A prototype bioreactor for the water retting of hemp bast fiber: dynamics of the liquor bacterial consortium across sequential retting cycles.

The proper extraction of fibers from the surrounding tissues (retting) is a prerequisite for the textile and technical valorization of bast fibers. Fiber retting is naturally carried out by environmental microflora (microbial retting). Among microbial retting, water retting is considered the most effective in producing high-quality textile fiber from bast fiber crops. On the other hand, traditional water retting system resulted unsuitable for the industrial production of textile fiber, due to its environmental, economic and social concerns. A prototype bioreactor has been developed, based on a patented process, for the water retting of hemp bast fibers, overcoming the major constraints of the traditional method. The bacterial succession occurring in the retting liquor when a portion (5%) of the liquor is recycled has been studied across eight subsequent retting cycles. Retting liquor has been sampled before process starts, mid-process and endpoint of each cycle. 16S rRNA metabarcoding and functional predictions along the subsequent retting cycles gave back a succession resembling what has been observed in conventional retting ponds during a single retting cycle. The negative impact of liquor recycling on the predicted enzyme function abundances has been measured from the third retting cycle. Useful information was obtained on the possible valorization of liquor waste in sustainable agricultural practices.