| Characteristics of nano-SiO2 dispersions and application of nano-SiO2 as coagulation-aid in removal of dissolved organic pollutants were studied. A nano- SiO2 dispersion was obtained by adjusting of the dispersion to pH 7 and supersonic agitating it for 10 minutes. Results of SEM, TEM, and Laser seizer measurements indicated that there more than 99% of the SiO2 particles were less than 30 nm size. The dispersion could be stable with the particle size for 10 hours.Three organic compounds, humic acid(HA), anionic surfactant(SDS) and p-chlorphenol, representing different molecule size, were selected as typical organic pollutants for enhanced coagulation experiment with nano-SiO2 as the aid. For HA, a big molecule compound, results showed that it could be removed up to 73% by coagulation with Al2(SO4)3 (20mg/L) as coagulant and nano-SiO2 (Img/L) as the aid, comparing a lower removal of 30 % without the aiding of nano-SiO2 at the same conditions.Comparison to the big molecule compound HA, smaller molecule compounds SDS and p-chlorphenol, a much lower removal (less than 8%) was obtained under the same coagulation conditions with the aid of nano-sized SiO2 as the HA, indicating that the enhancement of nano-sized SiO2 was more effective for bigger molecule compound than the smaller ones.In addition, conditions such as pH volume, temperature, dosage of Al2(SO4)3 and SiO2, could also affect the removal of the dissolved organics. The suggested conditions for good removal of HA were pH 5-9, Al2(SO4)3 20mg/L, SiO2 1~10mg/L.
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