**2. Waste animal fat-oil (WaFO) biodiesel production**

Waste animal fats and oil used in this study includes beef tallow, chicken fat, mutton suet and pork lard, and fish fat oil; and were rendered from wide variety of animal wastes. For instance, beef tallow was rendered from tannery fleshing and meat processing wastes; while, chicken fat, mutton suet and pork lard were rendered from their respective wastes collected from different slaughter house units. Besides, waste fish fat oil was directly procured from the leather tanneries associated with oil tanning process; in its existing form. Here, waste fats (tallow, suet, lard and chicken fat) were rendered from their respective wastes using dry rendering technique; which involved with autoclaving each waste individually, at 120**°**C and 2 bar pressure [30]. Post rendering, each fat was filtered to remove any solid residues, washed with distilled water to remove suspended residues; and was dehydrated to remove residual moisture content by heating at 110**°**C. Likewise, similar pre-treatment process was followed for waste fish fat oil. Following that, the pre-treated waste fats and oil were refined to remove phospholipids by means of degumming using orthophosphoric acid as explained by Srinivasan et al., [22, 30].

Post refining, tallow, suet, lard, chicken fat and fish fat oil were mixed in equivalent proportion; and was blended into a homogeneous feedstock (WaFO). The blended waste Fat-oil (WaFO) was esterified by refluxing it with ethanol and 1 wt.% of concentrated sulfuric acid (conc. H2SO4), in order to reduce its overall free fatty acid (FFA) content so as to avoid formation of soap during transesterification. For the production of WaFO biodiesel, the WaFO sample was transesterified by following the under mentioned reaction parameters: (i) oil to ethanol molar ratio: 1:8; (ii) catalyst concentration: 0.75 wt.% of potassium hydroxide (KOH); (iii) reaction temperature: 72°C; (iv) reaction time: 150 mins. Here, the volume of ethanol was calculated from the optimized molar ratio using a simple equation Eq. (1), which correlates the molecular weight and density of triglycerides and ethanol [30].

$$V\_{alchol} = \frac{V\_{sample} \ast m \ast \rho\_{TG} \ast M\_{alchol}}{\left[\Re \mathtt{2}\mathtt{1}\mathtt{7} - \mathtt{3} + \left[\Im \left(\sum\_{i=1}^{n} M\_{FA} \ast \varkappa\_{i}\right) - \mathtt{1}\mathtt{7}\right]\right] \ast \rho\_{alchol}}\tag{1}$$

Completing the reaction, resultant mixture was decanted in a separating funnel for 24 h; when the residual glycerol got separated from the WaFO biodiesel and settled down at the bottom. Lastly, the separated biodiesel was washed with hot distilled water successively to remove residual ethanol and glycerol, soaps, and salts; and was dried at 110°C to remove moisture content from it.
