Composting of Green Waste Shredded by a Crush/Cut Roller Versus a Low Speed Counter-Rotating Shear Shredder

Abstract

Green waste was shredded at a commercial composting site by a conventional commercial low speed counter-rotating shear type shredder and an alternative shredder, a crush/cut roller mounted on and powered by a tracked excavator. Material from both shredding systems showed similar dry weight and dry bulk density patterns across a broad particle size distribution range. The crush/cut roller produced significantly different (p < 0.05) quantities of material in the 10-25 mm and 75-100 mm particle size ranges, whilst dry bulk density values were significantly different in the 16-25 mm range only. Over a three month windrow composting period, dry weight percentage and dry bulk density values from both systems tended to increase toward the lower end of the particle size range and decrease toward the higher end of the particle size range and were, with one exception, not significantly different. These values were similar in magnitude to those for material from commercial green waste composting windrows. Temperature profiles were comparable in both systems and indicated the existence of thermophilic conditions within each windrow for over 50 days, whilst product stability, as indicated by specific oxygen uptake rates, was the same for both treatments. It was concluded that any differences in particle size distribution between the two shredding systems were not important in relation to the biological aspects of the composting process. Development of a simple compost maturity test based on particle size profiling is suggested. It is proposed that the alternative, crush/cut roller, approach to green waste shredding could potentially reduce the economic threshold for organic recycling and allow many smaller communities to benefit from this environmentally sound waste management practice.