Joe S
Community Member
Mechanical Filtration: Overview and Comparisons
Joe Szczebak
The goal of mechanical filtration is to remove particulate organic matter (POM) and any other large suspended solids from the system. As such, mechanical filtration usually sits at the head of the LSS and is the first treatment component of the system. Depending on the size of your operation and the type of POM (i.e., coarse or fine) you need to remove, there are many different mechanical filtration tools available.
Coarse POM
The most common tools to remove the larger coarse POM include pre-filter mechanisms, sediment basins, and swirl separators. For the home aquarist, pre-filter mechanisms are the most cost- and space-effective tools. Examples include intake screens, strainers, and filter baskets.
Pre-filter
The purpose of pre-filtration (Fig. 1A) is to remove the large POM and debris that can cause subsequent filtration units. Thus, prefilters are usually the first line of defense for LSS. These filters require frequent cleaning to prevent clogging and maintain water flow through the LSS. Common examples are intake screens (shown here) and filter baskets.
Swirl separator
Another useful mechanical filter for larger POM and debris is swirl separators (Fig. 1B). Though expensive, these filters use centrifugal force to pull sediment and debris out of the water column where it is concentrated and removed at the bottom of the cyclone. The filtered water leaves at the top of the cyclone. Swirl separators are very effective and can operate at low pump pressure.
Figure 1: Prefilter (A) and swirl separator arrangements
Fine POM
To remove the smaller fine POM, common tools include bag filters, cartridge filters, sand filters, and bead filters. For the home aquarist, bag or cartridge filers are the most feasible option; however, those with multiple aquaria running as a single system, or those with larger single aquaria may consider the larger and more expensive options (i.e., sand and bead filters).
Bag filter
Bag filters (Fig 2A), which can be either gravity- or pressure-fed, pass water through fine-mesh fabrics to remove coarse and fine POM. Bag filters are a low tech, inexpensive, and flexible mechanical filtration option for hobbyists. However, these filters are easily clogged and thus require frequent cleaning. In my opinion, 100-300 micron is the most effective mesh size range.
Cartridge filter
Cartridge filters (Fig. 2B) operate in a similar manner to bag filters. Water is pressure-forced through a tight and dense coil of fabrics of varying mesh sizes. Cartridge filters can be used to selectively filter out certain-sized particles, and can remove debris well below 1 micron in size. These filters are very low tech, cost effective and reliable. However, like bag filters, they require frequent cleaning to prevent clogging and ensure water flow efficiency.
Figure 2: Bag (A) and cartridge (B) filters
Rapid sand filter
Rapid sand filters (Fig 3A) pressure-force water through one or more layer of media (typically gravels and sands) to mechanically remove POM and other small debris from water. While large and complex sand filters are employed my municipal and wastewater treatment facilities, inexpensive small-scale versions are available for commercial and home aquarists. These efficient filters require occasional backwashes to clean the media and remove the collected sludge.
Modified bead filter
Modified bead filters (Fig 3B) pump water against gravity through a wall of floating plastic media. The sludge and debris blocked by the media collects and eventually falls off and settles in the bottom of the filter chamber. These units can be expensive and require very frequent backwashes to ensure water flow efficiency.
Figure 3: Rapid sand (A) and modified bead (B) filters
Comparison of mechanical filtration techniques
While this article by no means covers all the mechanical filtration options and considerations, it provides essential technical and comparative information to help new hobbyists understand some common filtration options and begin to create the ideal LSS for their particular aquarium. Mechanical filtration is unable to remove very small POM (>0.1 micron) or DOM from aquaria, and other LSS components, such as biological and chemical filtration also are needed. Further, it is important to note that there are other essential and/or alternative filtration methods commonly employed by both commercial and home aquarist.
Joe Szczebak
The goal of mechanical filtration is to remove particulate organic matter (POM) and any other large suspended solids from the system. As such, mechanical filtration usually sits at the head of the LSS and is the first treatment component of the system. Depending on the size of your operation and the type of POM (i.e., coarse or fine) you need to remove, there are many different mechanical filtration tools available.
Coarse POM
The most common tools to remove the larger coarse POM include pre-filter mechanisms, sediment basins, and swirl separators. For the home aquarist, pre-filter mechanisms are the most cost- and space-effective tools. Examples include intake screens, strainers, and filter baskets.
Pre-filter
The purpose of pre-filtration (Fig. 1A) is to remove the large POM and debris that can cause subsequent filtration units. Thus, prefilters are usually the first line of defense for LSS. These filters require frequent cleaning to prevent clogging and maintain water flow through the LSS. Common examples are intake screens (shown here) and filter baskets.
Swirl separator
Another useful mechanical filter for larger POM and debris is swirl separators (Fig. 1B). Though expensive, these filters use centrifugal force to pull sediment and debris out of the water column where it is concentrated and removed at the bottom of the cyclone. The filtered water leaves at the top of the cyclone. Swirl separators are very effective and can operate at low pump pressure.
Figure 1: Prefilter (A) and swirl separator arrangements
Fine POM
To remove the smaller fine POM, common tools include bag filters, cartridge filters, sand filters, and bead filters. For the home aquarist, bag or cartridge filers are the most feasible option; however, those with multiple aquaria running as a single system, or those with larger single aquaria may consider the larger and more expensive options (i.e., sand and bead filters).
Bag filter
Bag filters (Fig 2A), which can be either gravity- or pressure-fed, pass water through fine-mesh fabrics to remove coarse and fine POM. Bag filters are a low tech, inexpensive, and flexible mechanical filtration option for hobbyists. However, these filters are easily clogged and thus require frequent cleaning. In my opinion, 100-300 micron is the most effective mesh size range.
Cartridge filter
Cartridge filters (Fig. 2B) operate in a similar manner to bag filters. Water is pressure-forced through a tight and dense coil of fabrics of varying mesh sizes. Cartridge filters can be used to selectively filter out certain-sized particles, and can remove debris well below 1 micron in size. These filters are very low tech, cost effective and reliable. However, like bag filters, they require frequent cleaning to prevent clogging and ensure water flow efficiency.
Figure 2: Bag (A) and cartridge (B) filters
Rapid sand filter
Rapid sand filters (Fig 3A) pressure-force water through one or more layer of media (typically gravels and sands) to mechanically remove POM and other small debris from water. While large and complex sand filters are employed my municipal and wastewater treatment facilities, inexpensive small-scale versions are available for commercial and home aquarists. These efficient filters require occasional backwashes to clean the media and remove the collected sludge.
Modified bead filter
Modified bead filters (Fig 3B) pump water against gravity through a wall of floating plastic media. The sludge and debris blocked by the media collects and eventually falls off and settles in the bottom of the filter chamber. These units can be expensive and require very frequent backwashes to ensure water flow efficiency.
Figure 3: Rapid sand (A) and modified bead (B) filters
Comparison of mechanical filtration techniques
While this article by no means covers all the mechanical filtration options and considerations, it provides essential technical and comparative information to help new hobbyists understand some common filtration options and begin to create the ideal LSS for their particular aquarium. Mechanical filtration is unable to remove very small POM (>0.1 micron) or DOM from aquaria, and other LSS components, such as biological and chemical filtration also are needed. Further, it is important to note that there are other essential and/or alternative filtration methods commonly employed by both commercial and home aquarist.
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