How to treat aquaculture wastewater?
Aquaculture, as an important agricultural production method, has been widely used all over the world. With the expansion of aquaculture, the treatment of aquaculture wastewater has become increasingly prominent. Aquaculture wastewater contains a large amount of organic matter, nitrogen, phosphorus and other nutrients. If it is not properly treated, it will cause serious pollution to the water body when discharged into the natural environment. Therefore, scientific and rational treatment of aquaculture wastewater has become an important issue to ensure environmental sustainable development.
What are the composition and characteristics of aquaculture wastewater?
To treat aquaculture wastewater, we first need to understand its composition and characteristics. Aquaculture wastewater mainly comes from aquaculture pond water, feed residues, fish and shrimp excrement, and microbial metabolites. Usually, these wastewaters contain high concentrations of suspended solids, organic matter, nitrogen, phosphorus, and pathogenic microorganisms. Its specific characteristics are as follows:
1. High organic content: Aquaculture wastewater contains a large amount of feed residues and fish and shrimp excrement. These are organic pollutants, which can easily cause eutrophication of water bodies and lead to excessive growth of algae and other aquatic plants.
2. High nitrogen and phosphorus content: Nitrogen and phosphorus are the main causes of eutrophication of water bodies. The feed put in during aquaculture contains a large amount of nitrogen and phosphorus. The unabsorbed part is discharged with the wastewater, which can easily cause eutrophication of water bodies.
3. High suspended matter content: The suspended matter in the wastewater mainly comes from feed residues and fish and shrimp excrement. The suspended matter is easy to settle at the bottom of the water body, causing water quality deterioration.
4. High microbial content: Aquaculture wastewater contains a large number of pathogenic microorganisms, such as bacteria and viruses. If it is discharged directly without treatment, it may cause biological pollution of the water body and endanger the health of humans and animals.
Based on these characteristics of aquaculture wastewater, its treatment requires a combination of multiple technical means to achieve the purpose of effectively removing pollutants.
What are the treatment methods for aquaculture wastewater?
The treatment methods for aquaculture wastewater mainly include physical treatment, chemical treatment and biological treatment. Different treatment technologies can be used for different pollutants in wastewater.
Physical treatment method
The physical treatment method mainly removes suspended matter and some organic matter in wastewater through physical action. This method is simple to operate and low in cost. It is one of the basic methods for treating aquaculture wastewater.
● Sedimentation method: Through the action of gravity, the suspended matter in the wastewater is settled to the bottom of the pool, thereby achieving the effect of solid-liquid separation. Sedimentation method is suitable for removing large particles of suspended matter, such as feed residues, fish and shrimp excrement, etc.
● Filtration method: The suspended matter in the wastewater is intercepted by a filter screen or filter bed, which is suitable for removing smaller particles of suspended matter. Commonly used filter materials include sand, gravel, etc. Filtration method can further purify wastewater.
● Flotation method: By passing fine bubbles into the wastewater, the suspended matter is attached to the bubbles and floats to the water surface to form scum, and finally the scum is scraped off. Flotation method has a good effect on removing suspended matter that is difficult to precipitate.
Chemical treatment method
Chemical treatment method is to use chemical agents to react chemically with pollutants in wastewater to remove or transform pollutants. Commonly used chemical treatment methods include neutralization, oxidation-reduction, coagulation and sedimentation, etc.
● Coagulation and sedimentation method: Add coagulants to wastewater to make suspended matter and colloidal substances in the water condense into larger particles and settle. Common coagulants include aluminum salts, iron salts, etc. Coagulation and sedimentation method can effectively remove suspended matter and some organic matter in wastewater.
● Oxidation method: By adding oxidants to wastewater, organic pollutants are oxidized into harmless substances such as water and carbon dioxide. Commonly used oxidants include ozone, chlorine, potassium permanganate, etc. Oxidation method is suitable for treating organic pollutants and pathogenic microorganisms in wastewater.
● pH adjustment: The pH value of aquaculture wastewater sometimes deviates from neutrality. By adding acid or alkali to adjust the pH value, the treatment effect of wastewater can be improved and the impact on the environment can be reduced.
Biological treatment method
Biological treatment method uses the metabolism of microorganisms to degrade organic matter and nutrients in wastewater. It is one of the most commonly used methods for aquaculture wastewater treatment.
● Activated sludge method: Use microorganisms in wastewater to convert organic pollutants into inorganic substances. These microorganisms attach to suspended sludge particles to form activated sludge. The activated sludge method has a high removal rate for organic pollutants, but it needs to maintain suitable environmental conditions, such as temperature, pH value and dissolved oxygen concentration.
● Biofilter method: The wastewater is passed through a filter filled with filter media, and the organic pollutants are degraded by microorganisms attached to the filter media. Commonly used filter media include gravel, ceramsite, etc. The biofilter method is easy to operate and manage, and is suitable for small and medium-sized aquaculture farms.
● Biofilm method: By introducing wastewater into a biofilm reactor, the microorganisms on the biofilm are used to degrade organic matter. The biofilm method has a high removal efficiency and is highly adaptable to water quality fluctuations.
Key technologies and practices for aquaculture wastewater treatment
In practical applications, aquaculture wastewater treatment needs to be combined with the specific breeding environment, wastewater composition and treatment objectives to select appropriate technical solutions. The following is a summary of some key technologies and practical experiences:
Graded treatment of wastewater
The composition of aquaculture wastewater is complex and the types of pollutants are diverse. Therefore, the wastewater can be graded, that is, different treatment technologies are used in stages according to the type and concentration of pollutants. For example, large suspended solids are first removed by physical treatment, then organic matter and pathogenic microorganisms in the water are treated by chemical treatment, and finally residual pollutants are further degraded by biological treatment.
Resource treatment
Organic matter, nitrogen, phosphorus and other nutrients in aquaculture wastewater can be recycled under certain conditions, such as converting organic matter into biogas through anaerobic fermentation technology, or using treated wastewater for farmland irrigation to promote resource recycling. This resource treatment method not only reduces the pollution burden of wastewater, but also produces certain economic benefits.
Automated monitoring and management
Various parameters in the aquaculture wastewater treatment process, such as dissolved oxygen, pH value, temperature, etc., have an important impact on the treatment effect. The use of an automated monitoring system can monitor these parameters in real time and make timely adjustments to ensure the stable operation of the treatment system. At the same time, automated management can also reduce labor costs and improve treatment efficiency.
Application of combined treatment technology
A single treatment technology is often difficult to completely remove all pollutants in aquaculture wastewater. Therefore, combined treatment technology has become an effective choice. For example, physical treatment is combined with biological treatment to remove suspended solids through sedimentation and filtration, and then use biological filters to degrade organic matter. This combined process can achieve the synergistic removal of multiple pollutants and achieve better treatment results.