|Inland Aquaculture Engineering (1984)|
|DESIGN OF FISH HATCHERIES|
|Chapter 12 Planning of Fish Hatcheries|
A characteristic flow diagram is shown in Figure 4. Some parts of the installation shown in the flow diagram can be abandoned depending on local situation.
In principle the water source can be of three kinds, as follows:
- surface waters (rivers, lakes, natural beach, artificial beach);
- subsurface waters (ground water, deep-seated water, cavern water, spring water, filtered at the riverside water);
- other water sources, secondary utilization (mine waste water, secondary utilization of industrial effluents, cooling water).
Surface waters are for exploitation of a high quantity of water, but they always need purification. Subsurface waters are as clear as drinking water or close to it. Energy requirement of the water intake and costs of constructions of the water intake are specifically higher in case of subsurface waters. In case of a water source containing a large quantity of silt, construction of a separate gravitation settling pond is needed (a), and for intake of subsurface water a separate temperature control pond (b) is needed.
First phase of the water purification is a filtering wall (c) constructed into the settling pond or the temperature control pond. Quantity of water flowing through the unit area of filtering wall is generally 0.15 - 0.20 m3/m2 . h.
Sand or gravel can be used as filter media. After getting plugged the filter media can be replaced easily. The water supply of the hatchery can be ensured by gravity or by pumping. Figure 4 shows a water supply by pumping when the capacity of the pumps are calculated from the water requirement. The water needed for backflushing the filters and the social water requirement, have to be taken into account.
If it is necessary, a second filtering unit has to be installed for secondary treatment. This unit usually is a quick sand or gravel filter. The plugged filter media can be backflushed with compressed air and/or high pressure water.
A closed, pressurized quick filter can be seen in Figure 4, that is backflushed with water and compressed air. For the continuous operation two filters are available and only one operates simultaneously while the second is backflushed. The water needed for back-flushing is stored in a separate clear water tank denoted with f in the figure. The pumps denoted with g ensure the water supply for normal operation and for backflushing. A pressure chamber h is used in order to keep the pressure within a certain range. If the temperature of the supplying water is less than required the water has to be heated and its temperature has to be regulated. The heating and temperature control can be ensured with boiler (i), heat exchanger (j) and temperature control valve as is shown in Figure 4.
Oxygen concentration of purified and optimum temperature water generally must be at least 5 g/m3. For this purpose an aeration device (k) must be constructed. If there is no heating, dilution of oxygen can be carried out in the filtering water tank as well (f).
Breeder tanks can be one of two shapes. The bigger ones (1-10 m2 footing area, 1-1.5 m depth) can be constructed of concrete, and coated with plastic material or glazed tile, the smaller tanks (0.5-2 m3 volume, 0.6-1.2 m depth) of plastic material or aluminium. The necessary constant water pressure needed for hatching jars (m) and for larval rearing tanks (n) is ensured by an elevated tank (p). The outflowing water from breeder tanks, hatching jars and larval rearing tanks is collected in a drainage pit, from which it is removed by a pump (r). Compressed air for aeration, or rather for backflushing of filters is ensured by a compressor (s) and a pressure tank (t).
For hypophysation and stripping at least one table of 3 × 1 m size is needed. General laboratory benches can be used for this purpose.