An integrated electrodialysis-biocatalysis-spray-drying process for efficient recycling of keratin acid hydrolysis industrial wastewater

Abstract In this work, a novel and efficient electrodialysis-biocatalysis-spray-drying integrated process was developed for the complete recycling of keratin acid hydrolysis industrial wastewater. The ionic species including ammonium chloride, l -aspartic acid, and l -glutamic acid were removed from the wastewater by electrodialysis, and their removal efficiencies were 99.96%, 91.62%, and 84.58%, respectively. Compared with the formation of a light brown paste of the original wastewater, the wastewater treated with electrodialysis was concentrated to a high concentration of l -serine solution (120 g/L). Although l -serine from the wastewater could be converted into l -cysteine, l -tryptophan or S-phenyl- l -cysteine by recombinant tryptophan synthase, the production of l -cysteine was the optimal route to efficiently recycle the wastewater. The efficiency of production of l -cysteine increased approximately five times via electrodialysis treatment. In the scale-up study, the molar conversion rate of l -serine reached 96%, and l -cysteine was purified from KHW as its oxidized form, l -cystine, with a total yield of 90%. After l -cystine was collected, the conversion fluid was dried by spray-drying to yield a mixture of amino acids, which could be used as feed additives or fertilizer. In comparison with directly draining or concentrating the original wastewater to obtain the low-value mixture, this study has for the first time provided an effective strategy for completely recycling keratin acid hydrolysis industrial wastewater to produce high-value products including l -cysteine and a mixture of amino acids.