Towards a better environment - the municipal organic waste management in Brisbane: Environmental life cycle and cost perspective

Abstract

Different options for treating organic fraction of municipal solid waste were assessed. Four composting scenarios were designed based on different scales (i.e. home vs centralised) and technologies (i.e. windrow vs in-vessel composting) in Brisbane. The environmental and economic performance were analysed and compared to the existing practice: landfilling, using life cycle assessment and life cycle costing analysis with the consideration of the costs of externalities and potential avoided costs. The treatment of 1 Mg of home organic waste was selected as one Functional Unit. The system boundaries start from waste collection to the use of the final product (i.e. compost). The compost was assumed to be applied on private gardens and tropical horticultural crops in home and centralised composting scenarios, respectively. Shared home composting bin in a small community (HC-II) presented the best overall performance from both environmental and economic perspectives, meanwhile, landfilling was found to be the worst option. The home composting scenarios require less energy which results in four times lower fossil depletion and human toxicity potential compared to centralised composting scenarios. However, the greenhouse gas (GHG) emissions released through organic waste degradation, due to potential partial anaerobic conditions, were identified as the major environmental impact factor, followed by the compost bin manufacturing. In both centralised composting scenarios, the energy consumption was found as the main environmental impact factor, which accounted for more than 45% of the total GHG emissions, followed by the waste collection and transportation process. Regarding the economic performance, the HC-II scenario has the lowest life cycle cost ($22.93/FU). Monte Carlo Analysis was carried out to test the effect of overall uncertainties. Our result showed that the compost application rate had the highest sensitivity in home composting scenarios because the unused compost would need to be collected and sent to the landfill. Consequently, extra transportation emissions and life cycle cost will incur, thus, the benefits from compost application will also be reduced. However, the overall uncertainties did not affect the ranking of the centralised (windrow) composting scenario, which remained the best environmental performer. Meanwhile, HC-II option had the better economic performance that marginally over-weighed the environmental performance of the centralised windrow composting; hence result in the best overall performer. However, in order to encourage residents to participate, enabling policies and incentives may be required to influence the behaviour of the independent households to share a composting bin.