Odor Control

Odor Control of Food Processing Operations by Air Cleaning
Technologies (Biofiltration)


1. INTRODUCTION

As environmental awareness increases among the general public so do environmental restrictions among regulators. Odors emitted from food processing plants are becoming more of a concern as food plants and residential areas grow closer in proximiy. The objectionable odors in the food industry are generally a result of the physical processing of foods in which biological or chemical reactions form volatile organic compounds (VOC). These reactions are often precipitated by such processes as heating, drying, or smoking of foods. Odor thresholds are subjective among neighbors of processing plants and for this reason standard methods have been approved for testing odors.

The accepted method for quantifying these odors is the use of an odor panel and a testing protocol approved by the American Society for Testing and Materials (ASTM):E-679. Thresholds are determined by selecting random participants and exposing them to different concentrations of odors. These results then determine thresholds for the general public.

Several technologies have been developed or improved recently to control odors from various industries. The best method for controlling odorous compounds is by eliminating the odor before it is formed thus eliminating the need for further processing of the air. This is not an easy task. Many food manufacturers cannot control all of the volatiles released during processing. Most odorous compounds emitted from food plants are not a public health concern but can be considered a public nuisance and, therefore, are subject to local governmental regulations.

Methods for controlling odor include but are not limited to: biofilters, bioscrubbers, activated sludge scrubbers, trickling filter scrubbers, and reactive chemicals. This report summarizes some of these technologies and focuses on the use of biofilters and their applications in the food industry. Technologies for controlling odorous compounds and VOCs are listed in
Table I and must meet the following criteria to be effective in the food processing industry:

• stable and predictable performance in removal of odorous compounds from the contaminated air stream,
• easily adaptable for applications experiencing large variations of air-flow rates and odor control intensity,
• no or low generation of environmentally harmful chemical by-products,
• low generation of solid and/or liquid waste materials, and
• low equipment costs and low operational and maintenance requirement.


Table I — Comparison of Biofilters to Other Odor Control Methods
Operating Cost Material Cost Maintenance Cost Pollution Risk Removes All Odors Removal Efficiency
Water Stripping High Low Low Yes No Low
Incineration High High High Yes Yes High
Carbon Sorption High High High No Yes High
Chemical Scrubbing Low High High Yes Yes High
Biofilters Low Low Low No Yes High
Zeager Bros. Inc., (1992)


Before an odor control/removal method can be selected, odor control objectives must be considered. The source of the odor must be determined. An evaluation of the concentration of
VOCs in the waste stream is also necessary. These can be measured using a flame ionization detector (FID) which measures the minimum, maximum, and averaged concentration of VOCs over an extended period of time. Gas chromatography and mass spectrophotometry can be used to identify each individual compound in the stream. The temperature, relative humidity, flow rate, and number of particulates in the gas stream are all variables which must be measured. Once these variables have been identified and measured, parameters can be set for the control of the VOCs and odorous compounds.