Plant-based coagulants have gained popularity as a sustainable and cost-effective alternative to chemical coagulants. In this work, a novel plant-based coagulants, produced from seeds of Chelidonium majus L., Dactylis glomerata L., Festuca ampla Hack., Tanacetum vulgare L. and rachis of Vitis vinifera L. were applied in combination with bentonite, aiming at the removal of methylene blue (MB) from aqueous solution. The analysis performed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET), showed that these are porous materials with capacity to adsorb the contaminant from the solution.

The coagulation-flocculation-decantation (CFD) process was optimized, by variation of the pH (3.0 – 7.0, coagulant dosage (0.1 – 2.0 g/L), agitation conditions and bentonite dosage (0.1 – 2.0 g/L), with a sedimentation time of 12 h. Under the best operational conditions, it was observed a MB removal of 90.9, 91.9, 91.4, 86.9 and 88.9%, respectively. In conclusion, plant-based coagulants mixed with bentonite are a biologic, sustainable and cheap alternative for MB removal.