Structural analysis and flocculation performance of ASP-1: A polysaccharide bioflocculant from asparagus root waste

This study reports the extraction of a bio-flocculant polysaccharide, designated ASP-1, from asparagus processing waste and its evaluation for flocculating properties and potential in wastewater treatment. ASP-1 is primarily composed of polysaccharides (92.5 %), along with minor amounts of protein (4.23 %) and impurities (3.27 %). Its monosaccharide composition includes rhamnose, galacturonic acid, glucose, galactose, xylose, and arabinose in a molar ratio of 6.72:1.76:1.00:38.65:8.10:2.23. The molecule contains key functional groups such as hydroxyl, carboxyl, and amine, and has a molecular weight of 2.36 × 10 4 Da. ASP-1 demonstrated a maximum flocculation efficiency of 81.2 % under optimized conditions (pH 6, 60°C). It remained stable across a pH range of 5–8 and temperatures from ambient to 60°C when tested in kaolin suspensions. Mechanistic studies revealed that ASP-1's flocculation activity is cation-sensitive but not directly dependent on cation valence, and is affected by HCl and EDTA while showing a limited response to urea. The dominant flocculation mechanisms involved ionic interactions, adsorption bridging, and, to a lesser extent, hydrogen bonding. Beyond Kaolin, ASP-1 also effectively removed dyes Methylene blue (MB), Rhodamine B (RhB), heavy metals, and suspended particles. Overall, ASP-1 shows strong potential as an eco-friendly flocculant for wastewater treatment applications. • A polysaccharide flocculant ASP-1 from asparagus root waste with good flocculation activity. • The flocculation activity exhibited stability within a pH (5−8) and temperature range (room temperature to 60°C). • ASP-1 exhibits superior removal activity for low-concentration pollutants(5 mg/L, 10 mg/L) compared to high-concentration (50 mg/L, 100 mg/L). • The combination 1/2 ASP-1 and 1/2 PAC showed excellent flocculation performance.