Flocculation of coal washing wastewater using polysaccharide produced by Paenibacillus mucilaginosus WL412

Natural polymeric flocculant shows effectiveness in wastewater treatment without increasing the environmental burden. The extracellular substance produced by Paenibacillus mucilaginosus WL412 was identified as an anionic polysaccharide composed of five types of monosaccharides, namely, D-mannose, D-glucuronic acid, D-glucose, D-galactose, and L-fucose with the molar ratio of 2.8:1.2:2.0:1.8:0.8. The purified polysaccharide, POS412, presented high efficiency in flocculating coal washing wastewater and kaolin suspension without the assistance of inorganic coagulants. Addition of POS412 resulted in the polymer bridging phenomenon in suspensions, which was observed by means of scanning electron microscopic imaging, size grading, and ζ-potential analyses. More importantly, POS412 exhibited satisfactory stability after storage in various conditions. The flocculation rate was more than 91% for coal washing wastewater when POS412 was stored for 264 h in the wide range of pH (3-11) and temperature (20-50 °C) before use. Results indicate that POS412 is a competent bioflocculant for wastewater treatment.