Recirculating Aquaculture Breeding – Step Four

Ammonia is a mixture of ammonia and ammonium (Total) = ammonium (NH4 +) + ammonia (NH3) in which ammonia forms the major part of the waste. But the amount of ammonia in water depends on the table:

In this picture you can see the equilibrium between ammonia (NH3) and ammonium (NH4 +) at 0 ° C. No toxic ammonia is present at low pH but increases with increasing pH. The pH level can be detected in the figure, which shows the equilibrium between ammonia (NH3 +) and ammonium (NH4 +). In general, toxic ammonia is toxic to fish at more than 0.02 mg / L. The following figure shows the maximum concentration of toxic ammonia, which is permissible at different pH levels if a level below 0.02 mg / L is guaranteed. A lower pH level reduces the risk of exceeding the permissible level of ammonia by 0.02 mg / L, but the fisheries manager is advised to reach a level below the minimum pH of 7 to achieve bio-filtering.

n the other hand, the whole idea of Recirculating Aquaculture Breeding is fish storage, and in some cases water saving is a big goal. Under such conditions, the nitrate concentration can be reduced to nitrogen uptake. Under normal conditions, water consumption of more than 300 liters per kilogram of feed used is sufficient to dilute the nitrate concentration.

Most of the dominant bacteria are called pseudomonas. This is an anaerobic process (without oxygen) to reduce nitrate to atmospheric nitrogen. In fact, this process separates nitrogen from water into the atmosphere, where the nitrogen load is reduced to the surrounding environment. This process requires an organic source (carbon), for example wood alcohol (methanol), which can be added to the nitrate chamber. In practical terms, 2.5 kg of methanol is required for each kg of nitrite (NO – N) denitrified.

Most nitrate decontamination rooms are equipped with bio film or special surfaces designed with a 2 to 4 hour residence time. The flow must be controlled to keep the oxygen concentration of the output in the program. If oxygen is produced more than one milligram per liter, hydrogen sulfide (H2S) will occur, which is highly toxic to fish and also has a nasty smell (rotten eggs). In the process of nitrating, the obtained sludge production is very high, and the nitrate removal unit should be washed once a week.

Examples of bio-films for use in bio-filters:
Bio-filters are usually made using plastic media that give a high level per cubic meter. The bacterium will grow as a thin layer on the media, thus occupying a very large surface. The purpose of a well-designed bio-filter is to achieve a high level per cubic meter without clogging with organic matter. Therefore, it is important to have a high percentage of free space for water to pass through the bio-filter and to have a good overall flow with adequate washing. Such steps should be performed at intervals of three weeks or one month depending on the load on the bio-filter. Compressed air is used to create a continuous flow in a filter in which the organic matter is removed. As the washing process occurs, it will be cleaned and the dirty water discharged into the filter and discharged before it can be reconnected.

Design flat bed filters or removable bed filters. All bio filters used in closed circuit farms today act as submerged units. In a fixed flat filter, the plastic media is stationary and does not move. Water flows through the media as a quiet stream to communicate with film bio. In the removable bed filter, the plastic media moves through the water with the flow created by the air pump. Due to the constant movement of media, removable bed filters can be harder than fixed bed filters, resulting in higher displacement rates per cubic meter. However, there is no significant difference in the calculated turnover rate per square meter (filter surface area) as the bacterial film bioassay efficiency in either.