News background

At this year's "two sessions", to fix the problem of soil pollution has become the hot topic in the members, one of the soil pollution prevention and control planning has listed as twelfth session of the standing committee of the National People's Congress legislation. Compared with the control of air pollution, water pollution, as one of environmental protection "three battles" soil pollution prevention and control is actually more difficult task.

Soil pollution hazard cannot ignore the soil pollution is given priority to with no models

Soil pollution, refers to the industrial and urban waste, chemical fertilizers, pesticides, heavy metals, radioactive substances and harmful microbes and other material into the soil, more than the soil self-purification ability, cause changes in the structure and function of soil, microbial activity is restrained, the soil ecological balance is damaged, soil degradation, affecting the normal development of crops and the quality of products. Pollutants through the "soil - plant - the human body" or by "soil - water - the human body" indirect absorbed by human body, endanger human body health, endanger human survival and development.

China's economic development at a faster pace for a long time, some consumption, high pollution of extensive production pattern, also produced a large number of hazardous waste, contaminated soil and groundwater, and endanger human body health.

National soil pollution condition investigation gazette in 2014, according to the national soil environmental condition overall is not optimistic, in some parts of the soil pollution is heavier, the soil environmental quality, GongKuangYe remnant soil environmental problems. The national soil total points which was 16.1%, with a slight, mild, moderate and severe pollution levels were 11.2%, 11.2%, 1.5% and 1.1%. From the pollution types is given priority to with no models, a model. In general, the soil pollution over the north, the south Yangtze river delta, the pearl river delta, northeast old industrial base and other parts of the soil pollution problem is more outstanding, southwest, central south area of soil heavy metal exceeds bid scope is bigger.

Concealment and more lag

According to the China tianchen engineering co., LTD. High Xue Zuyuan is introduced, compared with air and water pollution, soil pollution has concealment and hysteresis, often through representative soil samples by the system analysis, crops, and even affect the health of human and animal studies to determine its nature; Soil pollutants are harder to migration, diffusion and dilution, so will accumulate in soil; Pollution of heavy metals on soil is basically a process cannot be completely reversed, many organic pollutants in the soil also need a long time to degradation.

As early as in 1955, Japan has "cadmium rice" event happened, as a result of Japanese toyama county farmers with long-term avatar sichuan upstream of lead and zinc smelter wastewater irrigation paddy fields, increase the cadmium content in soil and rice. General requirements cadmium content in soil is less than 0.5 mg per kilogram, the local people to eat the rice, caused by cadmium accumulation in human body and cause diseases such as systemic neuralgia, serious when even death.

City land management has just started

From the perspective of the trend of domestic industrialization of soil restoration, soil repair key areas will be focused on the future urban development and pollution of farmland pollution two plates. The quickening pace of urbanization and industrial transfer, urban land use function transformation, a large number of industrial land into land for business or life, coupled with the adjustment of industrial structure, the original high pollution energy-intensive products production enterprises, left a large, diverse, complex pollution sites. These contaminated sites related to soil pollution, groundwater pollution, and waste pollution, and many other very prominent problem. Therefore, for the restoration of contaminated sites and development has become the primary problem.

At present, the urban land soil bioremediation is mainly concentrated in Shanghai, Beijing and other major cities. The current farmland soil bioremediation in domestic also is almost a blank.

Soil restoration means situation

Contaminated soil remediation technologies research started in the late 1970 s. In the past 30 years, Europe, America, Japan, Australia and so on have made the soil restoration plan, huge investment to study the soil remediation technology and equipment, and make soil remediation technology got rapid development.

According to the department of chemical engineering, tsinghua university professor liu is introduced, the existing soil remediation technologies including method, chemical remediation, bioremediation, electrical repair and hot repair, etc.

Replacement of fresh soil contaminated soils

Method is to use fresh and unpolluted soil to replace or partly replace the original pollution of soil, to dilute the pollutants concentration, increase the soil environmental capacity. Method: dug, and replace with out-soil in soil three methods. Soil is a soil of the commune, scatter gathered at the surface of the pollutants to soil deep; In soil is a take off contaminated soil, change into the new clean soil, this method is applicable to a small area of serious pollution of the soil, so generally applies only to the simple processing of incident; Method of replace with out-soil is to join in the contaminated soil within a lot of clean soil, covering on the surface or blender, lower the concentration of pollutants.

Chemical solvent cleaning of heavy metals

Chemical remediation is using can promote the dissolution of pollutants in soil environment or migration of chemical solvent, under the action of gravity or through head pressure push eluent injecting into the contaminated soil, and then the solution containing the pollutants from the soil extraction, separation and wastewater treatment technology. For example use appropriate complexing agent cleaning in the soil heavy metal elements, with a surfactant or organic solvent to clean the organic pollutants in soil.

The data shows, clean with citric acid soil contaminated with heavy metals, can remove 99% of uranium contaminated soil, 95% of lead and other toxic metals. Chemical repair costs low, the operator is not direct contact with the pollutants. But only applies to sand soil permeability coefficient of soil, and the introduction of cleaner is easy to cause secondary pollution.

Using the electric field separation of pollutants

Soil electrical repair is a pay attention to and development in the 1990 s after the emerging of soil remediation technologies. Its basic principle is on both ends of the contaminated soil and a low voltage dc field, use of electric field force of migration, the pollutants (such as heavy metals or organic pollutants migration to end electrode chamber (generally for cathode chamber), so that pollutants get separated. Electrical repair is more suitable for the governance of the permeability coefficient of low quality, and the soil.

Heating evaporation of harmful substances

Hot fix is to use hot volatile pollutants, adopt the method of heating the mercury or steam pressure desorption from the soil organic matter a way out. In nanjing qixia swallows angeles, for example, "peony" (i.e., nanjing chemical plant, etc.) of "soil" repair was the introduction of GTR repair technology from the United States, deep in the proper soil buried pipeline first, and then heated, the temperature above 100 ℃, after a certain period of time, make the soil benzene, mercury, the harmful material such as dioxin evaporate at high temperatures and equipped with facilities for vacuum pulling away, to escape the harmful gas collected material, again for final processing. Hot repair method is simple, can use the existing mature technology; But the method of energy consumption is too large, the high cost of operation, and is only applicable to volatile contaminants.

Bioremediation is very effective

Bioremediation including microbial remediation plants, animals, repair, repair, etc. Of bioremediation, which make use of the original indigenous microorganisms in the soil, or to complement to pollute the environment after domestication of efficient microbes, the optimization of operating conditions, accelerate the decomposition of pollutants, repair contaminated soil. Bioremediation is the pollution of soil more effective method. At a cost lower than that of hot repairing and chemical remediation; Don't destroy the soil environment required for plant growth; Pollutants degradation is more completely, does not produce secondary pollution; Of low molecular weight of pollutant removal rate can reach more than 99%; Can be in situ treatment, the operation is simple.

Background knowledge

Soil pollution type

Soil pollution according to the type of main pollutants. Can be roughly divided into: organic matter pollution, radioactive pollution, heavy metal pollution, pathogenic bacteria pollution, solid waste pollution and so on a variety of types. The heavy metal pollution and organic pollution is the most common type.

Heavy metal pollution mainly from the iron and steel smelting enterprises, tailings and chemical industry solid waste storage field. Typical pollutants including arsenic, lead, cadmium, chromium, etc.

Petroleum, chemical, coking industry pollution soil is given priority to with organic pollutants, etc. Pollutants in organic solvent such as benzene, halogenated hydrocarbon. Also often compound with other pollutants such as heavy metals, etc. Domestic once production and extensive use of pesticides such as DDT, hexachlorobenzene, chlordane and mirex, etc., also can cause organic matter on soil pollution.

Use the earthworm to absorb the heavy metals in soil.