Purification,Structural Characterization And Flocculation Activity Of Polysaccharide-Based Bioflocculants From Bacillus Megaterium

Microbial flocculants have attracted widespread attention in recent years due to their environmentally friendly features and properties of easily being degraded.An endophytic Bacillus megaterium was screened out from the leaves of Camellia assamica,its fermentation broth had a great flocculation activity.Further studies confirmed that the polysaccharide-based bioflocculant BM2,which was produced by B.megaterium PL8 had high-efficiency flocculation effects on a series of wastewater.In this study,the purification,structural characterization and flocculation mechanism of BM2 were investigated,and we applied BM2to a series of wastewater.This study provided rudimentary support for the industrial application of this bioflocculant.The experimental results of this study are as follows:?1?Crude bioflocculant with a yield of 0.784±0.08 g/L was obtained from the 3-days fermentation broth of B.megaterium.The content of polysaccharide was found to be 78.5%?w/w?and protein in the crude EPS was 9.2%?w/w?.The proteins in the bioflocculant were removed after the Sevag reagent treatment and then DEAE-52 was used to further purify the crude bioflocculant.Two independent fractions BM1 and BM2?eluted with 0 M Na Cl and 0.2M Na Cl,respectively?were collected.The molecular weight of BM2 was 4.55×10⁶ Da.The results indicated that BM2 was a complex heteropolysaccharide which was composed of Gal,Gal UA,Glc,Glc UA,and Man at a molar ratio of 45.1:33.8:9.3:9.2:2.4,respectively.The FTIR and XPS analysis indicated the existence of abundant carbonyl groups and a few amino groups.The results of methylation analysis showed that BM2 were consisted of 7 linkage forms:?1?3?-linked Gal,?1??-linked Gal,?1??-linked Glc,?1?2?-linked Glc,?1?3?-linked Glc,?1?3,4?-linked Man and?1?2,6?-linked Man.?2?The application research of BM2 showed that the maximum flocculation rate was 90.23%at the dosage of 30 mg/L.The p H values ranging from 4 to 11 were applicable to obtain over80%flocculation activity of kaolin clay suspension and BM2 had the highest flocculation activity?88.66%?when the p H was 8.The results also showed that BM2 had a high flocculation activity?over 87%?from 20°C to 100°C,and the maximum flocculation activity of BM2 was90.45%when the temperature was 60°C.BM2 had a strong ability of decolorization on Congo red.When the initial concentration of Congo red was 100 mg/L,the dosage of BM2 was 150mg/L,and p H value was 7,the dye decolorization rate achieved the highest efficiency?88.14%?.Besides,BM2 has a strong adsorption effect on heavy metals.When the initial concentration of metal solutions were 100 ppm and the dosage of BM2 was 1250 mg/L,the Pb²⁺iron exhibited the highest removal efficiency?82.64%?,and Zn²⁺and Ni²⁺were 51.82%and 33%,respectively.?3?The main bonding between the BM2 and kaolin particles in the flocs was ionic bond,which was measured by chemical method.The results of zeta potential before and after the flocculation reaction showed that the main mechanism of BM2 towards kaolin clay may be adsorption bridging.