MECHANICAL FILTRATION

 

Proper removal of suspended solids is one of the key factors that determine the proper operation of recirculation systems. These substances in suspension do not only cause turbidity, but they also have a negative impact on water quality, in the performance of water treatment equipment and, furthermore, can effect the development of many aquatic species.

 

The elimination of these particles can be made from different computers depending on the specific needs of filtration:

 

 

- Drum Filter

 

- Sand Filter

 

- Cartridge Filter

 

- Bag filter

 

 

It is common practice in many facilities to make a removal of suspended solids in two parts: an initial separation of solids by heavy roughing systems (static and mobile systems), followed by filtration which removes the finer particles. In this way the filter is much more efficient and requires less maintenance.

 

 

Drum Filter

 

 

The operative cycle is simple: the fluid to be filtered enters into a rotating drum. The periphery of the drum is made of solid stainless steel perforated plates.

 

Impurities larger than the holes are trapped on the inside of the filter plates.

 

The drum rotates slowly (3 - 8rpm, depending on model) dragging the impurities out of water. A ramp located flush at the top of the drum, then cleans the plates to evacuate the impurities in the output channel of the sludge.

 

The filters are designed to withstand any corrosion, as they have been built in stainless steel 304L or 316L stainless steel for salt water applications.

 

Requires little maintenance. Constructed entirely of stainless steel, can be installed quickly thanks to a unique mounting system.

 

Drum filters are available in three different models, depending on the needs of the facility and the flow to be treated:


 

 

Filters are available from 25um to 120um and with water flow from 30 m3 / h to 2,700 m3 / h.

 

As options, filters can be equipped with:

 

- Main control Panel. Electrical control box with selector MANUAL/STOP/AUTOMATIC, made of polyester reinforced with fiberglass IP65.

 

- Backwash pump. Vertical Pump 304L or 316L stainless steel. The pump is supplied with all fittings in PVC.

 

- Water level probe. A level sensor detects and controls the filter mesh (variation of water level in the filter) and sends a signal to the relay timed level, located in a control cabinet, which enables the implementation of the pump and drum rotation for a few seconds.

 

 

 

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Sand Filter

There is a wide range of sand filters for different water flows and use. Filters are made in polyester and fiberglass, loaded with natural sand media with a high silica content and particle sizes between 0.5 and 1.0mm. In addition to the layer of filter media, there is usually placed a support layer with a medium consisting of coarser gravel (up to 5mm).

 

In addition of traditional vertical sand filters, horizontal filters are also more suitable in cases where required to treat large volumes of water to optimize the available space.

 

There are some very specific parameters that must be taken into account when selecting the most suitable sand filters for each installation type:

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-Filtration speed: Indicates the volume of water filtered per unit time per unit area. At lower speeds smaller particles are retained, greatly increasing the performance of the filtration. Filtration in aquaculture is recommended at speeds between 20 and 30 m3/h/m2.

 

- The height of the filtering bed: A greater height of the sand bed allows more volume to the retention of particles and thus increases the filter's performance. The filter bed height is 1.2m recommended to allow also the use of media filter beds.

 

-The filtering media used: with smaller grain, the size of retained particles decreases but increases the pressure needed to filter water. A suitable measure for filtration is commonly used of 0.4-0.8mm. The gravel used as a carrier may have a particle size of 1 to 2mm, and is used to cover the collecting system, promote drainage of water and wash the filter.


- The type of collector system of the filter: This is the internal elements of the filter for collecting the filtered water and channelling it toward the filter output. Their role is very important during the back washing of the sand, as they must distribute the water evenly. There are 2 types of collection systems:

 

- The system of collecting arms, where grooved tubes are distributed as a thorn or star. The arms are joined in a collector that communicates with the outlet of the filter.

 

- Nozzle plates. These are horizontal nozzle plates at the bottom of the tank on which rests the media. There are uniformly distributed a number of nozzle responsible for collecting the filtered water. This system allows excellent distribution of water during the anti-laundering and is very suitable for those cases that require an air wash.

 

 

The washing of sand filters is a fundamental process which, when done correctly, can restore the filtration capacity of the filter. Over time, the filtering bed of the sand filter fills with particles retained and need to be removed. At the same time, due to bacterial growth, the bed also tends to conform and thus requires breaking up the media again to allow uniform water passage across the filtering bed. The washing is advised at a speed of 40m / h if with water, and takes place when the filter pressure drops to between 0.5 and 0.8 bar.

 

In aquaculture an effective method for cleaning the filters is the use of air. When air is used for washing, the speeds are set at 60m / h. On the one hand the injected air at a speed of 60m / h leads to a disintegrating action of the environment but allows a considerable saving of wash water.

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Cartridge Filter

 

Cartridge filtration consists in water flow, at pressure, into a cartridge holder where the filter cartridges are housed. The fluid passes through the filter cartridge leaving all selected contaminants within it.

 

Cartridge filtration is the filtering technique most recommended for those applications whose demands for quality and safety are high. The filter cartridges can be made of different materials, polypropylene, PTFE, cellulose, nylon, stainless steel, etc.., determining the use of one or another depending on the characteristics of the fluid to be filtered and the quality targets of the liquid filtered .

 

The filter cartridges, according the different type of filtering to be achieved, can be:

 

-Depth Cartridge Filter: roughing filtration, clarification and polishing products. Supporting high loads of pollutants.

 

-Pleated Filters: polishing filtration products and protection of final filter cartridges. Lower pollutant loads.

 

-Inorganic filters: filtration surface work only for screening.  Lower pollutant loads.

 

-Membrane filters; final filtration. Integrity testable by standard, nondestructive, correlated with bacterial retention.

 

 

 

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Bag Filter

 

Bag filtration is particularly suitable for applications where the liquids have high concentrations of contaminants, or of high viscosities. Needing to pass through a filter medium that is easy to reuse, that supports large volumes and is as cost economically as possible.

 

The fluid to be filtered is circulated through a filter bag that is housed in racks, the contaminants being retained in it.

 

 The bags can be chosen from a wide variety of sizes and construction materials (polypropylene, polyester) approved by the FDA and a wide range of filtration (1 to 1000 microns), to suit any application to be considered.

 

The racks are available in special materials; stainless steel, carbon steel and polymer materials, and different sizes; from one bag filters to multi- bags filters.

 

 

SUBIR