Nature-based solutions for wastewater treatment: Biodegradable freeze-dried powdered bio-flocculant

A significant problem concerning the utilisation of nature-based coagulants (or biocoagulants) in practice and for commercialisation, is their stability (i.e., of their active components) and durability over long periods. In this context, a powdered biocoagulant was produced from common bean seeds (Phaseolus vulgaris) by extraction and freeze-drying and then tested for its stability and durability. Four powdered biocoagulants were tested and compared in terms of their coagulation activity, hygroscopicity, water solubility and moisture content. All 4 maintained high efficiency for turbidity removal (50.6–80.2 %) despite and during several months of storage (in both controlled and non-controlled conditions). Similarly, these biocoagulants had low hygroscopicity (between 7.6 and 8.5 g of water per 100 g of sample), moisture content (< 8 g per 100 g of sample) and high water solubility indices (between 88.0 and 92.7 % and between 62.6 and 78.1 % for salt and distilled water extracts, respectively) with a low coefficient of variation (< 5 %) during the testing period and within repeated experiments. Biocoagulants extracted with 0.5 M salt solution showed better results in terms of their tested physico-chemical properties. However, biocoagulants extracted by ultrasound extraction using distilled water as a solvent showed the highest consistency in terms of optimal coagulant dosage and achieved turbidity removal. Instrumental characterisation through SEM/EDX, FTIR, XRD and XPS analysis were included for the coagulant with the best consistency in coagulation activity over the time. Biocoagulants were also tested using lake water and several types of industrial wastewater (i.e., from a whisky distillery and a meat processing plant) and showed good potential for organic matter reduction even in real (complex) environmental matrices.