Mechanical filtration is possibly the most important filtration element of any re-circulatory filtration system. Solid waste must be removed from the system quickly and effectively so that it is not allowed to break down into undesirable dissolved compounds which will further pollute the system. The type of filter required will depend primarily on the flow of water to be treated, the size of the particles which need to be removed and the clarity required. Different types of filters can be used in series, to achieve the desired water quality criteria.
By far the most cost effective means of removing solids from water is by using gravity fed bag filter units. Installatiion on the retrurn flow from the livestock tanks is simple, providing there is enough fall to accomodate the filter unit. It also means that waste products are removed as a first point of filtration. Bags are relatively inexpensive, come in a variety of sizes, and can be washed and reused. However, the surface area of teh bags is low, and they need to be manually changed. If maintenance is neglected then the bags will block, and be bypassed, as well as meaning the waste products will be left in the water to break down into dissolved waste products.
Roller filters are also, like bag filters, gravity fed and are installed on the livestock return flows. They have a filter roll that is fed through a chamber through which the water must pass, trapping the suspended solids. When the filter material becomes blocked, the roll can be advanced - either manually or in more advanced designs, automatically through the use of a level sensor and motor. The automatic versions are a step up on bag filters in that maintenance is significantly reduced, and waste products will not be left in contact with the water for prolonged periods.
Cartridge filters are availabel in various sizes and designs that can treat small to medium flow rates. They are pressurised filters, and so must be installed on the supply side of the livestock supply pump, typically just prior to the UV steriliser. Multiple units can be used in series to enhance filtration down to finer micron ratings. Surface areas are higher than bag filters, meaning lower maintenance, but cleaning is typically undertaken chemically. Their small surface area, low cost and ability to filter to low micron ratings make them a popular choice for hatchery and other small volume clean water applications.
The Waterco Multicyclone filter is a unique pressurised filter that essentially spins the particles out of the water using a centrifugal force. The units have no moving parts and accumulated solids are easily flushed to waste. INitially designed as a prefilter to Sand Filters, to reduce backflushing and hence water wastage in the pool inductry, these can be used as a handy standalone filter too, and are available in multiple sizes capable of processing up to 90m3/hr.
Pressurised Sand Filters
Pressurised sand filters work by forcing water at pressure through a bed of carefully graded media that collects any dirt and solids present in the water. Sand filters are a versatile addition to a range of aquaculture, aquarium and pond applications as they can be used in conjunction with a variety of media, providing either mechanical or biological filtration or both. For mechanical only appliactions, it is advisable to use a glass media. Traditional sand media has a habit of "caking" and "channelling" over time, requiring physical maintenance to break it up. This will not be the case for glass media, which will not channel, and will also require less energy and water to backflush (clean). Sand filters are available to treat smal to large water flow rates, and typically down to 20 micron.
Mechanical Filters Maintenance Tips
Filter bags require regular cleaning to operate effectively - the amount of maintenance required will vary from system to system depending on various factors such as feeding regimes. Failure to maintain the bags will result in them becoming clogged and water over spilling the bags, along with the associated solids. The best results are achieved by turning them inside out and pressure washing, however spraying with a hose will suffice. It is recommended that bags are replaced on a regular basis as, over time, there will be a build up of deposits in the filter material which will result in ineffective filtration and increased cleaning requirements. The bag size required will be dependant on the application. However, it can sometimes be beneficial to combine different sized bags to reduce cleaning frequency. 400-micron bags can also be utilized to house filtration media such as carbon.
Settled debris can easily be removed from the bottom of the filter by using one of the outlet drains. The unique Hidroclean cartridges, which are made up of a series of plastic discs, can be cleaned with a standard hose. The water pressure causes the filter rings to turn on the central axis and dirt and trapped debris are quickly washed away. No chemicals or special tools are required.
Under certain circumstances, hard water or high pH can cause calcification in the sand filter, causing the sand to solidify and reducing the efficiency of the sand filter. Regular backwashing can avoid this. We recommend periodic manual inspection of the sand filter interior and stirring-up the media inside to ensure continuous peak performance.