A biological denitrification method for low-carbon membrane concentrated liquid

Abstract

The invention discloses a biological denitrification method for low-carbon membrane concentrate, wherein the membrane concentrate to be treated is pumped into a short-range denitrification tank by a pump, an electron donor is introduced into the short-range denitrification tank, and then the bottom sediment enters a sedimentation separator for separation, and the partially separated calcium salt and the effluent of the short-range denitrification tank overflow into an autotrophic denitrification tank and are finally discharged, mainly solving the problem of BOD of membrane concentrate. 5 When / N is less than 1, the removal efficiency of more than 95% of the total nitrogen in the membrane concentrate can be achieved with almost no addition of carbon source, ensuring that the discharge of the membrane concentrate meets the standards. The economic cost is low, the reaction control is simple, and it is conducive to large-scale promotion and application.

Description

Technical Field

[0001] The invention relates to the field of environmental pollutant treatment, and in particular to a biological denitrification method for low-carbon membrane concentrated liquid. Background Art

[0002] Environmental issues have attracted great attention from all parties. Among them, membrane technology is often used in sewage treatment to separate pollutants. Membrane technology plays an important role in the field of sewage treatment. It is based on the selective barrier effect of membranes on molecules or particles of different sizes, shapes, charges or other characteristics, and can efficiently remove suspended solids, organic matter, microorganisms, heavy metals and other pollutants in sewage. Existing membrane technologies include microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes and nanofiltration membranes. However, after sewage treatment, the other side of the membrane retains a byproduct that is more harmful to the environment: landfill leachate concentrate. The membrane concentrate contains a large amount of refractory organic pollutants, such as humic acid, as well as high concentrations of salts and organic matter. The ammonia nitrogen and nitrate nitrogen are between 100-5000 mg / L, and the chemical oxygen demand (COD) concentration is usually between 200-50000 mg / L. The content of refractory organic matter is high and the biodegradability is poor.

[0003] The key problem of membrane concentrate being difficult to treat is that the organic carbon source available to microorganisms in the influent is low, and the economic cost of adding an external carbon source is high. Common physicochemical treatment technologies mainly include evaporation, crystallization, ion exchange, etc. These methods are not economical, and the economic cost of initial equipment construction is higher, which greatly increases the treatment cost of the concentrate. When using methods such as advanced oxidation + traditional biochemistry + aerated biological filter to deal with membrane concentrate with a low carbon-nitrogen ratio (BOD5 / N<1), the cost of denitrification will be greatly increased due to the strong dependence of traditional denitrification on carbon sources.

[0004] CN201510780322.7 discloses a device and method for treating landfill leachate concentrate, the method comprising: (1) the landfill leachate concentrate is injected into the membrane assembly from the landfill leachate concentrate injection port; clean water is injected into the concentration zone from the clean water injection port, and the voltage-stabilized power supply is turned on at the same time; under the action of the cathode sleeve, the cations and anions in the wastewater pass through the membrane assembly and enter the concentration zone; (2) the effluent of the membrane assembly is pumped into the oxidation zone, and the remaining organic matter is removed by the action of microorganisms, and the effluent meets the discharge standards; the effluent of the concentration zone is pumped into the reduction zone, and the heavy metal ions are removed by the action of the cathode sleeve, and the final effluent is pure salt water. The method combines membrane treatment with bioelectrochemical treatment, so that it can more effectively treat the refractory organic matter and heavy metals in the membrane concentrate under high salt conditions.

[0005] CN202010306118.2 discloses a treatment device for landfill leachate membrane concentrate, including a pretreatment tank, a first pH adjustment tank, an ultraviolet catalytic oxidation device, a second pH adjustment tank, a sedimentation tank, a denitrification reaction tank, a nitrification reaction tank, an MBR reaction tank and a plate-frame filter press. Although this method can degrade macromolecular organic matter in the concentrate, the steps are cumbersome and it is not suitable for decomposing nitrogen-containing pollutants in water bodies in a low-carbon environment.

[0006] At present, many experts and scholars have proposed the treatment process of membrane concentrate, but the existing technology has the problems of complex operation, high cost or unsatisfactory treatment effect. In addition, it is urgent to find a low-cost technology that can promote the efficient and stable removal of nitrogen-containing pollutants by autotrophic biological denitrification bacteria in membrane concentrate with a low carbon-nitrogen ratio. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention aims to achieve a removal efficiency of more than 95% of the total nitrogen in the concentrate when the BOD5 / N of the membrane concentrate is less than 1 and almost no carbon source is added.

[0008] The invention provides a biological denitrification method for low-carbon membrane concentrated liquid, comprising the following steps: pumping the membrane concentrated liquid to be treated into a short-range denitrification tank by a pump, introducing an electron donor into the short-range denitrification tank, then the bottom sediment enters a sedimentation separator for separation, and partially separated calcium salts and effluent from the short-range denitrification tank overflow into an autotrophic denitrification tank and are finally discharged.

[0009] Preferably, activated sludge is added into the short-cut denitrification tank.

[0010] Preferably, the electron donor comprises sodium acetate, methanol, trivalent iron ions or divalent sulfide ions.

[0011] Preferably, the autotrophic denitrification tank contains anammox bacteria, which can convert nitrite produced in the short-range denitrification process and ammonia nitrogen in the water body into nitrogen gas.

[0012] Preferably, the added amount of the anammox bacteria is 0.1 g VSS / L.

[0013] Preferably, the pH in the short-cut denitrification tank is greater than 8.

[0014] Preferably, the COD of the membrane concentrate is in the range of 200-50000 mg / L, the concentrations of ammonia nitrogen and nitrate nitrogen are in the range of 100-5000 mg / L, and the conductivity is greater than 2000 S / m.

[0015] The beneficial effects of the present invention are:

[0016] (1) When the BOD5 / N ratio of the membrane concentrate is less than 1, a removal efficiency of more than 95% of the total nitrogen in the concentrate can be achieved with almost no addition of a carbon source.

[0017] (2) The anammox bacteria attached to the surface of the calcium scale utilize the calcium, carbonate and other components in the calcium scale and quickly aggregate by secreting extracellular polymers, thereby improving the system's removal efficiency for different types of nitrogen pollutants.

[0018] (3) This method uses simple equipment, has low economic cost, and simple reaction control. By controlling the progress of short-range denitrification, the production and separation of specific precipitates can be achieved, and specific autotrophic microorganisms such as anammox can be enriched to aggregate, thereby achieving low-carbon removal of nitrogen pollutants, reducing the dependence of the biochemical process on carbon sources and achieving efficient treatment of nitrogen pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A process flow sheet was designed for the biological denitrification of a low-carbon membrane concentrate.

[0020] Figure 2 This is the purification process flow of traditional membrane concentrate. DETAILED DESCRIPTION

[0021] The technical solution of this patent is further described in detail below in conjunction with the specific implementation methods. It should be pointed out that the following specific implementation methods are detailed descriptions of the preferred implementation methods of this patent, but this patent is not limited to the above implementation methods. Various changes can be made within the scope of knowledge possessed by ordinary technicians in this field without departing from the technical scope of this patent.

[0022] In the embodiments of the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0023] It should be noted that the activated sludge is the activated sludge taken from the biochemical section of the landfill leachate; the anammox bacteria are bacteria cultured in the laboratory for a long time, and the cultured sludge inoculation amount is 0.3g MLSS / L.

[0024] like Figure 1As shown, the present invention discloses a biological denitrification method for low-carbon membrane concentrated liquid. The core part of the method consists of three parts: a short-range denitrification tank, a sedimentation separation tank, and an autotrophic denitrification tank. The short-range denitrification tank can discharge the sediment to the sedimentation separation tank, and the sedimentation separation tank separates the calcium scale from the sediment and returns it to the autotrophic denitrification tank. At the same time, the effluent of the short-range denitrification tank enters the autotrophic denitrification tank, and part of the coagulant can be added at the effluent to separate part of the newly generated precipitate from the effluent of the short-range denitrification tank, thereby improving the denitrification effect of the subsequent autotrophic denitrification tank to a certain extent.

[0025] By regulating the flow paths of the membrane concentrate to be treated and the precipitate, adding electron donors, and directional cultivation of bacterial flora, the treatment capacity of the biochemical treatment membrane concentrate is improved, and low-carbon and high-efficiency denitrification is achieved. The method of the present invention is described in detail below. Specifically, it comprises the following steps:

[0026] Step 1: The membrane concentrate to be treated is pumped into the short-range denitrification tank through a sewage pump. The sewage after biochemical treatment is discharged through overflow or secondary pumping into the autotrophic denitrification tank. All the sediments produced enter the sedimentation separation tank from the bottom of the tank. The COD range of the membrane concentrate is 200-50000 mg / L, the concentration of ammonia nitrogen and nitrate nitrogen is 100-5000 mg / L, and the conductivity is greater than 2000 S / m;

[0027] Among them, the short-range denitrification tank contains activated sludge.

[0028] Step 2: Depending on the water quality in the short-range denitrification tank, an electron donor is added to the short-range denitrification tank. The electron donor includes sodium acetate, methanol, trivalent iron ions or divalent sulfide ions.

[0029] Step 3: Control the short-range denitrification in the short-range denitrification tank by adjusting the pH and electron donor in the short-range denitrification tank, so that the nitrate in the water is reduced to nitrite. At the same time, the short-range denitrification is regulated to make the pH in the reaction tank greater than 8, and the generated precipitate is discharged into the sedimentation reaction tank in time. The calcium scale in the precipitate is separated by the sedimentation tank and returned to the autotrophic denitrification tank.

[0030] Step 4: Use calcium scale as the core to promote the aggregation of autotrophic denitrifying microorganisms, mainly anammox, to improve their autotrophic denitrification performance.

[0031] It should be noted that the short-range denitrification tank, sedimentation separation tank, and autotrophic denitrification tank are all closed.

[0032] It should be noted that the anammox autotrophic biological denitrification process is achieved by introducing appropriate autotrophic microorganisms into the membrane concentrate. Due to the presence of calcium scale, they can adhere well to the surface of the calcium scale, utilize the calcium, carbonate and other components in the calcium scale, and quickly aggregate by secreting extracellular polymers, thereby improving the system's removal effect on different types of nitrogen pollutants. Example

[0033] Step S1: Building a biological denitrification system

[0034] According to the biological denitrification method of low-carbon membrane concentrated liquid described in the present application, an inlet pipe, a short-range denitrification tank, a sedimentation separation tank, an autotrophic denitrification tank, an outlet pipe (such as Figure 1 ).

[0035] Step S2: Prepare membrane concentrate

[0036] Water quality of membrane concentrate A produced by nanofiltration membrane:

[0037] index COD (mg / L) <![CDATA[NH4-N(mg / L)]]> TN (mg / L) Conductivity (ms / cm) Numeric 4375 10 175 57

[0038] Water quality of membrane concentrate B produced by reverse osmosis membrane:

[0039] index COD (mg / L) NH4-N (mg / L) TN (mg / L) Conductivity (ms / cm) Numeric 267 22 764 55

[0040] Step S3: Biological denitrification

[0041] After the equipment is running stably, activated sludge with an MLSS concentration of 5000 mg / L is inoculated in the short-cut denitrification tank, and the membrane concentrate A in step S2 is set as experimental group A; the membrane concentrate B in step S2 is set as experimental group B; the membrane concentrates of experimental group A and experimental group B are pumped into the short-cut denitrification tank through the water inlet respectively, and the denitrification reaction is carried out for 10 hours. Depending on the water quality in the denitrification tank, electron donor sodium acetate is added in batches to make the pH in the denitrification tank greater than 8, and nitrate is reduced to nitrite.

[0042] The generated sediment is discharged into the sedimentation reaction tank in time, and the calcium scale in the sediment is separated through the sedimentation tank and returned to the autotrophic denitrification tank.

[0043] The autotrophic denitrification tank was opened and anammox bacteria cultured in the laboratory for a long time were added at a dosage of 0.1 g VSS / L.

[0044] After the equipment is turned on, the supernatant discharged from the outlet of the autotrophic denitrification tank is filtered through a 0.45-micron filter membrane every day for COD and three nitrogen determinations. Example

[0045] The biological denitrification system in step S1 of Example 1 was replaced with a traditional biochemical pool (a reaction pool that does not provide calcium scale reflux, does not control short-range denitrification, and cannot independently enrich the autotrophic denitrifying bacteria). The membrane concentrate A in step S2 of Example 1 was set as the control group A; the membrane concentrate B in step S2 was set as the control group B (such as Figure 2 );

[0046] The membrane concentrates of control group A and control group B were respectively passed into the traditional biochemical pool for reaction without adding any substances, and the water quality at the outlet was measured.

[0047] Operation effect:

[0048] With the continuous supply of electron donors, the total nitrogen concentration of the effluent of experimental group A and experimental group B began to decrease, and the total nitrogen removal rate of experimental group A reached more than 95%, which was significantly higher than the 50% of control group A. The total nitrogen removal rate of experimental group B reached more than 80%, which was significantly higher than the 7% of control group B. This situation shows that the design of this process significantly improves the removal capacity of total nitrogen in membrane concentrate. As the treatment process progresses, the difference between experimental group A and control group A, which are fed with nanofiltration concentrate, has no significant change, and remains at 97% and 49% respectively, but the denitrification efficiency of experimental group B and control group B, which are fed with reverse osmosis membrane concentrate, has changed significantly. Due to the low COD of the influent, the total nitrogen of the effluent of control group B is generally maintained at more than 700 mg / L, and the removal rate is very low, while the total nitrogen of the effluent of experimental group B has been declining.

[0049] The results of 16S rRNA analysis showed that a large number of autotrophic and heterotrophic denitrifying bacteria were detected in the short-range denitrification tanks of experimental groups A and B. Combined with the operating efficiency, this technical solution effectively achieved the short-range denitrification process. A large number of anammox bacteria were detected in the autotrophic denitrification tank, and the relative abundance reached more than 20%, indicating that the separated and recirculated calcium scale played a role in stabilizing the establishment of the anammox bacterial community. In addition, a large amount of calcium scale and other forms of sediment were gathered in the bottom sedimentation tank and successfully returned to the autotrophic denitrification tank. X-ray photoelectron spectroscopy (XPS) analysis showed that the solid matter (non-microorganisms) in the autotrophic denitrification tank was mainly Ca, CO3 2- , achieving the technological purpose.

[0050] The technical solution adopted by the present invention completes the short-range denitrification process with only a small amount of electron donors, produces more nitrite, and the simultaneous process of nitrate dissimilatory reduction to ammonium (DNRA) also produces a small amount of ammonia nitrogen, so that the nitrogen pollutants in the sewage are converted into nitrite and ammonia nitrogen and enter the autotrophic denitrification tank, and a large amount of inorganic salts are converted into usable calcium scale through indirect regulation of the process. The calcium scale returned to the autotrophic denitrification tank constructs a stable anammox biological flora, realizing efficient treatment of ammonia nitrogen and nitrite nitrogen under zero carbon investment, and realizing efficient denitrification when the influent BOD5 / N ratio is less than 0.3, and the final total nitrogen removal rate reaches more than 95%, even 98%, and can be maintained stably for a long time. Obviously, the experimental group can obtain better nitrogen removal efficiency. The above content shows that the present invention realizes the low-carbon autotrophic nitrogen removal of membrane concentrate by reasonable process design, reaction pool layout and reaction pool structure design. Compared with the general process, the process has a huge treatment gain effect on the reverse osmosis membrane concentrate, wherein the addition of electron donors and pH regulation realize the stable operation of short-range denitrification, saving energy consumption; at the same time, it is confirmed by experiments that calcium scale can be effectively separated, and a stable anammox bacterial community is established based on this calcium scale, realizing low-carbon and efficient removal of nitrogen pollutants, and the reaction control is simple, without more precise control of the numerical values ​​of various indicators. In addition, the process involved in the present invention is simple, which is convenient for promotion and application in the field of sewage treatment.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A biological denitrification method for low-carbon membrane concentrated liquid, characterized in that: The membrane concentrate to be treated is pumped into the short-cut denitrification tank by a pump, and an electron donor is introduced into the short-cut denitrification tank. Then, the bottom sediment enters the sedimentation tank for separation, and the calcium scale in the sediment is separated by the sedimentation tank and returned to the autotrophic denitrification tank. The effluent of the short-cut denitrification tank overflows into the autotrophic denitrification tank and is finally discharged; The COD of the membrane concentrate is in the range of 200-50000 mg / L, the concentration of ammonia nitrogen and nitrate nitrogen is 100-5000 mg / L, and the conductivity is greater than 2000 S / m; The electron donor is sodium acetate; The activated sludge with an MLSS concentration of 5000 mg / L is added to the short-cut denitrification tank; The pH in the short-range denitrification tank is controlled to be greater than 8, and the reaction time in the short-range denitrification tank is controlled to be 10 hours; 0.1 g VSS / L of anammox bacteria is added to the autotrophic denitrification pool, and the anammox bacteria can convert nitrite produced in the short-range denitrification process and ammonia nitrogen in the water into nitrogen gas; The membrane concentrated liquid includes a membrane concentrated liquid produced by a nanofiltration membrane or a membrane concentrated liquid produced by a reverse osmosis membrane, and the BOD5 / N of the membrane concentrated liquid is less than 1.

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