Methane is generated from solid waste and wastewater through anaerobic decomposition. Together, solid waste and wastewater disposal and treatment represent about 20 per cent of human-induced methane emissions. Emissions are expected to grow in the future, with the largest increases coming from developing countries.

Methane emissions can be reduced in many ways, including reducing waste generation (source reduction), diverting waste away from disposal sites (i.e., through composting, recycling, or incineration), recovering methane generated from the waste, or ensuring that waste does not decompose in an anaerobic environment. In general, any technique or technology that reduces methane generation or converts methane into carbon dioxide through combustion will reduce greenhouse gases (GHGs). The most effective mitigation approaches are those that either reduce overall methane generation (because methane collection efficiencies rarely approach 100%) or ensure that the combusted methane is substituted for fossil-based energy.

Extensive technology transfer aimed at improving waste management is underway both within and between countries, although most activities have been, and will likely continue to be, domestic in nature. In many regions, large investments are still required to provide adequate waste management services. In the past, the climate-related impacts of waste management choices were not routinely considered. Mitigation technologies can be readily deployed in this sector, however, and provide benefits beyond the reduction of GHG emissions, such as reduced landfill space requirements or additional energy generation through methane recovery.

Technology transfer in the waste management sector occurs predominately along government driven pathways, with several levels of government (from the national to the municipal level), participating. Key government priorities are establishing appropriate policy/regulatory frameworks, supporting the expansion of private sector participation, participating in technical assistance and capacity building activities, particularly with community groups, and in some cases providing incentives to catalyze desirable actions. This is discussed in more detail in Section 5.2.

Historically, the private sector (including both domestic and multinational companies, as well as more informal local enterprises) and community-based organisations have been somewhat limited participants in government-driven technology transfer. The private sector has an increasingly important role, however, because meeting future waste management needs depends on expanded private investment. Private sector driven pathways are already used routinely for some types of investments (such as methane recovery at landfills), and efforts are underway to expand private sector participation across the full range of waste management services and technologies. The involvement of community organisations is also increasing as the link between community support and project sustainability has become clear. Soliciting local input and providing local training are two ways of ensuring sustainability. In many areas, locally developed and implemented projects are also being used to quickly address serious local concerns.

This review of the waste management sector reveals several key findings. This sector can contribute to greenhouse gas mitigation in ways that are economically viable and meet many social priorities. Already, extensive technology transfer is underway, and it will continue due to the continuing need to provide and improve waste management services for the world's population. In the past, the government driven pathway has dominated this sector, and it will likely dominate in the future as well. However, additional levels of government are becoming involved, as national government agencies devolve responsibilities for waste management to regional and municipal agencies. Private sector and community driven pathways are also becoming more important in this sector. Regardless of the pathway, it is important that projects emphasise the deployment of locally appropriate technologies, and minimise the development of conventional large, integrated waste management systems (with their attendant financial, institutional and technical requirements) in situations where lower cost, simpler alternative waste management technologies can be used.

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