A range of systems for processing mixed waste have been examined in this study. These vary from composting processes (which are net consumers of energy) to anaerobic digestion processes, which are net exporters of energy. Many of these are mature technologies with plants operating both in Australia and overseas. The applicability of certain technologies depends very much on a range of issues such as waste stream characteristics, distance to markets, the financial situation of local government and waste quantities.
When a mixed waste composting process is geared towards producing a saleable compost, it becomes more complicated and expensive to operate, and the amount of residual material increases, as contaminants are removed from the incoming waste stream or screened from the raw compost to meet higher standards. Mixed waste treatment processes therefore carry a greater risk as far as acceptance of the resulting compost than composting processes that are based on treating separated food and garden wastes.
Anaerobic digestion processes are more technically complex than composting processes, and therefore have a higher capital cost, but they produce a commodity (green energy) that is in high demand. Generally there is less residual material for landfill disposal than comparable composting processes.
Many emerging technologies such as pyrolysis, plasma arc, hydrolysis and irradiation for the processing of mixed waste are in still in the early development or in pilot plant stages overseas. Some of these technologies are still considered to be commercially risky at a large scale and their widespread adoption in Australia is therefore likely to be delayed until they are proven overseas by a number of years of continuous operation.
Emerging technologies for the processing of toxic or difficult materials such as e-waste, treated timber and tyres among others, include pyrolysis, chemical extraction, electrodialytic remediation and hydrometallurgy. Many of these technologies and their applications to various materials are still in their early stages of development. There are only relatively small quantities of these materials in Australia and few economies of scale compared to Europe, Asia or the Americas, which have much larger volumes to be processed.
However, smaller scale plants could be established in some capital cities if extreme measures, such as banning the landfilling of particular wastes were adopted. The main barrier to introduction of some of these technologies in Australia is that more convenient alternatives, such as landfilling, or exporting the wastes have existed for a long time. Mechanisms such as advanced disposal fees (deposits paid at the point of sale or import) would assist in attracting sufficient quantities of these items to reprocessing facilities..