Put a lid on it: Keep moisture out

In this second installment of the “Put a lid on it” mini-series, we continue to explore the initial findings of a litter, moisture and time-and-motion audit conducted in Durham Region in the fall of 2020.

Part I focussed on litter, including the causes, composition and lids as a potential solution. In addition to controlling litter, the crumb-rubber lid may have the added benefit of keeping moisture out of the blue box materials. What follows are the initial findings with regards to moisture.

Rain and snow cause sorting issues at MRF and degrade quality

Snow, ice, and soggy blue box materials can cause problems at the sorting facility, and ultimately impact the quantity and quality of the materials. At the MRF, snow and ice can make it difficult for both mechanical and human sorters to effectively separate different materials. This results in either recyclables ending up in the residue, or more residue ending up in the materials to be marketed.

If fibre is exposed to ice or snow, either at the curb, during transport, or in the inbound fibre, this can impact the quality of the material shipped to the end markets. Fibre mills do not want to pay for the unwanted moisture soaked into the loads. Moisture can also be an issue for aluminum buyers, as aluminum will stain under certain conditions, requiring additional surface finishing or fabrication during the recycling process.

Chunks of frozen materials and snow cannot be sorted at the MRF and end up in residue increasing contamination rates and ultimately processing costs.

George South, District Manager, Northern Ontario – Waste Connections Canada

Moisture adds weight, increases processing costs

Some municipal collection contracts and most processing facilities charge a cost per tonne for picking-up materials either curbside or depot and/or processing them. With open blue boxes, carts, or bins, exposure of recycling materials to the elements can add moisture, which in turn adds unnecessary weight, upwards of 22%. This added weight, in contracts with costing by heaviness, can have an obvious impact on overall program costs.

Moisture audit measures impact of lid

In the moisture audit conducted, AET consulting took samples of open top and lidded blue box materials, from both fibre and container streams. The materials were weighed (wet weight), spread on tarps and left to dry for seven days, then weighed again (dry weight). Moisture content percentage was calculated using the equation (wet weightdry weight) / dry weight x 100.

Auditors collected 193 samples of “open boxed” materials (100 fibres and 93 containers) and 55 samples of “lidded” materials (43 fibres and 12 containers). The hypothesis was that if materials were kept dry at the curb with the use of a lid, then the moisture content percentage change would be lower when compared to the open box. As shown in this graph, the moisture audit showed that the difference between the moisture change for lidded fibre materials versus open box was 8.74%. Containers generally maintained their moisture whether they were lidded or in an open box. More samples of lidded recycling will be collected in Spring 2021 for stronger statistical analysis.

Keeping in mind that moisture levels can vary a lot throughout the year, and assuming a processing cost of around $100 a tonne, a municipality that collects 30,000 tonnes of fibre annually, could see a potential savings of $26,200 in processing costs with only a 10% participation rate on the lids. Although this is a very basic calculation, it illustrates the potential for the lids to have a positive impact on system costs.