As indicated earlier, in a new approach to strategic resource management, the concepts of WtP and WtE are implemented for every different type of waste. As shown in Figure 6.2, there are numerous technologies now avail­able to convert waste to heat, electricity, transportation fuels, chemicals, or materials. These technologies are generally broken down into three catego­ries: thermochemical, physicochemical, and biochemical. In each of these categories, a process can be catalytic or noncatalytic. Thermochemical con­version of waste to energy is illustrated in more detail in Figure 6.3 [7, 8]. All advanced technologies such as pyrolysis, gasification, and plasma-based technologies have been developed since 1970 [9]. In the past, thermochemi­cal techniques were predominantly used to generate energy. In recent years, these techniques are also used to generate chemicals and materials [9] via var­ious methods of product upgrading. For example, gasification of biomass can produce syngas which can be further converted to a host of liquid products such as methanol, diesel fuel, gasoline, and jet fuel via Fischer-Tropsch and related syntheses such as methanol and iso — or oxy-synthesis. Liquefaction can produce liquids that can be upgraded by hydro-deoxygenation, hydro­genation, hydrocracking, or catalytic cracking to produce a host of chemicals and fuels. Pyrolysis can produce gases, liquids, or solids depending upon the reaction conditions. The gases can be used as fuel or raw material for polymers such as polyethylene and polypropylene, and others. Pyrolysis oil can also be upgraded to use as fuels or refined into a number of chemicals.

The solid residues from pyrolysis can be important raw materials for the construction and fertilizer industries [10].

Biochemical conversion techniques used to convert lignocellulosic waste can also generate chemicals and materials. The LCM can be fractionated into hemicellulose, cellulose, and lignin by selective solubilization of hemicellu — loses via hydrothermal processing with water or prehydrolysis with externally added mineral acids. The liquor produced by this process can contain oligo­saccharides, fermentable sugar, furfural, low molecular weight phenolics, and levulinic acid depending on the reaction operating conditions. Various prod­ucts can be extracted from the liquor. The sugar can be further fermented to produce a host of alcohols and acids such as ethanol, butanol, xylitol, butane — diol, and lactic acid, among others. The solids coming from the solubilization step mainly contain cellulose and lignin and can be further hydrolyzed by acids or enzymes to give a fermentable glucose solution and a solid phase that largely contains lignin. This solid material can either be used as fuel or a raw material for gasification or pyrolysis. The fermentable glucose solution can be converted to a host of products such as lactic acid, citric acid, succinic acid, itaconic acid, or bioplastics by the suitable fermentation process [10].

The strategy for each type of waste is to apply the appropriate technol­ogy for the desired end product. The choice of the best technology will

depend on various factors such as environmental regulations, local eco­nomics, resources available to use the technology, and the market for the end-product. Some of the major technologies are further described later in this chapter.