A Study commissioned by Zero Waste SA and the Local Government Research and Development Scheme has found the average percentage of rejected materials in South Australian loads did not increase significantly as the compaction rates of kerbside collection increased. It recommends a standard compaction setting of 200kg per cubic metre, with a ceiling of 225kg/cu.m.
A similar NSW study in year 2004 by a Prince Consulting Recommended compaction standards be within 120-140kg/cu.m, which would generate losses of 26.5%. And for every 10kg/cu.m above the 120kg/cu.m benchmark, the proportion of broken glass would increase by 1.9%.
The difference is because the container deposit scheme in SA changes the composition of dry recyclables presented at the kerbside.
Zero Waste SA project manager Said the compaction rate was an important variable for Councils to consider. It influenced the load density (payload) and the time the collection vehicle spent on the road, which has direct operational cost implications.
The load density can also directly affect the quality of the collected recyclables. Over-compaction can lead to difficulties at the MRF, including separating materials into commodity streams and in the glass breakage, which can in turn become embedded in paper and cardboard.
Glass was the major reason for the differences between SA and NSW. The container deposit scheme means glass containers account for 12-19% of the recycling stream in SA, but as much as 26% in other states. Less glass reduces the potential for bottle breakage during collection and transit, and significantly reduces levels of contamination.
The mix is also different. Lightweight beverage glass is part of the deposit system in SA, so only small quantities are found in Kerbside recycling bins. The glass containers that do present tend to be heavier, such as wine and champagne bottles, which are excluded from the deposit scheme, and condiment, sauce and coffee containers.
In others states the beer stubby is the major glass item found in recycling bins.. Its light weight means it rarely gets all the way through the collection and processing cycle intact.
It has interesting implications for a national container depsit scheme as the NSW study found the higher potential load density without beer bottles in the mix was able to facilitate a 10% - 12% reduction in collection costs per household.