The Research On Fermentation Of Flocculant-producing Strains And Application Of Microbial Flocculant In Sludge Dewatering

Microbial flocculants, which can make particulates in water flocculated and settled, are polymers produced by microorganisms during their growing periods. Compared with inorganic and organic synthetic flocculants, the greatest advantage of microbial flocculants is non-poisonous, harmless and non-secondary pollution. The study of environmental protection awareness increases, but it's still in the beginning now. Although many flocculants-producing microorganisms have been found at present, and the flocculating activities of flocculants produced by them are excellent, there are too many limiting factors to apply microbial flocculants into large-scale production and use.In this study, a flocculant-producing bacteria, named B2, was screened with isolation medium containing phenol. Its flocculating activity to kaolin clay suspension could get higher than 80%. Another flocculant-producing bacteria N10 conserved in the lab was also rejuvenized and selected. The flocculating activity of N10 was reduced from 90% to 70% due to the long-term unadvisable conservation. After rejuvenation, the flocculating activity was resumed to 85%.N10 and B2 were identified primarily to be Klebsiella sp. and Serratia sp., respectively. There were some differences in flocculating characteristics between N10 and B2. Firstly, the flocculating activities of N10 strain to suspensions such as kaolin clay, soil were higher than that of B2. Secondly, the optimal culture time for B2 strain to produce flocculant was 48h, which was shorter than N10 strain (60h). But the main difference was on the distributions of flocculating activity. The flocculating activity of N10 strain was mainly concentrated in the extracellular culture broth while the flocculating activity of B2 strain was mainly concentrated on the cell. The culture broth of B2 was treated with ultrasonic oscillation and high temperature. The results indicated that the flocculating activity distribution of B2 could be changed by ultrasonic oscillation. The most abundant composition of flocculant was saccharide, with good heat-resistant performance.Based on results of tests above, N10 and B2 were mixed and cultured with the ratio of 1:1. After fermentation, the flocculating activity of mixed strains was between the values of N10 and B2 which were cultivated solely. And the flocculating activities of cells and supernatant could both reach higher than 70%, due to the different flocculant distributions of these two strains. It was confirmed that N10 and B2 strains were preponderate with the tolerance to CuSO4 and phenol, respectively. And the tolerance of coexisting N10 and B2 to phenol-CuSO4 was stronger than any sole strain. It was noticed that, there was a complementary relationship between N10 and B2 while they were cultured together, and the tolerances of them to toxic environment were enhanced.In order to achieve the continuous production of microbial flocculants, the N10 strain was immobilized by supporter absorption and entrapment method. The absorbent carriers were chosen to be granular activated carbon and sponge. It was found that the adsorption capability of sponge for N10 cells was much higher than activated carbon. There was little difference between free and immobilized cells on the flocculant production. But the immobilizing effect of absorption method was not ideal, as the cells would be broken off from the carriers during the fermentation. N10 strains were also immobilized by entrapment method, while alginate and polyvinyl (PAV) were used as the entrapping agents. The results indicated that the immobilizing effect of entrapment method was good, and the phenomenon on cell being lost was solved. But the immobilized cell beads would be broken up easily for their poor mechanical strength and existence of swelling property, and it's unsuitable to be cultured in a long time. In addition, the flocculant production of N10 was also restrained.At last, the crude flocculant MBF10 which was isolated from the culture broth of N10 strain was applied to sludge conditioning. It was found that the sludge conditioning performance of MBF10 was limited, worse than some polymer flocculants such as PAC and CPAM. But the sludge dewatering performance was enhanced with dual use of MBF10 and alum, which were more effective than the use of single flocculants. SRF of sludge was reduced from 10.87×1012m/kg to 1.20×1012m/kg, while the water content was reduced from 98.7% to 75.0%.