Bad smells are beginning to get the attention they deserve from decision-makers and enforcement officers. They are often a key nuisance factor in the siting or operation of a solid waste or wastewater facility.

Readers of ES&E may have noticed a dramatic rise in the number of technical and specialised conferences on odour control (e.g. composting), in new odour control products, and in regulatory enforcement of odour complaints. In the USA the regulations that govern the discharge of VOCs to the atmosphere have recently been applied to landfill sites and to industrial and municipal wastewater treatment plants. Also worthy of note is the current Hamilton Air Quality Initiative (HAQI), an MOEE-led, multi-sector, voluntary enterprise designed to understand and improve air quality for the city as a whole.

For site and facility managers who face the prospect of lost management and production time, and possible closure, effective odour control is critical. The choices in odour control methods, products, and equipment available to environmental managers have changed dramatically in recent years, mostly for the better.

Go back in time to 1979 when the US National Research Council published a handbook entitled Odours from Stationary and Mobile Sources. It presented the following general methods of odour control:

1. Modify the process. Use less odorous materials, generate less residual wastes, process at more favorable temperatures.
2. Dilution in the atmosphere. Build a higher stack, locate a greater distance from people.
3. Dissolve odours in a liquid. Wet scrubbing in a mist or packed tower.
4. Oxidize odours with air. Includes high temperature oxidation in an incinerator.
5. Modify perception of the odour. Mask or counteract the unwanted odour.

The USNRC odour committee judged method #4 to be "the best opportunity for substantial and irreversible destruction".

Move forward to a 1993 list of odour control technologies produced by the Metro Toronto Works Department in a report to the Works Committee dated June 8, 1993. In this report we find three odour control methods that were not listed by NRC in 1979: Dry Scrubbing with Activated Carbon, a variation of method #3, Ozonation, a variation of method #4, and Biofiltration.

Biofiltration - a method driven by the increase in composting as a solid waste diversion program - is the use of organic media and may be referred to here as method #6.

Ecolo system similar to Three County's, with nozzles atomising airSolution® above a pile of mixed waste on the tipping floor.

Missing from the methods of odour control mentioned above is the use of essential oils to neutralise odours. The catalytic oxidation of odorous molecules with plant extracts is the "Good News" of our title.

The basic idea is straightforward. Atomised oils of certain plants brought into contact with odorous molecules accelerate the natural organic decay processes to produce odourless organic decay. Unfortunately, the theory of "catalytic oxidation" is not as straightforward. Nor is it widely documented in the literature (e.g. the fleeting reference on p. 185 of the 1994 volume edited by G. Martin and P. Laffort "Odours and Deodorization in the Environment.") As the only extended treatment in the literature, David Hill's recent paper "Exhaust Odour Neutralization," which was presented to ASHRAE's Toronto Seminar in November 1995, has quickly become the standard reference. Mr. Hill's paper also contains results of controlled tests of various products on various odorous gases.

The results of odour neutralisation are measurable. In addition to Mr. Hill's work, in-house scientists at several large industrial companies in various markets have analysed Ecolo's odour neutralization and conducted rigorous pre- and post-tests in the lab and in the field. Such tests have satisfied these companies on both effectiveness and health and safety.

Odours can be effectively and affordably neutralised out of doors, as well as indoors. Landfill site perimeter systems, gas cleaning cooling tower systems, and overhead systems at open air compost operations are examples.

For many applications - transfer stations, landfill sites, composts, heavy equipment, sewage treatment, and others - minor variations in generic or installed systems may be all that is required. Systems can be specified and installed in a matter of days or weeks.

One example is an innovative 1993 project in which Ecolo's UK distributor fitted a Caterpillar compactor with an airSolution® atomising system for controlling odours emanating from the working face of a landfill. When unfavourable winds want to blow the fresh waste odours toward adjacent residences, the operator toggles a switch in the cab to atomise airSolution® from nozzles on a bar on the roof of the Cat's cab. The Cat's own compressed air system powers the nozzles.

In 1995 Ecolo Toronto installed a similar system on a livestock transport. The driver activates the atomising nozzles when travelling through residential areas en route to the slaughterhouse.

A second example is at Three County Recycling and Composting Inc., of Aylmer in southwestern Ontario. Three County converts municipal solid waste and waste from food stores and food processors into agricultural compost, and recycles non-compostable fractions. It has a planned throughput of 300 tpd. Its Ecolo atomising system consists of a 200 litre drum with a pump and cycle timer which supplies airSolution® to over 100 spray nozzles in two buildings with a total of 58,000 sq. ft. The composting building has nozzles above the doors at both ends, with the remaining nozzles located about 30 ft. above the floor in the main tipping and sorting building.