CN110697983A

CN110697983A - Leachate treatment process

Info

Publication number: CN110697983A
Application number: CN201911010774.1A
Authority: CN
Inventors: 孙熠; 黄苏莺
Original assignee: Shaoxing City Shangyu Zhonglian Environmental Protection Co Ltd
Current assignee: Shaoxing City Shangyu Zhonglian Environmental Protection Co Ltd
Priority date: 2019-10-23
Filing date: 2019-10-23
Publication date: 2020-01-17

Abstract

The invention discloses a leachate treatment process, which comprises the following steps: (1) adding calcium chloride into the percolate, stirring, adding an alkaline substance to adjust the pH to be 7-7.5, and filtering to obtain a filtrate; (2) adding a hardness ion removing substance into the filtrate obtained in the step (1), and filtering to remove hardness ions; (3) aerating the filtrate from which the hardness ions are filtered in the step (2); (4) pumping the aerated filtrate into an evaporation device for evaporation and drying to obtain solid waste; (5) and performing resource recovery by salt washing after pyrolysis of the solid waste. According to the invention, calcium chloride is added into the leachate to remove fluoride ions, sulfate radicals, carbonate ions and the like, and the PH is finely adjusted to be between 7 and 7.5 for aeration oxidation, so that the discharge of alkaline gas is reduced, the environmental pollution is reduced, the problems that high-salt high-ammonia nitrogen wastewater is difficult to treat and the like are solved, and meanwhile, the generated waste can be used in a waste salt recycling treatment process.

Description

Leachate treatment process

Technical Field

The invention relates to a leachate treatment process, and belongs to the field of environmental protection.

Background

The leachate is sewage generated by extrusion of landfill bodies, rainwater leaching or underground water erosion in a dangerous waste landfill site, contains a large amount of pollutants and poses potential threats to the environment; dangerous waste landfill sites are filled with various organic and inorganic pollutants in the industries of electroplating, pesticides, petrifaction, fine chemical engineering and the like, so that leachate has the characteristics of high salt and high ammonia nitrogen, and the leachate is difficult to treat by a biochemical and recharge method due to poor biodegradability; the chemical oxidation method needs to consume a large amount of chemical reagents, for example, hydrogen peroxide commonly used in the Fenton method is expensive and has high treatment cost; the condensate obtained by the conventional evaporative concentration method often contains ammonia nitrogen, and the ammonia nitrogen can be discharged after reaching the standard after further treatment, which undoubtedly increases the treatment cost. The existing treatment method of leachate, such as chinese patent documents CN2015103131447 and CN105130075A, includes the basic steps of alkali adjustment, flocculation precipitation, mud-water separation, ammonia nitrogen stripping, evaporation concentration, and solidification landfill, the PH value of the leachate is adjusted to be above 9 in the alkali adjustment stage, the PH value of the solution is above 10 in the ammonia nitrogen stripping stage, a large amount of alkaline tail gas is discharged, if tail gas absorption is not performed, the environment is polluted, and simultaneously, hardness ions in the leachate are not removed, scaling is easy to occur in the evaporation concentration process, and adverse effects are generated on the service life and the evaporation efficiency of an evaporator.

The invention aims to solve the technical problem of providing a percolate treatment process, wherein calcium chloride is added into percolate to remove ions such as fluoride ions, sulfate radicals and carbonate ions, and the PH is finely adjusted to be between 7 and 7.5 for aeration oxidation, so that the discharge of alkaline gas is reduced, the environmental pollution is reduced, and the defects in the prior art can be overcome.

The technical scheme of the invention is as follows: a leachate treatment process is characterized by comprising the following steps: (1) adding calcium chloride into the percolate, stirring, adding an alkaline substance to adjust the pH to be 7-7.5, and filtering to obtain a filtrate; (2) adding a hardness ion removing substance into the filtrate obtained in the step (1), and filtering to remove hardness ions; (3) aerating the filtrate from which the hardness ions are filtered in the step (2); (4) pumping the aerated filtrate into an evaporation device for evaporation and drying to obtain solid waste; (5) and performing resource recovery by salt washing after pyrolysis of the solid waste.

The alkaline substance in the further step (1) is calcium hydroxide.

In the further step (2), the hardness-removing ionic substance is sodium oxalate with the concentration of 2 per mill.

And (3) further adopting an evaporator and a rake dryer as evaporation devices, pumping the filtrate into the evaporator for concentration by 1 time, putting the concentrated solid and liquid into the rake dryer from a bottom valve, and heating and drying the solid and liquid to obtain solid waste.

The evaporator is a scraper evaporator.

The mass ratio of the leachate to the calcium chloride in the further step (1) is 100: 1.

in the further step (3), the filtrate is aerated in an aeration kettle for 6 hours, and the gas-liquid ratio is 2000.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the preparation method, fluoride ions, sulfate ions, carbonate ions and the like are removed through calcium chloride, the pH value is adjusted to 7-7.5 by using calcium hydroxide, and the hardness removal process by using sodium oxalate can prevent scaling in the evaporation concentration process;

(2) according to the preparation method, organic matters in the leachate are aerated and oxidized under the condition that the pH =7-7.5, COD (chemical oxygen demand) and ammonia nitrogen are degraded, a tail gas absorption device is reduced, and the cost is saved;

(3) 200-300ppm of ammonia nitrogen, 400-600ppm of COD and 0 of salt in the condensed water after evaporation and drying by the rake dryer, biochemical treatment can be carried out without dilution, and water resources are saved;

(4) the evaporation device adopts a scraper evaporator and rake dryer, and the problem that the evaporator cannot be normally and continuously used due to wall bonding is solved better. The effluent of the scraper evaporator is used as a heat source of the rake dryer, so that the defect of high steam consumption of the rake dryer is overcome;

(5) the method can solve the problems of difficult treatment of the high-salt high-ammonia nitrogen wastewater and the like, and simultaneously the generated waste can be used in the waste salt recycling treatment process.

Detailed Description

The embodiment of the invention comprises the following steps: a leachate disposal process, comprising the steps of: (1) pumping 30 parts of percolate into a 50-part reaction kettle by using a screw pump, adding 300kg of calcium chloride, uniformly stirring, adding 1.5kg of lime, measuring the pH =7.2, continuously uniformly stirring for 1h, and performing filter pressing by using a filter press; (2) pumping the filtrate obtained in the step (1) into a 50-square hardness removal kettle, starting stirring, adding 150kg of sodium oxalate with the concentration of 2 per mill, stirring for 1 hour, and pumping into a filter press to filter out hardness ions; (3) pumping the filtrate obtained after the hardness ions are filtered in the step (2) into a 50-square aeration kettle, starting an aeration device, aerating for 6 hours, and controlling the gas-liquid ratio to be 2000; (4) pumping the aerated filtrate into a scraper evaporator for evaporation and concentration by 1 time, putting solid and liquid into a rake dryer from a bottom valve, enabling the effluent of the scraper evaporator to flow into a thermal jacket of the rake dryer to be used as a part of heat source of the rake dryer, heating and drying the solid and liquid in the rake dryer to obtain solid waste, and enabling evaporated condensate water to enter a biochemical pool for biochemical treatment and be discharged; (5) and putting the solid waste into an incinerator for pyrolysis, dissolving, filtering, drying, adding into a saturated sodium chloride solution, and washing salt for several times to obtain the industrial sodium chloride.

Claims

1. A leachate treatment process is characterized by comprising the following steps:

(1) adding calcium chloride into the percolate, stirring, adding an alkaline substance to adjust the pH to be 7-7.5, and filtering to obtain a filtrate; (2) adding a hardness ion removing substance into the filtrate obtained in the step (1), and filtering to remove hardness ions; (3) aerating the filtrate from which the hardness ions are filtered in the step (2); (4) pumping the aerated filtrate into an evaporation device for evaporation and drying to obtain solid waste; (5) and performing resource recovery by salt washing after pyrolysis of the solid waste.

2. The leachate treatment process of claim 1, wherein: the alkaline substance in the step (1) is calcium hydroxide.

3. The leachate treatment process of claim 1, wherein: the hardness-removing ionic substance in the step (2) is sodium oxalate with the concentration of 2 per mill.

4. The leachate treatment process of claim 1, wherein: and (4) the evaporation device in the step (3) is an evaporator and a rake dryer, the filtrate is firstly pumped into the evaporator to be concentrated by 1 time, the solid and liquid after concentration are put into the rake dryer from a bottom valve, and the solid and liquid are heated and dried to solid waste.

5. The leachate treatment process of claim 4, wherein: the evaporator is a scraper evaporator.

6. The leachate treatment process of claim 1, wherein: the mass ratio of the leachate to the calcium chloride in the step (1) is 100: 1.

7. the leachate treatment process of claim 1, wherein: and (4) aerating the filtrate in the step (3) in an aeration kettle for 6 hours, wherein the gas-liquid ratio is 2000.