Optimum compaction rate for kerbside recyclables (2012)

Executive Summary: Zero Waste SA (ZWSA) and the Local Government Authority South Australia (LGA SA) are seeking to determine the optimum compaction rate for the collection of kerbside recyclables in South Australia (SA). Recent changes to specified recyclables compaction rates have led to some concern over the rates of recoverable-materials loss. As this study will benefit the entire industry, a number of project stakeholders were involved. The study was jointly funded by ZWSA and the LGA through the Local Government Research and Development Scheme (LRG&DS) with in-kind support from Solo Resource Recovery, East Waste, Campbelltown City Council, City of Charles Sturt and Visy Recycling. The LGA SA has recently revised the maximum compaction setting standard, outlined in its model Waste and Recycling Collection Contract from a rate not exceeding 170kg/m3 in 2009 to 200kg/m3 in 2011. Materials recovery facility (MRF) operators are also specifying load densities in an attempt to receive product that is not over-compacted, as the speed and ease of processing a delivered load is directly related to the degree of load compaction. MRFs have indicated the ideal compaction rate is 180kg/m3, however 200kg/m3 is acceptable. The current specified compaction rates appear to have little statistical basis. It is therefore timely for ZWSA to provide guidance to councils, their contractors and MRF operators on the impact that load density has on the loss of recoverable kerbside recyclables. Compaction is one of a number of variables that can lead to issues with recovery. Others include the vehicle design, height of discharge of the bin, the speed of the lift cycle, the vehicle size, the depth and size of the paddle and the packing mechanism. The methodology for this project required that a collection vehicle from two different waste collection companies be used in two representative council areas. The kerbside recyclables were collected fortnightly, from the same households at five compaction settings. The only key variable that changed for this study was the compaction setting (0, 150, 175, 200 and 225kg/m3) on the collection vehicles. The number of households collected, collection time and load weight increased steadily with increasing compaction levels. A total of 4,387 households’ kerbside recycling was collected with a total weight of 49.2 tonnes. Each load collected during the study was processed through the same MRF. The conveyor belt was slowed to recover the maximum amount of material. Materials were manually pushed onto the in-feed belt, creating minimal mechanised intervention that could impact the final results.