3. Advantages and disadvantages of common oxygenation methods and their impact on aquaculture water environment and aquaculture objects
1. Timely inject (change) new water to increase oxygen
Adding water is a primitive and simple method, which is based on the fact that the injected new water can bring more oxygen into the pond and some nutrients lacking in the old water, the oxygen-consuming organic matter in the flushing water, and some toxic and harmful metabolites. , Supplement new plankton species to form a new balance, make the pool water mix up and down, eliminate oxygen debt, make the water color tender and fresh, and the water quality is fresh. Farmed animals have strong food intake, free movement and accelerated growth.
But the premise of this method:
First, the injected "new water" must be uncontaminated, meet the surface runoff water class III standard or above, and be rich in dissolved oxygen. At present, in economically developed areas, it is very common for the water quality of the environment to be polluted. Not only is the water body seriously deficient in oxygen, but also toxic and harmful substances are worse than in aquaculture ponds.
The second is: the water temperature of the injected water should be basically the same as the water temperature of the pool water or the amount of injected (changed) water should not exceed 1/3 of the pool water. According to the occurrence of dissolved oxygen in the water body (mainly produced by the photosynthesis of aquatic plants, especially phytoplankton, and the reproduction and distribution of phytoplankton in the water body changes with the intensity of light and temperature when the nutrients are in balance) According to the principle, the dissolved oxygen content is affected by the changes of light intensity and temperature, wind direction and wind force to produce circadian rhythm, seasonal changes and differences and changes in vertical (thermothermia effect) and horizontal distribution.
Therefore, in the spring and autumn, when the temperature is relatively mild and the light time is relatively short, it should be selected to absorb the water from the upper layer (within 1m) at noon (11:00 to 14:00) on a sunny day for water injection. In hot weather in summer, it is advisable to absorb water from the surface layer (50cm) before 9:00 on a sunny day for water injection. Injecting (exchanging) into such water, the plankton species are comprehensive and the number of dissolved oxygen is abundant.
The water temperature is suitable, and there will be no stress response to the farmed animals. After the species and quantity of plankton are replenished, after an afternoon of light, there is enough time to generate a large amount of oxygen through the photosynthesis of phytoplankton, and the synergy of the convective mixing of the upper and lower aquifers caused by the agitation of water injection not only eliminates the "oxygen debt", but also eliminates the "oxygen debt". The toxic and harmful substances accumulated at the bottom of the pool can be released and alleviated during the redox process, and at the same time, the dissolved oxygen in the surface and middle water bodies can be "supersaturated", and the bottom water can also be transformed from "reduced state water (reduced environment)" It is "water in an oxidized state (oxidizing environment)".
The bottom water of the pond can maintain the state of "oxidative state water (oxidative environment)", which is extremely beneficial to improve the feeding ability of farmed animals, the digestion and absorption of feed, and the increase of feed remuneration. Secondly, it also reduces the oxygen consumption formed by the accumulation of residual bait and feces, making the algae in the pool suitable, and the water color changes to tender, lively and refreshing, which not only promotes the growth of farmed animals but also reduces the pollution caused by breeding and feeding.
The third is that when the water quality of the external source is indeed polluted and cannot be used very seriously, if conditions permit, it should be considered to use another pool of water to purify and then refill and replace the water.
2. Mechanical oxygenation
When the water quality of the exogenous water area is poor, the method of water injection and replacement cannot be used to increase oxygen, or when the breeding capacity is large and the pond water has reached the maximum water level, mechanical oxygenation should be considered.
Mechanical oxygenation is a traditional and advanced oxygenation method. The use of aerators has been used for decades to increase oxygenation. The oxygenation machinery has also been continuously improved and developed in practice in terms of form, performance, material and efficacy. , can be roughly divided into two types: stirring water type and inflatable type.
The principle is to expand the contact surface between the air and the water body by stirring the water or inflating the water, so that the oxygen in the air is input into the water body, and at the same time, the communication and mixing of the upper and lower sides of the pool water and the plane are promoted.
The advantage of aerator for aeration is that it is not limited by pond conditions, especially for high-density aquaculture ponds that encounter severe hypoxia in bad weather and preventative oxygenation in peacetime.
The disadvantages of aerators for oxygenation are large investment costs and high energy consumption. Now make a simple comparison and analysis of several widely used aerators, and put forward some suggestions on the use method.
3. Stirring aerator
This type of aerator is commonly used in two types: impeller type aerator and waterwheel type aerator. The working principle is to agitate the water body through the blades of the aerator to make the water body flow.
The difference is that the impeller type drives the water body to move vertically while stirring the water body to spread around, while the water wheel type pushes the water body to flow in one direction, and its force to push the water body to flow vertically is much smaller than that of the impeller type.
Compared with inflatable aerators, this type of aerator has the advantages of small size, convenient handling and installation, and is not limited by pond conditions, but it has disadvantages such as high noise and low unit oxygenation efficiency.
In production practice, there are also obvious differences in the use of these two aerators:
First, it is difficult to agitate the water body due to the presence of aquatic plants in the shrimp and crab breeding ponds.
Second, because the water depth is relatively shallow, the impeller-type aerator may mix the water body, and the noise is too large, which is not conducive to the growth of shrimps and crabs, and even directly damages the shrimps and crabs.
Third, in order to facilitate handling and installation, the power of a single waterwheel aerator is relatively small. In fish ponds and white shrimp culture ponds of more than 10 acres, multiple aerators must be installed to be effective, and the installation must have a certain angle and direction.