Fermentative production of poly (γ-glutamic acid) from renewable carbon source and downstream purification through a continuous membrane-integrated hybrid process

•Poly (γ-glutamic acid) produced in a fully membrane-integrated bioreactor.•The process ensures high degree of purity, yield and concentration.•Complete separation and recycle of cells and residual carbon source ensured.•This continuous system represents high process intensification.

Experimental investigations were carried out on continuous and direct production of poly-(γ-glutamic acid) in a hybrid reactor system that integrated conventional fermentative production step with membrane-based downstream separation and purification. Novelty of the integrated system lies in high degree of purity, conversion, yield and productivity of poly-(γ-glutamic acid) through elimination of substrate–product inhibitions of traditional batch production system. This new system is compact, flexible, eco-friendly and largely fouling-free ensuring steady and continuous production of poly-(γ-glutamic acid) directly from a renewable carbon source at the rate of 0.91 g/L/h. Cross-flow microfiltration membrane modules ensured almost complete separation and recycle of cells without much fouling problem. Well-screened ultrafiltration membrane module helped to concentrate poly-(γ-glutamic acid) while ensuring recovery and recycle of 96% unconverted carbon source resulting in yield of 0.6 g/g along with high product purity.