Abstract: Two processes for treating slightly contaminated source water, namely, the combinative process by flocculation and biological aerated filter and the single flocculation process, were experimentally compared. The results show that, when the CODCr of the source water, the mass concentration of NH3-N and the turbidity are respectively 20 -28mg/L, 5.2 -6.7mg/L and 8 -18NTU, with 1.5 -3.5 million algae in per liter source water, the combinative process can help decrease the corresponding values of the effluent by less than 10mg/L, 0. 6 mg/L and 2 NTU and that the efficiency of the combinative process to remove the contamination (especially the algae) is much better than that of the single flocculation process, and that the combinative process can remove 90% algae and save 45% flocculant.

Key words: slightly contaminated water, biological aerated filter, coagulation