Regular articleHigh-yielding, one-pot, and green production of biodiesel from waste grease using wet cells of a recombinant Escherichia coli strain as catalyst

- Wet cells are used, for the first time, in biodiesel production to give high yield.
- Wet cells of E. coli (TLL) can fully convert grease to FAME in 20-30 wt% water.
- Direct use of wet cell pellets as catalyst gives 99% FAME yield from waste grease.
- Wet cells-process is general, giving high FAME yield from different types of grease.
- Wet cells of E. coli (TLL) are recyclable, retaining 55% activity in the 5th cycle.

Green and efficient production of biodiesel from cheap and non-edible resources is highly desirable. Here we develop a practical method for the high-yielding one-pot conversion of low-cost waste grease to biodiesel (FAME) by using wet cells of E. coli expressing intracellular Thermomyces lanuginosus lipase (TLL) as catalyst. E. coli (TLL) was genetically engineered and grew easily to a high cell density with the functional expression of TLL. The easily available and easy to handle wet cells were directly used as catalyst for the biotransformation of waste grease to FAME, with water content of 20-30 wt% (based on grease) and stepwise addition of methanol (4:1 molar ratio to grease) as the optimum conditions. Biotransformation of waste grease from Singapore (21 wt% FFA) and Malaysia (9.8 wt% FFA) with 31 wt% wet cells (26 wt% water) gave 99% and 97% FAME yield, respectively. During the biotransformation, the esterification of FFA was faster than the transesterification of triglycerides and the hydrolysis of triglycerides, and nearly no hydrolysis of FAME was observed. Preparative biotransformation was demonstrated to give FAME in >90% yield with a simple isolation procedure. The wet cells were recyclable and retained 55% productivity in the 5th cycle.

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