**4. Waste to energy (WTE) technologies**

The increasing amount of mixed household waste has become a national problem in Thailand and elsewhere, the resolution of which may be to turn a crisis into an opportunity and reap benefits from garbage. The Thai government has instructed provincial authorities to find locations for constructing waste management facilities capable of using garbage to produce renewable energy. It is not only Thailand which lacks proper waste management systems and throughout the world peoples' attitudes to finding suitable sites to dump garbage have led to continuing conflicts and protests based on the "Not in my Backyard" (NIMBY) attitude. Therefore, it would be preferable to solve the problem by employing suitable waste management strategies as alternatives to disposal. The PM has declared that every province should build a WTE facility to convert waste to electricity which will support the country's efforts to reduce its dependence on natural gas and other fossil fuels. However, to-date, Thailand has just 3 WTE incinerators [19–21].

Nowadays, the use of WTE technologies is gaining momentum as a favorable waste management strategy. Unquestionably, WTE seems to be a viable option for diminishing the volume of waste as well as offering the additional benefit of producing alternative energy from waste recovery [21]. Already there has been increased recovery of recyclable materials from MSW rather than continued dependence on sanitary landfilling as the primary conventional method of solid waste disposal [22]. But the benefits of energy recovery from MSW are potentially more valuable, both as an alternative energy source and for the positive environmental implications, mainly relating to the saving of non-renewable energy derived from fossil fuels [23]. WTE or energy from waste refers to any waste treatment that transforms waste resources into electricity, steam, or heat energy. These include, for example, anaerobic digestion (hereafter AD), incineration, pyrolysis, gasification, plasma arc, and RDF. WTE technologies usually reduce the volume of original waste by as much as 90%, depending on the waste composition and the type of energy derived. A waste management hierarchy generally follows the pattern of waste avoidance or reduction, reuse, recycling, recovery treatment, followed by disposal. An integrated approach to WTE that practices waste segregation and pre-treatment of waste does not by-pass the waste hierarchy but precedes or replaces the disposal step which is a more sensible approach to WTE recovery than simply burning or converting raw unsorted waste. Nonetheless, the choice of WTE technology is important and the conversion plant itself may incorporate waste pre-treatment units to facilitate this approach.

Thailand has a recent history of developing projects in WM in terms of sanitary landfills and managing waste through WTE facilities. Moreover, Thailand has experience of WTE projects which have been developed locally and which date back at least a decade and from these, significant lessons related to both thermal and non-thermal technologies have been learned. Thermal treatments have involved both incineration and gasification processes and under the heading of nonthermal processes, biogas has been produced from, for example, waste fermentation or AD and the following sections will examine and compare case studies relating to both these technologies.
