4　Pretreatment System

4.1　General Requirements

4.1.1　The pretreatment of the seawater desalination system shall be determined on the basis of seawater quality and seawater desalination process specification.

4.1.2　A pre-sedimentation tank should be provided when the suspended solid and sediment content in the raw seawater exceeds the water inflow specification of the selected clarifier（tank）.

4.1.3　The coagulation，clarification，media filtration or ultra（micro）filtration process shall be used for the pretreatment of SWRO desalination system according to seawater quality，system scale and other factors.Typical processes include:

1　Seawater→coagulation，clarification→multiple media filtration→fine sand filtration；

2　Seawater→coagulation，clarification→media filtration ultra（micro）filtration；

3　Seawater→coagulation，clarification→ultra（micro）filtration；

4　Seawater→multiple media filtration→fine sand filtration；

5　Seawater→ultra（micro）filtration.

4.1.4　The pretreatment process of seawater distillation desalination system shall be determined according to seawater quality and desalination process，and shall comply with the following provisions:

1　For multi-stage flash desalination process，acid dosing and degassing unit only will be sufficient；

2　The pretreatment unit of the multiple effect distillation desalination process shall be provided according to the inflow water quality requirements of the distillation unit，and coagulation and clarification processes can be adopted.

4.1.5　The inflow water of ultra（micro）filtration unit should be determined according to Table 4.1.5.

Table 4.1.5　Inflow water specification of ultra（micro）filtration unit

4.1.6　The design of the pretreatment system shall comply with the relevant provisions in the current national standard GB 50013 Code of Design for Outdoor Water Supply Engineering and the current industrial standard DL/T 5068 Technical Code for Designing Chemistry of Fossil Fuel Power Plants.