Performance of a prefabricated concrete tower composter

The study looked at the performance of a three-level composting tower, each level of which could take around 200 t of shredded mixed municipal solid waste. The composting material moved sequentially down through the three floors, taking 8–10 days to complete the cycle, targeting an Animal By-Products Regulations (ABPR) compliance regime of 70°C for 1 h. Using a 16 mm trommel screen, the yield of compost-like output (CLO) was typically 25–30% of the input by weight. The post-composting separation plant was found to be very effective in giving a range of other products for recycling. An energy usage estimate for the tower alone (not including shredding or post-compost separation) showed consumption between 25 and 31 kWh per tonne of input. Detailed temperature measurements using 40 dataloggers in a batch of 200 t of material showed that the towers were not achieving ABPR compliance standards. Modifications to the towers, which included recirculating warm air from the top of the composting mass and auxiliary heating, are now producing ABPR-compliant CLO.