The moving bed filter is generally located after the fixed bed filter and before the degasser and oxygen enrichment, ahead of the water returning to the culture tank. Constant movement of all the biofilter media is essential for optimal nitrification, aeration and degassing. The aeration also maintains the optimal oxygen level for the bacteria.įigure. The beads or other bio-elements need to be in motion at all times, in every part of the filter! No dead areas are allowed to develop, as unwanted accumulation of organic matter could take place, and anaerobic conditions could arise. The moving bed biofilter predominantly performs nitrification, but also some aeration and degassing. A RAS farmer not only has to look after the fish but also after the bacteria. Again, this filter needs to be monitored daily, and care must be taken that the bacteria have the right conditions to break down ammonia. Organic matter in the moving bed filter can smother the nitrifying bacteria, and it may even lead to the development of heterotrophic bacteria that grow much faster than nitrifying bacteria. It is important to realise that prior to nitrification, as much organic matter as possible must be removed, as it will otherwise negatively interfere with nitrification. There are different types of bio-media, each with their own specifications, on the market.īesides the surface area of the filter medium, other important factors determining the rate at which the conversion of ammonia to nitrate takes place are ammonia concentration, O2 level, water temperature, pH, and organic matter in the system water. In order to have a compact moving bed filter, it is desirable to have a high specific, protected, surface filter medium on which the nitrifying bacteria can attach and grow. The efficiency of the biofilter is directly linked to the total amount of bacteria in the filter. In this way, the bacteria living on the bio-elements have constant access to oxygen and ammonia. Usually, the filter contains around 50% water and 50% bio-elements, which are moved around by blowers at the bottom of the filter. A moving bed filter contains bio-elements like beads, chips or porous foam with a high specific surface area on which the nitrifying bacteria can live.
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