Title page for ETD etd-11132008-144238


Type of Document Dissertation
Author Mbuligwe, Stephen Emmanuel
URN etd-11132008-144238
Title Optimization of Treatment of Chlorinated Volatile Organic Compound Mixtures in Constructed Wetlands: Vegetation and Substrate Effects
Degree Doctor of Philosophy (Ph.D.)
Department Civil & Environmental Engineering
Advisory Committee
Advisor Name Title
John H. Pardue Committee Chair
Clinton S. Willson Committee Member
Donald D. Adrian Committee Member
William M. Moe Committee Member
Richard Shaw Dean's Representative
Keywords
  • chlorinated volatile organic compounds
  • Engineered wetland systems
  • wetland plants
  • wetland substrates
  • engineered wetland soil
  • salinity
Date of Defense 2008-10-24
Availability unrestricted
Abstract
Microcosm and mesocosm scale experiments were carried out to investigate the effects of vegetation and substrates on the performance of engineered wetland systems (EWSs) meant to treat mixtures of volatile organic compounds (cVOCs). The experiments were conducted with a view to optimizing contributions of these wetland components. Phragmites communis and Typha latifolia, the commonest wetland plant species, were compared in mesocosm scale EWSs. Eight common wetland plant species were compared using microcosm experiments based on the potential of their rootmatter to enhance treatment of cVOC mixtures. Twelve common wetland plants were similarly compared but on the basis of their aboveground (AGB) biomass contribution. With respect to substrates, a BionSoil/peat/sand mixture was assessed for its ability to support dechlorination of cVOC mixtures. In addition, a mixture of compost materials and sand (row crop compost (RCC)/soil builder compost (SBC)/sand) was evaluated by comparing it to the BionSoil/peat/sand mixture. This study also investigated the effect of salinity on the treatment of cVOC mixtures in EWSs and effects of cVOC initial concentrations and loading rates on EWS performance. Under normal operating conditions, after being inoculated with a dehalorespiring microbial culture, Phragmites- and Typha-planted EWS units performed comparably, removing completely 1,1,2,2-TeCA and TCE and their daughter products within mainly 18 cm of their bed depths. Before the inoculation, incomplete dechlorination and breakthrough occurred. After a long period of exposure to high concentration cVOCs, Phragmites plants weakened and died while Typha plants flourished. Microcosm experiments based on both rootmatter and AGB indicated that different species of wetland plants can differ in their influence on dechlorination of cVOCs. Based on microcosm and mesocosm experiments, the compost/sand mixture performed better than the BionSoil/peat/sand mixture, demonstrating that the former is a better substrate for EWSs. Salinity was found to have a negative effect on treatment of cVOCs. Nonetheless, the salinity problem is manageable through proper design. Pollutant initial concentration and loading rates were found to influence the performance of EWSs. Increasing loading rates and initial concentrations resulted in a decrease in dechlorination rates. As such, loading rates and initial concentrations are important design considerations.
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