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Recently, sources of water have been widely polluted in the world, because of the fastly development of economy, the traditional water purification technique couldn’t eliminate such contamination as organic matter and ammonia nitrogen effectively in the raw water. Therefore, the purification technique for the micro-polluted raw water has been an important and urgent research subject. Some studies shows that the biologic treatment technology is not only economical and effective, but also is security in toxicology. The slow biofiltration is one of those technologies. This article studies the effect and mechanism of the slow biofiltration as pretreatment measures to process the micro-polluted water. This issue is the projects funded by Yunnan Province Department of Education (Project No:07C11440), Which study the organic pollution of raw water purification technology at the core of safety pretreatment.Previous slow biofiltration are placed after the conventional measure as the advanced treatment, but people found that biofilm will fall off and inflow water in water erosion if slow biofiltration used as advanced treatment. Because microorganism in biofilm is long-term fixed cultured, they have strong adaptability to all kinds of adverse environments, and they have stronger resistance to disinfectant, the general post-chlorination disinfecting is difficult to kill these organisms completely, it will increase the amount of disinfectant and halides in water, mutagenic activity increase, those make the safety of effluent water decreased. Some studies have pointed out that it would be better if the biological treatment is set in front of physico-chemical treatment as pretreatment, thus it can give full play to the role of microbial biodegradation, cope with adverse shocks which caused by the changes of water quality, protect the physico-chemical treatment following-up, and the metabolites of microbial, loss of biological organisms and other particles which biological treatment produced can be controlled by follow-up process, thereby the reliability of drinking water is increased. This issue study the effect of micro-polluted water that use the slow biofiltration as pretreatment measure.Microorganism play a major role on the removal of pollutants in slow biofiltration, through the biological observations, it can be founded that it is covered with a large number of biofilm on the surface of quartz sand in slow biofiltration, most of the biofilm exist in the form of agglomerate and flocculation, the shape and type of microorganisms present some diversity, the structure of ball, chain, spherical, rod-shaped, arcuate and clusters were distributed. It included bacteria, filamentous fungus, mold, vorticella and metazoan etc, which formed a stable microbial ecosystem jointly. The biomass in the biofilters decrease gradually from the top layer to the bottom along the water flow, the distribution of dissolved oxygen also show the same trend.The slow biofiltration have good removal for turbidity, CODMn,NH4+-N, TN and TP, the average removal rates reach to 92.3%,34.5%,90.2%,45.2%,30.6%. After treated by the slow biofiltration system, turbidity has been less than 1.2 NTU; the concentration of CODMn has been lower than 6.0mg/L, reach the standards of Class III water in surface water; the concentration of NH4+-N has been lower than 0.2 mg/L, reach to the standards of ClassⅡwater in surface water; the concentration of TN is lower than 2.0 mg/L, the level of water quality is improved; the concentration of TP is 0.14～0.20 mg/L, the level of water quality is improved. The micro-polluted water can reach to the standards as drinking water source if use slow biofiltration as pretreatment measures.Through the study on the affecting factors of slow biofiltration purify micro-polluted water, it have the following conclusions:(1)the removal of turbidity, CODMn and NH4+-N in the column of slow biofiltration occurred mainly in the upper, it should be ensured that the thickness of filter is not less than 700mm; (2) water temperature has some influence on the removal of organic matters, have little effect on removal of turbidity and NH4+-N, which indicated that slow biofiltration have better capacity of accommodation for the water temperature; (3) When the influent concentration of CODMn is low (<8.5mg/L), the removal rate of CODMn increase with the augment on the influent concentration of CODMn in the column of slow biofiltration, however, When the influent concentration of CODMn is too high (>8.5mg/L), the removal rate of CODMn decreases with the augment on the influent concentration of CODMn; the removal rate of turbidity and NH4+-N decreases with the augment on the influent concentration of CODMn; (4) When the influent concentration of NH4+-N is lower than 1.54 mg/L, the removal rate of NH4+-N increase with the augment on the influent concentration of NH4+-N, but the removal rate of NH4+-N decreased gradually if it continues to increase, When the influent concentration of NH4+-N is lower than 1.0 mg/L, the removal rate of CODMn increase with the augment on the influent concentration of NH4+-N, the removal rate of CODMn remained stability when it increase, the removal rate of CODMn decrease when influent concentration of NH4+-N is low to 0.5 mg/L.
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