CN113045091A - Membrane combination process system and method for recycling and zero-discharge treatment of effluent resources of garbage leachate membrane bioreactor - Google Patents

Membrane combination process system and method for recycling and zero-discharge treatment of effluent resources of garbage leachate membrane bioreactor Download PDF

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CN113045091A
CN113045091A CN202110290213.2A CN202110290213A CN113045091A CN 113045091 A CN113045091 A CN 113045091A CN 202110290213 A CN202110290213 A CN 202110290213A CN 113045091 A CN113045091 A CN 113045091A
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membrane
effluent
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landfill leachate
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赵姗姗
刘桂梅
孟凡刚
孟雅冰
韩木侨
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Sun Yat Sen University
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/447—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by membrane distillation
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05F—ORGANIC FERTILISERS NOT COVERED BY SUBCLASSES C05B, C05C, e.g. FERTILISERS FROM WASTE OR REFUSE
    • C05F7/00—Fertilisers from waste water, sewage sludge, sea slime, ooze or similar masses
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
    • C05G3/80—Soil conditioners
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
    • C05G5/00—Fertilisers characterised by their form
    • C05G5/20—Liquid fertilisers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
    • Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
    • Y02A40/20—Fertilizers of biological origin, e.g. guano or fertilizers made from animal corpses

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  • Organic Chemistry (AREA)
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  • Water Supply & Treatment (AREA)
  • Soil Sciences (AREA)
  • Nanotechnology (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

The invention belongs to the technical field of landfill leachate treatment, and particularly relates to a system and a method for treating effluent of a landfill leachate Membrane Bioreactor (MBR). The treatment system adopts a loose nanofiltration membrane filtering unit, and can efficiently separate humus and inorganic salt in MBR effluent; the membrane distillation process is adopted, so that the concentration of inorganic salt and the recovery of pure water can be realized; in the post-treatment unit, inorganic salt in the membrane distillation concentrated solution is subjected to solidification treatment or is reused as a draw solution in the forward osmosis process. Can realize the high-efficient recovery of humus fertilizer resource in landfill leachate MBR effluent, and realize the zero release treatment or the resource utilization of high concentration inorganic salt waste liquid to and the recovery of pure water resource, effectively solve the problem that high pressure membrane pollution is serious, the concentrate is difficult to handle and the energy consumption is high that faces among the mainstream treatment process of current landfill leachate.

Description

Membrane combination process system and method for recycling and zero-discharge treatment of effluent resources of garbage leachate membrane bioreactor
Technical Field
The invention belongs to the technical field of landfill leachate treatment. More particularly, relates to a system and a method for treating effluent of a landfill leachate membrane bioreactor.
Background
Landfill is an economic and practical urban solid waste solution, but because rainwater in the landfill process washes and drenches, the liquid that self organic matter biodegradation fermentation produced and the physical and chemical interaction between each component, the landfill leachate composition that produces is complicated, mainly contains organic matter humus class material, is brownish black, and COD is very high to contain a large amount of inorganic ions, must can satisfy the requirement of discharge to reach standard through advanced treatment, is one of the most difficult high concentration organic waste water of processing in the world.
The mainstream treatment technology of the landfill leachate at present is the combination of biochemical treatment and membrane filtration, for example, Chinese patent application CN107746149A discloses a novel landfill leachate treatment system, which mainly biodegrades partial organic matters through a Membrane Bioreactor (MBR) to remove most of ammonia nitrogen and phosphorus; and (4) performing advanced treatment on the MBR effluent by adopting high-pressure nanofiltration/reverse osmosis (NF/RO) filtration. However, this system has three problems: firstly, NF and RO units inevitably produce concentrated solution which accounts for 15 to 30 percent of the volume of the stock solution, and no effective concentrated solution treatment technology exists at present; secondly, the concentration of organic matters and inorganic salts in the effluent of the MBR is very high, and the surface membrane of the NF/RO membrane is seriously polluted and scaled in the high-pressure filtration process, so that a scale inhibitor needs to be added before NF/RO; thirdly, the existing NF/RO membrane has high inorganic salt rejection rate, so that the operation pressure is high and the energy consumption is high. The problems become difficult points and hot points for researching and developing the landfill leachate treatment technology.
Therefore, the effluent treatment system and the effluent treatment method of the membrane bioreactor for landfill leachate are urgently needed to provide, wherein the effluent treatment system and the effluent treatment method can remove pollutants, recycle resources, prevent membranes from being damaged and reduce energy consumption.
Disclosure of Invention
The invention aims to solve the technical problem that the existing garbage leachate treatment method has a large amount of concentrated solution which can not be further treated; the surface of the membrane is seriously polluted, scaled and damaged; the effluent treatment system of the membrane bioreactor of the landfill leachate has the defects of high operation pressure and large energy consumption, and can recycle resources and reduce energy consumption while removing pollutants.
The invention aims to provide a water outlet treatment system of a landfill leachate membrane bioreactor.
The invention also aims to provide a method for treating the effluent of the membrane bioreactor of the landfill leachate.
The above purpose of the invention is realized by the following technical scheme:
the utility model provides a landfill leachate membrane bioreactor goes out water processing system, is used for separating organic matter and inorganic salt including loose nanofiltration membrane filter unit, and the membrane distillation unit is used for separating inorganic salt and water resource, and the aftertreatment unit is used for handling the inorganic salt in the membrane distillation concentrate.
In the effluent system of the landfill leachate Membrane Bioreactor (MBR), the loose nanofiltration membrane filtering unit is adopted, organic humus fertilizer in the effluent of the MBR can be concentrated and recovered to allow inorganic salt to permeate, so that the effect of efficiently separating humus and inorganic salt in the effluent of the MBR is achieved, the obtained concentrated solution meets the requirements of humus water-soluble fertilizer, and the effluent system has the characteristics of high flux, low pressure, low energy consumption and low membrane pollution; the membrane distillation process is adopted, and the waste heat/waste heat of the landfill is utilized to drive the membrane distillation process to concentrate the loose nanofiltration permeating liquid, so that the concentration of inorganic salt and the recovery of pure water can be realized; in the post-treatment unit, inorganic salt in the membrane distillation concentrated solution is subjected to solidification treatment, or high-concentration inorganic salt can be reused as a draw solution in the forward osmosis process. By adopting the loose nanofiltration membrane-membrane distillation combined process, the humus fertilizer resources in the effluent of the landfill leachate MBR can be efficiently recovered, zero-emission treatment or resource utilization of high-concentration inorganic salt waste liquid and recovery of pure water resources are realized, and the problems of serious high-pressure membrane pollution, difficulty in treatment of concentrated solution and high energy consumption in the conventional main stream treatment process of the landfill leachate are effectively solved. The combined process is advanced, practical, low in energy consumption, stable in operation and simple and convenient to operate, and can realize resource recycling and zero discharge of wastewater.
A method for treating the effluent of a membrane bioreactor of landfill leachate comprises the following steps:
s1, treating the garbage leachate by a membrane bioreactor to obtain effluent, and allowing the effluent to enter a loose nanofiltration membrane filtering unit to obtain loose nanofiltration permeate and loose nanofiltration concentrate;
s2, allowing the loose nanofiltration permeating liquid obtained in the step S1 to enter a membrane distillation unit, and treating to obtain membrane distillation permeating liquid and membrane distillation concentrated liquid;
s3, feeding the membrane distillation concentrated solution obtained in the step S2 into a curing unit for curing treatment; or as draw solution for forward osmosis membrane processes.
Further, in the step S1, the COD of the effluent treated by the membrane bioreactor is 400-3000 mg/L, the conductivity is more than 10mS/cm, and the pH is 5-9. In the actual production process, the fluctuation of the process parameters may cause the fluctuation of the pH of the MBR effluent, and the increase of the pH is not beneficial to the separation of organic matters and inorganic salts, so that the recycling of the organic matters in the MBR effluent of the landfill leachate is influenced; however, too low a pH may damage the selective layer of the loose nanofiltration membrane, and the strong acid environment increases the hydrophobicity of humus in the MBR effluent, which is more likely to cause severe membrane fouling. Therefore, when the MBR effluent is treated by the loose nanofiltration process, the pH value should be preferably adjusted to be about 5.
Further, in step S1, the operating parameters of the loose nanofiltration membrane filter unit are as follows: the pressure is 0.05-1.0 MPa, and the initial flux is 30-80L/(m)2H) at a temperature of 5 to 40 ℃. In the actual production process, the change of temperature can be influenced by the change of seasons, and the operation temperature range from spring to winter can be 10-40 ℃; experiments show that the excessive temperature can reduce organic matters and inorganic matters in the effluent of the MBR by the loose nanofiltration membraneThe salt retention rate is preferably 5-25 ℃.
Further, in step S1, the filtering membrane of the loose nanofiltration membrane filtering unit is a flat membrane or a hollow fiber membrane, and the average molecular weight cutoff is 500-1000 Da. The loose nanofiltration process is based on a membrane screening mechanism, so that the interception molecular weight of the membrane has a large influence on the treatment effect of organic matters, and the experimental result shows that the interception rate of the organic matters and inorganic salts is higher when the average interception molecular weight is smaller, and the interception removal effect of the organic matters and the separation effect of the organic matters and the inorganic salts are balanced when MBR effluent is treated by the loose nanofiltration process. Preferably, the average molecular weight cut-off is 500-650 Da.
Further, in step S1, the material of the membrane is selected from one or more of polyacrylonitrile, polyethersulfone, sulfonated polyethersulfone and polyamide.
Further, in step S1, the loose nanofiltration membrane filtration unit filters in a cross-flow manner, and the membrane surface flow rate is 0.1-0.5 m/S.
Further, the concentrated solution of the borrelia nanofiltration obtained in step S1 may be used as a stock solution of a humic substance-containing water-soluble fertilizer.
Further, in step S2, the temperature difference between two sides of the membrane distillation unit is 30-70 ℃, and the concentration multiple is 3-20 times.
Furthermore, in step S2, the membrane of the membrane distillation unit is a flat membrane or a hollow fiber membrane, the pore size is 0.1 to 0.5 μm, and the material is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride and polypropylene; the membrane transmission layer is hydrophobic, super-hydrophobic or super-amphiphobic.
Further, in step S2, the membrane distillation unit flows in a cross-flow manner, and the flow rate of the membrane surface is 0.1-0.5 m/S.
Furthermore, the membrane distillation permeate obtained in step S2 can be recycled as clean water resource.
Preferably, in step S2, the membrane distillation unit may be operated by direct contact membrane distillation, air gap membrane distillation, reduced pressure membrane distillation or gas flow sweep membrane distillation.
Further, in step S3, the solidification unit includes an evaporation device (optionally selected according to the feed liquid concentration factor) and a solidification device for zero emission treatment.
The method is not only suitable for treating the MBR effluent of the landfill leachate, but also suitable for treating other sewage containing higher concentration of organic matters difficult to degrade and high concentration of inorganic matters.
The invention has the following beneficial effects:
(1) the effluent treatment system and the effluent treatment method of the landfill leachate membrane bioreactor separate humus and inorganic salt in MBR effluent by using a loose nanofiltration membrane, and concentrate and extract the humus as a liquid fertilizer; then, inorganic salt in the outlet water of the loose nanofiltration membrane is concentrated by membrane distillation, and membrane distillation produced water is recycled, so that the resource and zero emission of the outlet water of the MBR are realized; the method solves the problem of treatment of the membrane concentrated solution in the prior art, changes waste into valuable, and achieves the unification of environmental benefits, social benefits and economic benefits.
(2) The effluent treatment system and the effluent treatment method of the landfill leachate membrane bioreactor are applied to the effluent treatment of the landfill leachate MBR with high organic matters and high salt content, can effectively intercept the organic matters to reduce COD, and have higher inorganic salt transmittance, so that most inorganic salt ions in the MBR effluent permeate the membrane without accumulating on the surface of the membrane, the formation of inorganic scale is reduced, the concentration polarization is reduced, higher membrane flux can be maintained, the membrane pollution is slowed down, and the service life of the membrane is prolonged.
(3) The effluent treatment system and the effluent treatment method of the landfill leachate membrane bioreactor have the advantages of lower operating pressure, capability of operating by fully utilizing waste heat and waste heat of a landfill plant through membrane distillation, lower energy consumption, low operating cost, simple operating process and equipment, less occupied area, no secondary pollution, simple and reliable operation, suitability for zero discharge treatment of high-salt-content landfill leachate MBR effluent, suitability for other sewage treatment containing high concentration of refractory organic matters and high concentration of inorganic matters, and wide application range.
Drawings
FIG. 1 is a flow chart of the effluent treatment method of the landfill leachate membrane bioreactor of the invention.
FIG. 2 is a diagram showing the effect of the membrane distillation unit on the retention of organic and inorganic salts in the permeate of loose nanofiltration according to example 1 of the present invention.
FIGS. 3, 4 and 5 are graphs showing the effect of the loose nanofiltration unit of examples 1 and 2 of the present invention on the effluent treatment of the membrane bioreactor of landfill leachate.
FIGS. 6, 7 and 8 are graphs showing the effect of the loose nanofiltration units of examples 1, 3 and 5 of the present invention on the effluent treatment of the membrane bioreactor for landfill leachate.
FIGS. 9, 10 and 11 are graphs showing the effect of the loose nanofiltration unit of examples 1, 6 and 7 of the present invention on the effluent treatment of the membrane bioreactor of landfill leachate.
FIGS. 12, 13 and 14 are graphs showing the effect of the loose nanofiltration unit of examples 1, 8 and 9 of the present invention on the effluent treatment of the membrane bioreactor of landfill leachate.
Wherein, FIGS. 3, 6, 9 and 12 are statistical graphs of water flux change data in the water outlet process of the membrane bioreactor for treating landfill leachate by the loosening nanofiltration unit; FIGS. 4, 7, 10 and 13 are statistical graphs of flux change data of the loose nanofiltration membrane after the loose nanofiltration system processes effluent of the landfill leachate membrane bioreactor and after the pure water cleaning system; FIGS. 5, 8, 11 and 14 are statistics of the retaining effect data of humus and inorganic salts in the effluent of the membrane bioreactor of the landfill leachate by the loose nanofiltration unit.
FIG. 15 is a statistical chart of water flux change data of the membrane distillation concentrate used in the forward osmosis process in example 10 of the present invention.
Detailed Description
The invention is further described with reference to the drawings and the following detailed description, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.
Unless otherwise indicated, reagents and materials used in the following examples are commercially available.
Example 1 landfill leachate Membrane bioreactor effluent treatment
1. The treated object is leachate MBR effluent of a certain waste incineration plant, and the water quality is as follows:
TOC: 116mg/L, conductivity: 12.3mS/cm, pH: 8.3.
2. system setup
Loose nanofiltration membrane filtration unit: the effective area is 16cm2The cross-flow filter tank has a filter membrane which is a polyamide flat membrane and has an average molecular weight cutoff of 500 Da; firstly, pre-pressing with pure water for 1h under 0.3MPa, and then pre-pressing with NaCl solution with the conductivity of 12mS/cm, so that the membrane reaches stable flux under the salt solution with the concentration similar to that of the effluent of the MBR.
A membrane distillation unit: the effective area is 18cm2The membrane pool is directly contacted with a membrane distillation (DCMD) device, and a filtering membrane is a hydrophobic polytetrafluoroethylene flat membrane with the aperture size of 0.1 mu m.
3. The specific effluent treatment comprises the following steps:
s1, adjusting the pH value of effluent of the garbage leachate treated by the membrane bioreactor to 8, entering a loose nanofiltration membrane filtration unit, and adjusting the pressure to ensure that the initial flux is 45L/(m)2H), the temperature is 25 ℃, the flow rate of the membrane surface is 0.1m/s, and the filtration is carried out in a cross flow mode; collecting the loose nanofiltration permeating liquid in an effluent storage tank, continuously refluxing the trapped liquid to the effluent storage tank treated by the membrane bioreactor, concentrating to 4.3 times, and stopping the loose nanofiltration treatment to obtain loose nanofiltration permeating liquid and loose nanofiltration concentrated liquid;
s2, allowing the loose nanofiltration permeating liquid obtained in the step S1 to enter a membrane distillation unit, enabling the flow rate of a membrane surface to be 0.1m/S, filtering in a cross-flow mode, keeping the feeding temperature at 60 ℃, taking pure water as cold material liquid at a permeation side, controlling the temperature measurement of the cold material liquid to be 15 ℃ by adopting a circulating water chiller, starting a hot water circulating pump and a cold water circulating pump after the temperatures of the cold side and the hot side reach the set temperature, enabling membrane distillation trapped liquid to flow back to a loose nanofiltration permeating liquid storage tank, continuously concentrating the feeding liquid, allowing the membrane distillation permeating liquid to enter a membrane distillation permeation water outlet tank after being cooled, and stopping membrane distillation treatment after being concentrated to 5 times to obtain membrane distillation permeating liquid and membrane distillation concentrated liquid;
s3, the membrane distillation concentrated solution obtained in the step S2 enters a curing unit for curing treatment.
Example 2 landfill leachate Membrane bioreactor effluent treatment
The difference from the example 1 is that the average molecular weight cut-off of the loose nanofiltration membrane filtration unit in the example 2 is 650Da, and the rest parameters and operation refer to the example 1.
Example 3 landfill leachate Membrane bioreactor effluent treatment
The difference from the embodiment 1 is that the pH of the effluent of the landfill leachate treated by the membrane bioreactor in the embodiment 3 is adjusted to 6.5, and the rest parameters and operation refer to the embodiment 1.
Example 4 landfill leachate Membrane bioreactor effluent treatment
The difference from the embodiment 1 is that the pH of the effluent of the landfill leachate treated by the membrane bioreactor in the embodiment 4 is adjusted to 5, and the rest parameters and operation refer to the embodiment 1.
Example 5 landfill leachate Membrane bioreactor effluent treatment
The difference from the embodiment 1 is that the pH of the effluent of the landfill leachate treated by the membrane bioreactor is adjusted to 3 in the embodiment 5, and the rest parameters and operation refer to the embodiment 1.
Example 6 effluent treatment of landfill leachate Membrane bioreactor
The difference from example 1 is that the initial flux in step S1 in example 6 is 30L/(m)2H), the remaining parameters and operations refer to example 1.
Example 7 effluent treatment for landfill leachate Membrane bioreactor
The difference from example 1 is that the initial flux in step S1 of example 7 is 60L/(m)2H), the remaining parameters and operations refer to example 1.
Example 8 effluent treatment for landfill leachate Membrane bioreactor
The difference from example 1 is that the temperature in step S1 of example 8 is 15 ℃, and the rest parameters and operation refer to example 1.
Example 9 effluent treatment for landfill leachate Membrane bioreactor
The difference from example 1 is that the temperature in step S1 of example 9 is 35 ℃, and the rest parameters and operation refer to example 1.
Example 10 effluent treatment for landfill leachate Membrane bioreactor
This example applies the membrane distillation concentrate obtained in step S2 of example 1 as a forward osmosis draw solution to a forward osmosis process:
NaCl solution with similar conductivity is used as a draw solution of a control group, a commercial Cellulose Triacetate (CTA) forward osmosis membrane is adopted in the forward osmosis process, and the effective area is 0.0024m2The active layer of the forward osmosis membrane faces the draw solution side (AL-DS), the membrane distillation concentrate or NaCl solution obtained in step S2 of example 1 was used as the draw solution, and the raw material solution was deionized water. Respectively circulating the raw material solution and the drawing solution by using a peristaltic pump at the flow rate of 300mL/min, starting recording after the peristaltic pump is opened and the solution is filled in a pipeline and stably runs until the flux is stable, monitoring the quality of the raw material solution in real time by using an electronic balance, and calculating the water flux in the forward osmosis process by using a formula.
Experimental example analysis of effluent treatment effect of membrane bioreactor for landfill leachate
1. Analytical method
(1) The concentration factor (η) characterizes the multiple of concentration of the feed solution after the membrane process, defined as the ratio of the initial feed solution volume to the final membrane concentrate volume during the concentration step, and is calculated as follows:
Figure BDA0002982150970000071
in the formula, V0And VtThe volumes of the starting feed solution and the membrane concentrate are indicated, respectively.
(2) The organic matter concentration is tested by a total organic carbon analyzer (TOC), and the retention rate (R) of the organic matter is calculated by the following formula:
Figure BDA0002982150970000072
in the formula, TOCPAnd TOCRRespectively representing the concentration of organic matter in the permeate and the feed.
(3) The inorganic salt rejection rate (R) is obtained by measuring the conductivity by a conductivity meter and calculating, and the calculation formula is as follows:
Figure BDA0002982150970000073
in the formula, KpAnd KfThe conductivity values of the salt solution in the feed and filtrate are indicated.
(4) The pure water flux of the forward osmosis membrane is calculated by adopting the following formula:
Figure BDA0002982150970000081
in the formula, JwIs the water flux of the forward osmosis membrane (L/(m)2H), LMH), Δ t and Δ W represent the change in operating time by weight of the feed solution, a represents the effective area of the membrane, and ρ represents the density of the feed solution.
(5) The reverse salt flux during forward osmosis was calculated using the following formula:
Figure BDA0002982150970000082
wherein Js is the reverse salt flux (g/(m) of the forward osmosis membrane2·h)，gMH)，CtIs the salt concentration V of the raw material liquid at different timestIs the volume of the stock solution at different times.
2. Results of the experiment
(1) The conductivity, the salt content and the TOC of the treated effluent of the landfill leachate membrane bioreactor in example 1 are measured, and the results are shown in Table 1; when the concentration factor of the loose nanofiltration is 4.3 and the concentration factor of the membrane distillation is 5, the flux of the membrane distillation process and the retention effect on organic matters and inorganic salts in the permeation liquid of the loose nanofiltration are shown in fig. 2.
TABLE 1 example 1 landfill leachate membrane bioreactor effluent treatment Effect
Item Conductivity (μ S/cm) Salt content (mg/L) TOC(mg/L)
MBR effluent of landfill leachate 12270 6130 116
Nanofiltration concentrate 16420 8210 497
Loosening nanofiltration permeating liquid 12730 6360 6.6
Membrane distillation concentrate 65450 32.7 87.5
Membrane distillation permeate 3.87 1.94 0.75
As can be seen from table 1, the nanofiltration concentrate contains high-concentration organic matter, and the nanofiltration permeate contains high-concentration inorganic salt and low-concentration organic matter, which indicates that the nanofiltration unit can effectively retain most of the organic matter and has high transmittance for the inorganic salt, so that the nanofiltration unit can remove the organic matter in the effluent of the landfill leachate MBR and simultaneously effectively separate the organic matter and the inorganic salt;
the conductivity of the membrane distillation permeate liquid is lower than 5 mu S/cm, the content of organic matters is almost zero, and the membrane distillation permeate liquid can reach the standard of standard discharge. The membrane distillation concentrated solution contains low-concentration organic matters, has the conductivity as high as 65.5mS/cm, has the characteristic of high salt content, can be used for drawing liquid in the forward osmosis membrane process, and can reduce the energy consumption of evaporative crystallization if being solidified.
As can be seen from FIG. 2, the membrane distillation unit can achieve 100% rejection of both organic and inorganic salts in the feed solution.
(2) Determination of influence of different average molecular weight cut-off of loose nanofiltration membrane filtration unit on flux and cut-off rate
The retention rates of organic matters and inorganic salts after effluent treatment of the landfill leachate membrane bioreactors in examples 1-2 are measured, and changes of effluent flux of the loose nanofiltration permeate are monitored, and the results are shown in figures 3-5.
As can be seen from fig. 3, the loose nanofiltration membrane of example 1 has a smaller pore size (500Da), and more contaminants are trapped on the membrane, resulting in a decreased flux; FIG. 4 shows that flux recovery of more than 96% is achieved in the subsequent pure water washing process after contamination of the loose nanofiltration membranes with two pore sizes (500Da and 650 Da);
as can be seen from fig. 5, the rejection rates of the loose nanofiltration unit for organic matters in the MBR effluent are 91.7% and 97.9%, respectively, and the rejection rates for inorganic salts are 6.7% and 27.8%, respectively; the smaller the molecular weight cut-off of the loose nanofiltration membrane is, the higher the cut-off rate of organic matters and inorganic salts is, so that when MBR effluent is treated by the loose nanofiltration process, attention should be paid to balance the effect of removing the cut-off of the organic matters and the effect of separating the organic matters from the inorganic matters.
(3) Measuring the influence of different pH values of MBR effluent on flux and rejection rate
The retention rates of organic matters and inorganic salts after effluent treatment of the landfill leachate membrane bioreactors of examples 1, 3-5 are measured, and changes of effluent flux of the loose nanofiltration permeate are monitored, and the results are shown in fig. 6-8.
As can be seen from fig. 6, when the MBR effluent of example 5 has a pH of 3, the membrane pollution of the loose nanofiltration unit is the most severe, and the flux reduction degree is the highest, and when the MBR effluent of example 4 has a pH of 5, the membrane pollution of the loose nanofiltration unit is the lightest; figure 7 shows that the flux of example 4(MBR effluent pH 5) decreased only 24.58% after 4.3-fold concentration, with minimal flux reduction, minimal membrane fouling, and essentially complete flux recovery after pure water washing (flux recovery 100%);
as can be seen from fig. 8, when the pH of the MBR effluent is adjusted to 3, 5, 6.5, and 8, the retention rates of the loosening nanofiltration unit for organic matters in the MBR effluent are 97.8%, 96.9%, 98.6%, and 97.9%, and the retention rates for inorganic salts are 19.9%, 19.8%, 24.6%, and 27.8%, respectively, which indicates that the adjustment of pH has little influence on the removal of organic matters by the loosening nanofiltration process, but the increase of the pH of the raw material liquid is not favorable for the separation of organic matters and inorganic salts, and is not favorable for the recycling of organic matters in the MBR effluent of the landfill leachate. On the other hand, the selective layer of the loose nanofiltration membrane can be damaged by too low pH, and meanwhile, the strong acid environment enables the hydrophobicity of humus in MBR effluent to be enhanced, so that serious membrane pollution is more likely to be caused. Therefore, when the MBR effluent is treated by the loose nanofiltration process, the pH value is adjusted to be about 5 to be optimal.
(4) Determining the influence of different initial fluxes of the loose nanofiltration unit on the flux and the rejection rate
The retention rates of organic matters and inorganic salts after effluent treatment of the landfill leachate membrane bioreactors of examples 1, 6 and 7 are measured, and the change of the effluent flux of the loose nanofiltration permeate is monitored, and the results are shown in fig. 9-11.
As can be seen from fig. 9, with different initial fluxes, the flux variation curves of the bulk nanofiltration unit are not significantly different, which indicates that the initial fluxes have less influence on membrane fouling; figure 10 shows that the flux reduction is significantly positively correlated to the initial flux, while the flux recovery rate shows a decreasing trend with increasing initial flux, indicating that increasing initial flux increases membrane fouling, probably because increasing initial flux increases the driving force for solute to cross the membrane, thus resulting in a tighter fouling layer.
As can be seen from fig. 11, the initial fluxes of 30, 45 and 60LMH are adopted for filtration, the retention rates of the loosening nanofiltration unit on organic matters in the MBR effluent are all more than 97%, and the retention rates on inorganic salts are respectively 24%, 28% and 30%; it is shown that high retention of organic substances can be achieved with different initial fluxes, and although high initial fluxes can bring high filtration efficiency, the separation of organic substances and inorganic salts is not facilitated. Therefore, when selecting a loose nanofiltration process operating a press to operate at an initial throughput, care should be taken to balance filtration efficiency, membrane fouling level, and organic-inorganic separation effect.
(5) Determining the influence of different temperatures of the loosening nanofiltration unit on the flux and retention rate
The retention rates of organic matters and inorganic salts after effluent treatment of the landfill leachate membrane bioreactors of examples 1, 8 and 9 are measured, and the change of the effluent flux of the loose nanofiltration permeate is monitored, and the results are shown in fig. 12-14.
According to Guangzhou local climate, influence of temperature on the effect of MBR effluent treated by loosening and nanofiltration is researched, in example 8 and example 1, flux change of MBR effluent treated by loosening and nanofiltration is respectively carried out at 15 ℃ and 25 ℃ (simulating Guangzhou spring, autumn and winter temperatures), and as can be seen from FIG. 12, when the temperature is lower, pollution conditions of films of the loosening and nanofiltration process are similar, and flux change curves are not obviously different. However, when the reactor is operated at a high temperature of 35 ℃ (simulating Guangzhou summer temperature), the flux is reduced in a truncation manner when the concentration factor is 1.7-2, so that serious membrane pollution is caused, and the membrane fouling phenomenon is probably caused; as can be seen from fig. 13, the reduction degree of loose nanofiltration flux is not much different between 15 ℃ and 25 ℃, the recovery rate of membrane flux is above 96%, the membrane pollution is light, and is basically reversible pollution, however, when the membrane is operated at a high temperature of 35 ℃, the membrane flux is reduced by 79%, and the recovery rate of flux is only 71%, which indicates that the high temperature causes serious membrane pollution.
As can be seen from fig. 14, the filtration is performed at operating temperatures of 15, 25 and 35 ℃, the retention rates of the loosening nanofiltration unit on organic matters in the MBR effluent are 97.2%, 97.8% and 94.2%, and the retention rates on inorganic salts are 27.9%, 27.8% and 19.5%, respectively. The high operation temperature can reduce the retention rate of organic matters and inorganic salts in the effluent of the MBR, and is not beneficial to the removal of the organic matters, probably because the high temperature causes the membrane pores to expand and simultaneously increases the molecular diffusion rate, thereby causing the reduction of the retention rate. From the 3 above embodiments, it can be known that the operation temperature should be controlled below 25 ℃ by taking cooling measures at high temperature in summer.
(6) Determination of the Water flux Change during Forward osmosis in example 10
Referring to fig. 15, it can be seen that the water flux and the reverse salt flux of the experimental group are stable with time and are not much different from the control group results as the forward osmosis process proceeds. Therefore, the membrane distillation concentrated solution can be effectively utilized as a drawing solution in the forward osmosis process, and the byproduct membrane concentrated solution of the loose nanofiltration-membrane distillation unit can be recycled, so that the aim of sustainable development is fulfilled.
From the results, the loose nanofiltration-membrane distillation combined treatment system has excellent treatment effect on the effluent of the landfill leachate MBR, can obtain the loose nanofiltration concentrated solution containing high humic acid and low inorganic salt as concentrated liquid fertilizer, the membrane distillation concentrated solution containing low organic matter and high inorganic salt as the drawing solution of the forward osmosis membrane process or carry out solidification, evaporation and crystallization treatment, and the membrane distillation permeate as the final effluent of the treatment system can reach the pollution control standard of landfill sites (GB 16889 2008). Therefore, the treatment system and the method of the invention achieve the effects of sustainable development, resource recycling, wastewater reduction treatment, zero liquid discharge and energy consumption reduction, are suitable for separating and recovering organic matters and inorganic salts from wastewater containing high organic matters and high inorganic salts, and have important application value in the field of sewage treatment and recovery.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (10)

1. The utility model provides a landfill leachate membrane bioreactor goes out water processing system which characterized in that, is used for separating organic matter and the inorganic salt of membrane bioreactor play water including loose nanofiltration membrane filter unit, and membrane distillation unit is used for separating inorganic salt and water resource, and the aftertreatment unit is used for handling the inorganic salt in the membrane distillation concentrate.
2. A method for treating the effluent of a membrane bioreactor of landfill leachate is characterized by comprising the following steps:
s1, treating the garbage leachate by a membrane bioreactor to obtain effluent, and allowing the effluent to enter a loose nanofiltration membrane filtering unit to obtain loose nanofiltration permeate and loose nanofiltration concentrate;
s2, allowing the loose nanofiltration permeating liquid obtained in the step S1 to enter a membrane distillation unit, and treating to obtain membrane distillation permeating liquid and membrane distillation concentrated liquid;
s3, feeding the membrane distillation concentrated solution obtained in the step S2 into a curing unit for curing treatment; or as draw solution for forward osmosis membrane processes.
3. The treatment method according to claim 2, wherein in step S1, the COD of the effluent treated by the membrane bioreactor is 400-3000 mg/L, the conductivity is more than 10mS/cm, and the pH is 5-9.
4. The process of claim 2, wherein in step S1, the operating parameters of the loose nanofiltration membrane filtration unit are: the pressure is 0.05-1.0 MPa, and the initial flux is 30-80L/(m)2H) at a temperature of 5 to 40 ℃.
5. The treatment method as claimed in claim 2, wherein in the step S1, the filtering membrane of the loose nanofiltration membrane filtering unit is a flat membrane or a hollow fiber membrane, and the average molecular weight cut-off is 500-1000 Da.
6. The treatment method according to claim 5, wherein in step S1, the membrane is made of one or more materials selected from polyacrylonitrile, polyethersulfone, sulfonated polyethersulfone and polyamide.
7. The treatment method according to claim 2, wherein in step S1, the loose nanofiltration membrane filtration unit performs cross-flow filtration, and the membrane surface flow rate is 0.1-0.5 m/S.
8. The process of claim 2, wherein in step S2, the temperature difference between both sides of the membrane distillation unit is 30-70 ℃ and the concentration factor is 3-20.
9. The processing method according to claim 2, wherein in step S2, the membrane of the membrane distillation unit is a flat sheet membrane or a hollow fiber membrane, the pore size is 0.1-0.5 μm, and the material is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride and polypropylene; the membrane transmission layer is hydrophobic, super-hydrophobic or super-amphiphobic.
10. The process according to claim 2, wherein in step S2, the membrane distillation unit flows in a cross-flow manner, and the membrane surface flow rate is 0.1 to 0.5 m/S.
CN202110290213.2A 2021-03-18 2021-03-18 Membrane combination process system and method for recycling and zero-discharge treatment of effluent resources of garbage leachate membrane bioreactor Pending CN113045091A (en)

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