4.2　System Design

4.2.1　Design of clarification system shall comply with the following provisions:

1　For the clarification system，clarification（sedimentation）tank with coagulation function should be used，and the specific type shall be determined according to the seawater quality，treatment water flow and inflow water quality requirements of subsequent units，and in conjunction with local conditions；

2　There should be no less than 2 sets of clarification（sedimentation）tanks.When 1 set of equipment is under maintenance，the remaining equipment shall meet the normal water supply demand of the system；

3　The clarification（sedimentation）system shall be provided with storage and metering units for chemicals such as coagulant，coagulant aid，bactericide，acid and alkali.The types and dosing amount of chemicals shall be determined according to seawater quality，test results or with reference to operation experience under similar conditions.

4.2.2　Design of media filtration system shall comply with the following provisions:

1　Types of media filtration equipment shall be determined according to inflow water quality and in conjunction with project characteristics；

2　The output water turbidity of media filtration equipment shall meet the inflow water quality specification of the downstream equipment；

3　There shall be no less than 2 sets（cells）of media filtration equipment.When 1 set（cell）of equipment is under maintenance，the remaining equipment shall meet the normal water supply demand of the system；

4　When inflow water stability is required by the downstream system of the media filtration equipment，special backwash equipment should be provided；

5　The product water from the filtration equipment should be used as the backwash water source of the media filtration equipment.

4.2.3　Design of ultra（micro）filtration system shall comply with the following provisions:

1　In the design of the ultra（micro）filtration unit，the membrane assembly type，membrane materials and unit operation mode shall be selected according to the inflow water quality，treatment water flow and inflow water quality requirements of the downstream desalination unit；

2　The ultra（micro）filtration system can consist of ultra（micro）filtration feed water pump，cartridge filter，ultra（micro）filtration membrane assembly，monitoring instrument，backwash unit，chemical cleaning unit and dosing unit；

3　There should be no less than 2 sets of ultra（micro）filtration membrane assemblies；

4　The cartridge filters of the pressurized ultra（micro）filtration system shall be able to realize automatic cleaning，and the filtration precision shall meet the inflow water requirements of the ultra（micro）filtration membrane assembly；

5　The pressurized ultra（micro）filtration feed water pumps，cartridge filters and ultra（micro）filtration membrane assemblies should be connected in parallel.When there are less than 3 sets，the inflow water pumps，cartridge filters and membrane assemblies can also be connected in series；the product water pump and ultra（micro）filtration membrane assemblies of submerged ultra（micro）filtration system shall be connected in series；

6　The output water quality and producing water ratio of the ultra（micro）filtration system shall be determined according to the inflow water quality and characteristics of ultra（micro）filtration membranes，and the main design parameters should comply with the provisions in Table 4.2.3；

7　The dosing chemical types，amount and location，and chemical cleaning liquid of the ultra（micro）filtration system shall be determined by such factors as inflow water quality，membrane pollutant component，membrane assembly types and membrane materials.