Conventional water treatment with metal salts or synthetic polymers raises environmental and health concerns. This has driven the search for natural alternatives, and in this study investigates the coagulation-flocculation potential of 13 biomasses (soybean meal, rapeseed meal, linseed meal, sugar beet pulp, insect frass, Pleurotus ostreatus , Aspergillus niger , Althaea officinalis , Ludwigia peploides , Reynoutria japonica , Laurus nobilis , Opuntia ficus-indica , Prunus laurocerasus ) under standardized jar test conditions in synthetic water to assess turbidity removal and sedimentation kinetics. Aluminum sulfate and ferric chloride were tested in parallel as reference coagulants (1.0–250.0 mg/L, pH 5.0–9.0). The active fractions of the most effective candidates were then extracted and re-tested in the same aqueous matrix (synthetic water). Six biomasses showed promising activity (rapeseed meal, linseed meal, Aspergillus niger , soybean meal, Althaea officinalis , Opuntia ficus-indica ), yielding 40–79% turbidity removal at pH 5.0. The bioactive extracts from the most effective biomasses demonstrated high performance at low doses under the same pH: rapeseed protein and linseed mucilage achieved 76 and 96% turbidity removal, respectively, at 1.0 mg/L, while chitosan (commercial source: Aspergillus niger ) reached 98% at 0.5 mg/L. Kinetic analysis (sedimentation rate constants from Turbiscan) provided complementary indicators alongside turbidity removal, highlighting sedimentation efficiency as a key parameter. For instance, linseed meal and its mucilage significantly improved sedimentation, although they achieved slightly lower turbidity removal. Overall, selected biomasses and their extracts demonstrate strong potential as natural, effective, and sustainable alternatives to conventional coagulants and flocculants in water treatment under the tested laboratory conditions. • Evaluation of 13 biomasses as natural coagulants for water treatment. • Identification of six biomasses achieving 40–79% turbidity removal at pH 5.0. • Extraction of bioactive compounds enhances flocculation at low doses. • Demonstration of strong potential of rapeseed protein and A. niger chitosan. • Utilization of Turbiscan LAB for evaluating settling of flocculated structures.
Schwing et al. (2026) studied this question.