Integrated circular economic approach of solid waste management and resource recovery: Poultry feather-based keratin extraction and its application in leather processing

The tanning industry faces considerable environmental challenges due to effluent load and hazardous chemical generation during processes like tanning and retanning. Therefore, this research work addresses these issues focusing on the pilot scale extraction and application of poultry feather-based keratin hydrolysate (KH) in leather manufacturing. Through pilot-scale experiments, optimal parameters for NaOH concentration, reaction temperature, and time were used to extract KH effectively. The study explored KH's potential application in chrome tanning and retanning stages as a chrome exhaust aid and keratin filler, respectively. During basification, KH was introduced to enhance chromium uptake by creating additional sites through the provision of crosslinking with collagen (modifying collagen) for better interaction and formation of complex with chromium, which not only streamlined the process by reducing the need for additional chemicals but also improved the thermal stability of the resulting leather product and enhance, the quality of leather. The shrinkage temperature of experimental wet blue leather was recorded to be above 107oC compared to the control wet blue leather which start to shrink at 104oc. Similarly, the percentage chromic oxide content of the experimental wet blue leather was observed to be significantly higher (3.89±0.20%) than that of the control wet blue leather (2.59±0.15). Furthermore, KH replaced commercial protein fillers during retanning, resulting in leathers with enhanced mechanical strength and organoleptic properties. The experimental crust leather treated with keratin solution at pH (5.5) was determined to have better tensile strength (23.4 N/mm2) and tear load (38.7 N/mm) than the control leather with tensile strength and tear load of 19.4 N/mm2 and 29.1 N/mm, respectively. Analytical techniques such as FTIR and XRD confirmed the presence of essential functional groups and protein structures in the KH solution, respectively. Leathers treated with 100 % KH substitution at pH value of 5.5 exhibited superior properties, including increased mechanical strength and thermal stability. Environmental impact assessments revealed a significant reduction in total dissolved solids in the spent liquor when KH replaced conventional fillers. Overall, this research demonstrates the potential of poultry feather-based keratin as an efficient, environmentally friendly filler in leather manufacturing, offering promising results in improving prod