What is multigrade filtration in water treatment?

Multigrade filtration is a depth-filtration process that uses multiple layers of filter media, such as anthracite, quartz sand, and supporting gravel, to remove suspended solids and turbidity from water. It is commonly used as a pretreatment stage before RO, UF, softeners, EDI, and other water-treatment processes.

What does a multigrade filter remove?

A multigrade filter primarily removes suspended solids, turbidity, sand, silt, and other particulate matter. It can also capture precipitated iron and manganese when an appropriate oxidation stage is provided upstream. However, it does not remove dissolved salts and therefore cannot replace technologies such as reverse osmosis for TDS reduction.

Is multigrade filtration necessary before reverse osmosis?

Effective pretreatment is important for protecting RO membranes from particulate and colloidal fouling. An MGF can reduce suspended solids and turbidity before water reaches finer filtration and the RO system. The exact pretreatment configuration depends on the source-water quality and the requirements of the RO system.

How often should a multigrade filter be backwashed?

Backwash frequency depends on the feed-water quality, solids loading, filtration rate, and pressure differential across the filter. Backwashing may be initiated based on differential pressure, operating time, or changes in outlet water quality. The filter should be backwashed before excessive pressure loss or solids breakthrough occurs.

What is the difference between a multigrade filter and a sand filter?

A sand filter primarily uses sand as its filtration medium, while a multigrade or multimedia filter uses multiple media layers with different particle sizes and densities. This allows filtration to occur through a greater depth of the bed and can provide higher solids-holding capacity and longer filter runs for suitable applications.

Multigrade Filtration for Industrial Water Treatment | MGF Filter Guide