Coagulants from chestnut shell tannins - Synthesis, characterization and performance on water treatment

Ensuring access to safe drinking water is essential for public health. Coagulation/flocculation processes are critical for removing suspended particles, organic matter, and other impurities in water treatment. Tannins have been identified as promising coagulant precursors; however, a chemical modification is required to enhance their effectiveness. In this study, chestnut shell (CS) tannins underwent aminomethylation to increase their cationic properties. The success of this modification was confirmed through zeta potential measurements and chemical analysis. The performance of the lab-synthesized natural coagulants was then evaluated against Tanfloc SG, demonstrating comparable efficacy in turbidity and pollutant removal. Four distinct coagulants (C1-C4) were produced by varying the tannin:NH 4 Cl:formaldehyde ratios. Among these, the coagulants produced with 1:2.5:7.5 and 1:2.5:10 (T:NH 4 Cl:FA, molar ratios), corresponding to the highest formaldehyde amount, achieved over 95 % turbidity reduction, as well as effective removal of color (about 85 %), organic matter (29 %), phosphorus (34.6 and 49.3 %, respectively), and nitrogen (53.9 and 55.4 %, respectively). The presence of formaldehyde in treated water and sludge was also examined, revealing that coagulants produced with lower formaldehyde levels resulted in higher formaldehyde concentrations in the treated water due to the need for increased coagulant usage. CS tannins demonstrate significant potential as eco-friendly coagulants for water treatment applications. • Chestnut shell (CS) tannins are excellent for producing natural coagulants. • The aminomethylation process was successful even at lower formaldehyde dosages. • CS-based coagulants removed high turbidity, NOM, P, and N from river water. • CS-based coagulant effectiveness can be compared to Tanfloc SG. • Formaldehyde was detected in treated water and sludge at very low concentrations.