Screening Of Flocculating-producing Strains And Study On Their Culture Conditions

Microbial flocculants used in water flocculation and settlements are polymers produced by microorganisms during growing periods. They are new kinds of water-treatment agents extracted or purified from microorganisms or their secretes by means of biological techniques. The safe, high efficient, non-poisonous, harmless, non-secondary polluting microbial flocculants can be naturally decomposed.Several sorts of strains were isolated from many samples by a series of experiments, 12 strains producing microbial flocculants were obtained, with a flocculating rate over 70%, 10 of them were molds, named as M-5, M-12, M-17, M-19, M-25, M-26, M-30, M-37, M-44 and M-47, respectively, and the other 2 sorts were bacteria, Bacillus sp. and B-60.Many factors, such as initial pH of the medium, the rotating speed of the flakes, the culture temperature and the kind of the culture medium, affect the synthesis on bioflocculants. The sequences of importance and the primary culture conditions were found by orthogonality test. Three strains with a satisfactory activity were achieved. They are M-25, M-26 and M-30, In which M-26 and M-30 were first found to be bioflocculants producing strains, identified to be Aspergillus, Curvlaria Boedijn and Penicillium, respectively.The optimum culture conditions of strain M-25 were found by single factor test. Starch was used as carbon source, urea as nitrogen source, the ratio of C,N and P was 100:(3-5):1, initial pH 5.0-6.0, rotating speed 140r/min, cultural temperature 35℃, and 36-48 hours for cultivation. The addition of some inorganic salts such as CaCO3 and KH2PO4 could enhance the flocculating activity.The optimum culture conditions of M-26 were as follows, starch ascarbon source, urea as nitrogen source, initial pH as nature , rotating speed 140r/min, cultural temperature 35℃, 24-36 hours for cultivation. The optimum culture conditions of M-30 are , glucose as carbon source, (NH4)2SO4 as nitrogen source, initial pH as nature , rotating speed 140r/min, cultural temperature 25℃, 72 hours for cultivation.While the microbial flocculants produced by M-25 were used to clarify kaolin suspension, good performance can be achieved with the minimum dosage of 1.5-2.0mL/L, no obvious enhancements were observed with the addition of dosage. High flocculation efficiency can be achieved when the pH values of kaolin clay suspension were kept between 2-9, the concentration about 3-5g/L and the granularity between 60 -200. The addition of metal ion such as Ca2+, Mg2+and Fe2+ can improve the flocculation activity.This kind of bioflocculant presents a good flocculating effect against different suspension, such as powder activated carbon suspension, clay suspension, microbial cell suspension and other colloid solutions. The bioflocculant produced in these culture conditions is of a high acid-alkali and thermal stability.