With the development of animal husbandry in our country, industrial competition is becoming increasingly fierce. The scale and intensive development of animal husbandry has become an inevitable trend. Large scale breeding has high feeding technology, unified management, reduced costs, and improved economic benefits. However, the environmental pollution caused by the discharge of a large amount of concentrated feces and sewage is becoming more and more serious. The manure, urine, excrement, and wastewater from the aquaculture industry contain a large amount of organic matter, nitrogen, phosphorus, suspended solids, and pathogenic bacteria, which produce a foul odor. Direct discharge into rivers or surface water will seriously pollute water sources and soil environments, destroy the original functions of water bodies, endanger human health and agricultural and fishery production, such as eutrophication, and cause fatal damage to water quality. On the other hand, freshwater, as a resource that is closely related to the national economy and people's livelihood, is increasingly being raised to a strategic level.

The pollution in aquaculture farms mainly consists of two aspects: feces (mainly solid) and wastewater (including residual urine) formed by washing the farms, which vary depending on the type of aquaculture. But the treatment of feces is nothing more than dry cleaning and flushing with water. After solid-liquid separation, feces are discharged into the sewage treatment system. The difficulty in treating wastewater from aquaculture farms lies in the treatment of NH3-N and feces and urine; The key is to do a good job in solid-liquid separation before biochemistry. The excrement and wastewater discharged from the breeding farm contain a large amount of organic matter, ammonia nitrogen, total phosphorus, SS, pathogenic bacteria, and produce a nauseating odor, which greatly affects the environmental quality. It is highly valued by environmental protection and urgently needs to be treated.

Due to the fact that wastewater treatment in aquaculture farms is different from industrial wastewater treatment, the economic benefits of aquaculture farms are not high, which limits the possibility of investing a large amount of funds in sewage treatment plants. This requires less investment, good treatment effects, and certain economic efficiency. At the same time, due to the large amount of suspended solids in wastewater, it cannot be treated solely by biochemistry, but needs to be treated in combination with physical and chemical measures. The integrated aquaculture wastewater treatment equipment process has emerged.

For many years, China has conducted extensive research and exploration on the technology and process of integrated aquaculture wastewater treatment equipment. Various experiments and practices have been carried out on fecal wastewater treatment, and effective and successful experiences have been achieved. Gradually, a treatment process that focuses on biochemistry and combines biochemistry with physical-chemical methods has been formed. Various processes commonly used in biochemical methods include activated sludge process, biofilm process, anaerobic and aerobic combined process, hydrolysis acidification combined with aerobic process, etc. Engineering practice has proven that aerobic treatment of fecal wastewater from large and medium-sized farms after solid-liquid separation is feasible and efficient. For small-scale farms, a combination of hydrolysis acidification and aerobic treatment is more suitable. Adopting anaerobic digestion can not only reduce energy consumption and operating costs, but also recover methane gas and utilize it, thereby achieving waste utilization.

Introduction to each process:

1. Air flotation and sedimentation

Air flotation and sedimentation tank is a commonly used solid-liquid separation equipment in the sewage treatment industry, which can effectively remove suspended solids, oil, and gel substances in sewage and is the main process of sewage pretreatment. Dissolved air flotation technology has been widely used in water supply, drainage, and wastewater treatment in recent years. It can effectively remove light flocs that are difficult to precipitate in wastewater.

The wastewater discharged from aquaculture farms contains a large amount of manure and suspended solids, which is the main reason for the high CODcr and ammonia nitrogen in aquaculture wastewater. The large amount of suspended solids also has a significant impact on subsequent biochemical treatment. Therefore, the focus of aquaculture wastewater treatment is on the treatment of suspended solids. Based on our company's actual experience in aquaculture wastewater treatment, the pre-treatment adopts a process of regulating tank+air flotation primary sedimentation tank. By adding flocculants to the wastewater, the suspended solids in the wastewater can be removed, which can effectively reduce the workload of subsequent biochemical treatment and provide good conditions for subsequent treatment processes.

2. Hydrolysis acidification method

Hydrolytic acidification is mainly used in wastewater treatment processes with high organic matter concentration and high SS, and is a relatively important process. When organic matter in water has complex structures, hydrolytic acidification bacteria use H+and - OH ionized by H2O to open C-C in organic molecules. By adding H+at one end and - OH at the other end, long chains can be hydrolyzed into short chains, branched chains into straight chains, and cyclic structures into straight or branched chains, improving the biodegradability of wastewater. When SS is high in water, hydrolytic bacteria capture it through the extracellular mucosa, hydrolyze it into molecular fragments with external enzymes, and then enter the intracellular metabolism. Incomplete metabolism can turn SS into soluble organic matter, and the effluent becomes clear. During this process, hydrolytic bacteria utilize the covalent bond energy in organic matter that breaks bonds through hydrolysis to complete the activity of life. The principle of hydrolysis and acidification is to efficiently decompose organic matter that is difficult to degrade under aerobic conditions by facultative hydrolysis and acidification microorganisms. By increasing the B/C of wastewater, it facilitates the efficient operation of subsequent aerobic biological treatment. Hydrolytic acidification eliminates the methane production stage in anaerobic digestion, which requires strict environmental conditions and slow microbial proliferation. Greatly reducing the volume of anaerobic treatment equipment while eliminating the need for gas recovery and utilization systems.

The hydrolysis acidification reactor is not strictly an anaerobic reactor. Considering the dissolved oxygen concentration that needs to be maintained in the reactor, it can only be used as a type of facultative reactor and is not strictly an anaerobic environment. Therefore, it has little or no participation in the methane production process, and is usually only used as a system to improve biodegradability before the aerobic reactor, which can effectively improve the treatment efficiency of the aerobic reactor.

The hydrolysis process utilizes the hydrolysis and acidification stages of anaerobic treatment, while abandoning the methane production (alkaline fermentation) stage. The main purpose of hydrolysis treatment is to achieve the transformation of difficult to biodegrade organic matter through hydrolysis and non hydrolysis. By changing the molecular structure (ring opening, bond breaking, cracking, group substitution, reduction, etc.), complex and difficult to biodegrade organic matter molecules are transformed into slowly or rapidly biodegradable organic matter, thereby significantly improving the biodegradability and decolorization effect of wastewater, and ultimately including difficult to biodegrade organic matter (groups or chemical bonds in molecular structures) as electron acceptors. To stabilize the effluent quality, reduce the impact load, and create conditions for aerobic treatment, this process can effectively solve the problem of suspended solids (SS). On the other hand, the characteristic is that all or part of the remaining sludge generated in the aerobic section is refluxed to the anaerobic section. Due to the sufficient biological solid retention time (SRT) in the anaerobic section, the sludge can undergo thorough anaerobic digestion in the anaerobic section, so that the remaining sludge is completely decomposed into H2O and CO2 in the circulation process, and the entire system reaches its own sludge balance, with less or no sludge discharge, effectively solving the problem of wastewater sludge and also playing a role in biological denitrification.

3. Contact oxidation method

Biological contact oxidation method is a type of biofilm method, consisting of a tank body, packing material, and aeration system. Microorganisms such as bacteria, fungi, and post protozoa grow and reproduce on packing carriers. Microorganisms take up organic matter in wastewater as nutrients, adsorb and decompose it, and continuously metabolize and maintain activity, thus purifying the wastewater. In the presence of sufficient dissolved oxygen and food, microbial reproduction is very rapid, and the biofilm gradually thickens. Dissolved oxygen and organic matter in sewage are utilized by microorganisms through diffusion. When the biofilm reaches a certain thickness, oxygen cannot diffuse into the interior of the biofilm, aerobic bacteria die, and facultative bacteria and anaerobic bacteria begin to multiply in large numbers, forming an anaerobic layer. The dead aerobic bacteria are used as a substrate, and anaerobic bacteria continue to grow on this basis. After a period of time, the number begins to decrease, and coupled with the escape of metabolic gases, large pieces of biofilm fall off. On the surface of the detached biofilm, new biofilm develops again. In the contact oxidation tank, due to the large surface area of the filler, every stage of biofilm development exists, stabilizing the ability to remove organic matter at a high level. The BOD removal rate is generally between 80% and 90%.

The advantages of this process are stable operation and reliable treatment effect. High volume load and short processing time. Low power consumption, simple operation of the treatment system, convenient maintenance and management, and low sludge production.

4 Ozone oxidation process

The ozone generated by the ozone generator is diffused into the water to be treated through gas water contact equipment, usually using microporous diffusers, bubble towers or injectors, turbine mixers, etc. The utilization rate of ozone should strive to reach over 90%, and the remaining ozone should be discharged with the exhaust gas. To avoid air pollution, the exhaust gas can be catalytically decomposed using activated carbon or Hoggart agent, or catalytic combustion can be used to decompose ozone. The ozone oxidation technology has the following characteristics:

① Ozone, due to its strong oxidizing ability, can remove substances that are difficult to remove by other water treatment processes;

② The reaction rate of ozone oxidation is fast, which can reduce the volume of reaction equipment or structures;

③ The remaining ozone will quickly convert into oxygen, which not only does not produce secondary pollution, but also increases dissolved oxygen in water;

④ While sterilizing and killing viruses, it can also eliminate odors and odors;

⑤ Odorization helps with flocculation and can improve sedimentation efficiency.

Advantages of aquaculture wastewater treatment equipment:

1. The equipment runs stably, with a small total installed capacity and low daily operating costs.

2. The process selection is simple but stable and reliable, and the scientific combination of processes creates efficient processing results.

3. The system has strong resistance to impact loads, strong adaptability, and the impact of environmental temperature changes on the system is relatively small.

4. The system can be designed for fully automated control, requiring only daily inspection and maintenance by personnel, without the need for dedicated supervision.