How to deal with excessive salt water in fish ponds

1, oxidation method

The nitrogen in nitrite ion is in the middle valence state and has the characteristic of being oxidized. When NO2- in the medium meets the oxidant, it will change the valence state of nitrogen, change the gain and loss of electrons and be oxidized, and eventually NO2- ions will be transformed into less toxic or even non-toxic substances. There are many substances that have the ability to oxidize nitrite ions, such as ozone, hydrogen peroxide and sodium hypochlorite, but only trichloroisocyanuric acid, dichloroisocyanuric acid, bromochlorohydantoin and chlorine dioxide are suitable for use in aquaculture water.

The advantages of oxidizing NO2- ions into NO3- ions with strong oxidant are fast reaction speed, low cost and high oxidation efficiency. However, this method is rarely used to degrade nitrite in actual production, mainly because the degradation rate of nitrite by these strong oxidizing disinfectants is low at conventional concentration (the effect of degrading nitrite at low concentration is not obvious, and high concentration will cause phytotoxicity), and the oxidative degradation of nitrite also has the weakness of easy rebound. This method is the first choice when the following situations occur in production: ① Normal prevention and disinfection, but when the nitrite content is about 0.2 mg/L, granular trichloroisocyanuric acid (such as chlorhexidine, which can directly reach the bottom of the pond, improve the bottom material and control the generation of nitrite) can be used to prevent fish diseases and control nitrite; (2) The outbreak of fish diseases requires disinfection. When the content of nitrite is about 0.2 mg/L, binary chlorine dioxide is given priority, which not only kills pathogens, but also improves the environment and shortens the rehabilitation time.

2. Reduction method

In recent years, some experts consider using the characteristic that NO2- is oxidized and reduced under acidic conditions to reduce NO2- to volatile gas with a reducing agent, which automatically leaves the reaction system. For example, Zhang found that cast iron chips had a certain removal effect, and the removal effect increased with the increase of cast iron chips. According to the standard redox potential, iron can transform nitrite into N2 or ammonia nitrogen under weak acid conditions. Li Xue et al. treated the wastewater containing sodium nitrite with ammonium salt method at 65438 000℃ for 65438±0h, and the NO2- content in the wastewater reached the discharge standard. The basic principle of this method is: NH4++NO2-→ NH4NO2 → N2 =+H2O. There are many similar studies, but these chemical reactions need conditions and are only suitable for industrial water treatment. Through the efforts of aquatic drug researchers, a safe and economical reducing agent-nitrite degrading agent (for the benefit of enterprises, the author can't disclose it) was found, and it was processed into various dosage forms for sale through advanced preparation technology.

The raw material cost of this nitrite degrading agent is low, about 3000 yuan/ton, which is suitable for the production of fishery and pharmaceutical enterprises, so it occupies a high share in degraded products. This kind of product has the following advantages in use: ① it degrades quickly, and it only takes about 5 hours from spraying into water to the end of the reaction, which is especially suitable for the first aid of nitrite poisoning in shrimp; (2) Safety and environmental protection. The medicine has simple structure, can be rapidly degraded after reacting with nitrite in water, has no toxic and side effects on cultured animals, and does not cause secondary pollution to cultured water bodies. It is worth noting that the medicine can be used in rainy days. (3) Denitrification is complete, nitrite nitrogen can be directly reduced to nitrogen and volatilized into the air, and nitrate ions generated by oxidation may return to nitrite under the action of denitrifying bacteria; ④ The degradation rate is high, up to 90%, which is unmatched by other methods. Reduction method and oxidation method have a weakness, that is, the maintenance time is short and nitrite in water is easy to rebound.

3. Physical adsorption method

Physical adsorption method is to adsorb nitrite in its structure by using adsorbents with strong adsorption capacity, such as zeolite powder, silica gel, activated carbon and sepiolite. This method is widely used in production, and many bottom modified products contain adsorbent components. Its advantages are short action time and low cost. The disadvantage is that the dosage is large, such as zeolite powder, 50- 100kg/ mu.

4. Fertilizer and water method

Nitrite is rich in nitrogen fertilizer, which is the basic nutrition for algae growth and reproduction. Therefore, accelerating the growth and reproduction of algae in water can effectively reduce the concentration of nitrite. The production method is realized by using single-cell plant growth regulators (sodium nitrophenolate, biochemical fulvic acid, sodium humate, amino acids, etc.). ), photosynthesis catalyst, trace elements, silicon fertilizer, etc. It is worth noting that when the nitrite in the water is high, it means that the nitrogen fertilizer is sufficient. Don't use nitrogen fertilizer again, which will increase the burden of nitrogen circulation in water. Phosphate fertilizer can be applied to achieve the purpose of "promoting nitrogen with phosphorus"

Nitrite degradation by fertilizer and water method is worth popularizing in modern ecological farming, but it is restricted by the following conditions: ① the transparency of water body is required to be greater than 30 cm, if the transparency is low due to organic matter, sundries and other reasons, flocculation purifying agent should be sprayed; ② The weather will be fine in the next three to five days, and the temperature is suitable for algae reproduction; (3) When the concentration of nitrite in the water is lower than 0.4 mg/L, and there is no influence on the cultured animals; ④ The algae in the water is homogeneous. If harmful algae are prevalent, measures such as changing water and putting in excellent algae seeds should be taken first. ⑤ For microscopic examination of water samples, if there are too many zooplankton, pesticides should be sprinkled first. For example, in areas with serious rotifer hazards, it is difficult to dispose of nitrite by any method without killing rotifers first.

5, bacterial decomposition method

At present, we know two kinds of bacteria: nitrifying bacteria and denitrifying bacteria. Nitrifying bacteria can convert nitrite into nitrate, which needs to be carried out under aerobic conditions. Denitrifying bacteria reduce nitrite to N2 or nitrogen oxides under anoxic conditions.

Many degradation products in the market are labeled as nitrifying bacteria and denitrifying bacteria, but they have not shown ideal effect in practical application, and can only talk about prevention and mitigation. Theoretically speaking, nitrifying bacteria and denitrifying bacteria can reduce nitrite, but because they are chemoautotrophic bacteria, their growth and reproduction speed are slow, and it takes more than 20 hours to reproduce the first generation. In addition, the preservation technology of fungi, the survival rate after being put into water, and the water environment have all caused the degradation of nitrite by nitrifying bacteria and denitrifying bacteria to be unsatisfactory. More importantly, if the dissolved oxygen in the pond is insufficient, denitrification will occur more easily. Denitrification may reduce nitrate to nitrite, but it will increase nitrite in a certain period of time, so be careful.

The latest research shows that the reduction of nitrate to nitrite is carried out by alienated nitrate reductase. The author has successfully developed a passivator for alienated nitrate reductase, which is specific and does not affect the biochemical enzyme activity of other microorganisms. The results showed that the growth rate and nitrification rate of nitrifying bacteria were improved after applying the passivator, and nitrite was controlled in the safe concentration range within 30-40 days. The preparation is almost unaffected by water environment, and it is expected to completely solve the worldwide problem of nitrite disturbing aquaculture. Related experiments are still being further improved.

Second, the indirect control method

1, change water

Changing water is a common method in production, and it is also the need of aquaculture management. This method is suitable for small-scale aquaculture water bodies with sufficient water sources and convenient access to water, and it is required to follow the basic principle of changing water, and a large amount of water is prohibited. The method of controlling nitrite by changing water has the weakness of treating the symptoms rather than the root cause, so it is advisable to use substrate improver in combination.

2. Microbiological assay

At present, the microorganisms used mainly include photosynthetic bacteria, Bacillus, EM bacteria, lactic acid bacteria, actinomycetes and so on. The difference between nitrifying bacteria and the above microorganisms is that nitrifying bacteria can absorb and utilize high concentration of nitrite in water and convert it into harmless substances such as nitrate and nitrogen, while the above microorganisms have no such degradation function on nitrite. Their mechanism is mainly to repair the micro-ecological environment of water, improve water quality and sediments, indirectly increase dissolved oxygen in water, and ensure the normal cycle of nitrification and denitrification. With this understanding, we should get rid of the misunderstanding that photosynthetic bacteria, Bacillus and EM bacteria can degrade nitrite, and their functions are only to improve the environment and repair the micro-ecological environment of water bodies. We can take it as a daily management measure to prevent high nitrite. When the concentration of nitrite in water is higher than 0.5 mg/L (shrimp pond), it is not appropriate to use the above microorganisms, especially Bacillus, immediately, which will lead to the increase of nitrite concentration in a short time. In view of this situation, quick-acting methods should be taken to reduce the concentration of nitrite to a level harmless to cultured animals, and then the above microorganisms should be considered.

In actual production, there are many methods to control the harm caused by high nitrite, such as various methods of increasing oxygen to improve the efficiency of nitrifying bacteria, using substrate improvers, sprinkling brown sugar, salt and sodium thiosulfate. Without exception, they can't solve the fundamental problem. It only plays the role of mitigation and control.