Cost-benefit analysis of introducing technology to rapidly degrade municipal solid waste

Due to an increasing awareness of the true economic and environmental cost of conventional landfilling, recent interest has developed in Australia in technologies that accelerate the degradation of the organic fraction of mun icipal solid waste (MSW). The management of the organic waste stream, which typically makes up 60 to 70% of MSW in Australia, is central to reducing t he reliance on landfill space. One option is to digest the organic fraction prior to landfilling, or preserve landfill space by accelerating the decom position of the organic fraction within the landfill, This paper quantifies the benefits of digestion as a function of the degradation time, rd. The a nalysis considers both invessel and landfill-based bioreactor technologies and calculates net economic impact, expressed as $US t(-1) MSW, as the sum of enhanced and more rapid biogas retrieval, saved landfill space, reduced environmental disamenity and reduced postclosure costs, minus the capital a nd operating costs to implement the technology. The benefits, on a per tonn e basis, are shown to be insensitive to the size of the waste stream while costs diminish as the waste stream size increases. A conventional landfill with t(d) = 20 yr is used as a basis of comparison. At 1800 t day(-1), the maximum level of benefit is 13 $US t(-1) at t(d) = 2 months, diminishing mo notonically to zero at t(d) = 20 yr. The cost of achieving t(d) = 2 months is the cost of invessel digestion, estimated to be 99 SUS t(-1), resulting in an overall increase of 86 $US t(-1) in waste management costs. Similarly , degradation times of 2 < t(d) < 5 yr provide a benefit of 8 to II $US t(- 1) for a waste stream of 1800 t day(-1). This rate of degradation can be ac hieved with landfill-based bioreactor technology. The cost of additional in frastructure needed to implement accelerated degradation, such as pretreatm ent pads, internal leachate distribution networks and additional gas wells and generators, is estimated to be less than I $US t(-1). Bioreactor techno logy is therefore appealing, although their is uncertainty about the additi onal operating costs needed to Nn a landfill as a bioreactor. Additional op erations would mainly revolve around segmenting the waste mass to tightly c ontrol leachate distribution. The cost of these additional operations are u nlikely to exceed the operating cost of a modem conventional landfill, esti mated at 9 $US t(-1). Therefore, landfill bioreactor technology should be c ost effective.