Multi Media Filters / Sand Filters
Designed for the removal of small particles, organics, and floating contaminants to protect downstream equipment or meet discharge requirements.
Sand filters are used to remove suspended solids from water flow. Sand filters are design to remove relatively large solids (50-100 microns), given that they have one size of filtration media. The coarseness of the filtration process can be determined by adjusting the size of the filtering sand. The effective size of each granule of sand typically varies from 0.35mm – 1.2mm. Sand filters can use graded support media layers or be installed directly over or on a distribution plate or header/lateral under-drain.
Multi-Media Sand Filters are for removing suspended solids of finer sizes. These filters utilize either two or three layers of filter media to accommodate greater solids loading and finer particle removal. These filters typically are able to filter particles down to 15-25 micron and can achieve as low as 5 micron filtration depending on sizing and arrangement of vessels. As water flows downward through the bed, it encounters layers of filtration media with decreasing porosity. Successively smaller particles are then trapped in each layer, thus providing true depth filtration and increasing the filters capacity considerably over a sand filter. Multimedia filters are also sometimes referred to as dual media, anthracite, granular media, multi-layer or pressure filters. Multi-media filters use graded support media layers over the under-drain to prevent the layers from migrating into each other during backwashing.
Manganese Greensand is used to reduce iron, manganese, and hydrogen sulfide from water through oxidation and filtration. Manganese greensand consists of a manganese dioxide coating deposited on the surface of glauconite clay grains. The manganese dioxide acts as a catalyst in the oxidation reduction reaction of iron and manganese.
Typical Filtration Applications:
Typical Filtration Uses:
- Suspended Solids Filtration (TSS)
- Metals Filtration
- Sediment Filtration
- Iron Filtration
- Lead Filtration
Specialty Design Considerations:
- ASME Standard vessel construction
- FRP vessel construction
- Fully-automatic backwash operation
- Self-source backwash or outside-source backwash
- Class 1, Division 1 & Class1, Division 2 environments
Sizing of sand filter vessels:
Sizing for multi-media/sand filters is based on several properties of the water stream the client needs to treat.
- Concentration of solids: Higher concentrations of solids will require lower loading rates through the filter vessels and as a result, larger diameter vessels.
- Application of discharge water and discharge limits: The required effluent concentrations in the process stream helps determine the size of the vessels. The diameter of the vessels will increase as the restrictions get tighter for discharge allowances.
- Size of particles you wish to filter: The loading rate required to adequately filter solids from the process stream needs to be lower for smaller sized solids. As a result, the diameter of the vessels will increase as the size of the particles that need to be filtered decreases.
- Source of backwash water: Backwash water is used to clean the filters and flush out the suspended solids that have been trapped in the media bed. Water for backwashing can come either from the filters themselves (Self Source) or from an external source of clean water (Outside Source, such as a domestic water line or a storage tank).
Self-Source Auto-Backwash is achieved by using the filtered raw water from two (2) or three (3) of the filtered cells and diverting over to the remaining cell. All cells are backwashed in sequence. The filtration process will continue while in the backwash cycle so the system is not “down” while backwashing. An independent backwash water supply is not required. Self-source system typically three or four filters to allow enough flow to reach 12-15 gpm/ft2 of filter bed surface back wash flow rate. During these periods (which typically last for several minutes per filter), the amount of filtered effluent flowing downstream of the filter is reduced or stopped completely by the amount of water required for backwashing, although the process flow into the system continues to while backwashing. It is easy to operate and maintain and a pressure sensor, timer or manual initiation can be used to initiate the backwash cycle.
Air Scour utilizes pressurized air to blow up through the filter media layers of the filter bed. Air scour before the backwash cycle breaks up the sediment from the filtering media allowing it to be backwashed out easily. Typically the air scour is done through a separate header which will be installed above the support bed.
Hydrocarbon or polymer loading in the process water can foul or blind the media bed permanently requiring media replacement. Hydrocarbons in particular will adhere to anthracite, so we do not recommend it be used when hydrocarbons are present. High residual concentrations of polymer should be eliminated and require more frequent backwashing to allow it be removed before forming a layer that is too thick to break up and backwash out of the filter bed.
Recommended Service Flow Rates/Ranges based on the sq.ft. of the tank/filter bed.
— 2-4 gpm/ft2 – Typical municipal loading rate for long bed life and 20 to 40 micron nominal filtering with less than 5 to 10 psi pressure drop when the bed is clean
— 4-7 gpm/ft2 – Typical industrial loading rate for large particle loading, long bed life and 20 to 40 micron nominal filtering with less than 5 to 10 psi pressure drop when the bed is clean
— 7-10 gpm/ft2 – Low loading industrial filtration for 40 to 100 micron nominal filtering with up to 10 to 20 psi pressure drop
— 10-15 gpm/ft2- Utility filtration only (no micron rating estimate) with up to 25 to 30 psi pressure drop
Recommended Backwash Flow Rates/Ranges based on the sq.ft. of the tank/filter bed.
— 12-15 gpm/ft2 – Typical multi-media filter backwash flow rate
— 15-20 gpm/ft2 – Typical sand filter only backwash flow rate
Recommended Air Scour Flow Rates/Ranges based on the sq.ft. of the tank/filter bed.
— 2-4 cfm/ft2 – Typical sand/multi-media filter air scour flow rate
See our attached sizing program to estimate which multi-media filter vessels from H2K Technologies would meet your filtration needs.
450 gpm acid resistant multi-media filter with automatic self-source backwash to polish precipitated lead from wastewater stream, filter system had to be able to resist acid loading from upsets in a clarifier upstream. The completed system, included (3) 6’ diameter filter vessels, PVC manifold and piping, PVC pneumatically operated diaphragm valves, locally mounted control panel, and skid for entire system.
120 gpm Multi-media filter with automatic self-source backwash and ASME rated vessels wastewater from painting line required filtration for TSS before discharge. The completed system, included (3) 3’ diameter filter vessels, PVC manifold and piping, PVC pneumatically operated diaphragm valves, locally mounted control panel, and skid for entire system.
Municipal water treatment works
800 gpm Multi-media filter with automated self-source backwash and ASME rated vessels. This turnkey package filtered TSS from municipal drinking water before chlorination and distribution. The completed system included (4) 8’ diameter filter vessels with schedule 40 carbon steel piping, fittings, and pneumatic-actuated cast iron valves.
25 gpm Multi-media filter with automatically operated self-source backwash and FRP pressure vessels. Wastewater from plant processes was to be filtered for suspended solids before discharge to sewer. The completed system, included (3) 18” diameter filter vessels with PVC manifold and piping, PVC pneumatically operated diaphragm valves, locally mounted control panel, and skid for entire system.