A variety of technologies and approaches are available to reduce the methane emissions associated with solid waste disposal and wastewater treatment. In the area of solid waste disposal, options include source reduction, methane recovery from disposal sites, and in some cases aerobic treatment of solid waste, through composting or other means. Similarly, methane emissions from wastewater treatment can be reduced through methane recovery or use of aerobic treatment facilities that do not generate methane. The available approaches are discussed in detail in several references (IPCC 1996a, WG II, Section 22.4.4.2; IPCC, 1996b, WG II, TP1; Thorneloe et al., 1993). The principal approaches are described briefly below and summarised in Table 13.1.

There are some important points to note:

• Any technique, such as flaring, which converts methane (which has a global warming potential of 21) to carbon dioxide (which has a global warming potential of 1) is climate friendly;
• All technologies mentioned are considered environmentally sound technologies (ESTs), according to the Glossary definition;
• If the methane conversion also involves energy substitution then it is even more climate friendly;
• The complete life-cycle of waste products needs to be considered. Thus, at first sight, the use of household anaerobic compost systems for organic waste would not appear to be a mitigation technology. Such compost bins generate methane, although most compost bins maintain aerobic conditions through frequent turning. However, if the compost from these bins is used instead of inorganic fertilisers or is used to fertilise growing plants which act as a carbon sink, then it can be argued that the technology is a mitigation technology, because it either replaces a source of carbon emission (manufacture of inorganic fertiliser), or enhances a carbon sink. The alternative use of the household organic waste -- namely disposal to landfill -- would not do this, especially if the landfill lacks a methane recovery system.

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