Divided by function
Sewage treatment can be divided into physical method, biological method and chemical method according to its function.
① Physical method: Insolubles in sewage are mainly separated by physical action, and their chemical properties are not changed during treatment. Commonly used are gravity separation, centrifugal separation, reverse osmosis, air flotation and so on. The physical treatment of structures is simple and economical, and it is used in villages and towns with large water volume, strong self-purification ability and low requirements for sewage treatment.
② Biological method: The dissolved or colloidal organic matter in sewage is decomposed and oxidized into stable inorganic matter by using the metabolic function of microorganisms, so that the sewage can be purified. Activated sludge process and biofilm process are commonly used. The treatment degree of biological method is higher than physical method.
(3) Chemical method: it is a method to treat or recover dissolved or colloidal substances in sewage through chemical reaction, which is mostly used in industrial wastewater. Coagulation, neutralization, redox and ion exchange are commonly used methods. Chemical treatment has good treatment effect and high cost, and it is mostly used as the effluent after biochemical treatment for further treatment to improve the effluent quality.
Depending on the degree of treatment
Sewage treatment can be divided into primary treatment, secondary treatment and tertiary treatment according to the treatment degree.
Primary treatment is mainly to remove suspended solids from sewage, and physical methods are commonly used. After primary treatment, the BOD removal rate of wastewater is only 20%, which is still not suitable for discharge and needs secondary treatment. The main task of secondary treatment is to remove a large number of colloids and dissolved organic substances from sewage, and the removal rate of BOD is 80% ~ 90%. Generally, the sewage after secondary treatment can meet the discharge standard, and the commonly used methods are activated sludge method and biofilm method. The purpose of tertiary treatment is to further remove some special pollutants, such as fluoride and phosphorus, which belongs to advanced treatment and commonly used chemical methods.
Selection of sewage process flow requires 1. To improve the existing primary treatment process to enhance the treatment effect, we should make full use of the existing treatment facilities according to the actual situation, reform the structure or operation mode of septic tanks and contact tanks widely used in existing hospitals, and add some facilities when necessary to improve the treatment effect as much as possible to meet the discharge standards of hospital sewage treatment.