Valorization of pulp reject into green flocculant for antibiotic wastewater: Performance, interfacial interaction mechanisms, and life cycle assessment.

The structural heterogeneity of natural biomass limits the rational design of bio-based flocculants for efficient antibiotic removal. To address this challenge and promote industrial waste valorization, a pulp reject-based flocculant (PRBF) was synthesized by activators regenerated by electron transfer atom transfer radical polymerization. This controlled strategy converted pulp reject into a polymer with well-defined branched architecture and narrow molecular weight distribution (Mw = 3.97 × 105 g/mol, PDI = 1.64). PRBF markedly outperformed conventional coagulants in removing representative antibiotics and showed stable performance under varying pH values and coexisting ions. Mechanistic analyses revealed that the uniform backbone and dense functional groups promoted synergistic interfacial interactions, with hydrogen bonding playing a dominant role in antibiotic capture, as supported by extended Derjaguin-Landau-Verwey-Overbeek theory and molecular dynamics simulations. Life cycle assessment further confirmed that PRBF had a lower environmental burden than conventional coagulants, highlighting its potential as a sustainable material for antibiotic wastewater treatment. This work demonstrates a promising pathway for valorizing pulp reject into a high-performance green flocculant and underscores the importance of precise molecular engineering in advancing sustainable wastewater treatment technologies.