The George Washington University
Engineering Management & Systems Engineering Department (EMSE)
Environmental & Energy Management Program (E&EM)
Fall 2000 (Volume 1, Number 3)

Orellana Defends Dissertation on Effects of Substrates on Anaerobic Biodegradation

On May 21, 2000, Rosa Isabel Orellana defended her doctoral dissertation to an inter-departmental examining committee.  The overall objective of Rosa’s research was to investigate the toxicity and the degree of inhibition of benzene and toluene under anaerobic (methanogenesis) conditions, using different substrates and temperature conditions.  The abstract of Rosa’s dissertation appears below.
 
Rosa Orellana defends her doctoral work during her final oral examination

Rosa Orellana is an Environmental Specialist with the Environment Division of the International Finance Corporation, World Bank, in Washington, D.C., where she has worked since 1996.  In her current capacity, she provides advice and technical support on environmental issues within IFC’s portfolio, with a current focus on the Latin America region.  Rosa also has worked extensively on projects in Africa, including the privatization of telecommunication networks in Kenya and Tanzania, as well as several Africa Enterprise Fund (AEF) projects.  Her responsibilities include review of new and existing projects concerning potential environmental issues.  Rosa also explains applicable World Bank environmental guidelines and policies to project sponsors and meets with host country governments to review local environmental standards to ensure compliance with World Bank environmental guidelines and policies. 
 
Faculty members from throughout the School of Engineering and Applied Science participated on Rosa's doctoral examining committee

Prior to working at the World Bank, Rosa was an Environmental Consultant with the United States Committee for the United Nations Environmental Program in Washington, D.C.  Prior to that, she was a Chemical Engineer with Clough, Harbour & Associates in Albany, NY, from 1992 to 1993.

Rosa holds a Bachelor of Science degree in Chemical Engineering from the State University of New York, Buffalo, N.Y.  She received her Master of Science degree in Environmental and Water Resources Engineering from GW in 1994, and graduated again from GW in May 2000 with a Doctor of Science degree in Environmental Engineering.  Hailing from El Salvador, Rosa is fluent in English and Spanish, and has a working knowledge of Portuguese and  Italian.  She is a member of the American Institute of Chemical Engineers, the American Chemical Society, and the American Society of Civil Engineers.


 

The abstract of Rosa’s doctoral research work follows:

EFFECTS OF VARIOUS SUBSTRATES ON ANAEROBIC BIODEGRADATION OF BENZENE AND TOLUENE
By
Rosa Isabel Orellana
  A considerable amount of petroleum is released into soil, ground water and the surface water from leakage of underground tanks and pipelines, accidental spills and various industrial activities.  A significant part of petroleum consists of BTX aromatics (benzene, toluene, and xylene), which are characterized as potential threats to the environment because of their toxicity and resistance to biotransformation under anaerobic conditions.

The overall objective of this research was to investigate the toxicity and the degree of inhibition of benzene and toluene under anaerobic (methanogenesis) conditions, using different substrates and temperature conditions.

The toxicity of benzene and toluene in anaerobic processes was studied in batch cultures with propionic acid, or methanol, or glucose as primary source of substrate.  Under test conditions, the toxicity of benzene and toluene to anaerobic degradation was dependent on:  concentration of benzene and toluene, the compounds present in the wastewater and period of acclimation.

Preliminary studies involved the acclimation of three source reactors to the substrates under appropriate environmental conditions maintaining a pH level between 7.0 to 7.6, and at temperatures of 35±2ºC and 25±2ºC.  Detailed studies involved determination of the toxic effect of toluene and benzene in mixed methanogenic cultures with the three different types of substrates.  The batch experiments were performed in duplicates.  The toxicant concentrations used were 10, 50, 100, 500, and 1000 mg/l.  During the batch experiments the specific methanogenic activity (SMA), kinetic activity, the relative anaerobic gasification and inhibition analysis were performed.  The semi-batch experiments were conducted at 35ºC only and at 500 and 1000 mg/l.  The semi-batch experiments determined the time necessary to reach the threshold concentration dose. 

The Specific Methanogenic Activity (SMA) test indicated that, as the concentration of toxicant was increased the potential of the bacteria to biotransform the toxicant decreased.  In addition, it was observed that the SMA values at 35ºC were higher than those at 25ºC.  The 50% inhibition concentration was between 500 and 1000 mg/l for both toxicants with all three substrates.  The toxicity-kinetics model was based on a weighted non-linear least squares analysis of the integrated Monod equation.  This model indicated that uncompetitive inhibition occurred throughout the experiments.  Uncompetitive inhibitors reduce the maximum specific rate of growth (k constant) and cannot be reversed by increasing the substrate concentration.

A computer model was prepared to describe the recovery behavior in this study.  This model was specified to describe the recovery pattern as a function of toxicant type, concentration and time.  The recovery pattern for both toxicants and the three substrates can be generally explained as reversible inhibition.  The recovery was not completely to the baseline gas production, but overall presented a recovery between 60 to 80% of the gas production.


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Jonathan P. Deason, Ph.D., Lead Professor