Screening Of Bioflocculant-producing Bacteria And The Study On Its Application In Clarification Process Of Sugarcane Juice

Flocculants are added to preliming juice for improving sedimentation effect and quality of sugarcane juice in the clarification process. At present, polyacrylamide(PAM) is widely used in the sugarcane factories for clarification. However, the use safety of PAM has become an increasingly important issue. Bioflocculants are metabolites with flocculating activities produced by microorganisms during growth. As a new kind of flocculant, bioflocculant is biodegradable, safe, and environment friendly.In the present study, two strains(N-25 and Z-24) of high bioflocculant-producing bacteria were isolated from activated sludge samples by enrichment culture, spread plate, and plate streaking method. Based on colony and cell morphology, biochemical properties, 16 S r DNA sequence and phylogenetic analysis, strains N-25 and Z-24 were identified as Proteus vulgaris and Klebsiella pneumoniae subsp. pneumoniae.Bioflocculants BN-25 and BZ-24 produced by strains N-25 and Z-24 were applied in clarification process of sugarcane juice. To improve the clarification efficiency of juice clarification, culture and clarification conditions of the two strains were optimized. Under the optimum conditions, applications of both bioflocculants were superior in the sedimentation time, the bulk of mud, the parent purity, and the decoloration rate, whereas weaker in the turbidity removal rate.Furthermore, clarification efficiency and reduction in the dosage of PAM was enhanced by the combination of bioflocculants BN-25 and BZ-24 with PAM, and by optimizing the conditions using orthogonal experiment and variance analysis. Under the optimal conditions, the addition of bioflocculants BN-25 and BZ-24 reduced the dosage of PAM by 75% and 62.5%. Moreover, the decoloration rates were 27.62% and 22.19% higher compared to that of PAM, and the turbidity removal rates of bioflocculant BN-25 compounded with PAM was 6.23% higher than that of PAM. However, while the turbidity removal rates of bioflocculant BZ-24 compounded with PAM was same with that of PAM. Relatively, the sedimentation time, the bulk of mud, and the parent purity of sugarcane juice treated by bioflocculants compounded with PAM have a great advantage than addition of PMA alone.The chemical compositions of bioflocculants BN-25 and BZ-24 were determined. Bioflocculant BN-25 was mainly composed of polysaccharide(89.1%) and protein(9.3%), and the contents of uronic acid, neutral sugar, and amino sugar were 12.3%, 72.5%, and 4.3%, respectively. And bioflocculant BZ-24 was composed of polysaccharide(76.5%) and protein(22.8%), and the contents of uronic acid, neutral sugar, and amino sugar were 7.9%, 51.7%, and 1.1%, respectively. The results of Ultraviolet(UV) further validated that the two bioflocculants contained a small amount of protein, and were free of nucleic acids. Additionally, Fourier transform infrared(FTIR) analysis revealed that the two bioflocculants contained large amount of amino, hydroxyl, carboxyl, and sulfate groups, which were favorable for flocculation. Gel permeation chromatography of the two bioflocculants exhibited that, BN-25 contained two components of polysaccharides with molecular weights of 2.61 × 105 Da and 1.14 × 104 Da, and bioflocculant BZ-24 contained a component of polysaccharide with a molecular weight of 1.95 × 104 Da.