In the process of shrimp farming, shrimp ponds are not eaten with feed, fertilizers, manure, carcasses and dead phytoplankton... A large amount of organic waste will form. Moreover, all these organic matter are deposited at the bottom of the pond in the form of sediment or sludge.
Sludge pumped from the bottom of the pond
Untreated sludge can cause many problems for shrimp farming, such as increased ammonia content, reduced dissolved oxygen (DO), and rapid deterioration of water quality. Therefore, farmers need good pond bottom management to ensure good water quality and optimal shrimp health.
Here are some recommendations for pool bottom management:
First, use the correct pond lining
Pond linings are a very useful infrastructure to ensure the biosecurity of shrimp farms. The interaction between water and soil in direct contact can cause the pond to cause a highly toxic hypoxia reaction of shrimp. Using plastic, high-density polyethylene (HDPE) or concrete linings can prevent these problems and make it easier to manage water quality and pond bottoms.
Pictured: Using pond linings can improve biosecurity and make it easier to manage pond floors
Second, consider the design of the pond
Ponds are designed in rectangular, square and circular shapes. The shape of the pond has a significant effect on water flow and sediment accumulation. Each shape has advantages and disadvantages, but round and square ponds are the most effective because they better promote water circulation, which makes sludge removal easier.
Figure: How the central drainage system works
Another important consideration in pond design is the bottom design,
Third, correctly install the aerator of the pond
The aerator is an important tool that not only provides dissolved oxygen, but also pushes the sludge towards the central drain. The most common aerator is the impeller aeration. There are two main considerations when using aerators: the number of ponds required and how they are arranged.
Each pond will require a certain number of aerators to ensure adequate dissolved oxygen and sediment emissions, but this will depend on the size of the pond and the density of the culture. Based on experience, we recommend placing 6 HP aerators in 1000 m2 ponds with a culture density of 100 PL/m2.
As for the installation of the aerator, it is important to ensure that all corners of the pond are covered so that no sludge is left behind. There are two main ways to design: parallel and diagonal (see figure below).
Figure: Layout of the aerator. Parallel line (right) and diagonal line (left)
In many cases, parallel arrangement is not recommended, as it leaves more dead shrimp. By arranging the diagonal lines, the water flow is distributed over a larger area, which greatly reduces the dead space
Fourth, regularly assess the pool bottom
As culture is cultivated for longer periods of time, it is crucial to understand the quality of the sediment to prevent negative impacts. This can be done by sampling and measuring the amount of sludge in the field, with the following four parameters:
1. Redox potential;
2. pH value;
3. Hydrogen sulfide;
4. Ammonia nitrogen
In the middle and late stages of culture, regular assessment of the bottom of the pond is particularly critical, and regular sampling should be taken at least twice per cycle as an assessment. If shrimp die, water quality deteriorates, and shrimp growth is slow, the assessment of the pool bottom should be strengthened.
Optimal and dangerous parameters for pool floor parameters
5. Manually clean the bottom of the pond
Artificial siphoning or cleaning of the bottom of the pool is a good way to maintain the best bottom quality. We recommend siphoning on the 13th day after seedling feeding. In general, pond suction does not have a fixed frequency because it depends on the bottom of the pond. However, we recommend doing it at least once a day or twice a day in the middle and late stages of farming. Every morning before the first feeding, the uneaten feed, feces, carcasses or dead shrimp that appear can be cleaned up with siphon sewage.
Farmers should clean up the bottom of the pond once a day.
Consider the use of chemicals and probiotics
Chemicals and probiotic products can reduce the harmful effects of organic waste on the bottom of ponds. Using these products helps to break down and increase the concentration of dissolved oxygen at the bottom of the pond.
Potassium permanganate (KMnO4) is a good choice because it allows the sludge to break down quickly. The treatment rate of KMnO4 depends on the condition of the pond water body and, most importantly, the level of organic matter or organic load. We recommend using 2ppm of KMnO4.
Hydrogen peroxide (H2O2) is also a beneficial oxidant that breaks down while releasing molecular oxygen. For 1 ml of 6% H2O2, approximately 3 mg/L of dissolved oxygen is provided. It is worth noting that the safe level of H2O2 as an oxygen source is 14.3 μL H2O2/L.
Probiotics are known for their numerous benefits in the shrimp farming industry. At times of high organic concentrations, the application of probiotics can improve sludge quality by utilizing nitrification processes (converting ammonia into nitrites and nitrates), which in turn greatly reduces the toxicity level of sludge.
Seven, the mapping of sludge
At the end of the culture cycle and after the ponds have been drained, sediment or sludge in some areas needs to be removed. But before doing so, it's a good idea to draw a sludge map for later use. A simple drawing is enough.
To do the mapping, simply draw the pond at a specific scale. Then, use the shadow to draw the location of the sludge. It is best to distinguish the thickness at each location. By mapping the formation of sludge, we can understand where they are and how to better implement the infrastructure to manage it in the next culture cycle. Here is an example of a simple sludge diagram:
Figure: Sludge mapping
It is important to remember that pool bottom management is closely related to water quality management. Since the organic waste generated by shrimp farms has a negative impact on the environment, management should also attract our attention and adopt the right solutions.
Source: No. 1 Aquatic Products