Scaling up a consolidated bioprocess for enzymatic depolymerization of PET waste

The global demand for plastic has been exponentially increasing during the last decades, reaching 460Mt in 2019. Predictions for 2050 foresee that plastic production will require 20% of all fossil resources if we continue with business as usual. Moreover, only 13% of plastic waste are being collected and only 9% being actually recycled, globally, indicating the inefficiency of the current recycling technology.
Biotechnology can contribute to a more sustainable plastic sector: Enzymatic recycling does not require the use of harmful solvents or high temperature and has the advantage that it can be applied without the need of previous sorting. Efficient depolymerization provides the opportunity for infinite recycling, however, we need to tackle challenges such as high cost of plastic pretreatment and of enzyme production.
We have developed a consolidated bioprocess for a one-pot enzyme production and PET depolymerization, without the need for lengthy and costly enzyme purification steps. Using an engineered E.coli BL21 strain expressing and secreting the cutinase LCC ICCG, we have compared the hydrolysis of different PET types, including low crystallinity GoodFellow PET and different post-consumer PET waste (e.g. trays and bottles). Different PET loadings were tested showing the best performance for concentrations up to 80 g/L, using only the supernatant. Further increase up to 160 g/L led to a significant decrease of weight loss. Depolymerization efficiency ranged between 60-90% depending on the PET type used in lab scale tests and 20L reactors. Finally, the process was scaled up to 300L reactor using mixed PET waste.