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Waste water treatment
Farming fish in a recirculation system where the water is constantly reused does not make the waste from the fish production disappear. Dirt or excretions from the fish still have to end somewhere. Figure 6.1 Excretion of nitrogen (N) and phosphorus (P) from farmed fish. Note the amount of N excreted as dissolved matter. Source: Biomar and the Environmental Protection Agency, Denmark. The biological processes within the RAS will in a smaller scale reduce the amount of organic compounds, because of simple biological degradation or mineralisation within the system.
· Food and Agriculture Organization of the United NationsRunning a recirculation system
Figure 5.1 Water quality and flow in filters and fish tanks should be examined visually and frequently. Water is distributed over the top plate of a traditional trickling filter (degasser) and distributed evenly through the plate holes down through the filter media. Moving from traditional fish farming to recirculation significantly changes the daily routines and skills necessary for managing the farm. The fish farmer has now become a manager of both fish and water.
· Food and Agriculture Organization of the United NationsProject planning and implementation
The idea of building a recirculation fish farm is often based on very different views on what is important and what is interesting. People tend to focus on things they already know or things they find most exciting, and in the process forget about other aspects of the project. Five major issues should be addressed before launching a project: Sales prices and market for the fish in question Site selection including licences from authorities
· Food and Agriculture Organization of the United NationsFish species in recirculation
A recirculation system is a costly affair to build and to operate. There is competition on markets for fish and production must be efficient in order to make a profit. Selecting the right species to produce and constructing a well functioning system are therefore of high importance. Essentially, the aim is to sell the fish at a high price and at the same time keep the production cost at the lowest possible level.
· Food and Agriculture Organization of the United NationsThe recirculation system, step by step
In a recirculation system it is necessary to treat the water continuously to remove the waste products excreted by the fish, and to add oxygen to keep the fish alive and well. A recirculation system is in fact quite simple. From the outlet of the fish tanks the water flows to a mechanical filter and further on to a biological filter before it is aerated and stripped of carbon dioxide and returned to the fish tanks.
· Food and Agriculture Organization of the United NationsIntroduction to recirculation aquaculture
Recirculation aquaculture is essentially a technology for farming fish or other aquatic organisms by reusing the water in the production. The technology is based on the use of mechanical and biological filters, and the method can in principle be used for any species grown in aquaculture such as fish, shrimps, clams, etc. Recirculation technology is however primarily used in fish farming, and this guide is aimed at people working in this field of aquaculture.
· Food and Agriculture Organization of the United NationsWorking within the tolerance range for each organism
As discussed in Chapter 2, aquaponics is primarily about balancing an ecosystem of three groups of organisms: fish, plants and bacteria (Figure 3.2). Each organism in an aquaponic unit has a specific tolerance range for each parameter of water quality (Table 3.1). The tolerance ranges are relatively similar for all three organisms, but there is need for compromise and therefore some organisms will not be functioning at their optimum level.
· Food and Agriculture Organization of the United NationsWater testing
In order to maintain good water quality in aquaponic units, it is recommended to perform water tests once per week to make sure all the parameters are within the optimum levels. However, mature and seasoned aquaponic units will have consistent water chemistry and do not need to be tested as often. In these cases water testing is only needed if a problem is suspected. In addition, daily health monitoring of the fish and the plants growing in the unit will indicate if something is wrong, although this method is not a substitution for water testing.
· Food and Agriculture Organization of the United NationsWater quality for plants
Section 3.3 discussed water quality parameters for the aquaponic system as a whole. Here specific considerations for plants are considered and further expanded. pH The pH is the most important parameter for plants in an aquaponic system because it influences a plant’s access to nutrients. In general, the tolerance range for most plants is 5.5-7.5. The lower range is below the tolerance for fish and bacteria, and most plants prefer mildly acidic conditions.
· Food and Agriculture Organization of the United NationsWater quality for fish
Chapter 2 discussed water quality for aquaponics. Here, the most important water quality parameters are listed again briefly and summarized in Table 7.1. Nitrogen Ammonia and nitrite are extremely toxic to fish, and sometimes referred to as “invisible assassins”. Ammonia and nitrite are both considered toxic above levels of 1 mg/litre, although any level of these compounds contributes to fish stress and adverse health effects. There should be close to zero detectable levels of both of these in a seasoned aquaponic system.
· Food and Agriculture Organization of the United Nations