Kinetic studies of biodegradation of insoluble compounds by continuous determination of oxygen consumption

Continuous determination of oxygen consumption by electrolytic respirometry has been experimented as a means to study the biodegradation kinetics of scarcely soluble environmental pollutants. The substrates used were the polycyclic aromatic hydrocarbons (PAH), naphthalene, phenanthrene, anthracene, fluoranthene and pyrene. The definition of an appropriate mode of PAH supply, either as crystals or more generally as a solution in a water non-miscible solvent, was found essential for yielding reproducible biodegradation kinetics. In these conditions, for all compounds tested, oxygen determination was found suitable for quantitative evaluation of PAH biodegradation and formation of biomass and soluble metabolites. The study of biodegradation kinetics with this methodology showed that a first phase of exponential growth could be characterized in most cases, followed by a phase of limited growth. Possible mechanisms involved in insoluble substrate uptake are discussed. During exponential growth, the bacteria utilized (although not necessarily exclusively) the PAH solubilized in the aqueous medium.