CN114538686A

CN114538686A - Reclaimed water recycling process for treating leachate

Info

Publication number: CN114538686A
Application number: CN202210138363.6A
Authority: CN
Inventors: 沈彦志; 张磊; 牟凯丽; 谭健; 初沙沙; 董超; 于丽萍
Original assignee: Shandong Dongshun Environmental Protection Technology Co ltd
Current assignee: Shandong Dongshun Environmental Protection Technology Co ltd
Priority date: 2022-02-15
Filing date: 2022-02-15
Publication date: 2022-05-27

Abstract

The invention discloses a process for recycling reclaimed water in leachate treatment, which comprises the following steps: acidifying the percolate, performing Fenton oxidation, neutralizing with acid and alkali, performing flocculation precipitation, and filtering to obtain a filtrate 1; evaporating the filtrate 1, performing sand filtration and carbon filtration to obtain a filtrate 2; and (4) performing reverse osmosis on the filtrate 2 to obtain water. The process has good treatment effect on the percolate, the percolate after treatment reaches the water quality standard and can be repeatedly used in a certain range, thereby realizing the double functions of saving water resources and treating sewage and relieving the overload phenomenon of an urban sewage treatment plant; the method has universality and does not need to be continuously adjusted along with the change of the pollution characteristic of the percolate; the method is suitable for areas with underdeveloped economy, dispersed pollution sources and small infiltration liquid amount; the method can save the construction and operation cost of subsequent sewage treatment facilities, effectively reduce the treatment cost and the treatment difficulty, simplify the treatment process, reduce the difficulty of subsequent sewage treatment, and has wide application prospect.

Description

Reclaimed water recycling process for treating leachate

Technical Field

The invention relates to the technical field of leachate treatment, in particular to a process for recycling water in leachate treatment.

Background

At present, the most applied harmless treatment method adopted at home and abroad is a landfill method, but one main content of landfill design and management is the control and treatment of leachate. The leachate contains high-concentration organic matters and toxic substances, the water quality is complex, the water quality is greatly changed, the pollution to the environment is large, the environment is seriously polluted secondarily due to improper treatment, and the property of the leachate is changed along with the composition, the year, the geography and the climate environment of waste. Therefore, the problems of leachate treatment, such as leachate salt enrichment in the landfill, high energy consumption of treatment engineering, unclear leachate removal and the like caused by aging of the landfill, carbon-nitrogen ratio misadjustment, denitrification and return of concentrated solution after membrane return, are always one of the key points and difficulties of research at home and abroad.

At present, common treatment technologies for leachate include: biological treatment, physicochemical treatment, land treatment, evaporation treatment, and the like. (1) Biological treatment method: the leachate is treated in a biological way, and the leachate is treated by utilizing the metabolic process of microorganisms and the adsorbability of the microorganisms. The pollutant components in the percolation liquid vary greatly, the COD can reach 70000mg/L to the maximum, the BOD can reach 38000mg/L, the mass concentration of ammonia nitrogen can reach 1700mg/L and even higher, and the concentration of Fe, Pb and the like in heavy metals is the highest. High-concentration ammonia nitrogen in the leachate has a strong inhibition effect on the activity of microorganisms, and the biological treatment method has a very limited effect on certain leachate pollutants with high degradation difficulty and high toxicity. (2) Physical and chemical treatment method: the physicochemical treatment method mainly aims at removing toxic and harmful heavy metal ions, ammonia nitrogen and the like in the percolate. But the treatment effect of the chemical oxidation method is unstable; the activated carbon adsorption method is suitable for wastewater with high organic matter content, and the activated carbon has serious pollution, difficult regeneration, very high operation cost and low feasibility; the removal rate of organic matters by a coagulating sedimentation method is not high; the stripping method only has the function of removing ammonia nitrogen in the wastewater. Therefore, the physicochemical treatment method has strong pertinence and single treatment effect, and still needs to be further perfected and optimized. (3) Land treatment technology: the land treatment technology is to treat the landfill leachate by utilizing a self-regulation mechanism of a land ecosystem consisting of soil, microorganisms and plants and a comprehensive purification function of pollutants. The pollutants are removed through physical filtration, adsorption, volatilization, leaching, chemical decomposition and transformation, plant absorption, microbial degradation, absorption and the like. However, the percolate land treatment is greatly influenced by the climate conditions and is generally applicable to areas with evaporation capacity far greater than precipitation. (4) An evaporation treatment technology: the evaporation treatment technology is that the water in the percolate is evaporated by using external energy, so that the volume of the percolate is greatly reduced, and the obtained concentrated solution can be recharged or solidified and then buried. Although the leachate can reduce the organic components after being recycled for many times, the leachate still has high content of heavy metals, ammonia and other substances, so that the components need to be treated by other processes after the recharging treatment is finished. At present, the technology needs to be further improved and optimized.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a process for recycling water in the leachate.

The purpose of the invention is realized by the following technical scheme: a process for treating leachate for recycling water comprises the following steps:

(1) acidifying the percolate, performing Fenton oxidation, neutralizing with acid and alkali, performing flocculation precipitation, and filtering to obtain a filtrate 1;

(2) evaporating the filtrate 1 obtained in the step (1), performing sand filtration and carbon filtration to obtain a filtrate 2;

(3) and (3) performing reverse osmosis on the filtrate 2 in the step (2) to obtain water.

Preferably, the acidification in step (1) is to adjust the pH to 3-4 with sulfuric acid.

Preferably, the concentration of the sulfuric acid is 30%.

Preferably, in the fenton oxidation in the step (1), ferrous sulfate with the concentration of 10% and hydrogen peroxide with the concentration of 30% are adopted, wherein the ferrous sulfate accounts for 5% of the mass of the raw water, and the hydrogen peroxide accounts for 3% of the mass of the raw water.

Preferably, the Fenton oxidation time in the step (1) is 0.5-4 h; more preferably, it is 2 h.

Preferably, the acid-base neutralization in step (1) is adjusted to 10-12 by using sodium hydroxide pH.

Preferably, the concentration of sodium hydroxide is 30%.

Preferably, the flocculation precipitation in the step (1) adopts polyaluminium chloride (PAC) and Polyacrylamide (PAM).

Preferably, the polyaluminium chloride accounts for 5% of the mass of the raw water, and the concentration of the polyaluminium chloride is 5%.

Preferably, the polyacrylamide accounts for 1% of the mass of the raw water, and the concentration of the polyacrylamide is 1%.

Preferably, the flocculation precipitation time of the step (1) is 15-45 min; more preferably, it is 30 min.

Preferably, the filtration in the step (1) adopts a plate-and-frame filter press.

Preferably, the evaporation in step (2) is triple effect evaporation: negative pressure of-70 KPa and temperature of 60 ℃.

Preferably, the sand filter adopted in the sand filtration in the step (2) takes quartz sand as a filter material, and the water filtration amount is 6-8m³The height of the quartz sand bearing layer is 800mm, the filtration period is 4-72h, the design pressure is 0.6Mpa, the pressure difference between an inlet and an outlet is 0.05Mpa, the maximum working pressure is 0.6Mpa, and the strength of backwash water is 10-12L/(m)²S), backwash water pressure 0.1 Mpa.

Preferably, the carbon filter adopted in the carbon filtration in the step (2) takes activated carbon as a filter material, and the amount of filtered water is 6-8m³H, the height of the active carbon filter material layer is 1000mm, the height of the quartz sand bearing layer is 500mm, the filtration period is 4-72h, the design pressure is 0.6Mpa, the inlet-outlet pressure difference is 0.05Mpa, the maximum working pressure is 0.6Mpa, and the strength of backwash water is 14-16L/(m²S), backwash water pressure 0.1 MPa.

Preferably, the cartridge filter adopted in the reverse osmosis in the step (3) is made of stainless steel, 10-40 inches and 5-20 cores, and the filtering precision is 1-10 μm.

Preferably, the reverse osmosis in the step (3) adopts a plurality of reverse osmosis membrane elements which are arranged in a two-stage way, the number ratio of the elements in the first stage to the elements in the second stage is 2:1, and the pressure bearing capacity is more than 4 Mpa.

Preferably, the reverse osmosis membrane element is of a spiral roll type structure and consists of multi-leaf membrane bags, each membrane bag consists of two membranes with opposite membrane fronts, a product water flow channel arranged between the two membranes and a water inlet turbulence network flow channel arranged on the surface of the membrane, three sides of the membrane bag are sealed by adhesive, and the fourth side of the membrane bag is opened on a perforated product water collecting pipe; the diaphragm is a polyamide composite membrane and has a three-layer composite structure: the polyamide membrane is characterized by comprising a polyester material reinforced non-woven fabric with the thickness of 120 mu m, a polysulfone material porous middle supporting layer with the thickness of 40 mu m and the pore diameter of 150 angstroms, and a polyamide material ultrathin separating layer with the thickness of 0.2 mu m; more preferably, the reverse osmosis membrane element is an HPA1-8040 anti-pollution anti-aromatic polyamide composite membrane element of Heiden company in America.

Preferably, the system throughput of reverse osmosis in the step (3) is 4-19m³The water supply temperature is 5-45 ℃, the operation pressure is less than or equal to 600psi, the pressure difference is less than or equal to 15psi, the operation ph is 2-11, the water supply pollution index SDI is less than 5, the water supply turbidity is less than 1NTU, and the free chlorine tolerance c is less than 0.1 mg/L.

Preferably, the reverse osmosis in the step (3) is performed once every 120min, and the cleaning system is flushed at low pressure; the cleaning system is washed once under high pressure every 30min of the reverse osmosis; and (4) performing low-pressure flushing for 3-5min after the reverse osmosis operation is finished.

Preferably, the flushing flow rate of the low-pressure flushing is 7-10 tons/h, and the flushing time is 2 min.

Preferably, the flushing flow rate of the high-pressure flushing is 9-12 tons/h, and the flushing time is 2 min.

Preferably, in the use process of the cleaning system, the dosage of the adopted scale inhibitor is 8ppm, and the concentration of the RO scale inhibitor in the medicine tank is 3%.

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

1. the process for treating the leachate by recycling the reclaimed water has good treatment effect on the leachate, the leachate after treatment reaches the water quality standard and can be repeatedly used in a certain range, the dual functions of saving water resources and treating sewage are realized, and the overload phenomenon of an urban sewage treatment plant can be relieved.

2. The process for recycling the water in the leachate has universality and does not need to be continuously adjusted along with the change of the pollution characteristic of the leachate.

3. The process for recycling the water in the leachate treatment process is suitable for areas with underdeveloped economy, dispersed pollution sources and small leachate amount; the method is used for treating the percolate of a landfill which is not provided with an independent sewage treatment facility and is far away from a municipal sewage pipe network, and can reduce the impact on a municipal sewage treatment system.

4. By adopting the process for treating the leachate and recycling the reclaimed water, the construction and operation cost of subsequent sewage treatment facilities can be saved, the treatment cost and the treatment difficulty are effectively reduced, the treatment process is simplified, the difficulty of subsequent sewage treatment is reduced, and the process has wide application prospect.

Drawings

FIG. 1 is a schematic view showing the construction of a water reuse apparatus for treating leachate in example 1; wherein, the raw water pool, the fenton oxidation tower, the precipitation tower, the flocculation reaction pool, the plate-and-frame filter press, the triple effect evaporation system, the sand filter, the carbon filter, the reverse osmosis system, the adding tank of the sulfuric acid at the red water,

a sodium hydroxide dosing tank for adding sodium hydroxide into the liquor,

a hydrogen peroxide adding tank is arranged in the device,

a ferrous sulfate dosing tank is arranged on the upper portion of the iron core,

the PAC dosing tank is provided with a PAC dosing tank,

PAC dosing tank。

Figure 2 is a schematic flow diagram of a process for recycling water in the treatment of leachate.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A water recycling device for treating percolate comprises a raw water pool, a Fenton oxidation tower, a precipitation tower, a flocculation reaction pool, a plate-and-frame filter press (all the devices form a pretreatment system), a three-effect evaporation system, a sand filter (a), a carbon filter (a), and a reverse osmosis system (a reverse osmosis system). The pretreatment system also includes a drug adding tank for R & OH in sulfuric acid

Hydrogen peroxide adding pot

Ferrous sulfate dosing tank

PAC medicine adding pot

PAM (polyacrylamide) and medicine adding tank

The original water pool is connected with sulfuric acid medicine-adding tank, and the Fenton oxidation tower is connected with ferrous sulfate medicine-adding tank

Hydrogen peroxide adding tank

The settling tower is connected with a sodium hydroxide dosing tank

PAC dosing tank connected to flocculation reaction tank

PAM (polyacrylamide) and medicine adding tank

The process of treating leachate for recycling water is shown in figure 2, and specifically comprises the following steps:

(1) adding sulfuric acid solution in the R (R) of the sulfuric acid dosing tank into percolate in the original water pool, acidifying (adding 30% sulfuric acid into original water via the dosing tank to adjust pH to 3), and acidifying to reduce Cr⁶⁺Reduction to Cr³⁺Then the ferrous sulfate dosing tank

Adding ferrous sulfate and hydrogen peroxide (the concentration of the ferrous sulfate is 10 percent of the mass of the raw water) into the raw water flowing out of the raw water pool I and entering the Fenton oxidation tower II, and adding medicaments into the raw water by the hydrogen peroxide

Adding hydrogen peroxide (with the concentration of 30 percent) accounting for 3 percent of the mass of the raw water), and performing Fenton oxidation for 2 hours to realize Fenton collateral breaking. Under acidic conditions, H₂O₂In Fe² ⁺In the presence of the organic matter, hydroxyl free radicals (. OH) with strong oxidizing capability are generated, and more other active oxygen is initiated, so that the organic matter is degraded. The raw water after the Fenton reaction enters a precipitation tower III in which a sodium hydroxide dosing tank is arranged

Adding 30% sodium hydroxide into raw water for acid-base neutralization, adjusting pH of the raw water to 12, and adding medicine into PAM tank

P and PAC dosing tank

Adding PAC and PAM (PAC 5% and PAM 1% respectively), flocculating for 30min to precipitate heavy metal components and suspended matters in water, and filtering with plate-and-frame filter press to remove precipitate to obtain filtrate 1.

(2) The filtrate 1 is treated by introducing into a triple effect evaporation system (negative pressure-70 KPa, temperature 60 ℃). Volatile substances in the treated water are not effectively removed, and are pretreated by a sand filter and a carbon filter before entering a reverse osmosis system, so that the pollution and blockage of the membrane are reduced, the cleaning frequency is reduced, the maintenance cost is reduced, and the irreversible pollution and blockage are prevented. The filtering material of the sand filter is quartz sand, has strong adaptability, has the advantages of small filtering resistance, large specific surface area, high filtering precision, strong acid and alkali resistance, good pollution resistance and the like, can effectively remove suspended matters in water, and has obvious removing effect on pollutants such as colloid, iron, organic matters, pesticides, manganese, bacteria, viruses and the like in water. The sand filter (c) has the main technical parameters: the water filtration amount is 6-8m³The height of the quartz sand bearing layer is 800mm, the filtration period is 4-72h, the design pressure is 0.6Mpa, the pressure difference between an inlet and an outlet is 0.05Mpa, the maximum working pressure is 0.6Mpa, and the strength of backwash water is 10-12L/(m)²S), backwash water pressure 0.1 MPa. The filter material of the carbon filter is activated carbon, and can deodorize and dechlorinate, quickly separate insoluble substances in water, intercept macromolecular solid particles and colloids in water, effectively adsorb organic substances and chromaticity in water, be used for pretreatment equipment of an RO reverse osmosis system, and reduce load for subsequent working sections. Main technical parameters of the carbon filter (c): the water filtration amount is 6-8m³H, the height of the active carbon filter material layer is 1000mm, the height of the quartz sand bearing layer is 500mm, the filtration period is 4-72h, the design pressure is 0.6Mpa, the inlet-outlet pressure difference is 0.05Mpa, the maximum working pressure is 0.6Mpa, and the strength of backwash water is 14-16L/(m²S), backwash water pressure 0.1 MPa.After sand filtration and carbon filtration, filtrate 2 is obtained.

(3) And (c) introducing the filtrate 2 into a reverse osmosis system ninthly. In the reverse osmosis system ninthly, the reverse osmosis membrane elements are 12 anti-pollution anti-aromatic polyamide spiral wound composite membrane (HPA1-8040, material FRP, 4 core package) elements of the American Heidence company, are arranged in a two-section mode, 8 elements in one section and 4 elements in the second section, the system recovery rate is shown in table 1, and the requirement that the recovery rate is more than or equal to 75 percent is met. The diaphragm is of a three-layer composite structure: the composite material comprises a polyester material reinforced non-woven fabric with the thickness of 120 mu m, a polysulfone material porous middle supporting layer with the thickness of 40 mu m and the pore diameter of 150 angstroms, and a polyamide material ultrathin separating layer with the thickness of 0.2 mu m. Most of salt, colloid, organic matters and the like in the water cannot permeate the reverse osmosis membrane, and remain in a small amount of concentrated water, namely concentrated water, and the concentrated water is discharged from a concentrated water pipe; most of water molecules and trace other ions permeate the reverse osmosis membrane and are collected to form product water which is discharged by a fresh water pipe, and the water quality detection result is shown in table 2.

The reverse osmosis system comprises a cleaning system, and the reverse osmosis system is adopted to perform low-pressure flushing once every 120min, wherein the flushing flow of the low-pressure flushing is 10 tons/h, and the flushing time is 2 min. And (3) adopting a cleaning system to perform high-pressure washing once every 30min of the reverse osmosis, wherein the washing flow rate of the high-pressure washing is 9-12 tons/h, and the washing time is 2 min. And (3) automatically flushing for 5 minutes (the flushing flow is 8 tons/h, and the flushing time is 2min) after the reverse osmosis is finished, and removing dirt deposited on the surface of the membrane, so that the system and the reverse osmosis membrane are effectively maintained. After the reverse osmosis membrane is operated for a long time, certain dirt which is difficult to wash, such as organic matters, inorganic salt scaling and the like, can be accumulated, so that the performance of the reverse osmosis membrane is reduced. Such foulants must be removed by cleaning with chemicals to restore the performance of the reverse osmosis membrane.

TABLE 1

TABLE 2

Serial number	Detecting items	Unit	Numerical value	Standard of merit
					1	pH	Dimensionless	6.8	6.5-8.5
2	Suspended Substance (SS)	mg/L	17mg/L	≤30mg/L
					3	Chemical Oxygen Demand (COD)_Cr)	mg/L	58mg/L	≤60mg/L
4	Index of Ammonia Nitrogen content (NH)₃-N)	mg/L	10mg/L	≤10mg/L
					5	Total Dissolved Solids (TDS)	mg/L	980	≤1000
6	Total Phosphorus (TP)	mg/L	0.35	≤1
					7	Total hardness (as CaCO)₃Meter)	mg/L	275	≤450
8	Petroleum products	mg/L	Not detected out	≤1

The water quality detection result of the product water treated by the leachate reclaimed water reuse process meets the process and product water quality standard required by the quality of municipal sewage recycling industrial water, and the effluent is reused in the production process.

The inventor has tried a leachate process lacking sand filtration and carbon filtration steps, but after the treatment of the triple-effect evaporation system, volatile substances in raw water are not effectively removed, which causes fouling and blocking of a reverse osmosis membrane in the reverse osmosis system, increases the cleaning frequency, and causes cost increase and even irreversible fouling and blocking. Therefore, the service life of the reverse osmosis membrane component is shortened to about one year, and whether the reverse osmosis membrane component is replaced or not is determined according to the operation condition of the system after one year. In addition, it results in an increased rate of fouling of the reverse osmosis membrane.

The foregoing is directed to the preferred embodiment of the present invention, and it is understood that various changes and modifications may be made by one skilled in the art without departing from the spirit of the invention, and it is intended that such changes and modifications be considered as within the scope of the invention.

Claims

1. A process for treating leachate and recycling reclaimed water is characterized by comprising the following steps:

(3) and (3) performing reverse osmosis on the filtrate 2 obtained in the step (2) to obtain effluent.

2. The process for recycling leachate of claim 1, wherein the leachate is treated by the method,

the acidification in the step (1) is to adjust the pH to 3-4 by using sulfuric acid;

in the Fenton oxidation step (1), ferrous sulfate accounting for 5% of the mass of the raw water and having a concentration of 10% and hydrogen peroxide accounting for 3% of the mass of the raw water and having a concentration of 30% are adopted;

the acid-base neutralization in the step (1) is to adjust the pH value to 10-12 by adopting sodium hydroxide;

the flocculation precipitation in the step (1) adopts polyaluminium chloride and polyacrylamide.

3. The process for treating leachate for recycling water as claimed in claim 2, wherein,

the concentration of the sulfuric acid is 30%;

the concentration of the sodium hydroxide is 30 percent;

the polyaluminium chloride accounts for 5% of the mass of the raw water, and the concentration is 5%;

the polyacrylamide accounts for 1% of the mass of the raw water, and the concentration of the polyacrylamide is 1%.

4. The process for recycling leachate of claim 1, wherein the leachate is treated by the method,

the Fenton oxidation time in the step (1) is 0.5-4 h;

the flocculation precipitation time in the step (1) is 15-45 min;

and (2) filtering by using a plate-and-frame filter press in the step (1).

5. The process of claim 4, wherein the leachate treatment process is carried out in a water recycling manner,

the Fenton oxidation time in the step (1) is 2 h;

the flocculation precipitation time in the step (1) is 30 min.

6. The process for recycling leachate of claim 1, wherein the leachate is treated by the method,

the evaporation in the step (2) is triple effect evaporation: negative pressure of-70 KPa and temperature of 60 ℃;

the sand filter adopted in the sand filtration in the step (2) takes quartz sand as a filter material;

and (3) the carbon filter adopted in the carbon filtration in the step (2) takes activated carbon as a filter material.

7. The process for recycling leachate of claim 1, wherein the leachate is treated by the method,

the reverse osmosis in the step (3) adopts a plurality of reverse osmosis membrane elements which are arranged in two sections, the number ratio of the elements in the first section to the elements in the second section is 2:1, and the pressure bearing capacity is more than 4 Mpa.

8. The process for recycling the leachate-treating water in accordance with claim 1, wherein the filtration precision of the cartridge filter used in the reverse osmosis in step (3) is 1-10 μm.