GRAVITY/RAPID SAND FILTRATION

 

 

Process Description

 

 

Filter Bed Materials

 

Generally, filter beds are made from granular materials.

 

 

 

Impurities Removed

 

   

Filtration Mechanisms

 

Physical and Chemical Process

 

Based upon:

 

 

 

Removal Processes

 

 

 

TYPES OF FILTERS

 

Gravity Filters

 

Gravity Filters Water moves downward through filter media by gravity.

 

 

 

Slow Rate Gravity Filtration

 

 

 

Rapid Rate Gravity Filtration

 

 

 

FILTER CONTROL SYSTEMS

 

Filter control systems regulate flow rates by maintaining adequate head above the media surface. This prevents sudden flow increases, or surges, which could dislodge trapped solids.

 

 

 

Common Filter Control Systems

 

Constant Rate

 

 

 

Declining Rate

 

 

 

PERFORMANCE CONSIDERATIONS

 

Filter Media Materials

      

 

Filter Media Support

 

Media Characteristics

 

 

 

Media Classification

 

Effective Size (ES)

 

 

 

Uniformity Coefficient (UC)

 

 

 

Specific Gravity (SG)

 

 

 

Hardness

 

 

 

 

Filter Underdrains

 

Filter Underdrains collect filtered water during normal operation and distribute backwash water during backwash process.

 

 

 

Underdrain Types