Ultrafiltration as a simple purification method of a water extract of common bean seed as a natural coagulant

Natural coagulants from a crude water extract of common bean seed showed very good efficiency of turbidity removal from water of ~89 % under optimal coagulation conditions, which were determined using response surface methodology (RSM). However, they also increased the content of organic matter in treated model water by ~66 %, which is the main drawback of usage of natural coagulants, in general. Thus, ultrafiltration was applied for processing of the crude water extract in order to separate biomolecules, which exhibit the coagulation activity. Four fractions obtained by ultrafiltration were applied in coagulation tests under the same conditions as the crude extract, and the 4 th fraction (molecules with molecular weights >30 kDa) with the predominant content of proteins with molecular weights 50 – 60 kDa, achieved almost as high efficiency of turbidity removal (75 %) as the crude extract. At the same time, the content of organic matter in treated water increased just for 16 % in comparison to the blank (model water processed in the same way but without coagulant). After optimization of process parameters by RSM for usage of the 4 th fraction, the coagulation activity increased further to 80 %.