A novel bio-adsorbent development from tannery solid waste derived biodegradable keratin for the removal of hazardous chromium: A cleaner and circular economy approach

The chromium (Cr) used in leather processing has well-known negative impacts on the environment, as the disposing of tannery effluent contains a significant amount of Cr. Alongside this, the tanning industry also generates a large amount of solid keratinous waste during the unhairing process, which also burdens to the environment. There is an urgency to recover this Cr from tannery wastewater and manage yielded solid waste by adopting an affordable and ecologically beneficial alternative. Previous studies attempted to develop bio-adsorbent from other types of bio-waste, and could not show the circular way of the reusing process of recovered Cr. Also, there needs to be more studies on bio-adsorbent preparation from tannery solid waste. This study developed a novel biodegradable film as a bio-adsorbent from keratinous waste and examined its suitability to recover Cr from tannery wastewater. The recovered Cr has been reused in the tanning process. The removal of Cr from synthetic and actual tanning effluent was optimized using a multivariate approach using Central Composite Design under Response Surface Methodology, with a removal efficiency of 91.247% and 86.972%, respectively. A desorption investigation was performed, and the analysis showed that the films could be reused, and Cr can be recovered at a pH of around 10.5. Recovered Cr from wastewater was also utilized as basic Cr sulfate in tanning. Several experimental analyses of the obtained leather demonstrated good hydrothermal stability, Cr content, and physical properties with the negligible difference compared to conventionally processed leather. Experiment on the biosorption technique was also conducted to further understand the interaction and industrial feasibility of the technology. Overall, the findings encourage the 'use of solid waste for treatment of liquid waste', a circular economy approach that would contribute to cleaner leather production.