Abstract: The authors used the elastic packing for biofilm and fine bubble aeration for oxygen enrichment in the system of biological contact oxidation to rehabilitate the slightly polluted Chuanyang River in Shanghai. Parameters of water quality in Chuanyang River were as follows: turbidity 90～300 NTU, NH+4-N 0.5～10.0 mg/L, CODMn 4.0～10.8 mg/L, and pollution index 2～8. Establishment of biofilm was successful within seven days with the influent water having a concentration of NH+4-N 2.6～3.1 mg/L and temperature 20℃～22℃. The removal rates of NH+4-N was more than 90％. The authors washed the packing and removed the sludge periodically in order to avoid the occurrence of anaerobic condition in biofilm that would decrease the removal rate of the pollutants. Under the normal condition of biorehabilitation,i.e. HRT 1.3 h, DO 7.5～10.2 mg/L, the ratio of gas to water 0.5, The authors observed a biophase enriched with the bacterial species of various physiological characteristics (aerobic, heterotrophic, and autotrophic). The biofilm thickness was in the range of 0.09 to 0.13 mm and increased with decreasing NH+4-N of raw water. Due to the adequate concentration of dissolved oxygen, the rates of mass transportation and thus NH+4-N degradation were rapid. So,about 90% removal of NH+4-N was achieved within an hour.

Key words: water source, slight pollution, biorehabilitation