# Green hybrid polymeric magnetic nanocomposite from natural polycationic polysaccharides for sustainable alum sludge conditioning

## TL;DR

This paper introduces a green magnetic nanocomposite made from natural materials to improve the dewatering of alum sludge in water treatment.

## Contribution

A novel eco-friendly Fenton-based nanocomposite using chitosan and magnetite for sustainable sludge conditioning is developed.

## Key findings

- CSP@Fe3O4-(2−1) achieved a 75% reduction in Capillary Suction Time (CST) under optimal conditions.
- The nanocomposite outperformed commercial polyelectrolytes in sludge dewatering efficiency.
- The system uses environmentally benign materials and enhances sludge floc size and zeta potential.

## Abstract

The disposal of aluminum nature-based sludge that is so called alum sludge (AS) from water-works treatment plants for water drinking purposes is one of the expensive sectors in treatment plant due to the high-water content. Thus, dewatering is essential for sludge volume reduction, which requires further treatment and drying costs prior to sludge disposal. Based on the criteria of advanced oxidation processes (AOP), alum sludge is subjected to polycationic polysaccharide-magnetic catalyst as a catalyst-based Fenton oxidation treatment and its effect and mechanism on sludge dewatering were assessed in the current work. Polycationic polysaccharide, chitosan augmented with magnetite in various proportions named CSP@Fe3O4(1–1), CSP@Fe3O4-(2 − 1) and CSP@Fe3O4-(1–3) were applied as alum sludge flocculants. All the Fenton’s based composites could extrude sludge water and enhancing its dewaterability. Dehydration and sedimentation performance of alum sludge is enhanced by the improvement in Capillary Suction Time (CST) and Specific Resistance for Filtration (SRF). CSP@Fe3O4-(2 − 1) based Fenton’s coagulation is revealed the highest CST reduction reached to 75% at the optimal operational conditions of 40 and 400 mg/L of CSP@Fe3O4-(2 − 1) and H2O2, respectively at pH 3.0. The results compared with the commercial conditioners such as polyelectrolytes, which results in only 37% CST reduction. In comparison with chemical flocculants, the conditioning process based CSP@Fe3O4 Fenton’s reaction is ecofriendly since it uses both chitosan and magnetite substances that are environmentally benign materials. Also, the system is oxidizing the high proportion of materials in the sludge. Also, elevating temperature of the sludge showed a negative effect in CST enhancement compared to the room temperature. Further analysis showed that the change of the zeta potential (ζ-potential) of the sludge is changed to the more positive values, and the surface morphology attained bigger flocs than of the raw sludge.