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Water treatment department
In this department the equipment to control and eventually improve the water quality is installed. It is a very difficult department to design well, especially when much equipment is needed (Fig. 21.13). In several established farms this department looks a mess. When planning, it is important to allow sufficient space. The department will, in all proba-
bility, be changed and modified several times. It is advantageous to include several valves in the system so that water flows can easily be stopped and sent in different directions. It must be possible to remove all the individual pieces of equipment without having to shut off the inlet water supply to the farm.
The amount of equipment needed in this department varies with the quality of inlet water and therefore the need to treat it. In this department equipment is typically installed for:
· pH control
· Removal of suspended solids
· Heating and cooling.
If using a central re-use system, the equipment for ammonia removal and the re-use pumps may also be placed here.
Before starting to plan a water-treatment department on a new farm, it is always recommended that a flow chart be drawn that includes the different free water surfaces to prevent mistakes. It is quite normal to site the water treatment department in two rooms, a machine room and a water treatment room. Equipment for oxygen production together with equipment for heating and cooling can be placed in the machine room. In the water treatment room there are large free water surfaces and therefore high humidity, so proper ventilation is necessary here. Examples of equipment placed in this room include that for aeration, ammonia removal and solids removal. By having two rooms, the expensive mechanical equipment can be placed in a separate room with lower humidity.
It is advantageous to locate some equipment close to the water inlet or where the water transfer pipe to the farms starts. This ensures some exposure time before the inlet water reaches the farm. When using ozone as a disinfectant, or when adding chemicals for changing the pH, it can be done in the inlet and the need for a large retention basin inside the farm avoided.
There are advantages in having a feeder tank as a last step before the water reaches the production system. This will ensure equal pressure in the inter-
nal pipelines. At the same time, the pressure will not be too high. High pressure in the internal pipelines will create a lot of noise in the pipes and valves in the production hall. In addition, it may be necessary to use pipes and parts of a higher pressure class, which is more expensive. A feeder tank is also a suitable place to install the alarm sensors, because the level will immediately drop when there is trouble with the water supply (Fig. 21.14); some reaction time is also achieved if the water flowdrops, depending on the volume of the header tank. The disadvantages of using a feeder tank are that it is necessary to lift the water to a higher level, if no pressurized water is available. For this reason sea-water is sometimes sent directly through channels or pipes into the production room.
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