Biotransformation of grease to biodiesel with wet cells of E. coli
(Calb & Tll) as biocatalysts (4 wt%) was then investigated in more
details. FAME yield and the remaining FFA content at different time
points of biotransformation were shown in Fig. 4. FFA content in
the first 12 h increased with time, clearly suggesting the happening
of the hydrolysis of triglyceride to FFA by the enzymes. In the
meantime, the esterification of FFA with methanol as well as the
transesterification of triglyceride with methanol also took place
by the enzyme catalyses, giving rapid increase of FAME. After
12 h, FFA content decreased rapidly. At 48 h, FFA content was
2 wt%, and FAME yield reached 84%. The reaction became slow
afterwards, and the FAME yield was slightly improved to 87% at
72 h.