Grantee Research Project Results
1998 Progress Report: VOC Emissions from Sewers Process Drains and Drop Structures
EPA Grant Number: R823335Title: VOC Emissions from Sewers Process Drains and Drop Structures
Investigators: Corsi, Richard L.
Institution: The University of Texas at Austin
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1995 through September 1, 1998
Project Period Covered by this Report: October 1, 1997 through September 1, 1998
Project Amount: $271,896
RFA: Exploratory Research - Engineering (1995) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Safer Chemicals , Land and Waste Management
Objective:
The primary goal of this study is to develop a significantly improved understanding of volatile organic compound (VOC) and hazardous air pollutant (HAP) emissions from municipal and industrial sewers. The study is divided into two major phases. The first involves an analysis of emissions of volatile HAPs from industrial process drains. The second involves HAP emissions from industrial and municipal drop structures. Specific objectives are listed below.Phase I. Process Drains
- Determine those mechanisms that cause HAP emissions from industrial process drains, and the sensitivity of those mechanisms to environmental factors and drain design/operating conditions.
- Estimate HAP stripping efficiencies for drains under a wide range of HAP physicochemical properties, environmental conditions, and drain design/operating conditions.
- Develop a state-of-the-art model that will allow estimates of HAP stripping efficiencies at industrial process drains.
Phase II. Drop Structures
- Determine HAP stripping efficiencies over a wide range of HAP physicochemical properties and drop operating conditions.
- Determine the importance of air entrainment and gas-phase resistance to mass transfer at/below drop structures.
- Use the results of (1) and (2) to develop a state-of-the art model for estimating HAP stripping efficiencies at drop structures.
Progress Summary:
Updated AbstractAs a result of the Clean Air Act of 1990, several industries have come under increased regulatory scrutiny as sources of hazardous air pollutant (HAP) emissions to the ambient atmosphere. For example, one source of fugitive emissions that has recently received significant attention is on- site industrial sewers, including process drains, conveyance channel, and drop structures associated with junction boxes and wet wells. Publicly-owned treatment works (POTWs) have also received attention as sources of HAP emissions, with a focus on emissions from treatment systems due to a general lack of information related to emissions from public sewers. An understanding of, and an ability to accurately estimate, the extent and nature of gas-liquid mass transfer in municipal and on-site industrial sewers is important for (1) identifying the need for source-specific National Emission Standards for Hazardous Air Pollutants (NESHAPs), (2) providing the USEPA with scientific criteria for development of NESHAPs, (3) providing municipalities, industry, and regulators with the ability to routinely and accurately estimate HAP emissions from sewers, and (4) providing municipalities and industry with tools for determining the feasibility of low-cost methods for reducing HAP emissions, e.g., through minor process modifications. This study address these needs through the use of three novel pilot systems, one used to simulate industrial process drains and the other two used to simulate small and large drop structures. In each case, a cocktail of volatile tracers with varying chemical properties is introduced into the experimental system. The use of liquid and gas-phase sampling allows for mass closure analyses and the determination of tracer stripping efficiencies. The latter allows for the determination of fundamental mass transfer parameters, including gas and liquid-phase mass transfer coefficients, over a wide range of system operating conditions. The resulting database will be novel, and used to develop semi-empirical models that link chemical properties, system operating conditions, and environmental conditions to chemical stripping efficiencies.
Accomplishments
Accomplishments during the first two years of research were described in previous progress reports. These accomplishments included (1) completion of a detailed literature review, (2) site visits to large petroleum and chemical refining facilities (to gain practical insight as to various drain and drop configurations), (3) meetings with regulatory agencies and industry to ensure that the proposed research meets the needs of both the regulated and regulatory communities, (4) decisions on chemical tracers (acetone, ethyl acetate, methyl ethyl ketone, toluene, ethylbenzene, cyclohexane) and experimental conditions for drain experiments, (5) development of an experimental drain system, (6) development of experimental and quality assurance protocols, (7) completion of analytical methods development and training, (8) completion of all drain experiments, (9) development of a preliminary drains model, (10) development of the first- version of a system-wide emissions model (naUTilus), (11) development of an experimental plan for drop experiments, (12) design of an experimental system that simulates emissions from small drop structures, and (13) initiation of the design of an experimental system to simulate emissions from large drop structures.
Specific accomplishments during the past year are listed below:
Completion of emissions model for process drains: Emissions model has been developed for both open and trapped (water-sealed) process drains. The models account for gas-liquid mass transfer within a water seal and in the channel below a process drain. Relationships have been developed for both liquid and gas-phase mass transfer coefficients within each zone. The model also accounts for chemical tripping due to air entrainment in water seals.
Revisions to naUTilus: The system-wide emissions model (naUTilus) has been updated based on the completion of emissions models for process drains. The final version of the model will include the results of past and ongoing experiments involving emissions from drop structures. Supplementary funding from The University of Texas Environmental Solutions Program (ESP) allowed for the linkage of naUTilus with ArcView GIS software. The integrated model allows for a significantly improved user interface and an ability to rapidly identify spatial variations in HAP emissions from entire wastewater collection systems.
Construction of experimental system to simulate HAP emissions from small drop structures: An experimental system was constructed at The University of Texas Center for Research in Water Resources. A 61 m long sewer reach with variable channel slope was connected at the effluent end to a 190 L collection (junction box). The system allows for either co-current or counter-current flow, and the junction box can be ventilated separately to maximize stripping potential. The system is meant to simulate drop structures at small junction boxes, e.g., low flow, or lateral connections to street sewers.
Completion of small drop structure experiments: A series of experiments was completed using five volatile tracers (acetone, ethyl acetate, toluene, ethylbenzene, and cyclohexane). Wastewater flow rates were varied from approximately 0.2 to 2 L/s. Drop heights were varied from approximately 0.2 to 0.3 m. In general, co-current experiments led to very low to negligible stripping efficiencies from the drop structure. This was caused by a reduction of the concentration driving force along the sewer reach leading to the drop structure. Stripping efficiencies for counter-current flow varied from less than 1% for acetone to greater than 30% for cyclohexane. Results for toluene and ethylbenzene, two chemicals with very similar physicochemical properties, were nearly identical for every experiment. Stripping efficiencies for these two chemicals varied from 4% to 22% depending on system operating conditions. Lower liquid flow rates generally led to much higher chemical stripping efficiencies. This is believed to be due to an increase in the hydraulic residence time in the liquid pool below the drop structure, as liquid flow rate decreases, as well as a greater surface to volume ratio for the falling liquid film at lower flow rates.
Construction of large drop structure system: A large drop structure (allowing for drop heights of approximately 2.5 m and lower) has been constructed. It is constructed entirely of stainless- steel and glass (for viewing of the poll beneath the drop structure). The system allows for much greater fall heights, liquid flow rates, and underlying pool depths than the small-scale system described above.
Completion of several large drop structure experiments: Nearly all of the large drop structure experiments have been completed and data are now being analyzed. Specifically, degrees of mass closure, chemical stripping efficiencies and liquid and gas-phase mass transfer coefficients are being determined and reviewed for each experiment. Variations on stripping efficiencies and mass transfer coefficients as a function of system operating parameters are being studied.
Future Activities:
Future activities will include (1) complete integration of small and large-drop emissions and mass transfer data, (2) development of a state-of-the-art model for estimating volatile HAP emissions from drop structures, (3) incorporation of the results of 2 into naUTilus, (4) completion of a final report to the USEPA, and (5) completion of at least one additional journal manuscript related to gas-liquid mass transfer at drop structures.Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 14 publications | 6 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Corsi RL. HAP emissions from municipal sewers -- should facilities and regulators be looking upstream? Water Environment and Technology, June 1997;51-56. |
R823335 (1998) |
not available |
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Olson D, Rajagopalan S, Corsi RL. Ventilation of industrial process drains:Mechanisms and effects on VOC emissions. Journal of Environmental Engineering, ASCE 1997;123(9):939-947. |
R823335 (1998) R823335 (Final) |
Exit |
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Olson DA, Rajagopalan S, Corsi RL. Ventilation of sewers: the role of thermal gradients. Advances in Environmental Research 1997;1(3):312-322. |
R823335 (1998) |
not available |
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Olson DA, Varma S, Corsi RL. A new approach for estimating volatile organic compound emissions from sewers: methodology and associated errors. Water Environment Research 1998;70(3):276-282. |
R823335 (1998) R823335 (Final) |
Exit Exit |
Supplemental Keywords:
Scientific Discipline, Air, Water, POLLUTANTS/TOXICS, air toxics, Wastewater, Environmental Chemistry, Chemicals, Environmental Engineering, drop structures, hazardous air pollutants, mass transfer mechanisms, Clean Air Act, mechanistic behavior of HAP emissions, industrial sewers, process drainsRelevant Websites:
http://civil.ce.utexas.edu/prof/corsi/Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.