Biodegradation kinetics of mixed substrate systems in wastewater and soil systems.

摘要

A method for continuously and automatically measuring carbon dioxide evolution, which can be retrofitted to commercial respirometers, has been developed. For studied systems, experimental results using this method showed that the respiratory quotient (RQ) is close to one until the plateau of oxygen uptake. This indicates the primary biodegradation rate of those chemicals is close to their ultimate biodegradation rate. Experiments of mixed substrate (phenols and aniline) systems in aqueous environments were conducted. First, a mathematical model based on cybernetic concept was applied to systems with low concentration. Then, an improved mathematical model based on cybernetic frame was successfully applied to more general cases of mixed substrate systems in aqueous environments. Sequential and simultaneous utilization of those substrates were observed for those systems. In soil systems, the soil/sediment sorption coefficient normalized to organic carbon, K{dollar}sb{lcub}rm oc{rcub}{dollar}, is extensively used to assess the fate of organic chemicals in hazardous waste sites. An analytic equation was given to predict this coefficient for 133 organic compounds by starting with a neural network, converging the bias and weight values using the available data on water solubility (S), octanol/water partition coefficient (K{dollar}sb{lcub}rm ow{rcub}){dollar} and the normalized soil/sediment sorption coefficient K{dollar}sb{lcub}rm oc{rcub}{dollar}. Biodegradation kinetic forms in complex soil slurry systems was examined using nonlinear bioreaction rate models rather than linear models. Detail modeling of PAH in soil slurry reactors included selected biodegradation kinetic forms coupled with detail diffusion model for sorption effects. Different kinds of soils (high and low organic matter: 34.7% and 0.415%) were also used for this study. Results showed that content of organic carbon in the soil greatly affected rates of adsorption/desorption and equilibrium between aqueous and solid phases. The more content of organic carbon is there in soil, the shorter the time is needed for compound to reach equilibrium between soil and water phases. Finally, a protocol to mimic the real situations in soil bioremediation by using soil slurry, wafer and column reactors was developed and tested for naphthalene biodegradation.