Composting CRD*

*Construction, Renovation & Demolition

Composting is not the first solution that springs to mind when one thinks about how to reduce CRD waste, but some materials, like wood and drywall, that are not suitable for reuse or recycling, can be composted.

Wood
Some wood products, like treated lumber and painted or stained boards, don't make good compost because of their potential to contaminate the finished product. However, wood that is too short for re-use, pallets, and trees can all be composted. Large pieces of wood and trees decompose very slowly (witness how many years it takes a downed tree in a forest to break down completely). To effectively compost wood, it needs to be chipped.

Large scale wood chippers have magnets to remove nails and other metal pieces. Once it is chipped, wood is useful in a compost system. It provides a source of carbon and creates air space. In the past two years, Saskatoon has had great results creating compost piles by adding wood chips to the yard materials dropped off at its composting depots.

Drywall
Gyproc is difficult to recycle in places that are not close to drywall manufacturing facilities. Parts of it can be composted. Companies like Bio-Cycle in Alberta process drywall off-cuts to create a soil amendment. They grind and sift the drywall pieces. The paper facing is added to their compost system. The gypsum powder is used to add calcium and sulfur to soil for areas that are deficient in those minerals.

It is easy to see that composting can turn building materials that are no longer useful into a rich soil amendment. But the process requires that other compostable materials are available at the same time to complete the process. In order to get clean compost, the construction material also has to be clean - no mixed materials, no paint etc. This means that each step in the process has to be carefully monitored to avoid contamination, but the results are well worth it.

At the moment, facilities for composting CRD waste in Saskatchewan are limited, but we do have some promising options. Northstar Innovative Developments recycles gypsum in Saskatoon, but they are not taking construction gypsum yet. They are still processing stockpiled gypsum from the closed Domtar plant. Once they have processed and sold their materials they will look at collecting new gypsum for recycling. They are currently selling the gypsum as a soil amendment and the paper is being taken by a local landscaping contractor to be composted.

Titan Clean Energy has a commercial biorefinery near Craik. They use biomass feed stocks, such as waste wood, in their process. The biomass is used to generate heat and electricity, as well as fertilizer products and more. Their facility handles creosote-treated lumber because of the slow pyrolisis process they employ. They haven added gypsum recycling to their process.

Plywood

Chipped plywood and similar products can be used as part of a compost mix, as long as it has not been painted or stained.

The main reason that questions arise about composting engineered wood products is that they contain formaldehyde-based glues. Laboratory tests and field experience indicate that the formaldehyde is broken down by the composting process and gaseous emissions are not a problem. Urea-formaldehyde and phenol-formaldehyde are the two glues in common use. The urea-containing formula is a source of nitrogen (rare in woody products), but tests indicate that it is not readily available at the beginning of the compost process.