With the rapid development of industry, the problem of organic pollution has become increasingly prominent. A large number of compound organic pollutants in soil will change the physical and chemical properties of soil, destroy the local ecosystem, have indirect and direct toxic effects on regional animals and plants, and cause serious harm to human health through the enrichment and amplification of food chain, thus seriously affecting the land use function. The problem of soil organic pollution has aroused widespread concern, and soil remediation is imperative.
At present, the pollution of organic sites in China is mainly non-chlorinated organic pollutants and persistent organic pollutants such as petroleum hydrocarbons, organic pesticides and insecticides. This paper mainly introduces the soil remediation technology of non-chlorinated organic contaminated sites.
classify
At present, theoretically and technically feasible remediation technologies for non-chlorinated organic contaminated soil can be divided into physical remediation technology, chemical remediation technology, biological remediation technology and composite remediation technology from functional carriers.
2. 1 physical repair technology
Physical remediation technology is mostly ectopic remediation technology, which makes it difficult for pollutants fixed in soil to spread and migrate by using the respective characteristics of soil and pollutants, or destroys pollutants by means of high temperature to reduce their damage to the environment. Physical remediation technologies of soil non-chlorinated organic pollution mainly include heat treatment, isolation and soil replacement.
(1) heat treatment heat treatment technology is mostly ectopic treatment, which usually refers to a repair process of transferring the polluted medium to a specific treatment unit or combustion chamber and then exposing it to high temperature, thus destroying or removing the pollutants in it. The main advantages of ex-situ remediation technology are short treatment period, visible treatment process and easy control of continuous mixing and homogenization of contaminated media, so the treatment degree is relatively uniform; However, the ex-situ repair needs to excavate soil, which increases the repair cost and the demand for repair engineering equipment, and also leads to the application for ex-situ repair permit and the safety of material transfer.
Heat treatment technology mainly includes thermal desorption, high temperature purification, high temperature decomposition, traditional incineration destruction technology and vitrification technology.
A. Incineration technology has been applied in the field of incineration and destruction of contaminated media for many years, and it is a relatively mature remediation technology.
B. Ectopic thermal desorption technology uses heat to volatilize pollutants and water in polluted media, and usually uses carrier gas or vacuum system to transport volatilized water vapor and organic pollutants to subsequent units such as thermal oxidation or recovery for further treatment. According to the different operating temperatures of the desorption tower, the thermal desorption process can be divided into high-temperature thermal desorption (320-560℃) and low-temperature thermal desorption (90-320℃).
C. High-temperature purification technology refers to raising the temperature of polluted solid media or equipment to 260℃ and keeping it for a certain time. The airflow generated in the medium enters the combustion system for treatment to remove all volatile pollutants. The residue obtained by this method can be used as harmless waste for disposal or resource utilization.
D pyrolysis refers to the process of chemical decomposition of organic pollutants by heating under oxygen-free conditions. Pyrolysis generally occurs at a temperature higher than 430℃ and a certain pressure. The pyrolysis gas produced in the process of chemical decomposition needs further treatment. The target pollutants of pyrolysis are volatile organic compounds and pesticides. This technology is suitable for separating organic components from refinery waste, coal tar, wood processing waste, soil contaminated by creosote, soil contaminated by hydrocarbons, mixed waste (radioactive and dangerous), rubber synthesis and waste in paint.
E. Vitrification technology is to melt polluted soil at high temperature (1600-2000℃) by using electric current, and form vitrified product after cooling, which is a glass or crystal substance with stable chemical properties similar to basalt. High temperature treatment can destroy and remove organic pollutants in soil. This technology can be used for in-situ or in-situ soil remediation.
(2) Isolation method
Isolation method is to isolate the soil polluted by non-chlorinated organic compounds from the surrounding environment with clay or other synthetic inert materials. This method does not destroy non-chlorinated organic hydrocarbons, but only prevents pollutants from migrating to the surrounding environment (groundwater and soil). This method is suitable for controlling any soil polluted by non-chlorinated organic hydrocarbons, especially in areas with poor permeability. Compared with other methods, the operation cost of this method is lower, but for non-chlorinated organic hydrocarbons with long toxicity period, it only temporarily prevents their migration, and there is a risk of secondary pollution.
(3) Soil replacement method
Soil replacement method is to replace or partially replace the original polluted soil with fresh unpolluted soil, so as to dilute the content of pollutants in the original polluted soil and eliminate the residual pollutants by using the ability of the environment itself. Soil replacement method can be divided into three methods: soil turning method, soil replacement method and guest soil method.
The heat treatment method, isolation method and soil replacement method of physical remediation technology give full play to the respective characteristics of soil and pollutants, and do not need to use other chemicals or organisms for treatment, but they also have the limitations of high treatment cost and heavy workload, and can only treat a small area of polluted soil. Therefore, how to make better use of the characteristics of soil and break through its limitations will be the development direction of physical remediation technology.
2.2 chemical repair technology
Chemical remediation technology is an environmental chemical technology that uses the chemical reaction between pollutants and modifiers to reduce the content of pollutants in soil by means of redox, separation and extraction. Chemical remediation technologies of soil non-chlorinated organic pollution mainly include extraction method, soil leaching method and chemical oxidation-reduction method.
(1) extraction method is based on the principle of similarity and compatibility, which uses organic solvents to extract non-chlorinated organic compounds from non-chlorinated organic contaminated soil, and then separates and recovers the non-chlorinated organic compounds in the organic phase to realize the recycling of waste. This method is suitable for the soil with high content of non-chlorinated organic pollutants, but for the soil with low content of non-chlorinated organic pollutants in a large area, its treatment cost is too high and it will cause secondary pollution. So before choosing this method, you need to evaluate the cost and then decide whether it is feasible.
(2) Leaching method Soil leaching method refers to the method of separating pollutants adsorbed on the surface of soil fine particles from soil in a system with water. Some alkaline solvents, surfactants, chelating agents or pH regulators can be added to the rinse water to enhance the removal effect of pollutants. In this treatment process, the reaction between soil and leaching water is usually carried out in a reaction tank or other treatment units, and leaching water and soils with different particle sizes are separated under the action of gravity settlement.
Soil washing method has high cost and complicated operation. For example, the soil should be graded first and then treated separately. The engineering application of this method lags far behind the laboratory research, and a series of technical problems need to be solved to realize its wide engineering application.
(3) Chemical oxidation-reduction method Chemical oxidation-reduction method is to spray or inject chemical oxidation-reduction agent into the soil polluted by non-chlorinated organic hydrocarbons, so that it can react with pollutants to achieve the purpose of purification. Commonly used chemical oxidants are ozone, hydrogen peroxide, potassium permanganate and chlorine dioxide. Compared with extraction method and soil leaching method, this method generally does not cause secondary pollution, and the removal efficiency of non-chlorinated organic hydrocarbons is higher. Redox reaction can be completed in an instant, but its operation is more complicated and requires higher technical level.
2.3 Bioremediation Technology
Bioremediation refers to a low-consumption and safe environmental biotechnology, which uses the metabolism of specific organisms to absorb, transform and degrade environmental pollutants, and finally decomposes site pollutants into harmless inorganic substances (water and carbon dioxide) to realize environmental purification and ecological effect recovery. Bioremediation technology of non-chlorinated organic pollution in soil can be divided into plants, animals and natural attenuation according to different application types.
In recent years, bioremediation technology has developed rapidly at home and abroad. A number of plants and microorganisms with special physiological and biochemical functions came into being, and the penetration of modern biotechnology such as gene modification, transformation, cloning and gene transfer further promoted the application and development of bioremediation technology. Compared with other methods, bioremediation technology has the advantages of low treatment cost, good treatment effect (no secondary pollution, and the final products of carbon dioxide, water and fatty acids are harmless to human body) and low pollutant residue after biochemical treatment. However, bioremediation takes a long time, and it is usually difficult to complete the remediation of site pollution within the specified time.
2.4 composite repair technology
To sum up, the technologies to control soil non-chlorinated organic pollution mainly include physical remediation technology, chemical remediation technology and natural attenuation technology, but all of them have problems such as high remediation cost, long remediation time and difficulty in realizing remediation technology on a large scale. Therefore, according to the advantages of various remediation technologies and the actual site pollution characteristics, reasonable combination of various remediation technologies will be the main trend of site remediation in the future.
For example, BIOX long-acting bio-oxidant is an efficient materialized material, which is composed of oxidant precursor, stabilizer, biological carrier and efficient degradation flora. In the process of use, BIOX can continuously produce oxidants, rapidly degrade organic pollutants through advanced oxidation, improve soil quality, promote water and oxygen transport and mass transfer of pollutants, and strengthen biodegradation. At the same time, by screening, separating, enriching and optimizing the ratio of different organic pollutants (such as gasoline, diesel oil, crude oil, etc.), the BIOX-loaded high-efficiency degrading flora was made. ). Its different series are suitable for the degradation of gasoline, diesel oil, crude oil and other pollutants, with strong pertinence and stable community function. Compared with traditional oxidants (such as ozone, Fenton reagent, hydrogen peroxide, etc.), BIOX has the characteristics of high oxidation efficiency, convenient application and good safety.
Through the joint action of physical chemistry and biology, the toxicity reduction and total amount removal of pollutants can be realized quickly. Compared with other technologies, this agent has the advantages of high removal efficiency (above 80%), short remediation time (6- 12 months), no damage to soil matrix, low treatment cost and so on. It is suitable for treating organic pollutants such as TPH, BTEX, PAH, VOC and SVOC. It can be repaired in many ways, such as in-situ repair or ectopic repair.
Comparison of BIOX Oxidant Remediation Technologies
Biooxidants, common chemical oxidants, common biodegradation
The final removal rate of pollutants is higher than 80%, higher than 80% and lower than 50%-70%.
The repair time is short (3-6 months), short (1-2 months), several years.
The damage of soil matrix is basically not damaged, and there is no damage to a certain extent.