Present situation and treatment of Environmental Protection in aquaculture

I. introduction of aquaculture in China

Since the reform and opening up, China's aquaculture industry has developed rapidly, from 1978 to 1984 to solve the problem of eating meat, from 1985 to 1996 to solve the vegetable basket, from 1997 to 2006 to optimize the product structure, to the transition to modern animal husbandry since 2007, has gone through four stages of development.

In 2014, the per capita amount of meat in China reached the world average level, and the amount of eggs reached the level of developed countries in the world. Only the amount of milk was still less than the world average level of 1ax 4. The total output value of animal husbandry has reached 3.5 trillion yuan, the total output of meat is 87.07 million tons, the total output of poultry eggs is 28.94 million tons, and the total output of milk is 37.25 million tons. China's animal husbandry accounts for more than 30 percent of the total agricultural output value and has become an agricultural support industry.

In the future, the development of aquaculture will follow the total quantity control, strive for progress in stability, and accelerate the process of large-scale development. Adjust the structure of aquaculture industry and appropriately speed up the development of herbivores. Adhere to market regulation and continue to develop deep processing industries of meat, eggs and milk. The development of aquaculture will develop from the original total development type to large-scale and intensive development, and a large number of small and medium-sized aquaculture enterprises (households) will be eliminated by the market. Aquaculture enterprises must seek development opportunities in scale, industrialization, improving the ability of scientific and technological innovation, and enhancing unit productivity.

II. Analysis of pollution in aquaculture

By the end of 2014, the total output of China's aquaculture industry has reached 1.4 billion heads per year (pig equivalent). Such a large scale of aquaculture has also led to huge environmental pollution. According to statistics, last year, China's aquaculture industry discharged a total of 15 billion tons of sewage, 2.5 billion tons of feces, and 70 million sick and dead animals (in terms of pig equivalent). Its sewage discharge is equivalent to 1x4 of the total discharge of industrial, agricultural and domestic sewage in China, and the discharge of feces is 10 times that of urban residents in China.

According to statistics from the Ministry of Agriculture, in 2012, China's aquaculture industry emitted 17.226 million tons of chemical oxygen demand (COD), 351800 tons of total phosphorus (TP) and 370100 tons of total nitrogen (TN), accounting for 70% of China's total industrial and agricultural emissions, 57.2% and 67.4% respectively. The COD concentration of untreated aquaculture sewage is as high as 6000ml / 10000mg / ml / 10000mg / kg / kg / L ~ 1500mg / L ~ 1500mg / L TP concentration 80ml / 120mg / kg / kg / L ~ SS / 5000mg/L above. The concentration of pollutants is 50 times higher than that of domestic sewage of urban residents. Thus it can be seen that it is very harmful and difficult to deal with.

Taking an annual pig farm of 100000 as an example, 1.5 billion bacteria are discharged into the atmosphere every hour. 159kgNH3, 14.5 kg H2S dash 25.9 kg feed dust, the radius of air pollution of these substances can reach 4.5-5km, and the content of NH3 exceeds the hygienic standard of 0.2mg/L in the range of 3.5km in different directions from the pig farm. The pig farm discharges 300000 tons of sewage every year. Without any treatment, 90-150 million tons of groundwater dilution COD and 18-270 million tons of groundwater dilution NH3-N are needed to make the groundwater in this area not exceed the Ⅲ water standard. The average surface water content in China is 380000 tons / km2. If the pig farm sewage is discharged directly without treatment, the surrounding 300-600km2 water will be polluted within one year, and serious pollution will be formed within 3 years.

The harm of aquaculture waste to the environment and human beings is beyond people's imagination. The aquaculture sewage is discharged directly to the river, because the concentration of COD is as high as 6000mg/L, the dissolved oxygen in the water will be consumed rapidly. When the concentration of COD in the water exceeds 500mg/L, almost all aquatic animals in the water can not survive, and the water quality will deteriorate sharply, blackening and smelly.

N and P in sewage are eutrophication substances, which will cause aquatic plants to grow excessively and destroy the ecological environment when discharged into the water body in large quantities. Excessive breathing of ammonia and hydrogen sulfide in aquaculture waste gas will cause dyspnea and destroy human hematopoietic function, and a large amount of breathing will cause serious consequences such as human death.

The pathogenic microorganisms carried in the waste of aquaculture industry will cause cross-infection among animals, resulting in a large area of livestock deaths, and some livestock viruses will pose harm to human beings, such as avian influenza virus. Mouth-crying virus has caused disasters to human beings again and again.

China is a large farming country. Last year, 1.4 billion livestock were fenced (pig equivalent), and each pig discharged pollutant equivalent to 13 people, which is equivalent to 18 billion alternative people living with us. If the waste is not treated, the degree of harm can be imagined.

III. Environmental protection governance and current situation of aquaculture industry

Due to the characteristics of low scale of aquaculture, wide range of points, huge amount of aquaculture waste, and difficulties in the treatment of aquaculture waste, the environmental protection treatment of aquaculture waste in China lags behind seriously, and the situation of environmental pollution is very serious.

Since the reform and opening up, with the development of aquaculture from scattered farming to large-scale and intensive development, the environmental protection of aquaculture in China has been paid more and more attention by local governments at all levels as well as by the Party and the country, especially in recent years. With the increasingly serious environmental problems in China, the problem of pollution in aquaculture is becoming more and more serious. The comprehensive control of environmental protection in aquaculture has been taken as a key project of agricultural non-point source pollution by governments at all levels. The State Council, the Ministry of Environmental Protection and the Ministry of Agriculture have also issued new measures, new norms, new standards, new laws and regulations.

While strengthening supervision, national and local governments have also provided a number of special support funds and preferential policies for the comprehensive management of environmental protection in the aquaculture industry. However, in spite of this, the current situation of waste management in the aquaculture industry is not optimistic. According to authoritative statistics, the proportion of environmental protection facilities construction in China's large-scale aquaculture enterprises is still less than 30%. Less than 20% of the built facilities can meet the standards, and less than 10% of the built facilities can operate and manage effectively all the year round.

What is particularly serious is that with the increasing degree of scale, the problem of handling faeces and sick and dead animals in the breeding industry is becoming more and more serious. In particular, the treatment of smelling tail gas and feed dust in the aquaculture industry is almost blank so far.

We have noticed that a large number of aquaculture wastes are discharged directly, which poses irreparable harm to the surrounding environment; a large number of sick and dead animals flow into the black market and enter the catering and food processing industry, a large amount of feces accumulate like mountains, mosquitoes and flies crawl all over the place, and the stench is smelly. In many intensive farming areas, the air stinks and sewage flows across the country. People can't breathe fresh air and can't find clean water.

IV. Introduction of environmental protection control technology in aquaculture

The environmental protection problem of the aquaculture industry has to be solved. If we do not strengthen the rectification now, the pollution of the aquaculture industry will directly endanger our human survival in a few years' time.

Solve the problem of environmental protection in aquaculture. First of all, it is necessary to understand the pollution factors of aquaculture waste, and on this basis to seek treatment methods and measures. With the existing technical conditions of environmental protection, there are no environmental protection problems that can not be solved, but the key is three: the first is to choose the correct treatment process, the second is effective investment and construction, and the third is professional operation and management. It needs to be pointed out that, with the current technical conditions, although the effective management of waste can be ensured, its construction costs and operating costs are difficult for most aquaculture enterprises to bear.

Aquaculture wastes include sewage, feces, sick and dead animals, dust, tail gas and so on. The main pollution factors are COD, BOD5, NH3-N, TP, SS, H2S, NH3, PH, dust, anions, cations (heavy metals), microorganisms, antibiotics, animal drug residues and so on. Here we analyze the essentials and techniques of waste management according to the classification of waste.

1. Culture sewage

The sources of sewage in aquaculture mainly include livestock and poultry urine, flushing water, drinking water residue, dripping water, Rain Water, domestic sewage of breeders and so on. The main pollution factors in sewage are COD, BOD5, NH3-N, TP, SS and pathogenic microorganisms. The sewage also carries residual feed and dung, as well as animal drug residues, soluble volatile odor gases and so on.

Environmental protection departments focus on, or constitute pollution to the environment, the main pollution factors are: COD, BOD5, NH3-N, TP, SS, pathogenic microorganisms. In fact, the treatment technology of these pollution factors is already very mature:

The main results are as follows: (1) COD (BOD5) can be digested and decomposed by anaerobic and aerobic combined biochemical process.

(2) the treatment of NH3-N can be divided into three steps: ammoniation (anaerobic), nitrification (aerobic), denitrification (anoxic), and can also be removed by chemical synthesis or decomposition, such as MAP recovery process (ammonium magnesium phosphate recovery).

(3) in the treatment of TP, phosphorus is released by organic matter under anaerobic condition, and phosphorus can be absorbed by sludge under aerobic condition. Phosphorus can be removed by precipitating sludge or by chemical method.

(4) suspended solids (SS) can be effectively removed by precipitation filtration.

(5) pathogenic microorganisms can be effectively killed by adding enhanced oxidants, such as O3, ClO2, bleach and so on.

The complete technological process of aquaculture sewage treatment can be expressed as: anaerobic-anoxic-aerobic-precipitation-disinfection. In fact, the above are the processes with the lowest investment and lowest operating cost in the process of aquaculture sewage treatment. However, whether the above-mentioned processes can be skillfully and effectively used to solve the standard treatment of aquaculture sewage is indeed a difficult problem for most environmental protection workers. The selection of process parameters and the setting of process conditions are very difficult, especially the uncertainty and seasonal variation of the processing effect of the process unit, which makes most designers at a loss what to do. For this reason, many environmental protection scientists and technicians have turned to other processes and technologies in an attempt to solve these problems through more advanced processes. Membrane technology, strong oxidation technology and electrolysis technology were used in aquaculture wastewater treatment process. Although the effect has been immediately improved, but the input costs, operating costs soared, so that aquaculture enterprises can not bear.

Membrane technology for landfill leachate treatment has been widely implemented at home and abroad, the investment cost of membrane treatment process for each ton of landfill leachate is generally 8-100000 yuan / ton of water, and the lowest operating cost is more than 30 yuan / ton of water. When ozone (O3) is used as a strong oxidant for oxidation and decomposition, theoretically, it takes 3 grams of O3 per gram of COD and 2.2g of O3 per gram of NH3-N (in fact, the removal effect of O3 on NH3-N is very poor under normal conditions). However, O3 is generally produced by high voltage discharge, and the cost per gram of O3 is more than 0.02 yuan. The unit of COD in sewage is thousands, and the unit of NH3-N is hundreds. The decomposition cost of sewage needs dozens of yuan to hundreds of yuan, which can not be borne by breeding enterprises. Electrolysis process used in high concentration sewage treatment is still in the stage of laboratory research and industrial experiment, and there is no long-term effective marketing equipment. And the electrolysis process, analyzed from the principle of energy conservation and electrochemistry, although it will have a strong treatment capacity, but its treatment cost is also very high.

The aquaculture enterprise produces a large amount of sewage, especially blister dung and water flushing dung, even if it is dry manure removal (from the point of view of environmental protection and water saving, we recommend the dry manure cleaning mode, which is also a mode encouraged and promoted by the state), according to the calculation of each pig, from the piglet to the adult pig, the sewage production is 5 tons per pig, if the cost of sewage treatment is more than 30 yuan / ton. Then aquaculture enterprises will incur operating losses and will not be able to survive.

Therefore, the development and application of environmental protection technology with low investment and low operating cost is an important task in the environmental protection treatment of aquaculture industry, and aquaculture enterprises should strive to tap the potential in saving water, reducing sewage discharge, rain and sewage separation, solid-liquid separation and resource utilization.

2. Fecal treatment

Aquaculture manure has always been the best crop fertilizer for farmers, but with the improvement of the degree of scale and the increasingly obvious division of specialization, on the one hand, there is no sufficient farmland or woodland for consumption in and around the farm; on the other hand, aquaculture enterprises are no longer engaged in agricultural production activities, and there is no sufficient farmland and woodland for consumption. In this way, the manure produced by the farm must find a new way out. At present, the practice of most enterprises is to rely on the surrounding farmers to transport and digest, and a few with conditions can sign digestion contracts with organic fertilizer enterprises or farms.

What needs to be emphasized is that we have a misunderstanding that someone's outward transportation is to solve the problem of faecal disposal, but in fact this is not the case. There are two key problems that need to be clarified and solved. First, the transportation of fresh dung will inevitably lead to leakage, such as leakage, because the water content of fresh dung is as high as 80%, has a serious stench, and also carries a large number of pathogenic microorganisms, which will pose a serious pollution and threat to the environment and human beings, which is difficult to achieve unless a special environmental protection transport vehicle is used. Second, the return of fresh manure to the field will also bring serious pollution and threat to the environment and human beings, and the fertilizer efficiency is not high.

In fact, people realized this problem as early as BC and began to rett fertilizer first and then return it to the field. Therefore, the treatment of feces includes two aspects: one is to complete the harmless treatment when leaving the field, that is, deodorization, sterilization and dehydration; the other is to compost and then return to the field.

The methods of harmless treatment of feces and coarse composting are very simple, including anaerobic composting, aerobic composting and anaerobic-aerobic composting. However, the choice of composting technology and technology, especially the construction mode of composting facilities directly affects the composting effect and composting cost. This is what aquaculture enterprises must consider.

3. Treatment of sick and dead animals.

The treatment of sick and dead animals has gone through four stages: (1) human and animal consumption; (2) disposal and landfill; (3) incineration; and (4) biological treatment. The first method has been strictly prohibited; the second method not only pollutes the environment but also wastes land; the third method produces secondary pollution and wastes energy; the fourth method is the national key support and promotion method at the present stage.

The biological treatment method can be divided into two paths: one is the biological path, which dissolves the sick and dead animals through biological decomposition and fermentation, and turns them into organic fertilizer raw materials that can be used by crops. After sterilization at high temperature, the dead animals are broken into tiny particles, and fermented by adding fermentation bacteria and dry matter excipients to ferment into coarse compost. The other is the biochemical pathway, in which dead animals are sterilized and broken at high temperature, and then biochemical decomposition is carried out to turn them into chemicals such as oils and amino acids, and the residue can also be composted.

4. Malodorous gas can be effectively removed by biological oxidation decomposition or strong oxidant oxidation decomposition, or biochemical adsorption decomposition.

5. Feed dust can be effectively removed by means of dedusting device (dust collector) or wet adsorption and precipitation.