kappa-Carrageenan-based hydrogel for leachate wastewater treatment and resource recovery

The current investigation examined the effectiveness of a kappa-carrageenan-activated carbon/polyethylenimine (kC-AC/PEI) hydrogel, with a surface area of 95.61 m²/g, in the removal and recovery of metal ions from leachate wastewater. Variations in kC concentrations are analyzed for their influence on the hydrogel's structural characteristics, adsorptive performance, water absorption capacity, and swelling behaviour. Additionally, optimization of operational parameters, including temperature and pH, is explored to achieve maximum adsorption efficiency. The hydrogel demonstrated exceptional efficiency in treating leachate, with rejection rates of 97.8 % for total organic carbon (TOC) and 94.4 % for turbidity. The kC-AC/PEI hydrogel exhibited 82.9 % to 87.1 % rejection for divalent ions and 46.9 % to 74.4 % for monovalent ions. In addition, permeation flow declined 12 % over three cycles, starting at 32.3 LMH and decreasing to 28.2 LMH in the third cycle. The kC-AC/PEI hydrogel exhibited excellent reusability after recycling, achieving 80.6 % rejection of Mg²⁺ and 40.3 % for Na⁺ ions. Other metal ions exhibited slight declines in rejection rates, demonstrating the hydrogel's enduring efficiency in removing ions even after recycling. At the end of the hydrogel tests, reverse osmosis effectively recovered approximately 70 % of metal ions from the hydrogel, making the hydrogel-RO system a sustainable and affordable approach for metal recovery from wastewater in small-scale treatment plants.