As outlined above many biological sources can be used for the generation of biofuels (Demirbas et al., 2011; Vasudevan et al., 2005); however, one source of biomass for the production of biodiesel that is often overlooked is the waste fat from animals (e. g. (Ali et al., 2012; Duku et al., 2011; Feddern, 2011; Panneerselvam et al., 2011; Wisniewski Jr et al., 2010)). Generally three broad categories of waste animal fats are described—tallow and related raw fats from process­ing industries, yellow grease from waste cooking oil used to cook, for example, chicken, and brown grease that is obtained from traps used to prevent waste fats and oils being released into the environment. Animal fats can be sourced as room temperature solids or semisolids from a variety of animals and include tallow and suet (cattle and mutton), lard (pigs), schmaltz (poultry especially chicken and goose), duck, fish oil and dairy products (milk, butter) (Jayasinghe and Hawboldt, 2011; Kerihuel et al., 2005; Mrad et al., 2012; Panneerselvam et al., 2011; Wisniewski Jr et al., 2010). It is also possible to reclaim waste animal fats from wastewater (Awad et al., 2012a). Many of the properties of animal fats used put to specific uses have been known for a long time (Andes, 1898; Shahidi and Zhong, 2005). A significant percentage of waste animal fat can be con­verted to biodiesel using similar techniques to those used for plant oils, the main process being transesterifi­cation, described later (Proskova et al., 2009). The triglycerides in animal fats are saturated, compared to unsaturated plant triglycerides, and this has some impli­cations when used as biodiesel. In particular the cloud point, the temperature at which the oils solidify, is higher for animal fats. However, when used as additives to other sources of diesel, for example, 5% or 20% biodiesel (B5 or B20 blends), the high cloud point does not affect the blend overall.

Production of biodiesel from waste animal fats has been shown using a variety of methods including a novel, integrated method in which fat from lamb meat is continuously extracted by supercritical CO2 followed by enzymatic production of biodiesel (Schenk et al.,

2008) . Feedstocks containing high levels of FFAs require an additional preproduction step to convert the FFAs into esters, which can subsequently be converted into biodiesel. Waste sources that contain high levels of FFAs require a separate step (acid catalyzed pretreat­ment) before the base catalyzed reactions can be used to provide maximal yields of biodiesel (Canakci and Van Gerpen, 2001; Knothe et al., 2005; Popescu and Ionel, 2011). Multistep processes using waste restaurant oil and animal (pig) fat containing high levels of FFAs can achieve high yields of biodiesel of up to 80% by volume on a small scale (Math et al., 2010). Other high FFA content oils, including used cooking oils, rendered animal fat and some inedible plant oils (Mathiyazhagan et al., 2011) can be processed in a similar fashion (Bakir and Fadhil, 2011).

The feasibility and sustainability of using waste animal fats as feedstocks for biofuel production has been the subject of many studies in many areas, for example, general studies (Demirbas, 2009; Nigam and Singh, 2011), Australia (Puri et al., 2012), Ghana (Duku et al., 2011), the United States (Groschen, 2002), Brazil (Aranda et al., 2009), Ireland (Thamsiriroj and Murphy,

2010) and Hungary (Lako et al., 2008). In addition, the use of animal fats from waste tissue may also have envi­ronmental benefits, such as being considered as a waste management process and as a fuel source that does not compete with food resources (e. g. soybean), the food versus fuel debate. Table 12.1 shows typical values reported for triglycerides in several animal fats in com­parison to values for soy, a commonly used plant — derived feedstock. In all cases, waste animal fats contain high levels of the fatty acids that are capable of being converted to methyl esters by transesterification reactions to produce usable biodiesel. From a sustain­ability point of view an estimate of the total annual US production of animal fats as compared to plant — derived oils is shown in Table 12.2.

Vegetable oils tend to be produced for human con­sumption, whereas animal fats form part of a wide group of animal by-products that are rendered into many products that may be used in part for human con­sumption (e. g. production of gelatin). All animal by­products, including fats, are coded and classified (Alakangas et al., 2011) according to their intended use and animal fats not intended for human consumption are controlled in the European Union by Regulation (EC) No 1069/2009 and related legislation. Similarly,

TABLE 12.2 Total Annual Production of US Fats and Oils

Vegetable Oil Production (billion pounds per year)

Canola 1.04

Corn 2.49

Cottonseed 0.617

Soybean 19.61

Sunflower 0.731

Total Vegetable Oil 24.49

Animal Fats (billion pounds per year)

Edible Tallow 1.859

Inedible Tallow 3.299

Lard & Grease 1.63

Yellow Grease 1.40

Poultry Fat 1.42

Total Animal Fat 9.61

Source: U. S. Department of Agriculture, 2010; U. S. Census Bureau, 2010.

the storage of animal fats for use as fuels also needs to be addressed. The storage of raw animal fat under unsuit­able conditions can lead to oxidation and other undesir­able chemical and microbial processes that can affect the quality of the final biodiesel product. The stability of the final biodiesel:diesel blend can also be affected by long­term storage under unsuitable conditions, and additives such as antioxidants might be added to improve stability (Geller et al., 2008; Jain and Sharma, 2010).

With the advent of Bovine spongiform encephalopathy (BSE) and more specifically Transmissible spongiform encephalopathies (TSE), there is a greater need to monitor human health issues when using waste animal fats for the production of biofuel, at all stages of the production pro­cess. The rendering industry recognizes that safe product (fats) can only be supplied if certain standards are adhered to (Woodgate and Van Der Veen, 2004). The raw materials could well have microbial contamination including path­ogenic bacteria and possibly prion material (Baribeau et al., 2005; Brown et al., 2007; Bruederle et al., 2008; Greene et al., 2007). There is also concern that prions will survive the rendering process itself (Bruederle et al., 2008). These concerns have in part led to the publication of guidelines for the safe handling and use of biodiesels (National Renewable Energy Laboratory, 2009).

Many trials of waste animal fat biodiesel-powered engines have been published (Darunde Dhiraj and Deshmukh Mangesh, 2012; Kleinova et al., 2011; Panneerselvam et al., 2011; Varuvel et al., 2012). One trial using public transport buses (Proc, 2006) showed that the biodiesel does not have any harmful effects on the engines at B5 and B20 mixes and also shows environmental benefit by way of reduced exhaust pollutants. However, there are other potential health and environmental issues in using animal fats as a feed­stock for biodiesel production (Greene et al., 2007) and the production of safe biodiesel is in part dependent on a safe feedstock (Woodgate and Van Der Veen,

2004) . Finally, the processes involved (e. g. rendering, cleanup, transesterification, etc.) in the production of biodiesel will generate waste that also needs to be assessed (Ellis, 2007).