Xiao Yutang and
his group used the biological contact oxidation in the pretreatment of the micro-polluted raw water of Yao Jiang, and the bio-film thickness of the water was 0.3-0.5mm, the effluent was 0.1-0.3mm, when the dissolved oxygen of the water was controlled in 7-9mg/L, the bio-film of the filler was full of aerobic layer with high aerobic oligotrophic microorganisms mainly [24].