Hydrolysate from leather tanning waste as clay modifier for pig manure treatment

The heavy metals pollution from agricultural waste is a significant concern. Among these, zinc and copper are prevalent pollutants that can be found in pig manure. The application of sorbents has emerged as a pivotal strategy for the effective removal of these pollutants from manure. One of the most well-known and widely used sorbents are clays and organoclays. In this work, both pristine Ca-montmorillonite (STx) and protein-functionalized Ca-montmorillonite (STx-HY) are tested as sorbents for Zn and Cu capture. Protein-functionalized organoclay was obtained by treating Ca-montmorillonite with two types of collagen hydrolysate (HY), the by-product of the leather tanning process (supplied by Ilsa Group). The synthesis of STx-HY was accomplished via a solid/liquid adsorption process in mild conditions. An uptake plateau was found corresponding to a loading of 0.42–0.44 mmolHY/gSTx. The metal uptake efficiencies of clay and organoclays were tested in solutions simulating the concentration of Cu and Zn in weaning pig's manure. The results obtained demonstrated near-total capture at 0.06 mmolCu/gSTx, irrespective of the sorbent used. Furthermore, an increase in HY loadings resulted in enhanced Cu capture at 0.38 mmolCu/gSTx, suggesting a saturation point of 2.00 mmolCu/gSTx for both hydrolysates, corresponding to a maximum Cu capture of 0.45 mmolCu/gSTx and 0.6 mmolCu/gSTx. In case of zinc, a maximum metal capture of 0.4–0.5 mmolZn/gSTx was obtained by both pristine and modified STx.