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Ecofuel conversion technology of inedible lipid feedstocks to renewable fuel 245
Table 9.4 Chemical composition range of dried spent coffee ground
Chemical component Range (wt%) Reference
Moisture 5.0–10.0 [28, 52, 53]
Lipid 2.29–18.3 [28, 54]
Protein 1.02–17.4 [28, 52]
Ash 1.3–1.6 [28, 54]
Carbohydrate 45.3–75.4 [28, 54]
Cellulose 8.6–12.4 [28, 54]
Hemicellulose 36.7–39.1 [28, 54]
Lignin 23.9–29.8 [28, 55, 56]
chemical constituents of dried spent coffee grounds compiled from various studies are
presented in Table 9.4.
Although spent coffee grounds are the waste sourced from human culture, spent
coffee is not inherently safe for direct disposal. Fernandes et al. reported the latent
danger of mutation and the cytotoxic effect of spent coffee ground waste leached
extract toward aquatic plankton [57]. The leaching extract of spent coffee grounds
contains a considerable amount of antioxidant compounds that can consume dissolved
oxygen in water. Utilization of spent coffee grounds as cattle feed or plant fertilizer
has been assessed to be ineffective. Plant growth inhibition, particularly during root
elongation, was reported due to the presence of fatty acids that formed an inhibition
layer for nutrients and oxygen absorption [58]. Composting of spent coffee grounds
was slow due to the lack of mobile ions for the growth of composting bacteria in addi-
tion to the slight antibacterial effect that was indicated by fewer bacteria present with
comparison to the control system [59]. On the other hand, Givens and Barber spotted
the low digestibility of spent coffee waste in sheep, deeming it a worthless ruminant
feedstuff [60]. The analysis showed that spent coffee grounds had quite a high content
of fiber, as reflected by the number of acid detergent fibers, yet the fact of the indi-
gestibility of spent coffee grounds implied more on the high content of recalcitrant
lignin bound with cellulosic fiber. Moreover, protein as the other valuable component
for animal feed can actually be so low since the measurement of protein that is based
on the nitrogen content, cannot distinguish between the nitrogen from amino acid and
nonprotein nitrogen such as caffeine and melanoidins (nitrogenous brown-colored
compounds of coffee from the Maillard reaction) [61].
9.3 Biodiesel conversion technology
9.3.1 Catalytic and noncatalytic biodiesel conversion
of rice bran/RBO
Biodiesel can be produced catalytically or noncatalytically. The three types of cata-
lysts commonly used are acid, base, and enzyme. Each type of catalyst has some
advantages and some drawbacks for biodiesel conversion. Furthermore, those