Date of Award

Spring 4-2018

Embargo Period

5-8-2018

Degree Type

Dissertation (CMU Access Only)

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Mitchell J. Small

Comments

Persistent organic pollution (POPs) is one of the top environmental issues worldwide. Most of these chemicals are synthetic, introduced through industry production for particular purposes. Due to the persistence and stability, POPs can travel long distances, and some of them can accumulate in biota tissues with high lipid contents and cause long-term toxicity and affect organism’s health when certain concentration levels are reached. This thesis aims to improve the understanding of organism impacts during POPs transport and to model the mechanisms of biota degradation processes. We are focusing on a specific type of POPs, polychlorinated biphenyls (PCBs). The chemical complexity and composition uncertainty of PCBs make it an excellent research object. Moreover, since the PCBs have been banned for production and background concentration is dropping, we could acquire a completed figure of POPs pollution for model development. By analyzing the PCBs transport history, we could improve current model designs to predict other POPs transport behaviors in various environmental media, assist further development on POPs control policy, and prevent issues and damages on public health in future. The first study intends to upgrade the current model performance for simulating complex PCBs fate and transport in a lake system, especially the organism effects during PCBs transport. Several improvements are made, such as integrating multiple biotic terms regarding the PCB transport to rebuild the feedback routines from biotic compartments to the environmental media. Facilitated intermedia transport through biota compartments is shown in the analysis and its contributions to overall PCBs transport is carefully evaluated and discussed. The second project aims to evaluate the performance of current empirical rules on PCB dechlorination study. The study aims to explore the mechanisms and principles behind PCB anaerobic biodegradation further since the empirical regulations are rough and unprecise for mathematical modeling. Moreover, the empirical rules mainly reflect the biotic features in PCB dechlorination process. Since the reaction involves both the biology and chemistry, it is rational to dig more information on impacts from the chemical side. The research not only reviews the microorganism’s bio-selectivity behind the existing empirical rule, but also discusses the possible mechanism based on chemical kinetics, trying to develop a hypothesis to explain and quantify the anaerobic degradation behaviors, such as quantum chemistry theory, molecule orbit theory, and so on. The final research focuses on simulating the PCB dechlorination through a redox potential based model. By introducing redox-potential as the thermal dynamic selection tool. This study provides one possible solution for predicting PCB dechlorination patterns and posting reaction products by tracking redox potential, as well as the bio-selectivity from microorganism features. The redox potentials of each dechlorination reaction can be calculated by evaluating the Gibbs free energy through quantum chemistry theories and several environmental factors. To realize a practical procedure, we created a model, using the Markov Chain method to monitor the continuous changes in the PCB concentration distribution. The new model proves its capability and accuracy by comparing the simulation results with several published reports on PCB dechlorination study.

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