KR20100083223A - Method for high class treatment of wastewater using gas permeable membrane-attached biofilm - Google Patents

Abstract

PURPOSE: A wastewater processing method using a gas permeable membrane is provided to improve efficiency of a wastewater processing process and to reduce costs for supplying gas regardless of organic materials in wastewater. CONSTITUTION: A wastewater processing method using a gas permeable membrane includes the following steps: removing and decomposing organic compounds or nitrogen compounds with a biofilm while maintaining an aerobic condition; removing the organic compounds or the nitrogen compounds while maintaining an anaerobic condition; and successively performing above processes. A gas-permeable membrane is used in each process.

Description

Method for high class treatment of wastewater using gas permeable membrane-attached biofilm}

The present invention relates to a method for advanced treatment of wastewater using a gas permeable membrane with a biofilm.

As an advanced treatment process to remove nitrogen and organics in wastewater, there have been recent attempts to use membrane-attached biofilm reactors (MABR). However, when the most common heterotrophic microorganisms are used in the denitrification process, the proper concentration of organic matter necessary for denitrification serves as an important limiting factor. Groundwater or some plant wastewaters with very low concentrations of organic matter require the addition of an external carbon source for nitrogen removal, which can result in increased treatment costs and the generation of secondary pollutants by residual organic matter.

In addition, the conventional method for removing nitrogen and organics using MABR is limited to an independent single process for nitrification or denitrification and organic pollutant removal, and there are few research cases of continuous operation for a long time by combining these independent processes. In addition, there are reports of autotrophic denitrification, such as sulphation, but studies on the removal of nitrate nitrogen using hydrogen and the advanced wastewater treatment process using MABR are insufficient.

The present invention is to provide an advanced wastewater treatment process for removing total nitrogen and organic contaminants in the wastewater by using the MABR process combined with the nitrification process and the denitrification process using hydrogen.

The present invention comprises the steps of decomposing and removing organic matter or nitrogen compounds by the biofilm attached to the outer wall of the gas-permeable membrane while maintaining aerobic conditions by supplying air or oxygen into the gas-permeable membrane; And a method of treating wastewater in a sequential or reverse order by decomposing and removing organic matter or nitrogen oxides by a biofilm attached to the outer wall of the gas-permeable membrane while supplying hydrogen into the gas-permeable membrane to maintain anaerobic conditions. to provide.

According to one embodiment of the present invention, the nitrogen compound present in the waste water can be stably decomposed and treated regardless of the presence or absence of organic matter, and as a carrier capable of attaching and growing nitrifying and denitrifying microorganisms, By treating the wastewater using a gas-permeable membrane which simultaneously functions as a supply device for effectively supplying oxygen and an electron donor, it is possible to reduce the gas supply cost and improve the efficiency of the wastewater treatment process.

One embodiment of the present invention is a biofilm which is a Membrane-Attached Biofilm Reactor (MABR) that directly supplies a gas-like electron acceptor and an electron donor such as oxygen or hydrogen to a biofilm formed on the surface of the membrane through an air gap of the gas permeable membrane. It is a construction method. Inorganic predation biofilm process provides oxygen directly for biodegradation or nitrification directly to biofilm, and theoretically 100% oxygen utilization efficiency can be achieved. In particular, in the high-efficiency treatment system using pure oxygen, stable nitrification can be maintained regardless of the concentration of organic matter, and ammonia nitrogen can be removed using MABR.

Hydrogen supply by MABR method has the advantage of supplying as much hydrogen as needed directly to the biofilm and minimizing the discharge to the atmosphere. In addition, when the hollow fiber membrane is used as the gas-permeable membrane in the MABR method, the effective surface area to which the biofilm is attached can be maintained significantly larger than other media, so that a highly efficient nitrogen removal system can be constructed.

One embodiment of the present invention is the aerobic aerobic bioreaction of the organic pollutants and nitrogen occurs by attaching and growing a biofilm for removing nitrogen and organic contaminants on the outer wall of the gas permeable membrane, aerobic bioreaction using oxygen as an electron acceptor The process of using the gas permeable membrane with a biofilm, and the process using the gas permeable membrane with the anaerobic biofilm which generate | occur | produces nitrate nitrogen by the anaerobic bioreaction using the electron donor, such as hydrogen and methanol, can be used.

Hereinafter, the present invention will be described in more detail.

The mechanism of nitrogen removal in the biological process is that NH ₄ ⁺ -N is oxidized to NO ₂ ^-- N and NO ₃ ^-- N by nitrifying microorganisms under aerobic conditions and then reduced to N ₂ gas by denitrifying microorganisms under anoxic conditions. In order. Denitrogen microorganisms are random microorganisms that use NO ₂ ^-- N and NO ₃ ^-- N as electron acceptors when oxygen is limited, and heterotrophic microorganisms using organics as electron donors and independent nutrient microorganisms using inorganic as electron donors. . In the denitrification process by heterotrophic microorganisms, the ratio between organic matter and nitrogen in the wastewater is an important limiting factor, and in case of lack of organic matter, an external carbon source should be added. The external carbon source mainly uses methanol, which is problematic in terms of cost and possibility of secondary pollution due to the addition of organic substances. Therefore, the use of an inorganic electron donor has become an alternative, and sulfur, iron, hydrogen, etc. can be used as an electron donor. Among them, hydrogen (H ₂ ) has the advantage that the cost per electron equivalent is cheaper than organic matter, less microbial production than heterotrophic microorganisms, and does not generate secondary pollutants. However, due to the low solubility of H ₂ and the risk of explosion, there is a need for research on how to effectively supply H ₂ to microorganisms. Autotrophic denitrification (independent denitrification) using H ₂ has been used in fixed bed and fluidized bed systems. In general, the method of supplying hydrogen was based on gaseous acid, but gas sparging tends to maintain hydrogen above the required concentration, thus dissipating electron donors, releasing explosive gas into the atmosphere, and denitrification intermediates NO and N ₂ O. Promotes degassing

Inorganic cell membrane delivery method using a gas-permeable carrier to overcome these problems prevents the above disadvantages in advance. Hydrogen flux is generally kept as low as lkg / 1,000 m ² · d in COD, with a low NO ₃ ⁻ -N concentration. If the goal is complete NO ₃ ^-- N removal, the flux can be kept high.

Hollow fiber Membrane Biofilm Reactor (HfMBR) forms a biofilm on the outer surface of the hollow fiber-type separator, and passes gas that can be used as an electron acceptor (eg O ₂ , Air) or an electron donor (eg H ₂ ). It supplies through the biofilm formed on the outer surface. Such gas supply characteristics enable efficient supply of electron acceptors and electron donors in various gas forms depending on the material to be removed, and can be configured as a high rate treatment system.

In an embodiment of the present invention, the air and hydrogen required for the aerobic / anaerobic removal reaction of the microorganisms are supplied through the hollow fiber membrane pipe, and the useful microorganisms are formed in the biofilm on the outer wall of the hollow fiber membrane. The purpose of the present invention is to effectively remove ammonia nitrogen and chlorine compounds using the forming process, and in particular, to provide a method for advanced treatment of wastewater through nitrogen removal in wastewater.

In an embodiment of the present invention, as shown in Figure 1 is composed of an aerobic reactor to perform the nitrification and organic contaminant decomposition process and the anaerobic process to perform the denitrification process. Each process obtained a module filled with a hollow fiber membrane or a flat membrane was used as a reaction tank. Since the raw water introduced into the module was difficult to have sufficient contact with the biofilm in the reaction tank, a circulation pump was installed in each reactor to maintain sufficient contact time for the reaction time. The nitrification tank maintained the aerobic state by supplying a gas mixed with oxygen and air into the membrane, and the denitrification reactor supplied hydrogen into the membrane. The gas supplied to the nitrification tank was oxygen at the beginning of operation, but the DO concentration in the reaction tank was excessively increased and mixed with air to control the DO concentration. After installing a pressure gauge in the lower part of each reactor, the amount of gas supplied to the membrane of each reactor was adjusted using the gas valve. The pressure gauge was used here as a device for measuring the amount of gas supplied into the membrane. NaHCO ₃ and phosphate buffer (K ₂ HPO ₄ + KH ₂ PO) were added to adjust the pH change by nitrification and denitrification in the reactor. NaHCO ₃ was simultaneously used as an inorganic carbon source for autotrophic microorganisms. As trace elements required for the growth of microorganisms, Mg, Ca, Mn, Co, K, Fe, EDTA and the like were added to the influent.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1

Figure 2 shows the NH ₄ -N concentration and NO ₃ -N concentration change in the aerobic reactor (R1) according to the operating time. The inflow NH ₄ -N concentration of 100 during the operation period mgN / L in temporarily for the period was increased to 150 mgN / L was increased the concentration of NH ₄ -N in the effluent, in the overall inflow NH ₄ -N concentration in the 50 The NH ₄ -N concentration in the effluent was maintained below 3 mgN / L even though it increased up to 150 mgN / L, and the nitrification rate was more than 99% and stable nitrification was maintained. During this period NO ₂ -N was not detected in the effluent and all NH ₄ -N contained in the influent was found to be fully oxidized to NO ₃ -N. This indicates that the biofilm is effectively formed on the membrane surface of the aerobic reactor, and thus the membrane can serve as a media for biofilm formation and at the same time, a smooth oxygen supply for nitrification.

In addition, as can be seen in Figure 2, the NO ₃ -N concentration of the effluent appeared lower than the concentration of NH ₄ -N of the influent. This indicates that the NO ₃ -N produced by the oxidation of NH ₄ -N was removed by the denitrification reaction because the DO concentration in the aerobic reactor was maintained in the range of 0.5-2.5 mgO ₂ / L. In this way, since the inner part of the biofilm that is in contact with the membrane is directly supplied with oxygen, the oxygen-rich aerobic state can be maintained regardless of the DO concentration of the bulk liquid, but the outer surface of the biofilm is kept at a low DO concentration. In this case, denitrification reaction may occur.

Example 2

Figure 3 shows the result of the nitrogen is removed by the denitrification reaction by autotrophic microorganism in the anaerobic reactor. The NO ₃ -N concentration of the influent increased from 30 mgN / L to 150 mgN / L in stages, and the hydraulic retention time (HRT) of the reactor remained the same for 6 hours. As shown in FIG. 3, the increase in NO ₃ -N concentration of the influent during most of the operation period except for the initial operation period of about 60 days at the beginning of operation and the increase of the NO ₃ -N concentration of the influent to 150 mgN / L. Regardless, stable autotrophic denitrification was performed.

NO ₂ -N was temporarily accumulated as the inflow load rate of NO ₃ -N increased from 117 days to 132 days, and the phosphate buffer was not included in the influent from 0 days to 60 days. The increase in pH due to OH ⁻ generated in the nitrogen reaction was considered to inhibit the denitrification reaction. At this time, the pH of the effluent increased to 8.3 and the denitrification rate by autotrophic microorganisms was 66% on average. However, after the addition of phosphate buffer in the influent, NO ₃ -N concentration in the effluent gradually decreased, and the nitrogen removal rate was over 99% while maintaining the autotrophic denitrification reaction using hydrogen as an electron donor.

Example 3

Figure 4 is the NO ₃ -N concentration in the effluent according to the change in the hydrogen to be independent to evaluate the efficiency of NOx removal nutritional changes in the NO ₃ -N concentration in the influent water 30 mgN / L, 50 mgN / L when pH of the pH changes It is shown. As shown in the figure, the denitrification was stable when the pH of the effluent was below 7.6, but the denitrification was inhibited when the pH was above 7.8. However, in the case of continuous experiments, the denitrification reaction was found to be stable even if the pH of the effluent was maintained between 7.7-8.2. In autotrophic denitrification using hydrogen, 2 moles of OH ^- are produced as 2 moles of NO ₃ -N are removed. Therefore, in autotrophic denitrification using hydrogen, it was found that a pH buffer system is necessary to prevent the increase of pH and the inhibition of denitrification.

<Example 4>

By combining aerobic and anaerobic reactors operated separately, the nitrogen removal efficiency according to NH ₄ -N loading rate in the hybrid Hf-MBfR system was investigated. Figure 5 shows the NH ₄ -N concentration change and the NH ₄ -N influent load rate of the influent and effluent in the aerobic reactor. NH4-N removal rate remained stable during the operation period except during the initial operation period. The NH ₄ -N removal rate was over 98% and the effluent's NH ₄ -N concentration ranged from 0-6 mgN / L. The average specific removal rate of NH ₄ -N in aerobic reactors was 0.49, 0.68, 1.33 gN / m ² · d, and the maximum removal rate per membrane surface area was 1.43 gN / m ² · d.

Figure 6 is the result of the denitrification reaction by autotrophic microorganism in the anaerobic reactor. From the start of operation to 6 days, NO ₂ -N was temporarily accumulated and increased to 47 mgN / L, but thereafter, a stable and effective denitrification reaction was maintained. As shown in FIG. 6, the average denitrification rate was 98% or more during the entire operation period, and the concentration of NO ₂ -N in the effluent was 0-2 mgN / L, NO except for the initial operation period in which NO ₂ -N was accumulated. _{The 3} -N concentration was found to be 0-7 mgN / L. The average denitrification rate in the anaerobic reactor was 0.48, 0.66, 1.30 gN / m ² · d and the maximum denitrification rate per membrane surface area was 1.43 gN / m ² · d.

The total nitrogen removal rate in this treatment system showed more than 98% removal rate in each operation stage, and the maximum removal rate per reactor volume was 1.20 kgN / m ³ · d.

1 is a schematic diagram of an advanced wastewater treatment process using a gas permeable membrane with a biofilm according to an embodiment of the present invention.

Figure 2 shows the NH ₄ -N and NO ₃ -N concentration change in the aerobic reactor according to the operating time.

Figure 3 shows the change in NO ₃ -N and NO ₂ -N concentration in the anaerobic reactor according to the operating time.

Figure 4 shows the change in NO ₃ -N concentration according to the pH change of the effluent in the anaerobic reactor.

Figure 5 shows the NH ₄ -N concentration change in the aerobic reactor in the hybrid process.

Figure 6 shows the change of NO ₂ -N and NO ₃ -N concentration in the anaerobic reactor in the hybrid process.

Claims (6)

Supplying air or oxygen into the gas-permeable membrane to decompose and remove organic substances or nitrogen compounds by the biofilm attached to the outer wall of the gas-permeable membrane while maintaining aerobic conditions; And A method of treating wastewater in which the organic material or nitrogen oxides are decomposed and removed by a biofilm attached to the outer wall of the gas permeable membrane while supplying hydrogen into the gas permeable membrane to maintain anaerobic conditions. The method according to claim 1, wherein the gas permeable membrane used in each process is operated in the form of a tubular membrane module or in the form of a gas permeable membrane immersed in an aeration tank. The method of claim 1, wherein the aerobic or anaerobic process is operated in series or in parallel and connected form. The method of claim 1, wherein the aerobic and anaerobic water treatment reactions are simultaneously performed by adjusting the supply pressure of air or oxygen supplied into the gas-permeable membrane for the aerobic process. The method of claim 1, wherein the aerobic and anaerobic water treatment reactions are simultaneously performed by adjusting the content and supply pressure of hydrogen supplied into the gas-permeable membrane for anaerobic fixation. The method according to claim 4 or 5, wherein the processes in which both aerobic and anaerobic water treatment are performed simultaneously are linked in series or in parallel.

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