Production Of Bioflocculants And Their Flocculation Properties

Bioflocculants are polymers produced by microorganisms during their growth, and their obvious advantages are non-poisonous, readily biodegradable and friendly to the environment. With the enhancement of people's environmental consciousness, the studies of bioflocculants have drawn more and more attentions and become front line of investigation. The isolation of flocculant-producing bacterium and optimization of culture conditions for flocculant production was first studied, and then the composition, characteristics and application of the bioflocculants were discussed systematically in this dissertation. The main results are as follows:1. Two strains of bacteria with high flocculating activity, Q-7 and T-11, were isolated from activated sludge with kaolin clay suspension as test sample. Based on the morphological, physiological and biochemical characteristics, Q-7 and T-11 were identified as Sphingobacterium thalpophilum and Serratia plumuthica, respectively. To our knowledge, it's the first time to find Sphingobacterium sp. and Serratia sp. producing bioflocculants.2. Cultivation conditions for flocculant production were optimized using "one-variable-at-a-time" method. The optimal cultivation conditions for strain Q-7 were 20g/L soluble starch, 2g/L (NH₄)₂SO₄, 1g/L MgSO₄·7H₂O, pH 7.0, 30℃, 150r/min and 24h. As for strain T-11, they were 30g/L sucrose, 2g/L NaNO₃, 0.5g/L MgSO₄-7H₂O, 0.5g/L K₂HPO₄, pH 6.0, 30℃, 125r/min and 10h. Under such conditions, the strain Q-7 and T-11 could reach the highest flocculating activity more quickly than other strains ever reported, which may reduce the producing cost.3. The feasibility that strain Q-7 could produce flocculant in starch wastewater was tested. Results showed that strain Q-7 could rapidly grow and reproduce well in starch wastewater when 0.8g/L (NH^SC^ and 0.6g/L MgSO4-7H2O were added, at the same time it also excreted extracellular flocculant.4. The two kinds of flocculants which were produced by strain Q-7 and T-11 were analyzed and results showed that they were both composed of polysaccharides. The factors that affect efficiency of flocculation were also tested systematically. The flocculant produced by strain Q-7 was found to be effective for flocculation of kaolin suspension when the dosage was 4⁵ml/L, pH was 2-7 and temperature was from 20°C to 60°C. As for strain T-11, the dosage was 0.4ml/L, pH was 2-7 and temperature was from 30°C to 80°C. Compared with other bioflocculants that were reported, the two kinds of bioflocculants show a good quality of less dosage, wider pH range and higher thermal stability.5. When studying the application of bioflocculants, bulking sludge, excess sludge and carbon ink water were selected as flocculating objects. Results showed that the two kinds of bioflocculants produced by strain Q-7 and T-11 had strong decoloring ability to carbon ink water with the aid of CaC^. When dealing with bulking sludge, the two kinds of bioflocculants could restore its settling characteristics within 18h. The two kinds of bioflocculants could also efficiently dewater excess sludge with the highest flocculating rate of about 85%.