Effect of ferrate preoxidation on coagulation of Songhua River

The preoxidation of polluted surface water with ferrate was conducted with respect to its impact on the following coagulation. It can be seen that UV₂₅₄-absorbance, turbidity and TOC substantially decreased by 36.7% ,80.2% ,31.1%, respectively, after coagulation, without ferrate preoxidation, and by 63.3%, 89.6%, 37.0%, respectively, after coagulation, with ferrate preoxidation. It is noted that NH₄⁺-N concentration is increased by 17% after coagulation with ferrate. This phenomenon can be explained by the fact that organics containing nitrogen in raw water were partly oxidized to inorganic nitrogen by ferrate preoxidation. After coagulation, AOC and AOC/TOC are increased from 998 μg · L^-1 to 1 241 μg · L^-1, from 28.4% to 38.7%, respectively, by ferrate preoxidation. AOC-P₁₇/AOC after coagulation is up to 83 % with ferrate preoxidation. These suggest that preoxidation with ferrate promoted the biodegradation of organics with substantial increases of AOC, AOC/TOC. The results indicate that the concentration of organics with relative molecular mass (M_r) of 10 000-100 000 and less than 500 were substantially increased after the raw water was coagulated with ferrate preoxidation, which suggested that some high molecular weight organic substances were broken into smaller ones during ferrate preoxidation. After coagulation, organics of less than M_r = 500 in TOC are increased up to 65.0% with preoxidation from 38.9% without ferrate preoxidation. These oxidation products are biodegradable.