Soil remediation system and method based on wet oxidation-leaching collaborative technology

Abstract

The invention provides a soil remediation system and method based on a wet oxidation-leaching synergistic technology. The remediation system comprises a slurry prefabrication unit, a multi-stage screening unit, a pretreatment reaction unit, a synergistic elution unit, a water treatment and water circulation unit and a dosing and water replenishing unit. The polluted soil is subjected to pulping treatment after being screened, then subjected to multi-stage hydraulic screening, subjected to physical and chemical reactions such as air flotation / oxidation / reduction according to pollution characteristics, and then subjected to chemical leaching, leached slurry enters a thickening pool to be subjected to liquid-solid separation, lower-layer bottom mud enters a plate-frame to be subjected to filter pressing dehydration, and dehydrated clean soil is maintained. Supernatant liquid and filter pressing effluent are jointly collected to a water treatment system and are subjected to coagulating sedimentation after oxidation or heavy metal capture reaction, and residual pollutants or harmful substances are adsorbed by activated carbon and sand filtration and then are recycled, so that the defects that an existing leaching process is low in adaptability to the pollutants and single in elution function are overcome, high-proportion recycling of chemicals is realized, and environmental pollution is reduced. The medicament cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation treatment, relates to the field of leaching treatment of heavy metal and organic contaminated soil, and particularly relates to a soil remediation system and method based on a wet oxidation-leaching synergistic technology. Background Art

[0002] The sources of pollutants in soil are wide and the types are numerous. Generally, they can be divided into inorganic pollutants, organic pollutants, and heavy metal pollution. Heavy metal pollution in soil refers to the phenomenon that the content of heavy metal elements in soil exceeds the environmental quality standard or poses a potential risk to the ecosystem and human health. It is one of the important challenges in current environmental problems. Inorganic pollutants are mainly heavy metals, such as cadmium, mercury, arsenic, lead, chromium, copper, zinc, nickel, and in some local areas, there are also manganese, cobalt, selenium, vanadium, antimony, thallium, molybdenum, etc. Organic pollutants are of various types, including volatile organic pollutants such as benzene, toluene, xylene, ethylbenzene, trichloroethylene, and semi-volatile organic pollutants such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organic pesticides.

[0003] Leaching is an effective method for removing heavy metals and organic pollutants from soil, which can eradicate heavy metals in soil and efficiently decompose or dissolve organic pollutants in soil. However, at present, the heavy metal leaching technology and organic pollution leaching technology have not formed relevant technical specifications. At the same time, the forms of soil pollution are complex, including: heavy metal pollution, organic pollution, heavy metal-organic compound pollution. Different heavy metals or organic pollutants require different leaching agents, and the physical and chemical reactions involved in different pollution forms are also different. The existing leaching process has a single structure and a low degree of modularization, making it difficult to meet complex pollution situations. A comprehensive leaching process with high applicability and high removal efficiency is needed to meet the actual remediation requirements. Summary of the Invention

[0004] The present invention aims at the above problems, and the purpose is to find an integrated process to meet complex and diverse pollution situations. The formed system can be used for the development of later leaching treatment equipment, realizing the efficient remediation of heavy metal pollution, organic pollution, and heavy metal-organic compound polluted soil, and continuously meeting the needs of the soil remediation market.

[0005] To achieve this purpose, the technical solution adopted by the present invention is outlined as follows: A remediation system is provided, which includes a slurry prefabrication unit, a multi-stage screening unit, a pretreatment reaction unit, a synergistic elution unit, a water treatment and water circulation unit, and a medicine adding and water supplementing unit.

[0006] The contaminated soil enters the mixing tank for pulping treatment after screening, and then undergoes multi-stage hydraulic screening. Physical and chemical reactions such as air flotation / oxidation / reduction are selected according to the pollution characteristics, and then it enters the leaching tank for chemical leaching. The leached slurry enters the thickening tank for liquid-solid separation. The bottom sludge in the lower layer enters the plate and frame filter press for dehydration, and the dehydrated clean soil is cured. The supernatant liquid in the upper layer and the filter press effluent are jointly collected into the water treatment system, coagulated and precipitated after oxidation or heavy metal capture reaction, and recycled after the residual pollutants or harmful substances are adsorbed by activated carbon and sand filtration.

[0007] The specific technical solution adopted in the present invention is as follows:

[0008] In the first aspect of the present invention, a soil remediation system based on the synergistic technology of wet oxidation-leaching is provided, which includes a slurry prefabrication unit, a multi-stage screening unit, a pretreatment reaction unit, an enhanced elution unit, a water treatment and water circulation unit, and a chemical dosing and water replenishment unit.

[0009] Among them, the minimum node of the screening particle size in the multi-stage screening unit is 0.075 mm; the form of the pretreatment reaction unit is selected and applied according to the pollution characteristics of the contaminated soil and the physical and chemical properties of the soil; the enhanced elution unit includes a leaching tank in series with multi-stage cyclone elution and mixing and stirring leaching.

[0010] Preferably, the slurry prefabrication unit includes an Allu screening hopper and a mixing tank connected in sequence.

[0011] The multi-stage screening unit includes drum screening, vibrating screening and cyclone separation in the leaching tank.

[0012] The pretreatment reaction unit is selected from any one of an air flotation treatment structure, a heat treatment structure, an ultrasonic treatment structure, an oxidation treatment structure and a reduction treatment structure.

[0013] The enhanced elution unit is composed of a first-stage cyclone elution, a mixing and stirring elution, and a second-stage cyclone elution structure, and the elution time is controlled within 1-2 h.

[0014] The chemical dosing and water replenishment unit includes multiple acid and corrosion-resistant chemical dosing pumps. It is set based on the dynamic parameters of the chemical agent loss and water loss of the whole system. For example, an acid and corrosion-resistant chemical dosing pump is equipped for the oxidation unit in the pretreatment reaction unit for the dosing of acidic agents and oxidants, with a dosing ratio of 1-4% (slurry mass ratio) and a replenishment ratio of 10-50%; an acid and corrosion-resistant chemical dosing pump is equipped for the leaching system for the dosing of acids, alkalis and inorganic salt leaching agents, with a dosing concentration of 0.01-0.2 mol / L (slurry liquid concentration) and a replenishment ratio of 10-30%; an acid and corrosion-resistant chemical dosing pump is equipped for the oxidation unit and the coagulation and precipitation unit involved in water treatment for the dosing of oxidants, heavy metal scavengers and coagulation and precipitation reagents, with a dosing ratio of 0.05-0.0005% (slurry mass ratio) and a replenishment ratio of 100%.

[0015] For the specific structural composition, please refer to Figure 1 , the soil remediation system of the present invention includes an ALLU screening bucket, a slurry mixing tank, a drum screen, a vibrating screen, a supporting reaction module (optional), a leaching tank, a thickening tank, a plate and frame filter press, an oxidation tank (optional), a coagulation sedimentation tank, an activated carbon adsorption device, and a sand filter tank, which are connected in sequence. The reaction tank in the supporting reaction module needs to be connected to the thickening tank for static solid-liquid separation, and the supernatant is recycled to the front end; the coagulation sedimentation tank is additionally connected to a plate and frame filter press or other dehydration equipment.

[0016] In the second aspect of the present invention, a method for soil remediation based on the above soil remediation system is provided, including the following steps:

[0017] (1) Select a suitable pretreatment reaction unit based on the pollutant situation of the soil to be treated, and the method is as follows: select a reduction tank for refractory organic pollutants, an oxidation tank for heavy metal-contaminated soil with high organic matter content, an oxidation or reduction tank according to the chemical properties of organic matter for the case of heavy metal-volatile organic pollution / semi-volatile organic pollution compound, a flotation tank for contaminated soil containing total petroleum hydrocarbons, a heating tank for refractory leachable heavy metals, and an ultrasonic tank for soil with clay content less than 25%.

[0018] (2) After the soil to be treated is screened by the ALLU bucket, it is pulped at the mixing tank according to a liquid-solid ratio of 3:1 to 6:1 (mass ratio), and then passes through a drum screen and a vibrating screen in sequence, and enters the pretreatment reaction unit selected in step (1);

[0019] (3) After pretreatment reaction, it enters the thickening tank for solid-liquid separation, and the supernatant is recovered and reused as a reagent, and the lower-layer slurry enters the leaching tank for multi-stage elution of hydrocyclone, mixing and stirring, and hydrocyclone in sequence to fully carry out chemical leaching and elution reaction. During the reaction process, recycled water is supplemented as needed to ensure a sufficient liquid-solid ratio; the specific steps are as follows:

[0020] The leaching reagent is selected according to the type of pollutants. Different types of chelating agents are selected for heavy metals; surfactants or oxidants are selected for organic pollutants. If the oxidation is difficult, nano-zero valent iron is added for preliminary reduction; for heavy metal-organic composite pollution, an oxidation reaction is selected to remove organic pollutants first, and then a chelation reaction is selected to remove heavy metals;

[0021] The proportion of recycled water in the thickening tank of the pretreatment reaction unit is 20-40%, which is directly recycled to the pulping and mixing tank. The proportion of supplementary water in the leaching tank is 20-40%. The wastewater loss caused by the leached soil is 10-20%. The final effluent of water treatment is 80-90%. The recycled water is divided into two parts. One part directly enters the system for the pulping mixing tank, and the other part is recycled to the leaching tank and is supplemented according to the flow situation on site.

[0022] (4) The slurry after sufficient reaction enters the thickening tank for solid-liquid separation. The supernatant is transported to the water treatment system, and the lower-layer sludge enters the plate-and-frame filter press for dehydration treatment. The filtrate is transported to the water treatment system, and the dehydrated soil is the repaired soil and is cured.

[0023] (5) Water treatment is carried out according to the types of pollutants and the chemical eluent used. The treated supernatant is reused after being adsorbed by activated carbon and filtered by sand filtration. The bottom sludge is accumulated and temporarily stored until a certain amount, then subjected to plate-and-frame filter press dehydration and disposed of as hazardous waste subsequently. The filtrate is circulated to the initial end of the water treatment unit. The specific method is as follows:

[0024] The arsenic-containing wastewater is first oxidized and then coagulated and precipitated; for other heavy metal wastewater, a certain proportion of heavy metal capturer, PAC or PAM is selected for dosing; for organic wastewater, a certain proportion of oxidant is dosed for supplementary oxidation.

[0025] Preferably, in the above reactions, the dosing amounts and supplementary ratios of the medicaments in each reaction step are as follows:

[0026] During the pretreatment reaction, if an oxidation reaction is carried out, acidic medicament and oxidant are dosed according to 1-4% of the slurry mass ratio, and the supplementary ratio is 10-50%; during the chemical elution and stripping reaction, surfactant, acid-base chelating agent and inorganic salt eluent are dosed, and the concentration after dosing is 0.01-0.2 mol / L, and the supplementary ratio is 10-30%; for the oxidation reaction and coagulation and precipitation reaction involved in water treatment, oxidant, heavy metal capturer and coagulation and precipitation reagent are dosed, and the dosing ratio is 0.05-0.0005%, and the supplementary ratio is 100%.

[0027] The beneficial guarantees and effects of the present invention:

[0028] 1. The applicability of this elution system is wide, and it can be simultaneously applicable to the elution and repair of heavy metal pollution, organic pollution, and heavy metal-organic composite pollution soil, and can realize the synchronous repair and treatment of various different types of pollutants in the soil.

[0029] 2. The modular degree of this elution system is high, and the modules can be selected according to the situation of pollutants, which is flexible, mobile and convenient.

[0030] 3. The reuse degree of the elution medicament of this elution system is high, which reduces the application cost. The medicament cost is one of the main costs in elution repair. By studying the operation and treatment conditions of different elution equipment and engineering experience data, the dosing and water circulation system and power parameters of the medicament loss and water loss of the whole system are formulated. Within the controllable range, the reuse amount of the medicament and water is more than 80%, reducing the application cost and wastewater discharge amount.

[0031] In summary, the system and method of the present invention can be used for the remediation of different heavy metal - contaminated soils, organic - contaminated soils, and heavy metal - organic composite - contaminated soils. Different physical and chemical reaction modules can be configured as pretreatment reactions according to requirements, combined with enhanced elution, to achieve the efficient removal of pollutants in different forms and degrees of pollution, and the synchronous removal of different types of pollutants; it solves the disadvantages of the existing leaching process, such as low adaptability to pollutants and single elution function; precisely refines the chemical dosing system, and makes a quantifiable plan for chemical recycling and the circulation of leaching solutions, achieving a high proportion of chemical reuse and reducing chemical costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following further describes the present disclosure with reference to the drawings. These illustrations are only for illustrating the embodiments of the present disclosure and are not intended to limit the scope of the present disclosure.

[0033] Figure 1 It is a schematic diagram of the overall structure and process of the soil remediation system based on the wet oxidation - leaching synergistic technology in the present invention;

[0034] Figure 2 It is a schematic diagram of the structure and process of the heavy metal - contaminated soil remediation system in Example 1;

[0035] Figure 3 It is a schematic diagram of the structure and process of the heavy metal - organic composite - contaminated soil remediation system in Example 2. SPECIFIC EMBODIMENTS

[0036] Example 1 Remediation of Heavy Metal - Contaminated Soil

[0037] The present system was used for a leaching pilot test on a heavy metal - contaminated soil in Putuo District, Shanghai. The pollutants in this contaminated soil were arsenic and antimony, with pollution concentrations of 76 and 80 mg / kg respectively, exceeding the screening values for first - class land (20, 20 mg / kg) in the "Interim Risk Control Standards for Soil Pollution of Construction Land" (GB36600 - 2018) by 2 - 3 times, indicating serious pollution.

[0038] The leaching system is as Figure 2 shown. According to the pollution situation, only the oxidation module was selected in the water treatment part of this system. The feeding speed (treatment speed) was 10 m 3 / h, the liquid - solid ratio was 5:1 (mass ratio), the leaching agent selected was a composite leaching agent of potassium dihydrogen phosphate and oxalic acid, and the water treatment chemicals used were calcium peroxide, ferric chloride, PAC, and PAM. The chemical supplement ratio was 20%, and the clear water supplement ratio was 20%.

[0039] The leaching process for this heavy metal - contaminated soil includes the following steps:

[0040] Step 1: The heavy metal contaminated soil is only contaminated by heavy metals, and the pollutants are arsenic and antimony. There is no need to select other pretreatment units, but an oxidation pretreatment needs to be set for the water treatment unit.

[0041] Step 2: After being screened by the ALLU bucket, the heavy metal contaminated soil is pulped at the slurry pond at a liquid-solid ratio of 5:1 mL / g, and then sequentially passes through a drum screen and a vibrating screen and enters the leaching pond for reaction.

[0042] Step 3: The slurry after sufficient reaction enters the thickener for solid-liquid separation. The supernatant is transported to the water treatment system, and the lower-layer sludge enters the plate and frame filter press for dehydration treatment. The filtrate is transported to the water treatment system. The soil after dehydration is the repaired soil and is cured.

[0043] Step 4: Calcium peroxide, ferric chloride, PAC, and PAM are sequentially added to the arsenic-containing wastewater. The heavy metals are first oxidized and then co-precipitated with Fe(OH)3, and then the wastewater is further coagulated and precipitated. The supernatant is adsorbed by activated carbon and filtered by sand filtration and then recycled. The bottom sludge is accumulated and temporarily stored until a certain amount, then plate and frame filter press dehydration is carried out, and it is disposed of as hazardous waste for subsequent treatment. The filtrate is circulated to the initial end of the water treatment unit.

[0044] Application result: After sampling and testing the leached soil, the concentrations of arsenic and antimony in the leached soil are measured to be 15 and 19 mg / kg respectively, which meet the repair target values and achieve effective removal.

[0045] Example 2 Remediation of Heavy Metal-Organic Composite Contaminated Soil

[0046] The system is used for pilot-scale leaching of a heavy metal-organic composite contaminated soil in Putuo District, Shanghai. The pollutants in the contaminated soil are arsenic and benzo(a)pyrene, and the pollution concentrations are 83 and 1.2 mg / kg respectively, exceeding the screening values for first-class land (20, 0.55 mg / kg) in the "Soil Pollution Risk Control Standards for Construction Land (Trial)" (GB36600-2018), and the pollution is serious.

[0047] The leaching system is as Figure 3 shown. According to the pollution situation, the oxidation module is selected in the pretreatment unit part of this system, and the oxidation module is selected in the water treatment part. The feeding speed (treatment speed) is 10 m 3 / h, the liquid-solid ratio is 5:1 (mass ratio), and the oxidation agents selected are sodium persulfate and ferrous sulfate; the leaching agent selected is a composite leaching agent of potassium dihydrogen phosphate and oxalic acid; the water treatment agents used are calcium peroxide, ferric chloride, PAC, and PAM. The supplementary ratio of the oxidation agent is 30%, the supplementary ratio of the leaching agent is 30%, and the supplementary ratio of clean water is 20%.

[0048] The leaching process of this heavy metal-organic composite contaminated soil includes the following steps:

[0049] Step 1: The heavy metal contaminated soil is contaminated with heavy metals - SVOCs, and the pollutants are arsenic and benzo[a]pyrene. Before leaching, an oxidation pretreatment unit needs to be selected, and an oxidation pretreatment needs to be set for the water treatment unit;

[0050] Step 2: After being screened by the ALLU bucket, the heavy metal contaminated soil is pulped at a certain liquid-solid ratio at the slurry pond, and then sequentially passes through a drum screen and a vibrating screen and enters the oxidation pond.

[0051] Step 3: After oxidation pretreatment, it enters the thickener for solid-liquid separation. The supernatant is recovered and reused as part of the reagent, and the lower-layer slurry enters the leaching pond for cyclone, stirring, and cyclone elution in sequence to fully perform chemical leaching agent synergistic elution treatment. Make-up water is added here to ensure a sufficient liquid-solid ratio.

[0052] Step 4: The slurry after sufficient reaction enters the thickener for solid-liquid separation. The supernatant is transported to the water treatment system, and the lower-layer sludge enters the plate and frame filter press for dehydration treatment. The filtrate is transported to the water treatment system, and the dehydrated soil is the repaired soil and is cured.

[0053] Step 5: Calcium peroxide, ferric chloride, PAC, and PAM are sequentially added to the arsenic-containing wastewater. The heavy metals are first oxidized and then co-precipitated with Fe(OH)3, and then the wastewater is further coagulated and precipitated. The supernatant is reused after being adsorbed by activated carbon and filtered by sand filtration. The bottom sludge is accumulated and temporarily stored until a certain amount, and then plate and frame filter press dehydration is carried out, and it is disposed of as hazardous waste. The filtrate is recycled to the initial end of the water treatment unit.

[0054] The preferred embodiments of the present invention have been specifically described above, but the present invention is not limited to the described embodiments. Those skilled in the art can also make various equivalent variations or substitutions without departing from the spirit of the present invention, and these equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A soil remediation system based on the synergistic technology of wet oxidation and leaching, characterized in that, It includes a slurry prefabrication unit, a multi-stage screening unit, a pretreatment reaction unit, a synergistic elution unit, a water treatment and water circulation unit, and a chemical dosing and water replenishment unit. Among them, the minimum node of the particle size screened by the multi-stage screening unit is 0.075 mm. The form of the pretreatment reaction unit is selected and applied according to the pollution characteristics and soil physical and chemical properties of the contaminated soil. The synergistic elution unit includes an elution pool in which multi-stage cyclone elution and mixing and stirring leaching are connected in series.

2. The soil remediation system based on the synergistic technology of wet oxidation and leaching according to claim 1, characterized in that: Wherein, The slurry prefabrication unit includes an Allu screening hopper and a stirring pool connected in sequence. The multi-stage screening unit includes drum screening, vibration screening, and cyclone separation in the elution pool.

3. The soil remediation system based on the synergistic technology of wet oxidation and leaching according to claim 1, characterized in that: Wherein, The pretreatment reaction unit is selected from any one of a flotation treatment structure, a heat treatment structure, an ultrasonic treatment structure, an oxidation treatment structure, and a reduction treatment structure.

4. The soil remediation system based on the synergistic technology of wet oxidation and leaching according to claim 1, characterized in that: Wherein, The synergistic elution unit consists of a first-stage cyclone elution, a mixing and stirring elution, and a second-stage cyclone elution structure, and the elution time is controlled within 1 - 2 h.

5. The soil remediation system based on the synergistic technology of wet oxidation and leaching according to claim 1, characterized in that: Wherein, The chemical dosing and water replenishment unit includes multiple acid and corrosion-resistant chemical dosing pumps.

6. A method for soil remediation using the soil remediation system according to any one of claims 1 to 5, characterized in that, It includes the following steps: (1) Select a suitable pretreatment reaction unit based on the pollutant situation of the contaminated soil to be treated. (2) The contaminated soil to be treated is screened by the ALLU hopper and then pulped at a certain liquid-solid ratio at the stirring pool, and then sequentially passes through drum screening and vibration screening and enters the pretreatment reaction unit selected in step (1). (3) After pretreatment reaction, it enters a thickening tank for solid-liquid separation. The supernatant is recovered and reused as a reagent, and the lower-layer slurry enters the elution pool for multi-stage elution of cyclone, mixing and stirring, and cyclone in sequence to fully carry out the chemical leaching and elution reaction. During the reaction process, recycled water is supplemented as needed to ensure a sufficient liquid-solid ratio. (4) The slurry after sufficient reaction enters a thickening tank for solid-liquid separation. The supernatant is transported to the water treatment system, and the lower-layer sludge enters a plate and frame filter press for dehydration treatment. The filtrate is transported to the water treatment system. The dehydrated soil is the repaired soil and is cured. (5) Water treatment is carried out according to the types of pollutants and the chemical leaching agent used. The treated supernatant is adsorbed by activated carbon and filtered by sand filtration and then reused. The bottom sludge is accumulated and temporarily stored until a certain amount is reached, and then it is subjected to plate and frame filter press dehydration and disposed of as hazardous waste. The filtrate is circulated to the initial end of the water treatment unit.

7. The method for soil remediation according to claim 6, characterized in that: Wherein, In step (1), the method for selecting a suitable pretreatment reaction unit based on the pollutant situation of the contaminated soil to be treated is as follows: select a reduction tank for refractory oxidizable organic pollutants, select an oxidation tank for heavy metal-contaminated soil with a high organic matter content, select an oxidation or reduction tank according to the chemical properties of the organic matter for the case of heavy metal-volatile organic pollution / semi-volatile organic pollution compound, select a flotation tank for contaminated soil containing total petroleum hydrocarbons, select a heating tank for refractory leachable heavy metals, and select an ultrasonic tank for soil with a clay content lower than 25%.

8. The method for soil remediation according to claim 6, characterized in that: Wherein, In step (2), the liquid-solid ratio of the pulping liquid is 3:1 to 6:

1. In step (3), the elution agent is selected according to the types of pollutants. Different types of chelating agents are selected for heavy metals; surfactants or oxidants are selected for organic pollutants. If the oxidation is difficult, nano zero-valent iron is added for preliminary reduction; for heavy metal-organic composite pollution, the oxidation reaction is first selected to remove organic pollutants, and then the chelation reaction is used to remove heavy metals. The proportion of the recycled water from the thickener in the pretreatment reaction unit is 20-40%, and it is directly recycled to the pulping mixing tank. The proportion of the make-up water for the elution tank is 20-40%. The wastewater loss caused by the eluted soil is 10-20%. The final effluent of the water treatment is 80-90%. The recycled water is divided into two parts. One part directly enters the system and is used for the pulping mixing tank, and the other part is recycled to the elution tank, and the diversion and supplementation are carried out according to the flow conditions on site.

9. The method for soil remediation according to claim 6, characterized in that: Wherein, In step (5), the method for water treatment is as follows: for arsenic-containing wastewater, it is first oxidized and then coagulated and precipitated; for other heavy metal wastewater, a certain proportion of heavy metal capturer, PAC or PAM is selected for dosing; for organic wastewater, a certain proportion of oxidant is added for supplementary oxidation.

10. The method for soil remediation according to claim 6, characterized in that: Wherein, During the pretreatment reaction, if an oxidation reaction is carried out, acidic agents and oxidants are added at a ratio of 1-4% of the slurry mass ratio, and the supplementary ratio is 10-50%. During the chemical elution and stripping reaction, surfactants, acid-base chelating agents and inorganic salt eluents are added, and the concentration after addition is 0.01-0.2 mol / L, and the supplementary ratio is 10-30%. For the oxidation reaction and coagulation and precipitation reaction involved in water treatment, oxidants, heavy metal capturers and coagulation and precipitation reagents are added, and the addition ratio is 0.05-0.0005%, and the supplementary ratio is 100%.

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