Solid Waste & Recycling


Mixed Solid and Liquid Waste Composting

The Conporec composting facility in Tracy, Quebec (located 60km North-East of Montreal) has developed an innovative odor-free composting process for municipal solid and liquid waste. The automated pro...

The Conporec composting facility in Tracy, Quebec (located 60km North-East of Montreal) has developed an innovative odor-free composting process for municipal solid and liquid waste. The automated process utilizes a bioreactor (originally developed in Europe and further improved by the company) which processes regular sorted or non-sorted waste into a quality compost. The facility processes 26,000 tonnes per year of municipal and commercial solid waste, with maximum capacity of 35,000 tonnes. All operations are conducted in an enclosed negative-pressure building and the air control technique is coupled with a biofilter that eliminates all remaining odor.

In operation since 1993, the company processes mixed waste for the Regional District of Bas-Richelieu (population 50,000) which achieves a diversion rate of up to 75 per cent by weight. In 1996, the company was granted an award for Environmental Merit from the Quebec government and, because of its continued success, was also awarded the 1998 Environmental Phoenix Award.

The process

When the municipal waste arrives at the facility, it is unloaded into a large, fully-enclosed waste pit. Industrial or commercial liquids are unloaded into a tank and then pumped into the bioreactor. The waste is then lifted from the pit using a grapple and overhead crane and fed into the bioreactor. This feedstock is loaded into the bioreactor 12 hours per day, seven days per week.

Operations are managed from an air-conditioned, central control room which overlooks the waste pit and receiving area. Programmable controllers and automated video equipment enable just one operator to control the entire composting operation.

The bioreactor, a long continuously rotating device which quickly transforms organic material into raw compost, is key to the accelerated maturation process. The feedstock remains in the bioreactor for a minimum of three days. Because of the high temperature in the bioreactor, the result is a mixture of biodegraded organic matter and non-compostable residues free of harmful pathogenic bacteria. After leaving the bioreactor, the composted organic matter is separated and conveyed to the maturation building for further maturation and stabilization for approximately six to eight weeks. The residue is brought to a sorting area where recyclables are recovered and non-recyclables are compacted into containers for disposal.

Maturation and secondary refining

The compost is mechanically placed in windrows between concrete walls. The temperature and moisture content are controlled by forced aeration from below. The controlled addition of water and regular turning of the windrows maintains the homogeneity of the compost. After several weeks, the compost is conveyed to a secondary refining area to remove the remaining non-organic matter (and to ensure that the compost complies with regulations).

An odor-control system captures and conveys all air from inside the building to the maturation building and uses it to aerate the compost. The compost is kept in a constant aerobic state which eliminates the generation of odorous gas. The air recovered from the maturation building is then sent through the biofilter, which consists of numerous cells that normally work in parallel. The gases are slowly filtered through the biofilter, allowing the micro-organism to eliminate the volatile compounds and all malodorous gases.

Pre-sorting of the compost is not required, which reduces collection costs. The automated process requires minimal human resources. So, the process is economically advantageous where landfill tip fees are greater than $60 per tonne. This process has also been estimated to extend the life of a landfill by at least four to six times.

Claude Marmen is vice-president of business development of Conporec (Groupe Conporec Inc.) in Tracy, Quebec.

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