Sewage treatment can be divided into three types: physical method, biological method and chemical method.
Physical method: The main use of physical action to separate non-soluble substances in sewage, in the process of treatment does not change chemical properties. Commonly used are gravity separation, centrifugal separation, reverse osmosis, and air flotation. The physical method is relatively simple and economical to deal with the structure. It is used in cases where the water body in the village has large capacity, strong self-purification ability, and low sewage treatment requirements.
2 Biological method: Using the metabolic function of microorganisms, the organic matter in the sewage that is dissolved or colloidal state is decomposed and oxidized into stable inorganic material, so that the sewage is purified. Commonly used are activated sludge method and Biofilm method. The degree of biological treatment is higher than the physical method.
Chemical method: It is a method that uses chemical reactions to treat or recover dissolved or colloidal substances of sewage, and is mostly used in industrial wastewater. Commonly used methods include coagulation, neutralization, Redox, and ion exchange. The chemical treatment method has a good effect and high cost. It is mostly used as a effluent after biochemical treatment to further treat and improve the water quality.
By level of treatment
Sewage treatment can be divided into primary treatment, secondary treatment and tertiary treatment according to the degree of treatment.
Primary treatment is mainly to remove solid substances in the suspended state of sewage, commonly used physical methods. The removal rate of BOD from primary treated wastewater is only 20 %, and it is still not suitable for discharge. Secondary treatment is also required. The main task of secondary treatment is to substantially remove organic matter in the colloidal and dissolved state of sewage, and the BOD removal rate is 80 % to 90 %. Generally after secondary treatment of sewage can meet the discharge standards, commonly used activated sludge and Biofilm treatment. The purpose of tertiary treatment is to further remove certain special pollutants, such as fluoride removal, phosphorus removal, etc., which are deep treatments and are commonly used chemical methods.
The existing treatment facilities should be fully utilized according to the actual conditions, and the septic tanks and contact pools used more frequently in existing hospitals should be modified in terms of structure or operation. If necessary, some additional facilities will be added to improve the treatment effect as far as possible in order to meet the emission standards for hospital sewage treatment.