Maria Fernanda de Almeida: Sustainable tannin coagulants with tailored structural features for industrial water treatment

Coagulation–flocculation is a widely used water treatment process that removes suspended particles from wastewater by neutralizing surface charges and promoting the formation of flocs. However, conventional chemical coagulants (e.g., metal salts and synthetic polymers) raise concerns due to their potential toxicity and environmental impact. Natural products such as tannins gain increasing attention as coagulants due to their abundance, safety, biodegradability, and effectiveness. This is enabled by the Mannich reaction, in which an amine and an aldehyde react with the phenolic sites of tannins under acidic conditions, introducing cationic groups. Nevertheless, a key limitation of many tannin-based coagulants is the use of toxic reagents during their synthesis. To address this challenge, a novel green synthesis route is developed using condensed tannins derived from Acacia mearnsii, ethanolamine, and safe aldehydes under mild reaction conditions. The process is optimized to enhance both product properties and reaction efficiency. Multiple analytical techniques are employed to characterize the modified products, confirming successful amination, the introduction of cationic charge, and an increase in molecular weight. The synthesized bio-based coagulants are evaluated for the treatment of high-turbidity wood-processing industry wastewater to remove organic extractives. These findings highlight the potential of the synthesized tannin-based coagulants as sustainable alternatives for industrial wastewater treatment applications.