WO2012046972A2

WO2012046972A2 - Treatment system for high-concentration wastewater

Info

Publication number: WO2012046972A2
Application number: PCT/KR2011/007097
Authority: WO
Inventors: Joong Chun Kwon; Eung Taek Lee
Original assignee: Ecodigm Co., Ltd.
Priority date: 2010-10-07
Filing date: 2011-09-27
Publication date: 2012-04-12
Also published as: KR101240541B1; WO2012046972A3; KR20120036147A

Abstract

Disclosed therein is a treatment system for high-concentration wastewater, which can treat high concentration organic matters and wastewater containing a great deal of nitrogen, reduce consumption of energy enhance stability of sludge, and reduce toxicity of high-concentration wastewater.

Description

TREATMENT SYSTEM FOR HIGH-CONCENTRATION WASTEWATER

The present invention relates to a treatment system for high-concentration wastewater, and more particularly, to a treatment system for high-concentration wastewater, which can treat high-concentration organic matters, such as food waste leachate, and livestock wastewater, and wastewater containing a great deal of nitrogen.

Particularly, the present invention relates to a high-concentration wastewater treatment system, which can generate methane gas, reduce consumption of energy, enhance stability of sludge, and reduce toxicity of high-concentration wastewater.

In general, wastewater, such as food waste leachate, livestock wastewater, and so on, has a high BOD (Biochemical Oxygen Demand) ranging from 20,000mg/l to 100,000mg/l and easily degraded but has a low total nitrogen (TN) concentration ranging from 1,000mg/l to 5,000mg/l.

Accordingly, in case that such wastewater, such as food waste leachate, livestock wastewater, and so on, are treated by the general aerobic activated sludge process, it spends lots of energy and deteriorates stability of microorganisms, and hence, it is preferable that such wastewater is treated by the anaerobic digestion process.

Such an anaerobic digestion process has a merit of obtaining methane gas during the wastewater treatment process, but requires additional organic matters and follow-up treatment processes due to the C/N ratio (Carbon-Nitrogen ratio) that is too low to apply it to a nitrogen removal process because the final effluent has the BOD ranging from 500mg/l to 2,000mg/l and the TN concentration ranging from 1,000mg/l to 3,500mg/l.

In other words, because the effluent discharged after the anaerobic digestion contains nitrogen more than organic matters, organic matters must be resupplied for denitrification for the want of the organic matters to biologically treat nitrogen, and hence, it takes a lot of treatment expenses and time.

Moreover, the activated sludge process has a problem in that, if the TN concentration is more than 150mg/l, it is difficult to carry out the process due to decrease of pH, bulking and deterioration in stability of sludge.

As shown in FIG. 1, the wastewater treatment system of the activated sludge process, one of representative biological processes to remove organic matters, includes a first settling tank 100, an aeration tank 200, and a final settling tank 300.

However, such a wastewater treatment system of the activated sludge process has a disadvantage in that it requires a sludge thickener for after-treatment of sludge because the sludge inside the final settling tank is within a range of 5,000mg/l to 12,000mg/l in concentration.

Furthermore, the wastewater treatment system of the activated sludge process has another disadvantage in that a wastewater treatment efficiency inside the final settling tank is decreased because the sludge concentration in the aeration tank is within a range of 1,500mg/l to 3,000mg/l. In addition, the quality of the effluent is deteriorated due to a sludge bulking occurring when the quality and flux of influent are changed

Accordingly, the present invention has been made in an effort to solve the above-mentioned problems occurring in the prior arts, and it is an object of the present invention to provide a treatment system for high-concentration wastewater, which can treat high-concentration organic matters, such as food waste leachate, and livestock wastewater, and wastewater containing a great deal of nitrogen.

Another object of the present invention is to provide a high-concentration wastewater treatment system, which can generate methane gas, reduce consumption of energy, enhance stability of sludge, and reduce toxicity of high-concentration wastewater.

To achieve the above objects, the present invention provides a high-concentration wastewater treatment system including: (A) a first upflow reactor, which performs an anaerobic digestion process while influent raw water containing organic matters of high concentration is introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part, methane gas is discharged to an upper part thereof, and just treating water is discharged to the top thereof; (B) a second upflow reactor, which performs a denitrification process while ① the influent raw water, ② effluent of the first upflow reactor, and ③ influent internally recycled from an aeration tank or a settling tank or mixture of the above are introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part and just treating water is discharged to the top thereof; (C) the aeration tank, in which the effluent of the second upflow reactor is aerated, and in which some of treating water is internally recycled to the second upflow reactor and the remaining treating water is discharged to the settling tank; and (D) the settling tank adapted to deposit and remove suspended solids remaining in the effluent of the aeration tank and to discharge the final treating water.

The BOD (Biochemical Oxygen Demand) is greatly reduced by the anaerobic digestion reaction in the first upflow reactor, nitrate nitrogen introduced by the internal reclcyle is denitrified in the second upflow reactor, and ammoniacal nitrogen is oxidized into nitrate nitrogen by oxygen and nitrate bacteria in the aeration tank. The produced nitrate nitrogen is returned to the second upflow reactor by the internal recycle and is treated.

According to characteristics of influent raw water or specifications or operation conditions of the wastewater treatment system, nitrogen exceeding the standard may still remain in the treating water passing through the aeration tank. For this case, the treatment system according to the present invention may include an additional denitrification device.

That is, between the aeration tank and the settling tank, (E) a third upflow reactor and (F) a second aeration tank may be additionally installed. The third upflow reactor, which performs re-denitrification process while the treating water discharged from the aeration tank is introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part and just the treating water is discharged to the top thereof; and a second aeration tank that is connected to a discharge part of the third upflow reactor and adapted to carry out nitrification of nitrogen and degradation of organic matters relative to the denitrified treating water.

Furthermore, it is preferable that the first, second and third upflow reactors respectively include: (a) a main shaft that is perpendicularly formed at the center of a reactor and is rotated by a driving means; (b) a stay part that is fixed around an upper portion or a lower portion of the main shaft in such a fashion as to be rotated together with the main shaft and passes the influent introduced through an inlet pipe; (c) at least one distribution pipe that is fixed at the main shaft in such a fashion as to be rotated together with the main shaft and has one end portion directly connected with the stay part and the other end portion located at the lower part of the reactor so that the influent passing through the stay part is discharged from the lower part thereof to the inside of the reactor; (d) a mixer having at least two mixing wings radially arranged on the main shaft; (e) a discharging device that is located at the upper part of the reactor and has a weir opened at the upper face so that the treating water separated from sludge is overflowed; and (f) a sludge collector for treating the sludge deposited by gravity, that is located at the lower part of the reactor.

Compared with the treatment system to which the conventional completely mixed type reactors, the treatment system according to the present invention can ① keep a multi-layer upflow flow, ② achieve ideal integration conditions of anaerobic/anoxic atmospheres, ③ condense sludge to the high concetration, ④ be efficient because it can reduce the stay time in the reactors, ⑤ treat high-concentration organic wastewater having various C/N ratios, and ⑥ widely control an internal recycle ratio (within a range of 0.5Q to 30Q), so that the treatment system can be operated resiliently.

In the upflow reactors, especially, in the first upflow reactor, a great deal of methane gases are generated during the treatment process. In order to prevent air pollution (bad smell) or to reduce green-house gases, it is necessary to use the gases as fuel gas or incinerate the gases after collecting and discharging them.

For this, it is preferable that the upflow reactors respectively further comprise: an airtight cover part disposed on the top of the reactor for preventing gases generated during the treatment process form being freely diffused to the outside air; and a gas discharging means for collecting and discharging the internally generated gases.

In this instance, the gas discharging means includes: a plurality of gas collectors, each of the gas collectors getting upward narrower in vertical section so that the lower portion is opened and the upper portion is closed and having an exhaust pipe connected thereto, and the gas collectors are different in size and alternatively arranged in at least two layers.

The high-concentration wastewater treatment system according to the present invention can purify and treat wastewater containing high-concentration organic matters and nitrogen through the process of treating wastewater containing high-concentration organic matters and nitrogen including the steps of preprocessing high-concentration influent introduced into the treatment system using the upflow reactor to generate methane gas, degrading the organic matters, mixing raw waster and the preprocessed water together, denitrating the mixture in the upflow reactor, and separating treating water from sludge.

In other words, the conventional treatment process to treat wastewater containing high-concentration organic matters and nitrogen is very complicated and requires a great deal of water to treat wastewater because treatment is carried out after wastewater to be treated is diluted with water to thereby reduce toxicity or concentration of the influent. However, the treatment system according to the present invention is simplified in the treatment process and reduces operation expenses because the preprocessed low-concentration wastewater is mixed with influent raw water to reduce concentration of organic matters without using dilution water.

Moreover, the treatment system according to the present invention can produce lots of methane gas during the preprocessing process.

FIG. 1 is a schematic diagram of a wastewater treatment system by an activated sludge process according to a prior art.

FIG. 2 is a block schematic diagram of a wastewater treatment system according to a preferred embodiment of the present invention.

FIG. 3 is a block schematic diagram of a wastewater treatment system according to another preferred embodiment of the present invention.

FIG. 4 is a sectional view showing an example of an upflow reactor of the wastewater treatment system according to the present invention.

FIG. 5 is a perspective view, in partial section, of the reactor of FIG. 4.

FIG. 6 is a sectional view showing another example of the upflow reactor of the wastewater treatment system according to the present invention.

FIG. 7 is a perspective view, in partial section, of an example of a gas collector of the upflow reactor.

Reference will be now made in detail to the example embodiments of the present invention with reference to the attached drawings. These example embodiments and the attached drawings are provided to enable those skilled in the art to easily understand the technical idea and scope of the present invention, and hence, the technical scope of the present invention is not limited to the example embodiments and the drawings. Furthermore, it should be understood that example embodiments of the invention are to cover all modifications, equivalents, and alternatives falling within the scope of the invention.

A treatment system for high-concentration wastewater according to the present invention is a system to treat wastewater containing a great deal of nitrogen and organic matters, such as food waste leachate, and can provide a better wastewater purification performance and obtain lots of methane gas.

As shown in FIG. 2, the treatment system for high-concentration wastewater according to the present invention includes: (A) a first upflow reactor 1, which performs an anaerobic digestion process while influent raw water (Q) containing organic matters of high concentration is introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part, methane gas is discharged to an upper part thereof, and just treating water is discharged to the top thereof; (B) a second upflow reactor 2, which performs a denitrification process while ① the influent raw water (Q), ② effluent of the

first upflow reactor

1, and ③ influent (Ca, Cs) internally recycled from an aeration tank 3 or a settling tank 4, which will be described later, or mixture (Ra) of the internally-recycled influents Ca and Cs are introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part and just treating water is discharged to the top thereof; (C) the aeration tank 3, in which the effluent of the second upflow reactor 2 is aerated, and in which some of the treating water is internally recycled to the second upflow reactor 2 and the remaining treating water is discharged to the settling tank; and (D) the settling tank 4 adapted to deposit and remove suspended solids (SS) remaining in the effluent of the aeration tank 3 and to discharge the final treating water.

The first upflow reactor 1 carries out complex functions of the first settling tank, the anaerobic tank and the sludge thickener of the conventional wastewater treatment system, wherein contaminants are removed and gas including methane gas is discharged out while the influent raw water (Q) containing the organic maters introduced into the inner lower part thereof flows upflow under an anaerobic (fermentation) atmosphere naturally created according to operation conditions.

A plurality of the first upflow reactors 1 as anaerobic digestion tank can be installed in order to produce more methane gases. That is, the first upflow reactor 1 consists of at least one pair of an acid fermenter and a methane fermenter to thereby increase an output of methane gases.

The treating water from which foreign matters are removed in the first upflow reactor 1 contains organic matters of lower concentration than the influent raw water (Q), and is repurified after being mixed with the influent raw water in the second upflow reactor 2. The treating water treated twice is nitrified nitrogen in the aeration tank 3 (which may have a biofilm carrier for promoting reaction), and then discharged to the settling tank 4 or recycled to the second upflow reactor 2 through an internal recycle line.

Of course, whether or not to recycle the treating water passing through the aeration tank 3 to the second upflow reactor 2 is determined by the concentration of organic matters or the TN concentration of the treating water discharged from the aeration tank 3. Namely, just when the concentration of organic matters or the TN concentration of the treating water exceeds the standard, some or all of the treating water is recycled to the second upflow reactor 2.

In the meantime, in order to perfectly mix the influent raw water (Q) and the internally-recycleed influent (Ca, Cs) or the mixture (Ra) introduced into the second upflow reactor 2, a mixer (not shown) having a stirrer may be installed at the front end of the second upflow reactor 2.

The wastewater treatment system having the above structure may include additional devices as shown in FIG. 3 in order to effectively remove organic matters and nitrogen.

That is, the wastewater treatment system according to the present invention may further include: a third upflow reactor 5, which performs re-denitrification process while the treating water discharged from the aeration tank 3 is introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part and just the treating water is discharged to the top thereof; and a second aeration tank 6 that is connected to a discharge part of the third upflow reactor 5 and adapted to carry out nitrification of nitrogen and degradation of organic matters relative to the denitrified treating water. In this instance, because the third upflow reactor 5 and the second aeration tank 6 are constructed and operated in the same way or in the nearly the same way as the first and

second upflow reactors

1 and 2 and the aeration tank 3, and hence, descriptions of the third upflow reactor 5 and the second aeration tank 6 will be omitted.

As shown in FIGs. 4 to 6, the first, second and

third upflow reactors

1, 2 and 5 respectively include: (a) a main shaft 12b that is perpendicularly formed at the center of a reactor 11 and is rotated by a driving means 12a; (b) a stay part 12 that is fixed around an upper portion or a lower portion of the main shaft in such a fashion as to be rotated together with the main shaft 12b and that passes the influent introduced through an inlet pipe 11a; (c) at least one distribution pipe 13 that is fixed at the main shaft in such a fashion as to be rotated together with the main shaft 12b and has an end portion directly connected with the stay part 12 and the other end portion located at the lower part of the reactor so that the influent passing through the stay part is discharged from the lower part thereof to the inside of the reactor; (d) a mixer 15 having at least two mixing wings 15a radially arranged on the main shaft; (e) a discharging device 14 that is located at the upper part of the reactor and has a weir 141 opened at the upper face so that the treating water separated from sludge is overflowed; and (f) a sludge collector that is located at the lower part of the reactor for treating the sludge deposited by gravity.

In the drawings, the stay part 12 is mounted at the upper portion of the main shaft 12b, but may be mounted at the lower portion of the main shaft 12b in order to discharge the influent from the inner face of the lower part of the reactor 11 to the inside of the reactor.

Such upflow reactors are operated as follows.

The influent raw water introduced through the inlet pipe 11a is stayed and mixed inside the stay part 12 for a while, and then, supplied to the lower part of the reactor 11 through the distribution pipe 13 connected to the bottom of the stay part 13. As shown in FIGs. 4 and 6, the distribution pipe 13 has an upper end connected to the bottom of the stay part 12 and a lower end extending horizontally. The distribution pipe 13 includes a plurality of drainage holes formed on the horizontally extending portion thereof, so that the influent can be evenly supplied to the lower part of the reactor 11 through the drainage holes.

Not shown in the drawings, but the upflow reactors may have a structure that the stay part 12 is mounted at the lower portion of the main shaft, the inlet pipe 11a is communicated with the stay part 12, the lower end of the distribution pipe 13 is connected with the stay part 12 and the upper end extends horizontally, and a plurality of the drainage holes are formed on the horizontally extending portion, so that the influent can be evenly supplied to the lower part of the reactor through the drainage holes.

It is preferable that the stay part 12 and the distribution pipe 13 are fixed at the main shaft 12b in such a fashion that they are rotated together with the main shaft 12b rotating by driving of a motor.

In the drawings, as an example, there are two distribution pipes 13, but distribution pipes 13 of more than two may be mounted at the main shaft 12b, and it is preferable that the distribution pipes 13 are mounted in proportion to an area of the main shaft 12b so that the center of gravity is placed on the main shaft 12b and the main shaft 12b can be rotated smoothly.

As a means for evenly mixing the influent and the treating water introduced into the reactor through the distribution pipes 13, the mixer 15 may be installed. The mixer 15 is a means of stirring and mixing the influent raw water or the mixture of influent raw water and internally-recycled treating water introduced into the upflow reactor, and has at least two mixing wings 15a radially disposed on the main shaft 12b. Accordingly, the mixer 15 is rotated by driving of the motor 12a to stir and mix the influent or the mixture of influent and treating water introduced into the reactor 11.

The discharging device 14 serves as a passage for discharging the purified treating water inside the reactor 11 to the outside of the reactor 11. As shown in the drawings, the discharging device 14 includes the weir 141 opened at the top thereof, and the weir 141 has a passageway 141a formed at the upper face of the weir 141.

In the discharging device 14 having the above structure, the treating water inside the reactor is overflowed along the side wall of the weir 141 and introduced into the passageway 141a, and the treating water introduced into the weir 141 is discharged to the outside of the reactor 11 through the discharge pipe 11b.

Gases are generated while the influent flows upflow and reacts inside the upflow reactor having the above structure, and hence, a gas discharging means 16 may be additionally mounted to discharge the gases to the outside.

The gas discharging means 16 may be a gas discharge pipe 161 mounted on an airtight cover part 111 of the top of the reactor 11 as shown in FIGs. 4 and 5, or may be gas collectors mounted inside the reactor 11 as shown in FIG. 6.

As shown in FIGs. 6 and 7, the gas collectors 162 are formed in a ring shape and are arranged in such a way as to form collection spaces 162a getting upward narrower in section, and an exhaust pipe is connected thereto.

As shown in FIGs. 6 and 7, the plural gas collectors 162 of different sizes are arranged on the same level in at least two layers in such a fashion that there are spaces between the lower layered gas collectors 162 and the upper layered gas collectors 162. Moreover, the lower layered gas collectors 162 are located between the upper layered gas collectors 162 to cover the entire face when it is viewed from the top, so that gases generated from the treated sludge and wastewater can be introduced into the collection spaces 162a of the gas collectors 162 and discharged out. In other words, the upper layered gas collectors 162 and the lower layered gas collectors 162 are alternatively arranged in such a fashion that gases generated from the lower part of the reactor are collected to the gas collectors 162 mounted on one of the two layers, so that all of the generated gases can be collected.

As described above, the wastewater treatment system constructed by the plural upflow reactors connected with each other can reduce the concentration of organic matters by recycling the treating water and mixing it with influent raw water to thereby treat wastewater without using dilution water. Furthermore, the upflow reactors and the aeration tanks are mounted in multiple stages to treat sludge and wastewater in multiple stages, so that further purified treating water can be discharged out.

Moreover, during the anaerobic digestion process carried out inside the upflow reactors, the wastewater treatment system according to the present invention can produce a lot of methane gases and collect the methane gases using the gas discharging means.

Embodiment: Wastewater treatment using the high-concentration wastewater treatment system according to the present invention

1.Capacity of Reactors

2. Operation Conditions

Flux:45㎥/day 2) Operation temperature: 35?

Internal recycle ratio: 1,700%

Sludge recycle ratio: 300%

Compared example: Wastewater treatment using a wastewater treatment system using the anaerobic digestion process

As a result of treating wastewater under the conditions of the embodiment and the compared example, the results indicated in the following table were obtained based on water flux of 45㎥/d.

As indicated above, the yield of methane gases obtained while treating wastewater using the wastewater treatment system according to the present invention was less than that of the conventional wastewater treatment system using the anaerobic digestion process, but the wastewater treatment system according to the present invention remarkably reduced amounts of solids, nitrogen and phosphorus contained in treating water.

In other words, the wastewater treatment system according to the present invention obtained methane gases less than about 20% of the conventional wastewater treatment system using the anaerobic digestion process, but could purify wastewater much cleaner.

Claims

A treatment system for high-concentration wastewater comprising:

(A) a first upflow reactor, which performs an anaerobic digestion process while influent raw water containing organic matters of high concentration is introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part, methane gas is discharged to an upper part thereof, and just treating water is discharged to the top thereof;

(B) a second upflow reactor, which performs a denitrification process while ① the influent raw water, ② effluent of the first upflow reactor, and ③ influent internally recycled from an aeration tank(Ca) or a settling tank(Cs), or mixture of the internally-recycled influents Ca and Cs are introduced into a lower part thereof and flows upflow, and in which produced sludge is deposited at the lower part and just treating water is discharged to the top thereof;

③ influent (Ca, Cs) internally recycled from an aeration tank 3 or a settling tank 4, which will be described later, or mixture (Ra) of the internally-recycled influents Ca and Cs are introduced into a lower part thereof and flows upflow,

(C) the aeration tank, in which the effluent of the second upflow reactor is aerated, and in which some of treating water is internally recycled to the second upflow reactor and the remaining treating water is discharged to the settling tank; and

(D) the settling tank adapted to deposit and remove suspended solids remaining in the effluent of the aeration tank and to discharge the final treating water.
The treatment system according to claim 1, between the aeration tank and the settling tank, further comprising:

(E) a third upflow reactor, which performs re- denitrification process while the water discharged from the aeration tank is introduced into a lower part thereof and flows upflow, and in which produced sludge and treating water are discharged out;

(F) a second aeration tank adapted to aerate the water discharged from the third upflow reactor.
The treatment system according to claim 1, wherein a plurality of the first upflow reactors are installed.
The treatment system according to one of claims 1 to 3, wherein the first, second and third upflow reactors respectively comprise:

(a) a main shaft that is perpendicularly formed at the center of a reactor and is rotated by a driving means;

(b) a stay part that is fixed around an upper portion or a lower portion of the main shaft in such a fashion as to be rotated together with the main shaft and passes the influent introduced through an inlet pipe;

(c) at least one distribution pipe that is fixed at the main shaft in such a fashion as to be rotated together with the main shaft and has one end portion directly connected with the stay part and the other end portion located at the lower part of the reactor so that the influent passing through the stay part is discharged to the inside of the reactor from the lower part of the reactor;

(d) a mixer having at least two mixing wings radially arranged on the main shaft;

(e) a discharging device that is located at the upper part of the reactor and has a weir opened at the upper face so that the treating water separated from sludge is overflowed; and

(f) a sludge collector that is located at the lower part of the reactor for treating the sludge deposited by gravity.
The treatment system according to claim 4, wherein the first, second and third upflow reactors respectively further comprise:

an airtight cover part disposed on the top of the reactor for preventing gases generated during the treatment process form being freely diffused to the outside air; and

a gas discharging means for collecting and discharging internally generated gases.
The treatment system according to claim 5, wherein the gas discharging means comprises:

a plurality of gas collectors, each of the gas collectors getting upward narrower in vertical section so that the lower portion is opened and the upper portion is closed and having an exhaust pipe connected thereto,

wherein the gas collectors are different in size and alternatively arranged in at least two layers.