The severity of sewage: surface water pollution is obvious, but it is shocking groundwater contamination. China's 1.3 billion people in the medical waste water treatment equipment offer, 70% of groundwater for drinking water treatment equipment medical supplies, more than 660 cities in more than 400 cities with groundwater as drinking water sources. But according to reports, over 90% of urban groundwater has been contaminated. Biological wastewater treatment: the use of microbial metabolism, the sewage was dissolved or colloidal state of decomposition of organic matter is oxidized to stable inorganic substances, sewage purification. Commonly used activated sludge and biofilm. Biological treatment level is higher than the physical law.