Odour control in composting is possible with award-winning biofilter

By Paul Yaremko
Big 'O' Inc.

A 56,000 square foot composting and recycling facility, now owned and operated by Three Counties Recycling and Composting Inc., was constructed in 1994 on the edge of Aylmer, Ontario. The most innovative feature of this facility is its newly constructed biofilter to eliminate all odours emanating from the operation. This biofilter is believed to be the largest in Canada.

The Aylmer facility is one of only a handful of operations licensed by the Ministry of Environment and Energy (MOEE) to compost municipal solid waste (MSW), more commonly known as curbside garbage. The license allows them to accept MSW from across Ontario and run up to 24 hours a day, six days a week. Not only are they composting the MSW from the Town of Aylmer, but also receive curbside garbage collected in the City of Strathroy, Town of Tillsonburg and Malahide Township.

750 mm corrugated HDPE biolfilter header main and perforated 200 mm laterals installation.

At present the materials recycling facility (MRF) is processing about 50 tonnes of MSW a day. The MSW is delivered to the MRF building and processing begins. The first step is to separate the recyclable and non-compostable materials. This is done through the use of a conveyor belt which has a magnet to pick out as much metal as possible. Plastic recyclable materials, metals not picked up by the magnet and any other non-compostable materials are then hand-picked off the conveyor belt. About 60% of the MSW finally makes it into the composting building. The remaining 40% of the MSW consists of about half recyclable materials and half residuals which are sent to a landfill. About 80% of the MSW is being diverted from local landfills.

The remaining compostable materials are transferred into the connecting composting building. The composting operation is performed in batches which are kept separate by concrete retaining walls; this allows for staggered stages of the process. Under normal operating conditions, the composting process is completed after 21 days.

Underneath the composting building is a series of corrugated High Density Polyethylene Pipe (HDPE) sewer pipes used to control the temperature, moisture content and oxygen levels of the compost heaps. A 900mm diameter corrugated HDPE header pipe is used to supply air to 250mm perforated laterals under the piles. Corrugated HDPE pipes were chosen due to their resistance to the highly corrosive gases and water vapours created by the composting process. The pipe and custom manufactured fittings were supplied by Big 'O' Inc.

Composting operations were performing well until some complaints started coming in from the community. There were concerns about odours wafting from the operation into town. The facility was looking at a possible legislated shutdown due to a contravention of Regulation 347 of the Environmental Protection Act. The composting was spoiling the quality of life of neighbours due to the odours. Something had to be done.

In a first attempt to control the odours, masking agents and essential oils were tried but did not work effectively. Time was running out when the biofilter system was given serious consideration. Marsun Lipsit, P.Ag., an agrologist with the 3R$ Company in London, Ontario, was contracted to design/build the biofilter system to eliminate the odour problem as well as hazardous fumes created from the recycling and composting operations. This particular biofilter system has since been recognized with an industry award from the Corrugated Polyethylene Pipe Association (CPPA) for the most innovative use of corrugated HDPE pipe in North America for 1996.

The system uses no chemicals and is an all natural process. Biofilters are living ecosystems which need the right moisture content, oxygen level, temperature, and food. One unique green feature of this biofilter's design, is its ability to collect, store and reuse rain water which falls onto it. The rainwater is stored in a cistern and is used to supplement the moisture content of the biofilter media. This feature not only eliminates runoff from the site but reduces the demand for municipal water.

"At its most basic, the biofilter system uses stainless steel fans to draw fresh air into and fouled air out of the composting and recycling facilities through corrugated HDPE pipes," Lipsit explained. "Then the fouled air is pumped through a 50-foot-wide by 400-foot-long area of buried corrugated HDPE drainage pipes, where it filters through layers of stone and organic material and becomes oxygenated and naturally sweet smelling before it is released into the atmosphere".

This article has been abridged from May 1997 issue.