Removal of multiple metals from real wastewater combining sludges with carbon black and chitosan: Integrating sustainable remediation and waste recycling

The escalating production of hazardous substances dramatically affects the quality of vital resources, such as water, soil, air, and food. Undoubtedly, waste products are responsible for environmental resource contamination. Waste recycling is, thus, emerging as the key to overturning this destructive trend. Here, wastewater sludges, one of the most abundant waste products, are used to obtain a composite with adsorbent properties toward multiple metals. The novelty of this work lies in the design of sludge-based composites using eco-friendly materials and without energy-intensive and environmentally impactful processes, applied to the simultaneous removal of multiple metals (i.e., Fe, Ni, Cu, Mn, Cr, Zn, As, Co, Pb, Cd, Ba, Be) in real wastewater. The adsorption properties and the interparticle cohesion of dried sludges were improved by adding the organic biopolymer chitosan and carbon black, a low-refined and low-cost carbon material. Amounts from 0 % to 10 % of both chitosan and carbon black were tested to evaluate their effects on the structural and adsorption properties toward metals. The adsorption properties were tested in real wastewater to prove the efficiency in a complex environment. Higher adsorption was observed for increasing amounts of chitosan and carbon black, with percentages between 50 % and 100 % using the sludge-based composite containing chitosan and carbon black at 10 % w/w. Morphological and FTIR characterization were provided to support the experimental evidence. This work provides a successful and inspiring example of waste recycling combined with environmental remediation, promoting the vision of the circular economy and sustainable development.