A Detailed Analysis of the Environmental Protection Status of the Livestock Industry and Treatment Approaches
I. Introduction to China's Livestock Industry
Since the reform and opening up, China's livestock industry has developed rapidly, from solving the meat shortage in 1978—1984, solving the vegetable basket issue in 1985—1996, optimizing the product structure in 1997—2006, to the transition toward modern animal husbandry since 2007, having gone through four stages of development.
In 2014, China's per capita meat availability reached the world average level, egg availability reached the level of developed countries, and only milk availability remained less than 1/4 of the world average. The total output value of animal husbandry reached 3.5 trillion yuan, total meat production was 87.07 million tons, total poultry egg production was 28.94 million tons, total milk production was 37.25 million tons. The proportion of China's animal husbandry in the total agricultural output value has exceeded 30%, becoming a supporting industry for agriculture.
In the future, the development of the livestock industry will follow total volume control, seeking progress while maintaining stability, and accelerating the process of large-scale development. Adjusting the structure of the livestock industry and moderately accelerating the development of herbivorous animals. Adhering to market regulation and continuing to develop deep processing industries for meat, eggs, and milk. The development of the livestock industry will shift from the original total-volume development type to a large-scale intensive type. A large number of small and medium-sized livestock enterprises (households) will be eliminated by the market. Livestock enterprises must seek development opportunities in large-scale operation, industrialization, improving technological innovation capacity, and enhancing unit productivity.
II. Analysis of Pollution from the Livestock Industry
By the end of 2014, China's total livestock production had reached 1.4 billion head/year (pig equivalent). Such a massive scale of livestock production has simultaneously generated enormous environmental pollution. According to statistics, last year China's livestock industry discharged a total of 15 billion tons of wastewater, 2.5 billion tons of manure, and 70 million dead animals (calculated by pig equivalent). Its wastewater discharge is equivalent to 1/4 of China's total industrial, agricultural, and residential domestic wastewater discharge, and the manure discharged is 10 times the amount of domestic solid waste generated by China's urban residents.
According to statistics from the Ministry of Agriculture, in 2012 China's livestock industry discharged 17.226 million tons of chemical oxygen demand (COD), 351,800 tons of total phosphorus (TP), and 370,100 tons of total nitrogen (TN), accounting for 70%, 57.2%, and 67.4% of China's total industrial and agricultural emissions respectively. The COD concentration of untreated livestock wastewater is as high as 6000—10000mg/L, NH3-N concentration 800—1500mg/L, TP concentration 80—120mg/L, and SS concentration above 5000mg/L. Its pollutant concentration is 50—100 times that of urban residential domestic wastewater. This shows the magnitude of its harm and the difficulty of treatment.
Taking a pig farm with an annual output of 100,000 pigs as an example, it emits 1.5 billion bacteria, 159kg NH3, 14.5kg H2S, and 25.9kg feed dust into the atmosphere every hour. The air pollution radius of these substances can reach 4.5—5km. Within 3.5km in different directions from the pig farm, the NH3 content exceeds the hygiene standard of 0.2mg/L. The pig farm discharges 300,000 tons of wastewater annually. If untreated, it would require 90—150 million tons of groundwater to dilute the COD, and 180—270 million tons of groundwater to dilute the NH3-N, in order to keep the groundwater in the area from exceeding Class III water standards. China's average surface water content is 380,000 tons/km2. If pig farm wastewater is discharged directly without treatment, within one year it can pollute 300—600km2 of surrounding water bodies, and within three years it will cause severe pollution.
The harm of livestock waste to the environment and human beings exceeds people's imagination. When livestock wastewater is discharged directly into rivers, because the COD concentration is as high as above 6000mg/L, the dissolved oxygen in the water body will be rapidly consumed. When the COD concentration in water exceeds 500mg/L, almost all aquatic animals in the water cannot survive, and water quality will deteriorate sharply, turning black and foul-smelling.
N and P in wastewater are eutrophication substances. Large amounts discharged into water bodies will cause aquatic plants to grow wildly and destroy the ecological environment. Ammonia and hydrogen sulfide in livestock exhaust gas, when inhaled excessively by humans, can cause breathing difficulties and damage human blood-forming functions. Massive inhalation can cause serious consequences such as human death.
Pathogenic microorganisms carried in livestock waste can cause cross-infection among animals, resulting in large-scale poultry and livestock death incidents. Some poultry and livestock viruses can harm humans, such as avian influenza virus and foot-and-mouth disease virus, which have repeatedly brought disasters to mankind.
China is a major livestock-producing country. Last year, 1.4 billion head of poultry and livestock were slaughtered (pig equivalent). If each pig's pollutant discharge equivalent is calculated as 13 people, then it is equivalent to 18 billion "alternative people" coexisting with us. If their waste is not treated, the degree of harm can be imagined.
III. Environmental Protection Treatment of the Livestock Industry and Its Current Status
Due to the low degree of large-scale operation in China's livestock industry, the wide distribution of numerous sites, the enormous total volume, and the difficulty of treating livestock waste, China's environmental protection treatment of livestock waste has been seriously lagging behind, and the environmental pollution situation is very severe.
Since the reform and opening up, as the livestock industry has accelerated its development from household free-range farming to large-scale and intensive operations, China's livestock environmental protection issues have received increasing attention from local governments at all levels as well as the Party and the state. Especially in recent years, as China's environmental problems have become increasingly severe and livestock pollution has become increasingly serious, comprehensive environmental treatment of the livestock industry has been treated by governments at all levels as a key project for agricultural non-point source pollution. The State Council, the Ministry of Environmental Protection, and the Ministry of Agriculture have successively issued new measures, new norms, new standards, and new regulations, striking hard and carrying out joint rectification.
While increasing regulatory efforts, the state and local governments have also provided multiple special support funds and preferential policies for comprehensive environmental treatment of the livestock industry. However, despite this, the current status of livestock waste treatment work is not optimistic. According to authoritative statistics, at present the proportion of large-scale livestock enterprises in China with environmental protection facility construction is still below 30%. Less than 20% of the facilities already built can achieve compliant treatment, and less than 10% of the facilities already built have long-term effective operation and management.
What is particularly serious is that as the degree of large-scale operation increases, the problem of treating manure and dead animals in the livestock industry becomes even more severe. In particular, the treatment of odorous exhaust gas and feed dust from the livestock industry remains almost a blank to this day.
We note that large amounts of livestock waste are directly discharged, causing irreparable harm to the surrounding environment; large numbers of dead animals flow into black markets and enter the catering and food processing industries; large amounts of manure pile up like mountains, with mosquitoes and maggots flying and crawling everywhere, and a stench filling the air. In many areas with concentrated livestock operations, the air is foul and sewage flows everywhere. People cannot breathe fresh air or find clean water sources.
IV. Introduction to Environmental Protection Treatment Technologies for the Livestock Industry
The environmental protection problems of the livestock industry have reached a point where they must be solved. If efforts to rectify them are not increased now, in a few years the pollution from the livestock industry will directly endanger human survival.
To solve the environmental protection problems of the livestock industry, it is first necessary to understand the pollution factors in livestock waste, and on this basis seek treatment methods and measures. With the existing technical conditions for environmental protection, there is no environmental protection problem that cannot be solved, but the key lies in three points: first, selecting the correct treatment process; second, effective investment and construction; third, professional operation and management. It should be pointed out that with current technical conditions, although effective treatment of waste can be ensured, both the construction cost and the operating cost are difficult for most livestock enterprises to bear.
Livestock waste includes wastewater, manure, dead animals, dust, exhaust gas, and so on. Its main pollution factors are: COD, BOD5, NH3-N, TP, SS, H2S, NH3, PH, dust, anions and cations (heavy metals), microorganisms, antibiotics, veterinary drug residues, etc. Here we analyze the treatment essentials and technologies according to the classification of waste.
1. Livestock wastewater
The sources of livestock wastewater mainly include livestock and poultry urine, flushing water, drinking water residue, dripping water, rainwater, and breeder domestic wastewater. The main pollution factors contained in the wastewater are COD, BOD5, NH3-N, TP, SS, and pathogenic microorganisms. The wastewater also carries residual feed and manure residue, as well as veterinary drug residues, dissolved volatile odorous gases, etc.
The main pollution factors that environmental protection departments focus on, or that cause pollution to the environment, are: COD, BOD5, NH3-N, TP, SS, and pathogenic microorganisms. The treatment technologies for these pollution factors are actually already very mature:
(1) COD (BOD5) treatment can be digested and decomposed through combined anaerobic and aerobic biochemical processes.
(2) NH3-N treatment can be divided into three steps: ammonification reaction (anaerobic), nitrification reaction (aerobic), and denitrification reaction (anoxic), or it can be removed through chemical reaction synthesis or decomposition, such as the MAP recovery process (magnesium ammonium phosphate recovery).
(3) TP treatment: under anaerobic conditions organic matter releases phosphorus, under aerobic conditions sludge can absorb phosphorus, and phosphorus can be removed through sludge settling, or it can be removed through chemical methods.
(4) Suspended solids (SS) can be effectively removed through sedimentation and filtration methods.
(5) Pathogenic microorganisms can be effectively killed by adding strong oxidants such as O3, ClO2, bleaching powder, etc.
The complete livestock wastewater treatment process can be expressed as: anaerobic——anoxic——aerobic——sedimentation——disinfection. In fact, the above is the process with the lowest investment and lowest operating cost among livestock wastewater treatment processes. However, whether the above processes can be skillfully and effectively used to achieve compliant treatment of livestock wastewater is indeed a difficult problem troubling most environmental protection workers. The selection of process parameters and the setting of process conditions are extremely difficult. In particular, the uncertainty and seasonal variation of the treatment effect of process units leave most designers at a loss. For this reason, many environmental protection science and technology workers have turned their targets to other process technologies, attempting to solve these problems through more advanced processes. Membrane technology, strong oxidation technology, electrolysis technology, etc. have been applied to livestock wastewater treatment processes. Although this achieves immediate improvements in results, investment costs and operating costs rise sharply, making them unbearable for livestock enterprises.
Membrane technology used in landfill leachate treatment has been widely implemented domestically and abroad. The investment cost of membrane treatment processes for each ton of landfill leachate is generally 80,000—100,000 yuan/ton of water, while the lowest operating cost also exceeds 30 yuan/ton of water. For oxidative decomposition using the strong oxidant ozone (O3), theoretically each gram of COD requires 3 grams of O3, and each gram of NH3—N requires 2.2 grams of O3 (in practice, under normal conditions O3 has very poor removal effect on NH3—N). O3 production generally uses high-voltage discharge. With current O3 generation technology, the generation cost of each gram of O3 is above 0.02 yuan. COD in wastewater is measured in thousands and NH3—N in hundreds, so its decomposition cost requires tens to hundreds of yuan, which is truly beyond what livestock enterprises can bear. Electrolysis processes used for high-concentration wastewater treatment are currently still in the laboratory research and development and industrial experimental stages, and there are no commercially available devices for long-term effective operation. Moreover, from the perspectives of energy conservation and electrochemical principles, although electrolysis processes may have strong treatment capacity, their treatment cost is also very high.
Livestock enterprises generate large amounts of wastewater. Especially with water-soaked manure and water-flushed manure cleaning methods, even with dry manure cleaning (from the perspective of environmental protection and water conservation, we recommend the dry manure cleaning model, which is also the model the state encourages and promotes), calculated per pig, from piglet to finished pig at slaughter, the wastewater generated is 5—6 tons/head. If the wastewater treatment cost exceeds 30 yuan/ton, livestock enterprises will suffer operating losses and be unable to survive.
Therefore, developing and applying environmental protection processes with low investment and low operating costs is an important research topic in the environmental protection treatment of the livestock industry, and livestock enterprises should work hard to tap potential in saving water, reducing pollution discharge, separating rain and sewage, solid-liquid separation, and resource utilization.
2. Manure treatment
Livestock manure has always been the best crop fertilizer for farmers, but as the degree of large-scale operation increases and specialized division of labor becomes increasingly obvious, on the one hand, farms themselves and their surroundings do not have enough farmland or forest land available to absorb it; on the other hand, livestock enterprises no longer engage in agricultural production activities, and they themselves do not have enough farmland and forest land available to absorb it. Thus, the manure produced by farms must seek a new outlet. At present, most enterprises rely on nearby farmers to transport it away for absorption, and a small number with suitable conditions can sign absorption contracts with organic fertilizer enterprises or farms.
It needs to be emphasized that we have a misconception, thinking that if someone transports it away for treatment, the manure treatment problem is solved, but in fact this is not the case. There are two key issues here that need to be clarified and solved. First, the issue of transporting fresh manure off-site. The transport of fresh manure inevitably produces leakage such as spillage and dripping, because the moisture content of fresh manure is as high as 80%, it has a severe foul odor, and it also carries large amounts of pathogenic microorganisms, which will cause serious pollution and threats to the environment and humans unless special environmental protection transport vehicles are used, which is very difficult to achieve. Second, returning fresh manure to fields will likewise bring serious pollution and threats to the environment and humans, and its fertilizer efficiency is not high.
In fact, as early as BC people had already recognized this problem and had already begun composting manure before returning it to fields. Therefore, manure treatment includes two aspects: first, harmless treatment must be completed before leaving the site, namely deodorization, sterilization, and dehydration; second, composting first and then returning it to fields.
The harmless treatment of manure and rough composting are very simple methods, mainly including anaerobic composting, aerobic composting, and anaerobic—aerobic composting. However, the selection of composting processes and technologies, especially the construction method of composting facilities, directly affects composting effectiveness and composting cost. This is something livestock enterprises must consider.
3. Treatment of dead animals.
The treatment of dead animals has gone through four stages: (1) human and animal consumption; (2) discarding and landfill; (3) incineration; (4) biological treatment. The first method has been strictly prohibited; the second method both pollutes the environment and wastes land; the third method produces secondary pollution and wastes energy; the fourth method is the method currently supported and promoted as a national priority.
Biological treatment methods can be divided into two paths: first, the biological path, which decomposes dead animals through biological decomposition and fermentation, turning them into organic fertilizer raw materials that can be used by crops. After dead animals are sterilized at high temperature, they are crushed into tiny particles, and fermentation strains and dry matter auxiliary materials are added for fermentation to become rough compost. Second, the biochemical path. After dead animals are sterilized and crushed at high temperature, biochemical decomposition is carried out to turn them into chemical substances such as fats and amino acids, and the residue can likewise be composted.
4. Odorous gas treatment can be effectively removed through biological oxidative decomposition or strong oxidant oxidative decomposition, or biochemical adsorption decomposition.
5. Feed dust can be effectively removed through dust removal devices (dust collectors) or through wet adsorption and precipitation methods.