aerator modification of activated sludge significantly increases the biodegradation of hydrocarbons requiring initial monooxygenation reactions, such as phenol and 2,4-dichlorophenol (DCP). The small accelerator tank has a controlled low dissolved oxygen (DO) concentration that can enrich the biomass in NADH + H+. It also has a very high specific growth rate (mu acc) that up-regulates the biomass's content of the monooxygenase enzyme. Here, we develop and test the ACCEL model, which quantifies all key phenomena taking place when the accelerator/aerator system is used to enhance biodegradation of hydrocarbons requiring initial monooxygenations. Monooxygenation kinetics follow a multiplicative relationship in which the organic substrates (phenol or DCP) and DO have separate Monod terms, while the biomass's content of NADH + H+ has a first-order term. The monooxygenase enzyme has different affinities (K values) for phenol and DCP. The biomass's NADH + H+ content is based on a proportioning of NAD(H) according to the relative rates of NADH + H+ sources and sinks. Biomass synthesis occurs simultaneously through utilization of acetate, phenol, and DCP, but each has its own true yield. The ACCEL model accurately simulates all trends for one-tank and two-tank experiments in which acetate, phenol, and DCP are biodegraded together. In particular, DCP removal is affected most by DOacc and the retention-time ratio, Theta acc/Theta total. Adding an accelerator tank dramatically increases DCP removal, and the best DCP removal occurs for 0.2 < DOacc < 0.5 mg/l and 0.08 < Theta acc/Theta total < 0.2. The rates of phenol and DCP utilization follow the multiplicative relationship with a maximum specific rate coefficient proportional to mu acc. Finally, mu acc increases rapidly for Theta acc/Theta total < 0.25, acetate removal in the accelerator fuels the high mu acc, and the biomass's NADH + H+ content increases very dramatically for DO acc < 0.25 mg/l.
authors.affiliation: ChemRisk, Inc., San Francisco, CA 94105-2703, USA. edahlen@chemrisk.com
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Dahlen
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Rittmann
mesh_terms: D000332:Aerobiosis; D018533:Biomass; D019149:Bioreactors; D001709:Biotechnology / Q000379:methods*; D006838:Hydrocarbons / Q000378:metabolism*; D007700:Kinetics; D008962:Models, Theoretical; D009243:NAD / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D019800:Phenol / Q000378:metabolism
chemical_list: D006838:Hydrocarbons; D009243:NAD; D019800:Phenol; D010100:Oxygen