The grease trap wastes collected from the surface of grease
traps operated by the 14 firms were consistently typical of these
firms. Their physical appearance showed a remarkably large variation
due to the very different schemes of waste management employed
by these companies. However, five major groupings were
identified based upon appearance and odour. These are as follows.
(a) Solid fatty waste containing substantial amounts of feathers,
blood, and skin; dark in colour with a strong, unpleasant smell
(Fig. 1a). (b) Solid fatty waste containing fine feathers; light brown
in colour with a slightly unpleasant smell (Fig. 1b). (c) Waste similar
in appearance to (b), but more oily in nature with an extremely
rancid smell (Fig. 1c). (d) Solid, globule-shaped waste containing
very little non-lipid material with an unpleasant smell (Fig. 1d).
(e) Oily, liquid fatty waste containing very little extraneous material
with an orange–red1 colour and an unpleasant smell (Fig. 1e).
Type (e) was typical of the waste generated by a firm (K3) that produced
cooked (deep-fried) chickens.