Phased approach to solving odour issues
can yield huge cost savings for plants

Scott Henderson at the control panel.

Undesirable odours pose a significant environmental issue for industrial facilities and are associated with an estimated 50% of complaints to environmental regulatory agencies such as the Ontario Ministry of Environment.

Widespread misunderstanding of how industrial odours should be handled often leads to great expense, and to orders or convictions under environmental legislation. It can result in civil lawsuits, not to mention a poor corporate reputation in the community. These results could be avoided or substantially alleviated by taking a phased approach to assessing, defining and solving individual odour issues as they occur. The aim is to ensure that the problem is clearly understood and solutions are developed to address the root cause of the emission.

Evaluation of odour issues

The first phase of this approach involves a qualitative evaluation of the odour issues and their sources and is conducted at the facility over a period of several days. The objective is to become familiar with the odour issue, evaluate potential factors contributing to off-site odours, and to identify a list of significant odour sources for subsequent sampling and modelling. Included in the first phase is a review of odour complaints records, stack emissions data and facility processes. All possible sources of odour from processes are identified and the surrounding area is surveyed to assess the relative odour impact from the plant.

Other steps include: identification of emission sources that warrant sampling and modelling; evaluation of building influences that may contribute to ineffective dispersion of stack emissions; and determination of appropriate process/production conditions for subsequent odour testing in cooperation with plant personnel.

Chemical constituent - odour sampling

The second phase involves chemical constituent and odour sampling. The sources identified in Phase 1 are sampled and analyzed to determine the odour emission rate and the emission rate of specific contaminants present in the discharge. The odour-testing program is based on acquiring samples from the most significant sources. Samples of stack gas are collected in Tedlar sample bags using a predilution procedure, which involves diluting the stack gas with purified nitrogen as the sample is collected.

An odour panel, which involves participants with average odour sensitivities, uses a dynamic dilution olfactometer to evaluate the odour samples. The panel is representative of the general population. The odour panel utilizes a ternary port system operated in a forced choice mode, with a descending series of known dilutions introduced simultaneously to all participants. When signalled, the panel members respond to each sample by indicating whether the odour is detectable. Panel responses are processed using regression analysis to determine the odour threshold value (OTV) of the sample. The OTV is the point at which, statistically, 50% of the panel could detect the odour (effective dilution to 50% response). An odour emission rate is the product of the measured OTV and the effluent flow rate.

Specific contaminants are identified for each emission source using available test data, material safety data sheets (MSDSs), formulation specifications, industrial hygiene reports and discussions with facility personnel. The sources may be sampled for these specific substances to determine the emission rate. Emission rates and concentrations are then compared to the odour testing results to determine whether specific components are contributing to the odorous emission.

Although it is not always possible to develop a correlation between odour and specific contaminants, a company improves its credibility by demonstrating clear knowledge of the components of the discharge during discussions with concerned citizens.

Emissions modelling

The third phase of the staged approach involves modelling of measured odour emissions. This can be done mathematically, using computer programs, or physically, using a scale model of the facility in a wind tunnel. Lehder has undertaken projects with both physical and mathematical modelling techniques. The approach taken depends greatly on where the receptors are located in relation to the facility.

Finding a solution

The fourth phase involves developing a solution. The information gathered during the first three phases is assessed in conjunction with a control technology review to develop odour abatement solutions.

Participants at the odour panel.

Case study

This strategic phased approach was applied to an odour evaluation for a manufacturing facility located in California. The plant had been identified in a number of odour emission complaints from employees of neighboring industrial and commercial facilities. There were two similar manufacturing lines at the plant, each with five unit operations (described as operations A, B, C, D, and E) and associated emissions.

Management of the facility believed that poor dispersion of emissions from Operation B might be the problem because that operation was specifically mentioned in the complaints. Lehder was asked to review the situation and comment on proposed changes to enhance the dispersion characteristics of the Operation B's stacks.

An initial survey indicated that the majority of complaints came from commercial/industrial neighbours to the north and east of the facility. Ambient odours attributable to the facility were present at levels likely to cause complaints and each unit operation had unique odour characteristics. The survey revealed that the discharge from Operation A was the major contributor to off-site odour. Odours from Operation B were detectable off-site but were not considered offensive.

In the second phase, odour testing was conducted for several discharges and process locations. During the subsequent Phase 3 impact assessment stage, odour emissions data was used for wind tunnel modelling of the facility.

Results of the overall odour evaluation led to the conclusion that Operation A stacks were the largest contributors to ground level odour. The rooftop penthouses located over this process also contributed. The compound or compounds which contributed to the odour were unknown. Additional conclusions were that the other odour sources present at the facility had significantly less impact on the community and that the impact of odour from Operation A could be reduced through improved stack design and increased height of discharge.

In the fourth phase of solution development, it was recommended that the facility identify the compound(s) giving rise to the odour generated by Operation A. If feasible, the facility should eliminate or reduce the emissions of the compound(s) through pollution prevention principles. It was recommended that the rain caps be removed from Operation A stacks to improve dispersion and improvements be made to internal ventilation to eliminate odorous exhaust from the penthouse louvers. Also recommended was the installation of taller stacks on Operation A to allow the effluent to exit the building envelope.

Subsequent investigations identified the compound that was the major contributor to odorous emissions from Operation A. The compound was generated by the decomposition of a raw material in the process. Based upon the findings of these studies, the client undertook a significant trial, reducing the amount of this raw material used in the process through material substitution. The purpose was to demonstrate that a reduction in raw material could reduce the odour emissions without adversely affecting the manufacturing process.

This trial was monitored through two further odour evaluations. The first was conducted after a 57% reduction in raw material and the second following the total elimination from the process.

Based on the results of the second odour evaluation, it was concluded that the elimination of the raw material reduced odorous emissions from Operation A by approximately 70% from those measured in the first trial. There remained a distinctive odour from Operation A and the specific compound(s) that contributed to it could not be determined without further investigation. The cost of any further investigation to define the source of odour had to be evaluated against the cost of implementing solutions that improve dispersion.

It was also concluded that the ground level impact of odour from Operation A could be reduced through increased height of discharge to 50 feet above the roof, or use of eductors to positively draw gases from Operation A and discharge from a height of about 20 feet above the roof.

A follow-up ambient odour evaluation was conducted the following year. The purpose was to provide a qualitative measure of the improvements implemented at the plant and to determine if further actions were required to continue to proactively address odour issues. From this evaluation, it was concluded that ambient odour levels were improved significantly from previous site evaluations. This improvement was attributable to raising the Operation A discharges to 50 feet above the roof and removing the rain caps.

Ambient odour attributable to Operation A was detectable off property during the survey. The current major contributor to this ambient odour was fugitive emissions from Operation A discharging through the louvers. The fugitive emissions were due in part to inefficient draw from the process through the vent stacks.

The California manufacturing facility also implemented several recommendations to reduce fugitive emissions with further significant improvements. After implementation, odours along the north side of the plant were insignificant. By using this phased approach, the facility gained a better understanding of its odour issue and was able to introduce a cost-effective long-term solution.