关键词:
monod biodegradation kinetics
sorption
undisturbed sediment
pseudo-homogenous
aged contaminant
摘要:
Rates of C-14-phenanthrene mineralization in contaminated, undisturbed marine sediments were measured using the whole core injection method to assess microbial natural attenuation activity as a function of sediment depth. Submerged sediments were sampled from Eagle Harbor, a marine superfund site in Puget Sound. Experiments show significant biodegradation activities (0.0012-0.0036 day(-1) in the sediment horizons from 0 to 10 cm. The purpose and scope of this paper is to evaluate the range of experimental conditions giving valid results;a mathematical simulation described competing contaminant C-14-phenanthrene diffusion and simultaneous biodegradation (Monod kinetics), both retarded by sorption. The effect of aging was examined with two sorption models in presumed pseudo-homogenous sediments having effective properties. The simulation predictions provide quantitative guidelines for the successful use of the whole core injection method. (1) The effective Monod constant K-S' in sediment is increased by a large partition coefficient K-P between sediment and water and makes the apparent C-14-phenanthrene biodegradation approach first-order kinetics. (2) When K-S' > 1 mg(-1) l(-1) the measured C-14-phenanthrene biodegradation extent is biased by inadequately distributed injected tracer only when less than 7% of the sediment horizon is initially probed and mixed with injected tracer. (3) A short incubation time (< 20 days) is necessary when a mobile indicator, e.g., gaseous (CO2)-C-14, is used. For longer incubation times, predictions show that a (CO2)-C-14 indicator diffuses to adjacent horizons, thus smearing the depth profile of biodegradation. (4) This method employing a radiolabeled tracer provides accurate biodegradation rates for freshly contaminated sediments, and represents an upper limit to the natural phenanthrene biodegradation extents if the contaminant is aged over 50 days. (c) 2007 Elsevier Ltd. All rights reserved.