Screening Of A Bioflocculant-producing Strain And Research On Its Cultural Conditions And Flocculating Characteristics

Bioflocculants, having good flocculating activity, are the metabolic products of the microorganism, which are safe, non-toxic and can be biodegraded easily. Since they overcome the shortcomings in utilizing safety and environmental pollution of the inorganic flocculants and organic flocculants, research and exploration of bioflocculants is realistically significant and have wide prospect in application.This research screened 5 strains of bioflocculant-producing microorganisms from activated sludge from a municipal wastewater treatment plant in Changsha, soil sample from Yuelu Mountain and sludge beside Xiangjiang River by conventional methods. A strain with high flocculating activity was obtained after rescreening, which was identified as Aeromonas sp. and was named Aeromonas sp. N11. Taking the Aeromonas sp. N11 as the subject investigated, .the effect of the cultural conditions and the medium composition and proportion on bioflocculant production was studied, and the flocculating characteristic of the bioflocculant produced by strain Aeromonas sp. N11 was studied also.The experimental results showed that the medium composition and proportion had significant effect on bioflocculant production. After single factor experiment and orthogonal experiment it was found that: high C/N ratio was beneficial to bioflocculant production; carbon source sucrose was beneficial to bioflocculant production of Aeromonas sp. N11; the compound nitrogen source was better than the single nitrogen source; yeast extract was beneficial to bioflocculant production; NaCl could increase the flocculating activity of the bioflocculant produced; carbon source sucrose and nitrogen source carbamide had the maximun effect. The optimium component proportion of medium obtained according to the orthogonal experiment was: sucrose 20g/L, yeast extract 0.8g/L, carbamide 0.5g/L, (NH4)2SO4 0.5g/L, NaCl 7g/L. The optimiun cultural conditions was: pH 7, 30, 170r/min, cultivated for 72hours in flakes.The results of the experiment on the flocculating characteristic of the bioflocculant produced by strain Aeromonas sp. N11 showed that the flocculating activity of the bioflocculant was due to the secondary metabolic product of N11. The bioflocculant was present in the fermentation liquid mainly and had a high thermostability. Univalent ions and divalent ions could promote the flocculating effect while Fe3+ of high concentration restrained flocculation, in which K+, Na+, Ca2+ hadthe best effects. The best dosage of the bioflocculant and the coagulant aids was different for different substances to be flocculated. pH and temperature had effect on flocculating activity of the bioflocculant. The optimum pH had reference to the coagulant aids and the substances to be flocculated. The bioflocculant also had a good effect on soil suspension and the highest flocculating rate was 96.6%. The bioflocculant was simply purified and the producibility of the crude bioflocculant was 2.25g/L, which is relatively high.The study on the bioflocculant produced by Aeromonas sp. N11 showed that the bioflocculant could keep high flocculating activity in wide range of pH and temperature and in low dosage, which indicated a good utilization prospective of the bioflocculant.