Putting the lid on odors and VOCs

  • Jul 01, 1999

How to track down odor-causing culprits

As a producer of bulk pharmaceuticals, Noramco Inc., Athens, Ga., wanted to minimize odor and volatile organic compound (VOC) emissions from its wastewater pre-treatment plant. Noramco installed structural-fabric covers on its neutralization and flow equalization basins as part of the solution.

Located east of downtown Athens, in a light industrial air emission attainment area, is the Noramco Inc. facility. Constructed in 1980, this facility produces bulk pharmaceuticals, food additives and medical devices, and also contains facility laboratories, administrative buildings, bulk chemical storage and a wastewater pre-treatment plant.

The wastewater pre-treatment plant is an activated sludge system permitted by the Athens-Clarke County Department of Utilities. The plant can hold 2.9 million gallons of process water with a 246,000-gallon-per-day maximum treatment capacity. Currently, the plant is pre-treating 100,000 gallons of process water daily.

Evaluating VOC emissions
Noramco's management, as well as its corporate parent Johnson & Johnson, is committed to reducing waste generation, water pollution, and odor and VOC emissions at the site. To maintain its environmentally proactive policy, Noramco began an evaluation of the site's VOC emissions in 1997.

The evaluation employed the U.S. Environmental Protection Agency's (EPA) WATER8, an analytical software model for estimating compound-specific air emissions from wastewater collection and treatment systems. WATER8's emission calculations are based on a number of factors, including organic loading rates and surface areas. Using the model, it was determined that one-third of the site's VOC emissions emanated from the wastewater pre-treatment plant. The model further indicated that if Noramco was to cover its 20-foot-by-40-foot neutralization basin and 70-foot-by-70-foot flow equalization basin, significant reductions in VOC emissions could be achieved.

In addition, by covering these wastewater pre-treatment basins, Noramco could be assured that its site would remain classified as a synthetic minor source under Title V of the Clean Air Act. This classification is given to air emission sources that would otherwise qualify for major source status, but have chosen to obtain a minor construction permit to limit their air emissions to below established threshold levels. Further, by agreeing to limit emissions to below these threshold levels, the site can delay or avoid more comprehensive major source emission control requirements. Indeed, by covering these basins, Noramco could delay the installation of a regenerative thermal oxidation system - a technology to control hazardous air pollutants - as well as reduce potential operator exposures to the VOC emissions.

Preventing odor emissions
Noramco was also experiencing a hydrogen sulfide odor emission problem from the flow equalization basin. This odor was caused by the basin becoming anaerobic at night, due to the cessation of photosynthesis. It was determined that covering the flow equalization basin and holding the basin's pH between 8 and 9 to keep the hydrogen sulfide in an aqueous form would resolve the odor emission issue.

Cover selection criteria
Thus, in early 1998, Noramco management began researching various cover options, including fiberglass, aluminum and structural-fabric cover systems. Noramco's selection criteria required that the two wastewater pre-treatment basin covers provide:

  • Total and long-term containment of odor and VOC emissions;
  • Enhanced resistance to 1 to 10 percent concentrations of various pharmaceutical wastewater chemicals, including acetone, methyl ethyl ketone (MEK), sulfuric acid, toluene and xylene;
  • Enhanced tank access to facilitate periodic tank maintenance;
  • "Clear-span" design - no intermediate cover supports on the 70-foot-by-70-foot flow equalization basin; and
  • Turnkey responsibility - no need to use Noramco personnel.

After a thorough evaluation of all cover options, a contract for Vapor Guard® structural-fabric covers was awarded to ILC Dover Inc. Key to this selection was Vapor Guard's performance on each of the selection criteria:

  • For total and long-term containment of VOC emissions, it was determined that Vapor Guard's heat-sealed seams were superior to aluminum or fiberglass' gasketed panels.
  • For maximum chemical resistance, the structural fabric incorporated DuPont's TedlarTM film. The hot-dip galvanized structural-steel support system was placed above the structural fabric, thereby totally isolating the support structure from wastewater contact.
  • For enhanced tank access, the flow equalization basin was designed with two 13-foot-by-20-foot removable modular sections, while the neutralization basin was designed with two 11-foot-by-20-foot and two 8-foot-by-20-foot removable modular sections.
  • For clear-span design, the covers spanned both tanks without the use of intermediate supports or elevated trusses.
  • For turnkey responsibility, ILC Dover assumed full contract responsibility for the design, fabrication and installation of the covers.

Installation of the covers was completed in September 1998. The covers have reduced Noramco's site-wide VOC emissions by one-third - approximately 22,000 pounds per year - and have delayed the installation of a regenerative thermal oxidation system that would previously have been required to maintain the facility's synthetic minor status. Furthermore, the flow equalization basin cover and pH management have eliminated odor emission complaints.

How to track down odor-causing culprits
By Angela Neville, JD, REM

Any number of sources at industrial and wastewater treatment plants can create olfactory nightmares for nearby residents. To combat this problem, environmental professionals are increasingly using atmospheric dispersion modeling to determine the impact of odor sources on off-site receptors.

Scientists first developed dispersion modeling to measure the emissions of hazardous air pollutants from industrial facilities and to gauge the facilities' compliance with air quality regulations. Then odor dispersion models were developed and adapted from these air quality dispersion models to deal with the growing public nuisance of noxious odors.

Modeling can focus on the need for odor control at a facility with multiple odor sources. In order to assess the odor impacts on surrounding areas, models use emission rate data from each odor source, which is the rate at which odors are emitted to the atmosphere from various sources. The mass emission rate of a source's odor can be calculated as the product of the volumetric flowrate from the source, multiplied by the detection threshold concentration.

The odor detection threshold for a given source is expressed as an odor unit (OU). This measurement is a dimensionless number that represents the number of cubic feet that 1 cubic meter (m3) of sample will occupy when diluted to the odor detection threshold. To calculate the mass emission rates, the detection threshold odor concentration (D/T) is expressed as odor units (OU)/(m3).

The person conducting the air quality study can model the facility's sources individually, or as a composite. Modeling individual sources enables the assessment of a single source's impact, but modeling sources as a composite is more representative of real life field conditions. In either case, the model is run to determine baseline conditions. Modifications can then be made to the modeled emission sources to simulate proposed control measures, such as the installation of structural-fabric cover systems.

To show the effect on surrounding receptors, each model can be depicted graphically. A cost-benefit analysis can then be used to assess which sources should be selected for control measures in order to most effectively reduce off-site impacts for the least cost.

For more information on air quality modeling, see the U.S. Environmental Protection Agency's (EPA) Web site: www.epa.gov/scram001/index.htm. It contains information on computerized models that support the regulatory programs required by the Clean Air Act. To learn more about WATER8, EPA's program for modeling air emissions from wastewater, check out www.epa.gov/ttnchie1/utils/readme8.txt.

This article originally appeared in the 07/01/1999 issue of Environmental Protection.