Freeze-thaw assisted immobilization of Rhodococcus erythropolis MTCC 3951 in kappa carrageenan for efficient terephthalic acid biodegradation.

Terephthalic acid (TPA) is widely used in the production of polyethylene terephthalate (PET) plastics and is one of PET's degraded products. However, TPA poses environmental health risks due to its persistence and potential toxicity, and thus, it is referred to as one of the major environmental pollutants. The present study describes the application of immobilized Rhodococcus erythropolis MTCC 3951 cells for TPA biodegradation to develop a viable bioprocess. Kappa carrageenan (KC) matrix was used to immobilize the cells. The entrapment conditions were modified for maximum TPA degradation and minimum cell leakage. The entrapped cells were cryofreeze at -20 °C for 24 h, followed by thawing at 24 °C for 4 h. Cryofreezing was introduced to enhance the cell's stability and mechanical strength, required for effective reusability. The stability of the matrix was confirmed by FTIR, TGA, and FESEM. The cryofreeze entrapped cells completely degrade 5 mM TPA within 14 h of treatment. The immobilized cells could be reused for at least 10 repeated cycles without loss in degradation efficiency. The cryofreezing of immobilized cells in KC is a novel technique to enhance the system's stability. The developed bioprocess could be used efficiently to alleviate TPA pollution from the environment.