Aquaculture sewage treatment process and technical points

Characteristics of aquaculture sewage:

The organic matter concentration is high, the suspended solids are many, and the color is deep. The NH3-N concentration is very high due to the large amount of animal feces, and it contains a large number of pathogenic bacteria. The pollutants in the sewage mainly exist in the form of solid and dissolved carbohydrates, which make the sewage show high BOD5, CODcr, SS and chromaticity. , P and other nutrients. Since the solid residues in the sewage are mainly organic substances, it is necessary to strengthen the pretreatment, carry out solid-liquid separation, and reduce the subsequent treatment load.

Classification of aquaculture sewage:

According to the different types of livestock and poultry, breeding sewage is divided into:

1.chicken sewage

2.duck (goose) sewage

3. rabbit sewage, pig sewage

4. cattle sewage and sheep sewage

There are certain differences in the quality of each type of sewage, but the sewage treatment technology and process are basically unchanged.

Technology of aquaculture sewage treatment :

Biological treatment

Biological treatment: Through the metabolism of microorganisms, the organic pollutants in the state of solution, colloid and fine suspension in the wastewater are converted into stable and harmless substances.

According to the different microorganisms, biological treatment methods can be divided into two types: aerobic biological treatment and anaerobic biological treatment. The aerobic biological treatment method is widely used in the biological treatment of wastewater. According to the different process methods, the aerobic biological treatment method is divided into two categories: activated sludge method and biofilm method. The activated sludge process is itself a treatment unit, and it operates in a variety of ways. The treatment equipment of biofilm method includes biological filter, biological turntable, biological contact oxidation tank and biological fluidized bed. Biological oxidation pond method is also called natural biological treatment method. Anaerobic biological treatment, also known as biological reduction treatment, is mainly used to treat high-concentration organic wastewater and sludge.

Physical treatment

Method for separating and recovering insoluble suspended pollutants (including oil film and oil beads) in wastewater by physical action.

It can be divided into gravity separation method, centrifugal separation method and sieve retention method. The processing units belonging to the gravity separation method include sedimentation, floating (dissolved air flotation), etc, and the corresponding processing equipment is a grit chamber, a sedimentation tank, a grease trap, an air flotation tank and its accessories; the centrifugal separation method itself is a kind of treatment. The processing devices used are disc separators and horizontal screw centrifuges, etc.; the screening and retention method has two processing units: grid screen retention and filtration. The processing equipment used in the former is mechanical bar screen and screen, while the latter uses The main ones are sand filters and microporous filters. The treatment method based on the principle of heat exchange also belongs to the physical treatment method, and its treatment unit includes evaporation, crystallization and so on.

Chemical treatment

A wastewater treatment method that separates and removes dissolved and colloidal pollutants in wastewater or converts them into harmless substances through chemical reactions and mass transfer.

In the chemical treatment method, the treatment units based on chemical reaction by adding chemicals are: coagulation, neutralization, redox, etc.; while the treatment units based on mass transfer are: extraction, stripping, stripping , adsorption, ion exchange, electrodialysis and reverse osmosis, etc. The latter two processing units are collectively referred to as membrane separation technology. Among them, the treatment unit that uses mass transfer has both chemical effects and physical effects related to it, so it can also be separated from chemical treatment methods and become another type of treatment method, which is called physical and chemical methods.

Natural treatment

Use the principle of self-purification of sewage by nature (natural water, soil, etc.) to play a role. Including land treatment system and aquatic plant treatment system.

Common ones are biological ponds, soil treatment methods, and artificial wetland treatment methods. Oxidation ponds use natural or artificial ponds for biological sewage treatment. The sewage stays in the pond for a long time, and the microorganisms in the water can metabolize and degrade the organic pollutants, and the dissolved oxygen is realized through the photosynthesis of algae and the reoxygenation of the pond surface, which can greatly reduce the organic pollutants in the water body, and to a certain extent. It removes nitrogen and phosphorus from the water and reduces the eutrophication of the water body. Constructed wetlands are a method of purifying water naturally by simulating the biodiversity of natural wetlands. It uses aquatic plants, gravel and coal beds, the composition of microorganisms, and physical processes such as filtration, adsorption, and replacement of sewage, as well as the absorption and degradation of microorganisms. It also belongs to a kind of aerobic treatment method. It can be transformed from abandoned or idle farmland, depressions or ponds, but it has a relatively large area and overloaded operation is easy to cause blockage.

Process flow of aquaculture sewage treatment:

No matter what process and measures are adopted for the treatment of farm wastewater, certain pretreatment methods should be adopted. Using the pretreatment method can reduce the load of wastewater pollutants in the subsequent treatment steps, and at the same time prevent large solids or debris from entering the subsequent treatment process, causing congestion or damage to the treatment equipment. For large particles in manure, pig farms can use solid-liquid separation technologies such as sedimentation, filtration and centrifugation to achieve pretreatment. Common mechanical strip screens, sedimentation tanks and screens belong to this category. Sedimentation is one of the most widely used methods in wastewater treatment. It is a treatment process in which suspended matter settles naturally and is separated from water under the action of gravity. At present, pig farms with wastewater treatment facilities in large-scale pig farms will basically connect 2-3 sedimentation tanks in series to treat manure through filtration, sedimentation and oxidative decomposition. In addition, some mechanical bar screen equipment including automatic rotary drum screen and disc stack centrifuges can be used in the pretreatment step of pig manure.