Plant for aerobic and anaerobic digestion treatment by PFR

Disclosed are a wastewater treatment plant and a wastewater treatment method. The wastewater treatment plant includes: a reactor including a gas outlet, a treated water outlet, and an inlet through which wastewater and gas are supplied, through which the wastewater is introduced, to perform aeration and denitrification; a sludge separation means including plural reaction unit bodies stacked inside the reactor to divide the interior of the reactor into upper and lower sides and separating sludge in a aeration process by forming a gas hold-up space for collecting the gas rising from a lower portion of the reactor; and a aeration unit introducing gas into the reactor.

TECHNICAL FIELD

The present invention relates to a water treatment plant and a water treatment method, and more particularly, to a water treatment plant capable of efficiently treating strong organic wastewater by stacking a plurality of reaction unit bodies and performing aerobic and anaerobic digestion treatments

BACKGROUND ART

In general, an aerobic or anaerobic digestion treatment is performed in a completely stirred tank reactor (CSTR) that is being currently used.

However, strong organic wastewater introduced into a CSTR is completely mixed in the reactor and is discharged by the amount of introduced strong organic wastewater, in which case treatment efficiency and treatment rate are low.

In addition, an aerobic or anaerobic digestion treatment must be essentially accompanied by mixing of fluids in consideration of the properties and reactions of the fluids, therefore it is difficult to avoid complete mixing of fluids while performing a desired mixing operation.

Accordingly, a sequencing batch reactor (SBR) controlling mixing and discharge together, a separation reactor, or an upflow anaerobic sludge blanket (UASB) are being used in a treatment process, but they also show efficiencies similar to that of a CSTR.

Moreover, induction of treatment of strong organic wastewater by a CSTR is problematic due to recent global warming, generation of a large amount of strong wastewater, and regulation of total emission.

DISCLOSURE OF INVENTION

Technical Problem

The present invention provides a water treatment plant and a water treatment method using a plug flow reactor in which the interior of a reactor is multi-staged, and gas hold-up space are formed between the stages to interrupt flow of fluid or increase fluidity of liquid, whereby the circulation and transfer rate between gas and liquid are increased.

The present invention also provides a water treatment plant and a water treatment method in which by applying a plug flow reactor (PFR) method, in the case of the aerobic treatment, high concentration of dissolved oxygen (DO), a large number of microorganisms, and a high concentrations of pollutants in wastewater are secured at the lowermost stage of the reactor and they become gradually reduced as they flow to the up stage of the reactor, thereby creating a typical reactor flow of a PFR, and, in the case of the anaerobic treatment, high concentrations of organic materials and microorganisms are secured at the lowermost stage of the reactor and their concentrations become lower resulting in maintaining an optimum pH, which can be lowered at the lowermost stage due to the fermentation processes.

The present invention also provides a water treatment plant and a water treatment method that can solve problems occurring in a conventional CSTR type wastewater treatment plant.

Technical Solution

Therefore, the present invention has been made in view of the above problems, and it is an objective of the present invention to provide a water treatment plant comprising: a reactor for aeration, nitrification and denitrification of wastewater; the reactor composed of plural reaction unit stacked stages dividing the reactor into upper and lower sides, and including sludge separation system during the aeration process by building up gas hold-up space which can hold up-rising gases from the lower stage of the reactor; and wastewater treatment equipments including air distribution units aerating the reactor.

Advantageous Effects

As the detailed description, according to the present invention, the wastewater treatment equipments and processes are composed of maintain the PFR characteristics of the reaction rate and fluid flow by the interior of the reactor or the flocculation system is multi-staged by plural stacking of reaction unit bodies and gas hold-up spaces are formed between the stages to interrupt flow of fluid or increase fluidity of liquid, whereby the circulation and transfer rate between gas and liquid are increased.

Further, construction time and cost can be reduced by the vertical plural stacking of reaction unit bodies, making installation of the reactor convenient.

Furthermore, the various types of designs for the reactor are possible by varying the shape of the unit body of the reactor.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a wastewater treatment plant according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As illustrated inFIG. 1, the wastewater treatment plant according to an embodiment of the present invention includes a reactor3into which wastewater and air are introduced to perform aeration and denitrification, at least one sludge separation unit S1, S2, and S3having plural reaction unit bodies stacked as five stages inside the reactor3to move the introduced wastewater and gases upward in the order of their densities and decompose contaminants by increasing the interfacial area between the wastewater and the bubbles and thereby increasing dissolved oxygen (DO), and a bubbling unit7introducing a gas into the interior of the reactor3.

The reactor3may function as an aeration reactor or a denitrification reactor according to its treatment process. The reactor3is tube-shaped to introduce wastewater and air into a space formed therein. The reactor shape may be cylindrical, hexahedral, or octahedral.

The reactor includes a gas outlet9through which the bubbles that have passed through the sludge separation units S1, S2, and S3are discharged outside the reactor3and a treated water outlet11through which the wastewater that has passed through the sludge separation units S1, S2, and S3is discharged to the outside.

A wastewater inlet pipe13for supplying wastewater and gas is connected to a lower portion of the reactor3. The gas includes air or methane gas. An aerobic treatment may be necessary when air is injected and an anaerobic treatment may be necessary when methane gas is injected.

When anaerobic treatment is carried out by injecting methane gas into the interior of the reactor3, a conventional gas collecting unit may be provided to the gas outlet9.

The wastewater introduced through the wastewater inlet tube13fills the interior of the reactor3from the bottom.

The aeration unit7is mounted to an upper portion of the wastewater inlet tube13to introduce exterior gas into the reactor3.

The aeration unit7includes an inlet tube15connected to the inside of the reactor3, at least one nozzle19protruding from the inlet tube15, and a blower P1provided on one side of the inlet tube15to blow out gas.

Accordingly, the gas introduced through the inlet pipe15by the blower P1may be uniformly injected to the wastewater through the plural nozzles19.

The sludge separation units S1, S2, and S3include at least one sludge separation section, preferably, a first sludge separation section S1, a second sludge separation section S2, and a third sludge separation section S3. A stack of reaction unit bodies5is stacked in each of the first to third sludge separation sections S1, S2, and S3.

The reaction unit bodies5have the same shape, in which case one reaction unit body5will be described in detail hereinafter.

As illustrated inFIGS. 2 to 4, the reaction unit body5includes upper and lower frames23and21corresponding to each other, a connection frame25connecting the upper and lower frames23and21, an oblique plate27provided inside the frame23and partitioning the interior of the reactor3into upper and lower sides, a fluid flow pipe29provided in the oblique plate27to function as a passage for upward and downward flow of a fluid.

The oblique plate27is provided inside the upper frame to interrupt upward and downward flow of a fluid. The oblique plate27has a downwardly slanted shape, and a plurality of fluid flow pipes29that are passages for upward and downward flow of a fluid is provided at a central portion of the oblique plate27.

Accordingly, when sludge is deposited on the upper surface of the oblique plate27, it flows downward along the oblique surface28to be prevented from being stacked.

A reinforcing member35disposed on the bottom surface of the oblique plate27supports the oblique plate27. The reinforcing member35protrudes downward from the bottom surface of the oblique plate27by a predetermined height and is transversely and longitudinally disposed about the fluid flow pipe29.

Accordingly, the reinforcing member35can prevent the oblique plate27from moving or deflecting due to wastewater or gas during water treatment. The reinforcing member35has a bent structure where microorganisms can grow up.

The fluid flow pipe29protrudes downward from an intermediate portion of the oblique plate27. The fluid flow pipe29is pipe-shaped and a fluid can flow upward and downward through the interior thereof.

Accordingly, when plural reaction unit bodies5are stacked inside the reactor3, the reaction unit bodies5make contact with each other with the oblique plate27being connected sideward.

As a result, wastewater may flow upward and downward through the fluid flow tube29with wastewater being interrupted by the oblique plate27.

More particularly, the fluid flow tube29has a funnel shape whose upper area is preferably larger than its lower area.

However, the fluid flow pipe29is not limited to the funnel shape, but may be conical or cylindrical. Furthermore, the same shape, size, length, and number of fluid flow pipes29may be provided in the same plate.

When the fluid flow tube29is varied as mentioned above, the wastewater introduced into the fluid flow tube29may variously induce the flow condition of fluid, the amount of high density material that moves downward from upside, and the various movement speeds according to the types of wastewater and the amount of gas. As a result, the efficiency and performance of water treatment may be increased by diversifying the shape of the fluid flow tube29.

For example, when the fluid flow tube29is fan-shaped, an upwardly moving fluid is dispersed to prevent peripheral sludge from being deposited and accumulated near the fluid flow tube29.

Meanwhile, the fluid flow tube29protrudes to the lower side of the oblique plate27by a predetermined length, and gas hold-up spaces Va, Vb, and Vc are formed on the bottom surface of the oblique plate27.

Accordingly, the gas rising from a lower portion of the reactor3is collected in the gas hold-up spaces Va, Vb, and Vc, and if more than a predetermined amount of gas is collected, the gas is dispersed in all directions by a pressure to be supplied to the fluid flow tube29.

Then, the fluid flow tube29preferably has the same length as that of a fluid flow tube29of an adjacent reaction unit body, but as illustrated inFIG. 7, the lengths of the fluid flow tubes29may be different.

In other words, in adjacent reaction unit bodies50and52, the length D2of the fluid flow tube56provided on one side may be longer than the length D1of the fluid flow tube54provided on the other side.

In this way, since the length D2of the fluid flow tube56is formed long, the change in water level and sludge movement may be activated inside the reactor3.

In other words, when a gas gradually rises to form the gas hold-up space Va, Vb, and Vc on the bottom surface of the oblique plate27, a first water surface L1is formed.

When the gas additionally rises, some gas rises through the fluid flow tube54having a shorter length. Then, some gas that has not escaped through the short fluid flow tube54is gradually collected to press the first water surface L1downward and form a second water surface L2.

The gas in the stay spaces Va, Vb, and VC formed in the second water surface L2flows upward through the short fluid flow pipe54.

The movements of the first water surface L1and the second water surface L2increase the fluidity of the fluid due to change in the water surfaces.

Then, the interval between the second water surface L2and a long fluid flow tube56is so short that the resistance of the gas is relatively small, whereby almost all the upwardly or downwardly flowing sludge flows downward through the long fluid flow tube56.

Gas does not flow or rarely flows at the upper end of the long fluid flow tube56, in which case MLSS of substantially high concentration gathers there and sludge of high concentration may selectively flow downward.

Maintenance of the high concentrated slurry at the lower end of the long fluid flow tube56is a very important factor in reducing the amount of transferred slurry and increasing treatment rate.

FIGS. 8 and 9illustrate a reaction unit body according to another embodiment of the present invention. The reaction unit body includes an upper frame80, an oblique plate97provided inside the upper frame80, upper and lower caps81and83provided in the oblique plate97, and a leg connected to the upper frame80.

The upper and lower caps81and83are provided on the upper and lower surfaces of the oblique surface97respectively and have the same shape.

The upper cap81includes a plate85and at least one support member supporting the plate85. The lower cap83also includes a plate and a support member.

Accordingly, the fluid rising from the lower side of the reaction unit body96is introduced into a side of the lower cap83and, after rising through a hole37of the oblique surface97, makes contact with the plate85of the upper cap81to flow to a side of the upper cap81.

As a result, the fluid is agitated in the process of passing through the upper and lower caps81and83to increase treatment efficiency.

Moreover, the lower frame21(refer toFIG. 2) is omitted in the reaction unit body96, and a leg L is mounted to the reaction unit body96instead.

As illustrated inFIG. 10, a hopper may be formed at a lower portion of the reactor90. In other words, the hopper91is formed by inclining a lower portion of the reactor by a specific angle, and an outlet tube92is provided at a lower portion of the hopper91.

Accordingly, the substances deposited at a lower portion of the reactor90flow downward along the inclined portion of the hopper91to be discharged outside through the outlet tube92.

Agitation units93,94, and95may be additionally mounted to the hopper91of the reactor. Each agitation unit93,94, and95includes a first pipe body93connected to the upper side of the hopper91, a second pipe body94connected to the lower side of the hopper91, and a pump95connected to the first and second pipe bodies93and94to pump fluid.

Accordingly, the fluid stored in the hopper91may be circulated through the first and second pipe bodies93and93to be agitated by driving the pump95.

Referring toFIGS. 2 to 4again, coupling bosses31protrude from the upper frame22. The coupling bosses31protrude by a predetermined length from the upper surface of the upper frame23at the corners of the upper frames23. Coupling recesses33are formed on the bottom surface of the lower frame21at the corners of the lower frame21.

Accordingly, the coupling bosses31of a reaction unit body5disposed on the lower side are inserted into the coupling recesses33of a reaction unit body5disposed on the upper side, so that plural reaction unit bodies5are coupled to each other.

Then, friction members made of rubber or a synthetic resin are attached to the coupling recesses33respectively, whereby when the coupling bosses31are inserted into the coupling recesses33, the reaction unit bodies5are supported by frictional forces to be prevented from floating due to the buoyancy.

Transfer holes h are formed in the upper and lower frames23and21at locations similar to that of the lower end of the fluid flow tube29. Accordingly, the bubbles and water flowing from the lower end to the upper end of the reaction unit body5are divided at the lower limit line of the fluid flow tube29.

Then, the water flows downward together with some bubbles, and some gas flows through the holes h according to the gas pressure, amount of gas, and distribution of gas in an adjacent reaction unit body5. A support connecting the upper and lower communication holes h may induce growth and attachment of microorganisms.

Then, the liquid flows downward and is mixed to maximize the mixing effect, and the gas uniformly flows to the adjacent reaction unit body5to induce a reaction unit body in which gas is stayed or is sufficient.

Accordingly, the force applied to the reaction unit bodies5by the buoyancy of gas helps mix the fluids, thereby maximizing the mixing effect, i.e. the purpose of the present plant and minimizing the influence of irregular waves or vibration obstructing the stability of the plant.

As mentioned above, treating water by stacking reaction unit bodies5enables mass-production of the reaction unit bodies5by a molding method.

Then, the reaction unit bodies5may be separately formed and manufactured and then be assembled together for the convenience of work.

As illustrated inFIG. 1, a fixing bar80is provided at the upper most end of the reaction unit bodies5to press the reaction unit bodies5, thereby preventing the reaction unit bodies5from rising due to the buoyancy.

One end of the fixing bar80is hingedly connected to a fixing bracket84provided on one side of the reactor3therein, and the other end thereof is connected to a locking bracket82provided on the other side of the reactor3therein.

Accordingly, the fixing bar80is hingedly fixed by the fixing bracket when it is fixed to the locking bracket82by fixing pins86to press the reaction unit bodies5, thereby preventing the reaction unit bodies5from rising due to the buoyancy.

A manhole (not shown) may be installed at an intermediate portion of the reactor3for cleaning.

A circulation unit for circulating gas and wastewater upward and downward is mounted to one side of the reactor3.

The circulation unit60includes a pipe62, a pump P2provided in the pipe62, an upper pipe64protruding from the pipe62and connected to an upper space of the reactor3, an intermediate pipe65connected to an intermediate space of the reactor3, and a lower pipe66connected to a lower space of the reactor3.

Accordingly, the wastewater and gas in the reactor3may be circulated by driving the pump P2. Then, valves are attached to the upper pipe64, the intermediate pipe65, and the lower pipe65to selectively circulate the wastewater and gas between the upper to lower side of the reactor3.

The circulation is performed with injection of the gas being stopped and is periodically performed, whereby the nitrogen in the sludge deposited in the sludge separation units is removed.

On the other hand, a gas discharge unit70is provided on the other side of the reactor3, whereby the gas collected in the sludge separation units is discharged outside.

The gas discharge unit70includes a main pipe72through which gas can flow, and auxiliary pipes74a,74b, and74cprotruding from the main pipe72and entering the reactor3to be communicated with the gas hold-up spaces Va, Vb, and Vc of t the sludge separation units S1, S2, and S3.

The auxiliary pipes74a,74b, and74care communicated with the gas hold-up spaces Va, Vb, and Vc of the sludge separation units S1, S2, and S3, whereby the collected gas flows to the auxiliary pipes74a,74b, and74cand is discharged outside through the main pipe72.

Accordingly, the gas discharge unit70discharges the gas inside the reactor3outside to be used in a non-oxidation reaction such as denitrification.

The wastewater treated by aeration and denitrification is discharged through an outlet pipe.

FIG. 5illustrates a coupling structure of a reaction unit body according to the embodiment of the present invention. As illustrated, when the reaction unit bodies are disposed, adjacent reaction unit bodies42are coupled to each other to be disposed more stably.

In other words, a coupling boss44protrudes from an upper portion of one reaction unit body40. An oblique surface48is formed on one side of the first coupling boss44. A second coupling boss46protrudes from an upper portion of the other reaction unit body42. A catching jaw49is formed on one side of the first coupling boss44. Then, the angle of the catching jaw49and the oblique surface are the same.

Accordingly, the reaction unit bodies40and42are transversely coupled to each other, and the catching jaw49of the second coupling boss46makes contact with the oblique angle48to be firmly coupled to the oblique angle48.

In this way, the reaction unit bodies40and42are firmly coupled to each other, whereby when the wastewater and gas rise or lower between the reaction unit bodies40and42, the reaction unit bodies40and42are prevented from rising due to the buoyancy.

The coupling structure of the reaction unit bodies may be as illustrated inFIG. 6. In other words, an insertion recess53is formed at the connection frame51of the reaction unit body41, and an insertion boss47protrudes from the connection frame45of the reaction unit body43.

Accordingly, the insertion boss47of the reaction unit body43is inserted into the insertion recess53of the reaction unit body41to couple the reaction unit bodies41and43to each other.

FIGS. 11 and 12illustrate a reaction unit body according to another embodiment of the present invention. As illustrated, the reaction unit body112according to the embodiment of the present invention includes a plate113, a support member110protruding to a lower portion of the plate113and connected to another reaction unit body, and a plurality of fluid flow pipes126,128,114, and116provided in the plate113and functioning as an upward and downward passage for fluid.

In the reaction unit body, the plate113has a predetermined area to interrupt upward and downward movement of fluid.

Four oblique plates118,119,120, and121are integrally formed in the plate113. In other words, four fluid flow pipes126,128,114, and116are provided in one plate113to improve treatment efficiency.

The four oblique plates118,119,120, and121are inclined toward the centers thereof by a predetermined angle. Accordingly, when sludge is deposited on the upper surface of the plate113, the sludge flows downward along the oblique plate118to be prevented from being stacked.

The four oblique plates118,119,120, and121have the same shape, but only the locations of the fluid flow pipes114,116,126, and128are different.

In other words, the fluid flow pipes114,116,126, and128maintain different intervals. For example, the interval D3between the first fluid flow pipe126and the second fluid flow pipe128and the interval D4between the third fluid flow pipe114and the fourth fluid flow pipe116are different.

When the intervals D3and D4of the fluid flow pipes114,116,126, and128are different from each other when the reaction unit bodies112,122, and124are stacked, the reaction unit bodies112,122, and124are rotated by 90 degrees about the support member110when they are assembled.

In other words, the second-stage reaction unit body122having the same transverse and longitudinal lengths is rotated by 90 degrees about the first-stage reaction unit body112when it is stacked, and the third-stage reaction unit body124is rotated by 90 degrees about the second-stage sludge unit assembly122when it is stacked.

As a result, the fluid flow pipes126and128of the first-stage reaction unit body122are deviated from the fluid flow pipes132and134of the second-staged reaction unit body122, and the fluid flow pipes136and138of the third-stage reaction unit body124are deviated from the fluid flow pipes132and134of the second-stage reaction unit body122.

Accordingly, the fluid flow pipes126,128,114,116,132,134,136, and138of the reaction unit bodies112,122, and124are deviated from each other to increase the agitation effect of the fluid passing through them.

The reinforcing member117is disposed on the bottom surface of the plate113to support the plate113. The reinforcing member117has a jaw-like shape protruding downward from the bottom surface of the plate113by a predetermined height and is transversely and longitudinally disposed about the fluid flow pipe126.

FIGS. 13 and 14illustrate a water treatment plant100including a reactor102having stacked reaction unit bodies112,122, and124.

As illustrated, plural reaction unit bodies112,122, and124are stacked inside the reactor102, and a bubbling unit107is provided at a lower portion of the reactor102. A wastewater inlet pipe104is provided on one side of a lower portion of the reactor102to introduce the wastewater into the reactor102. The gas outlet106and the treated water outlet108are provided at upper portions of the reactor102.

Accordingly, when plural reaction unit bodies112,122, and124are stacked inside the reactor102, the reaction unit bodies112,122, and124make contact with each other to maintain the plate transversely connected, in which case the wastewater may be interrupted by the plate113when it flows upward and downward through the fluid flow pipe118.

Hereinafter, a process of treating wastewater by the water treatment plant100will be described in detail.

The wastewater to be treated is introduced into the reactor102through the wastewater inlet pipe104, and external gas is introduced into the reactor102through the aeration unit107.

The gas injected into the aeration unit107may be injected through the supply pipe105and the nozzles103to effectively perform a bubbling process.

As mentioned above, the wastewater and gas introduced into the reactor102rises to reach the first reaction unit body112.

The wastewater that has reached the first reaction unit body112rises to an upper space through the fluid flow pipes126,128,114, and116.

The wastewater and gas that have passed through the first reaction unit body112reaches the second reaction unit body122. In the process of passing through the second reaction unit body122, materials may be separated through the same process as that of the first reaction unit body112.

The wastewater and gas that have reached the uppermost space of the reactor102is discharged through the gas outlet106and the treatment water outlet108.

FIGS. 15 and 16illustrate a reaction unit body according to another embodiment of the present invention. As illustrated, the reaction unit body150according to the embodiment of the present invention has a peripheral portion162on a side surface of the plate158.

The peripheral portion162of the plate158is formed to flow fluid upward and downward inside the peripheral portion162, whereby almost all forces generated by the buoyancy force of gas maximizes the upward and downward flow effect. Further, horizontal flow of the fluid may be prevented by adjusting the right and left forces of the fluid.

The horizontal flow of the fluid hampers recirculation of bubbles in the reactor and causes a stability problem of the reactor due to the vibration.

In particular, the reaction unit body having the peripheral portion162is applied to a large-sized treatment facility to reduce the overall vibration problem.

More particularly, the reaction unit body152according to the embodiment of the present invention includes a plate158, a support member151protruding to a lower portion of the plate158and connected to another reaction unit body, a plurality of fluid flow pipes164and166provided in the plate158to function as an upward and downward passage of fluid, and a peripheral portion162protruding downward from the periphery of the plate158.

The shapes of the plate158, the oblique surface160, the fluid flow pipes164and166, and the support member151are the same as those of the reaction unit body illustrated in the above-mentioned embodiment of the present invention, and the detailed description thereof will be omitted.

The peripheral portions162protrude downward from the periphery of the plate158by a predetermined distance. The peripheral portions162are formed at the periphery of the plate158to form a space at a lower portion of the plate158.

Accordingly, wastewater and air are stored in the space to be prevented from flowing right and left.

Holes168are formed at the peripheral portions162. The holes168are formed in the four peripheral portions162. Accordingly, the pressure of the wastewater stored in a lower space of the plate158is prevented from being concentrated in the peripheral portions162.

Hereinafter, a water treatment method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As illustrated inFIGS. 1,2, and17, the water treatment method according to the embodiment of the present invention includes a pre-treatment step S100of removing solids in introduced water and crushing the solid materials using a crusher, a aeration and denitrification step S120of injecting air and oxidizing organic materials and nitrogen through an aerobic process, and a step S130of aerobically treating the introduced water, precipitating sludge through solid-liquid separation, and returning some sludge to the reactor (aeration and denitrification vessel).

In the water treatment method, the pre-treatment step S100is performed in a general manner. In other words, wastewater passes through the crusher to remove solid materials contained therein, whereby the solid materials contained in the wastewater are crushed and miniaturized.

After the pre-treatment step S100is completed, the aeration and denitrification step S120is performed.

In the aeration and denitrification step S120, the wastewater to be treated is introduced into the reactor3through the wastewater inlet pipe13, and external air is introduced into the reactor3through the bubbling unit7.

The gas injected into the bubbling unit7is uniformly injected through a plurality of nozzles19to effectively perform the aeration process.

As mentioned above, the wastewater and gas introduced into the reactor3rises to reach the first sludge separation unit S1.

The multi-stage sludge separation units S1, S2, and S3disposed inside the reactor3may be created by stacking the reaction unit bodies5.

In other words, the coupling bosses31of the lower reaction unit body5are inserted into the coupling recesses33of the upper reaction unit body5to stack the reaction unit bodies5.

Through the process, the multi-stage sludge separation units S1, S2, and S3are formed by stacking the reaction unit bodies5.

The wastewater that has reached the first sludge separation unit S1rises to an upper space through the fluid flow pipes29provided in the reaction unit bodies5and the gas rises by buoyancy to be collected in the gas hold-up space formed at a lower portion of the oblique plate27.

Then, the gas hold-up space Va is expanded downward to form a water surface at the lower limit line of the fluid flow pipe29. Accordingly, the gas may be collected at the upper space above the water surface.

When the lengths of the fluid flow pipes29are different, gas gradually rises so that the first water surface L1is formed at the lower limit line of the longest fluid flow pipe29.

When the gas additionally rises, some rises through the shortest fluid flow pipe54. Then, some gas that has not passed through the shortest fluid flow pipe54is gradually collected to press the first water surface L1downward to form the second water surface L2.

Further, the gas in the gas hold-up space Va formed above the second water surface L2flows upward through the longest fluid flow pipe56.

In the process, the water surfaces are changed due to movement of the first water surface L1and the second water surface L2to increase the fluidity of the fluid.

Then, in the longest fluid flow pipe56, the interval between the second water surface L2and a fluid flow pipe is so short that the resistance of gas becomes smaller, whereby almost all sludge flowing upward and downward flows downward through the largest fluid flow pipe56.

Gas rarely or occasionally flows at the upper end of the longest fluid flow pipe56, whereby sludge of substantially high density is collected there and may selectively flow downward.

Maintenance of the high density of slurry at the lower end of the long fluid flow pipe56is a very important factor in reducing the amount of transferred slurry and increasing treatment rate.

Almost all the bubbles generated in the reactor3due to the structural characteristics of the fluid flow pipes29stays at the upper end of the wastewater and materials of relatively low density are mainly stayed on the surface of the wastewater due to the surface tension.

Accordingly, the materials of low density are located at upper portions of the stages, whereby the densities of the materials become lower as they go toward the upper end of the reactor3.

The amount and pressure of the gas introduced from the lower side are maintained above predetermined values to uniformly discharge the gas through the fluid flow pipes29.

The wastewater and gas that have passed through the first sludge separation unit S1reaches the second sludge separation unit S2through the process. Materials may be separated through the second sludge separation unit S2that is the same as the first sludge separation unit S1.

The wastewater and gas that have reached the uppermost space of the reactor3are discharged through the gas outlet9and the treated water outlet11.

In the bubbling and denitrification process, denitrification may be attempted by exhausting gas by the gas discharge unit when management of a non-oxygen vessel is needed.

In other words, after the aeration process, the gas existing inside the reactor needs to be removed for denitrification. To achieve this, the residual gas and some bubbles that have been collected in the gas hold-up spaces Va, Vb, and Vc of the sludge separation units S1, S2, and S3are discharged through the auxiliary pipes74a,74b, and74cby opening the valve76of the main pipe72of the discharge unit70.

Then, the pipes74a,74b, and74cneed to be spaced apart from the upper end wall of the reactor3to prevent the discharged gas from flowing upward by buoyancy.

If the valve76is opened, the gas and some bubbles at the stages are discharged outside to the initial position through the auxiliary pipes74a,74b, and74cand the main pipe72.

Accordingly, a non-oxygen vessel may be managed through the gas discharge process after the denitrification process.

After deposits are condensed in the sludge separation units after the reactor3is driven for a predetermined time period, a deposition step S130is performed.

In the deposition step S130, it is necessary to increase the condensation efficiency of the lower end of the reactor3and the denitrification efficiency by periodically flowing the deposits to the lowermost end of the reactor3through the circulation unit60. In other words, when the pump P2of the circulation unit60is operated, the deposits condensed at the stages are sucked through the upper, intermediate, and lower pipes64,65, and66by pressure.

The sucked deposits are introduced into a separate unit or the inlet pipe15of the bubbling unit17through the pipe62to be supplied to an arbitrary internal location of the reactor3and are circulated into the reactor3again.

Accordingly, during flow of the wastewater from upside to downside through the circulation process, unlike injection of gas, the wastewater itself flows to generate the concentration of sludge, and the condensation efficiency at the lower end of the reactor3may be increased and the difference between densities of the sludge at the upper and lower ends of the reactor3may be induced.

Denitrification is performed through the process, and the circulation may be performed from the uppermost end to lowermost end of the reactor3or from an intermediate portion to the uppermost end of the reactor3.

As another embodiment of the present invention, an aerobic treatment step S140may be performed after the pre-treatment step S100. In other words, methane gas is injected instead of the gas inside the reactor3, and the anaerobic treatment may be performed in the process of the methane gas and wastewater passing through the reaction unit bodies5.

The water treatment efficiency by the water treatment plant having the stacked reaction unit bodies may be expressed as in Table 1.

In other words, considering load of food wastewater to be introduced and removal efficiency, the removal efficiency is 97% for the aerobic treatment, and 85% for the anaerobic treatment, which are considerably high water treatment efficiencies.

The treatment efficiency means the difference between organic materials before and after a water treatment, and is the difference between the amounts of dissolved organic materials for the aerobic treatment and is the difference between the decomposable total solid material and the discharged decomposable total solid material for the anaerobic treatment.

The gas generated after the anaerobic digestion of food shows more than 1.0 m3/kg VS for removed organic materials (vs).

(The item 3 means the value of F/M calculated in consideration of OUR (Oxygen Uptake Rate))

Furthermore, by applying a plug flow reactor (PFR) method, in the case of the aerobic treatment, a large amount of dissolved oxygen, a large number of microorganisms, and a high concentration of original wastewater pollutants are secured at the lowermost end of the reactor and they become gradually reduced as they go to the upside of the reactor, thereby creating a typical reactor flow of a PFR. Further, in the case of the anaerobic treatment, high concentrations of organic materials and microorganisms are secured at the lowermost end of the reactor and their concentrations become lower. Therefore, a water treatment plant and a water treatment method of the present invention maintain a low pH at a lower portion of the reactor and a high pH at an upper portion of the reactor.

In other words, the growth expediting factors of microorganisms, i.e. organic materials, pH, dissolved oxygen, the number of microorganisms, oxygen, and organic acid simultaneously maintain flow of the PFR. Even when the PFR is operated in a downstream way according to the characteristics of the introduced water, a similar result may be induced.

FIGS. 18 and 19illustrate a result obtained by performing water treatment using the water treatment plant having the stacked reaction unit bodies.

As illustrated inFIG. 18, in the result obtained by performing an aerobic treatment using the reaction unit bodies, an arrow a showing a conventional digestion process is illustrated at an upper portion of the graph and an arrow c after the treatment is illustrated at a lower portion of the graph. In other words, the arrow is lowered by a predetermined distance L1to show an improvement.

In the case of the anaerobic treatment, an arrow b showing a conventional digestion process is illustrated at an upper portion of the graph, and an arrow d after the treatment is illustrated at a lower portion of the graph. In other words, the arrow is lowered by a predetermined distance L1to show an improvement.

As illustrated inFIG. 19, a result obtained by treating food wastewater, livestock wastewater, and sewage sludge using reaction unit bodies shows that the graph e of the food wastewater, the graph f of the livestock wastewater, and the graph g of the sewage sludge lower as time elapses, thereby improving treatment efficiency, for example, lowering the concentration of a dissolved material.

INDUSTRIAL APPLICABILITY

The present invention relates to a water treatment plant and a water treatment method, and more particularly, to a water treatment plant capable of efficiently treating strong organic wastewater by stacking plural reaction unit bodies and performing aerobic and anaerobic digestion treatments.