| Organic and inorganic flocculants have been used widely because of their economical and effective flocculating characters. However, their disadvantages caused people's attention for people's higher demands of health and environment in recent years. Often eating the materials treated by Al-flocculants may lead old people to stupid. The monomer of acrylamide cann't be degraded easily and it's both neurotoxic and a strong carcinogen in human body. The making process of traditional flocculants often produces new pollution. Thus, safe biodegradable flocculants that are able to minimize environmental and health risks are urgently needed. Micrdbioflocculant (MBF) is just this kind flocculant. MBF concludes both some microbes which have flocculation ability and some materials which are secreted by microbes, such as protein, fat, and polysaccharide etc.. Till now, many kinds MBF are found and made out, but they are not used widely for the reason of their high prices. However people belive MBF would take the place of the traditional flocculants in the fields of water treatment, food processing, pharmaceutical industry etc. for their advantages.The reason of MBF's high price is the high production cost and the low MBF output. This research focused on the point of how to increase the output of MBF, and at the same time also researched the purification, synthetics, flocculating mechanism of MBF, and so on. The following works had been carried out.Firstly, 26 strain flocculant producing microbes were screened from different samples, and in which 5 strains' flocculating activity is found more than 60% (transmittancy). In this research, one mould (designated Ml) whose flocculating activity is the greatest was selected as the research object. The culture broth of Ml is able to flocculate Kaolin suspension. After adding 2ml culture broth of Ml to 100ml Kaolin suspension (mean diameter 3.52μ m, 4g/L), then mixing the suspension and waiting for 5 minutes, the transmittancy of the supernatant of Kaolin suspension was found to be 72.8%.Secondly, the influence of culture conditions on the MBF output of Ml was researched. The single factor experiments showed that glucose, fructose, polypeptone and glutamic acid are favourable for the growth and MBF output of Ml, the culture temperature of 30℃ is favourable for the growth of Ml, and 26℃ is favourable for the MBF output of Ml. By the way of altering the culture temperature can increase the MBF output of Ml. The initial pH of culture medium of 6.5 is the optimum pH for Ml to secrete flocculant. The rate of rotary shaker of 160rpm is the optimum rate for the MBF output of Ml. Then the way of even-design experiment was used to investigate the influence of the synergisticeffect of above factors on the MBF output of Ml, and the optimum culture condition had been attained to be: the content of glucose and polypeptone of 9g/L and 6.5g/L respectively in culture medium, the initial pH of culture medium of 5.5, the rate of rotary shaker is ISOrpm, and the culture way of altering temperature. According to this condition, the MBF output of Ml can be increased to 79.6% (the transmittancy of the supernatant of Kaolin suspension). So it is obvious that changing the culture conditions of Ml can increase the MBF output notably.Thirdly, Ml was mutated by UV, and the MBF output of the mutant strain of Ml was researched. Using the UV-bulb (15W) irradiates the Ml mycelium suspension for certain time in the distance of 30cm. The result showed that the MBF output of the mutant strain (designated MIA) of Ml is improved to 83% (the transmittancy of the supernatant of Kaolin suspension) when the irradiating time is 90s. So it illustrates that the matagenesis can increase the MBF output of Ml obviously.Fourthly, by the way of ethanol precipitation, a white microbioflocculant (designated MBFXH) was separated from the culture broth of MIA and the output of MBFXH is about 0.86g/L. It was confirmed that MBFXH is a extrapolysaccharide by the way of element analysis, UV spectrum, Molish reaction etc. and its...
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