WO2006019256A1

WO2006019256A1 - Biological wastewater treating apparatus and method for biologically treating wastewater using the apparatus

Info

Publication number: WO2006019256A1
Application number: PCT/KR2005/002695
Authority: WO
Inventors: Jae Hyuk Yi
Original assignee: Jae Hyuk Yi
Priority date: 2004-08-17
Filing date: 2005-08-17
Publication date: 2006-02-23
Also published as: KR100491900B1

Abstract

The present invention relates to a wastewater treatment apparatus and for simultaneously and more effectively treating nitrogen and phosphorus in the wastewater which inflows into the apparatus, and a method for treating the water using the apparatus, wherein the wastewater treatment apparatus comprising a anoxic tank, an anaerobic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial comprises an inflow pipe for introducing waste waters into the anaerobic tank; a first internal circulation pipe for connecting the anaerobic tank and the anoxic tank and transferring a suspension in the anaerobic tank to the anoxic tank; a second internal circulation pipe for connecting the oxic tank and the anoxic tank and returning a suspension in the oxic tank to the anoxic tank; a returning sludge pipe for connecting the settling tank and the anoxic tank and returning a suspension in the settling tank to the anoxic tank; a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and a sludge discharging pipe serving as a passage for discharging sludge in the settling tank.

Description

BIOLOGICAL WASTEWATER TREATING APPARATUS AND METHOD FOR BIOLOGICALLY TREATING WASTEWATER

USING THE APPARATUS

Technical Field

[1] The present invention relates to a biological wastewater treatment apparatus and method for treating the water. More particularly, the present invention relates to a wastewater treatment apparatus for more effectively and simultaneously treating nitrogen and phosphorus in the wastewater which inflows into the apparatus, and a method for treating the water using the apparatus. Background Art

[2] In conventional wastewater treatments, attempts have been made to treat wastewater to be adaptive mainly to appropriate figures of COD and BOD. Because of eutrophication problem of water due to nitrogen and phosphorus contained therein, however, the government recently has come to enforce rules on the amount of nitrogen and phosphorus in the treated wastewater which were discharged from the wastewater treatment apparatus and the rules trend to be increasingly strict.

[3] Typical facilities for biologically treating nitrogen and phosphorus in wastewater consist of bioreactors and settling tanks, and the bioreactor may include various combination of an anaerobic area, an anoxic area, an oxic area and the like.

[4] In order to biologically treat nitrogen, the oxic area and the anoxic area are basically required. If an amnionic nitrogen is oxidized in the oxic area, nitrates resulted from the oxidized nitrogen is denitrified to be nitrogen gas and removed therefrom by het¬ erotrophic micro-organisms using the nitrates as electron acceptor in the anoxic area.

[5] Also, in order to biologically treat phosphorus, the anaerobic area and the oxic area are basically required. In the anaerobic area, PAO (phosphate accumulating organism) which over-absorbs phosphorus releases phosphorus, absorbs a volatile organic acid and then synthesizes PHA (polyhydroxy alkanoate) within the body. On the other hand, in the oxic area the above PAO grows using the PHA and over-absorbs phosphorus. As such, phosphorus is removed by discharging the PAO which has over- absorbed phosphorus through sludge. Disclosure of Invention Technical Problem

[6] Facilities have been developed for biologically and simultaneously treating nitrogen and phosphorus using the above principle and one example of such facilities is shown in Figure 1.

[7] Wastewater treating method called as A O process is a conventional method that treats nitrogen and phosphorus in wastewater by using an apparatus having a simple structure in which an anaerobic tank (101), an anoxic tank (102), an oxic tank (104) and a settling tank (105) are sequentially arranged thereto as shown in Fig. 1. According to this apparatus, however, a sludge from the settling tank (105) is also inflowed through a returning sludge pipe (205) to the anaerobic tank (101) to which the waste water is inflowed, and thus a significant amount of nitrates contained within the sludge hinders the treatment of phosphorus. That is, because organic acid contained within the inflowed wastewater and biologically divided RBCOD (readily biodegradable COD) are firstly exhausted by denitirfying micro-organisms before it is used by PAO in the anaerobic tank (101), the PAO does not sufficiently synthesize PHA into the body and resultantly the phosphorus is directly discharged together with the treated water, without being absorbed in the oxic tank (104). Particularly, the dete¬ rioration in the efficiency of phosphorus treatment by the above A O process is un¬ avoidable under the condition where the ratio of TKN (total kjeldahl nitrogen)/COD and TP (total Phosphorus)/COD is high and the content of RBCOD among COD is low, as in the case of general wastewaters in our country.

[8] In order to solve such problems in A O process, the arrangement of bioreactors such as anaerobic tank (101), anoxic tank (102), oxic tank (104) and the like is modified or similar A O processes in which some bioreactors are further added has been con¬ tinuously developed. Further, a method for removing nitrogen and phosphorous by ad¬ ditionally supplying an external carbon source to thereby increase the content of RBCOD in the anaerobic tank (101) is developed as disclosed in Korean Patent No. 375413. However, this method still has a basic problem that the nitrates-containing sludge in the settling tank (105) is returned into the anaerobic tank (101) and re¬ sultantly there is the limitation in removing phosphorus efficiently.

[9] Alternatively, instead of returning the sludge in settling tank (105) into the anaerobic tank (101), as noted in the foregoing as having the basic problem in the above A O process and other similar methods, there has been developed a DNR process for treating wastewater using an apparatus having the arrangement of a first anoxic tank (102) an anaerobic tank (101) - a second anoxic tank (103) an oxic tank (104) a settling tank (105) as shown in Fig. 2 in which the anaerobic tank (101) and the first anoxic tank (102) in the A O process are exchanged each other in the their position thereby letting the sludge in the settling tank (105) be returned into the first anoxic tank (102) (the anoxic tank (102) is referred to as a first anoxic tank) and a further one anoxic tank (referred to as a second anoxic tank) is deployed. According to this DNR process, because nitrates contained in sludge in the settling tank (105) is denitrified in the first anoxic tank (102) and then is transferred to anaerobic tank (101), in the anaerobic tank (101) PAO can absorb organic matter with no interference, and thereafter the PAO can grow up in the oxic tank (104) and thus excessively absorb phosphorus thereby increasing the removal efficiency of phosphorus. However, because the DNR method makes denitrification by endogenous respiration which uses internal biomass in the first anoxic tank (102), this process has a disadvantage that the treatment speed is significantly slow. In case of general wastewater, the speed of deni¬ trification of organic matter in the inflow water is 0.04 ~ 0.15g NO ^" - N/gVSS (volatile suspended solid) per date, while the speed of denitrification oxidation by the endogenous respiration is low to be 20 ~ 50% of the speed of denitrification using organic matter in the inflow water.

Technical Solution

[10] The object of the present invention is to provide a wastewater treatment apparatus for removing nitrogen and phosphorus in the wastewater simultaneously and in the high efficiency.

[11] Further, the object of the present invention is to provide a method for treating wastewater using the wastewater treatment apparatus according the present invention.

[12] The inventor of the present invention has repeatedly performed researches in order to solve that above problems in conventional arts and resultantly reached to complete the present invention by developing a biological wastewater treatment apparatus that minimizes the inflow of nitrates load due to the inflow of returning sludge into the anaerobic tank which is a disadvantage of A O process and enables more prompt deni¬ trification compared to the slow denitrification by the endogenous respiration which is a disadvantage of DNR process, resulting in the increased removal efficiency of phosphorus.

[13] According to an aspect of the present invention, in a wastewater treatment apparatus comprising an anoxic tank, an anaerobic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising:

[14] an inflow pipe for introducing waste waters into the anaerobic tank;

[15] a first internal circulation pipe for connecting the anaerobic tank and the anoxic tank and transferring a suspension in the anaerobic tank to the anoxic tank;

[16] a second internal circulation pipe for connecting the oxic tank and the anoxic tank and returning a suspension in the oxic tank to the anoxic tank;

[17] a returning sludge pipe for connecting the settling tank and the anoxic tank and returning a sludge in the settling tank to the anoxic tank;

[18] a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and [19] a sludge discharging pipe serving as a passage for discharging sludge in the settling tank. [20] According to other aspect of the present invention, in a wastewater treatment apparatus comprising a first anoxic tank, an anaerobic tank, a second anoxic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising:

[21] an inflow pipe for introducing waste waters into the anaerobic tank;

[22] a first internal circulation pipe for connecting the anaerobic tank and the first anoxic tank and transferring a suspension in the anaerobic tank to the first anoxic tank; [23] a second internal circulation pipe for connecting the oxic tank and the first anoxic tank and returning a suspension in the oxic tank to the first anoxic tank; [24] a third internal circulation pipe for connecting the oxic tank and the second anoxic tank and returning a suspension in the oxic tank to the second anoxic tank; [25] a returning sludge pipe for connecting the settling tank and the first anoxic tank and returning a sludge in the settling tank to the first anoxic tank; [26] a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and [27] a sludge discharging pipe serving as a passage for discharging sludge in the settling tank. [28] According to a further aspect of the present invention, in a wastewater treatment apparatus comprising a first anoxic tank, an anaerobic tank, a second anoxic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising:

[29] an inflow pipe for introducing waste waters into the anaerobic tank;

[30] a first internal circulation pipe for connecting the anaerobic tank and the first anoxic tank and transferring a suspension in the anaerobic tank to the first anoxic tank; [31] a third internal circulation pipe for connecting the oxic tank and the second anoxic tank and returning a suspension in the oxic tank to the second anoxic tank; [32] a returning sludge pipe for connecting the settling tank and the first anoxic tank and returning a sludge in the settling tank to the first anoxic tank; [33] a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and [34] a sludge discharging pipe serving as a passage for discharging sludge in the settling tank. [35] According to a still further aspect of the present invention, in a wastewater treatment apparatus comprising an anaerobic tank, a first anoxic tank, a second anoxic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising: [36] an inflow pipe for introducing waste waters into the anaerobic tank

[37] a sludge internal circulation pipe for connecting the anaerobic tank and the first anoxic tank and returning a suspension in the first anoxic tank to the anaerobic tank

[38] a second internal circulation pipe for connecting the oxic tank and the first anoxic tank and returning a suspension in the oxic tank to the first anoxic tank

[39] a third internal circulation pipe for connecting the oxic tank and the second anoxic tank and returning a suspension in the oxic tank to the second anoxic tank

[40] a returning sludge pipe for connecting the settling tank and the first anoxic tank and returning a sludge in the settling tank to the first anoxic tank

[41] a treated water discharging pipe serving as a passage for discharging treated water in the settling tank and

[42] a sludge discharging pipe serving as a passage for discharging sludge in the settling tank.

[43] Also, in the above wastewater treatment apparatuses according to the present invention, if the oxic tank includes a second internal circulation pipe, after removing the settling tank and the returning sludge pipe connected thereto, the treated water discharging pipe and the sludge discharging pipe may be removed, instead thereof, a submerged ultrafiltration membrane is installed into the oxic tank and the treated water discharging pipe and the sludge discharging pipe are connected to the oxic tank. Further, in the wastewater treatment apparatuses according the present invention, a flowing media or a fixed media may be additionally filled into the oxic tank, and the apparatuses may further comprise, in front of the inflow pipe, at least one device of a screen for removing impurities in the wastewater, a grit chamber for removing sediment such as sands, an equalization tank for equalizing the flowing amount and the quality of water and a first settling tank for removing suspended solids.

[44] In addition, in order to accelerate the treatment of nitrogen and phosphorus, the anaerobic tank and/or the first anoxic tank in the wastewater treatment apparatus according to the present invention may be introduced with at least one species of external carbon source selected from the groups consisted of an organic chemicals such as methanol, acetate, etc.; organic liquid wastes containing organic matter such as methanol, acetate, etc.; organic liquid wastes containing solid in great quantities such as night soil, sediment of septic tank, live stock waste water, food waste, etc.; raw sludge generated in a first settling tank in the wastewater treatment field; recirculated water such as supernatant from sludge concentration apparatus and digester, effluent from dehydrator in the wastewater treatment field; and acid fermentation products of the above organic liquid wastes and raw sludge. Brief Description of the Drawings [45] Figure 1 shows schematically a wastewater treating apparatus for a conventional A

O process.

[46] Figure 2 shows schematically a wastewater treating apparatus for a conventional

DNR process.

[47] Figures 3, 5, 7 and 8 show schematically one example of a biological wastewater treating apparatus according to the present invention.

[48] Figures 4, 6 and 9 show schematically other example of biological wastewater treating apparatus according to the present invention, wherein a submerged ultra¬ filtration membrane is installed into an oxic tank.

[49] Figures 10 to 12 show schematically another example of biological wastewater treating apparatus according to the present invention, wherein an oxic tank is filled with media. Best Mode for Carrying Out the Invention

[50] Now, a biological wastewater treatment apparatus according to the present invention and a method for treating the wastewater using the apparatus will be described in detail with reference to the accompanying drawings illustrating preferred embodiments of the present invention. The accompanying drawings and the relevant description are not intended to limit the present invention and it may be possible to make suitable variations and modifications based on the features as set forth in the claims.

[51] Fig. 3 shows schematically one example of a biological wastewater treatment apparatus according to the present invention.

[52] Waste water is firstly introduced from the outside through an inflow pipe (201) into an anaerobic tank (101). In this anaerobic tank, organic matter in waste water is anaerobically fermented and converted to fermentation products such as organic acid, etc. This organic acid is absorbed by micro-organisms, particularly PAO and then stored as PHA therein. Through this process, the PAO releases phosphorus from the anaerobic tank (101). After completion of reaction in the anaerobic tank (101), there exist, within the suspension in the anaerobic tank (101), organic matter in the form of fermentation products, PHA stored in the cell of PAO, non-fermentation organic matter from inflow water, etc. The suspension in the anaerobic tank (101) after the completion of the above reaction is sequentially transferred to the oxic tank (104) or to the first anoxic tank (102) through a first internal circulation pipe (202). The first anoxic tank (102) is a bioreactor in which electrons resulting from the oxidation of the organic matter which is an electron donor are transferred to nitrates which is an electron acceptor to thereby denitrify the nitrates. The supply of organic matter to the anoxic tank (102) in order to make the above reaction is accomplished by transferring the suspension in the anaerobic tank (101) through a first internal circulation pipe

(202) to the anoxic tank (102). Meanwhile, the supply of nitrate is accomplished by returning the suspension of the oxic tank (104) which contains nitrates and sludge in a settling tank (105) through a second internal circulation pipe (203) and a returning sludge pipe respectively to the first anoxic tank (102), which will be described in detail below. As such, since nitrates supplied to the first anoxic tank (102) is re-transferred to the anaerobic tank (101) after completion of denitrification reaction in the first anoxic tank (102), a competition between PAO and denitrifying micro-organisms to absorb RBCOD is blocked and thus the interference problem in treating phosphorus can be solved.

[53] Organic matters of the suspension transferred from the anaerobic tank (101) to the first anoxic tank (102) consist of anaerobic fermentation products, PHA stored in the cell of PAO, non-fermentation organic matter from inflow water, etc. These organic matters can be used as electron donor of denitrification generated by denitrifying micro-organisms which does not over-absorb phosphorus in the first anoxic tank (102) as well as dPAO (denitrifying phosphorus accumulating organism), denitrifying micro¬ organisms which over-absorbs the phosphorus. Among them, dPAO decomposes PHA and composes the cell in the anoxic state, (i.e. the state using nitrates as an electron acceptor), absorbs phosphorus and then stores the phosphorus in the cell in the form of poly-Phosphate. In this case, the suspension in the anaerobic tank(lθl) being introduced into the anoxic tank(102) is in the state that was already stored in the body as PHA using organic matter that PAO can utilize in the anaerobic state among organic matters in inflow water, the denitrifying micro-organisms that does not over-absorb phosphorus cannot be utilized.

[54] The oxic tank (104) is a bioreactor in which organic matter as electron donor is oxidized, and electrons are transferred to oxygen as electron acceptor to thereby cause the oxidation of organic matter. The organic matter is supplied through the suspension in the anaerobic tank (101). In the oxic tank (104), PAO which exists in the above suspension and stores organic matter of PHA in the body thereof decomposes the above PHA and composes the cell, over-absorbs phosphorus and then stores the phosphorus in the cell in the form of poly-phosphate. Meanwhile, amnionic nitrogen and the like in the inflowed waste water are converted to nitrates by nitrifying micro¬ organisms which is an independent nutrition micro-organisms multiplying and growing in the oxic tank (104). As such, most of the suspension in the oxic tank (104) which contains nitrates is returned and retreated through a second internal circulation pipe

(203) to the anoxic tank (102), while the remaining is directly to the settling tank (105) without returning the anoxic tank. The settling tank (105) is a zone in which the suspension in the bioreactor is soild-liquid separated. A supernatant in the settling tank (105) is a treated water and is discharged through the treated water discharging pipe (206). A settled sludge is returned through a returning sludge pipe (205) to the anoxic tank (102) in order to appropriately maintain the concentration of MLSS (mixed liquor suspended solids) in the bioreactor as well as further treat nitrates remaining in the sludge. Discharging of residual sludge is accomplished by discharging the settled sludge in the settling tank (105) through the sludge discharging pipe (207) and at this time, micro-organisms which over-absorbs phosphorus is discharged together therewith and thus the treatment of phosphorus is completed.

[55] As mentioned above, because the pipes connected to the anoxic tank (102) are various (including the first internal circulation pipe (202), the second internal circulation pipe (203), the returning sludge pipe, etc.,), it is important to control the flowing amount to the anoxic tank (102) in order to appropriately treat nitrogen and phosphorus in accordance with the present invention.

[56] First, the internal circulation rate (internal circulation amount/flowing amount of inflow water) for returning the suspension in the oxic tank (104) which contains nitrates to the anoxic tank (102) should typically be controlled depending on the con¬ centration of nitrogen in the treated water and organic load in the inflow water. In case that it is required to maintain the concentration of nitrogen in the treated water low, the internal circulation rate should be increased, but it is not preferable to increase it more than 500% because the increase of the internal circulation rate results in insignificant increase of the circulation amount of nitrates. Further, if the organic load in the inflow water is low, the internally circulated nitrates cannot be denitrified and thus the internal circulation should be limited. Resultantly, the internal circulation rate should be controlled depending on the organic load in the inflow water.

[57] Meanwhile, the inflow of organic matter into the anoxic tank (102) is controlled by the suspension transfer rate (suspension circulation amount/flowing amount in the inflow water) from the anaerobic tank (101) to the anoxic tank (102). The suspension transfer rate should be controlled depending on nitrates in the sludge returned from the settling tank (105) as well as the nitrates load in the suspension returned from the oxic tank (104), but it is not preferable to increase it more than 500% because the increase of the suspension transfer rate results in insignificant increase of nitrates amount in the suspension inflowed into the anoxic tank (102). Also, returning of sludge from the settling tank (105) to the anoxic tank (102), if it is on general waste water, is controlled to be the extent of 10 to 100% depending on general sludge returning rate (returning sludge amount/flowing amount of inflow water) to maintain the appropriate con¬ centration of MLSS.

[58] The apparatus according to the present invention as shown in Fig. 5 comprises one additional anoxic tank (103) between the anaerobic tank(lθl) and the oxic tank (104) compared to the apparatus according to Fig. 3. This is to prevent the suspension not transferred into the anoxic tank (102) among the suspension in the anaerobic tank (101) from being introduced directly into the oxic tank (104) when treating the wastewater using the apparatus of Fig. 3 (hereinafter, the anoxic tank is referred to as a first anoxic tank and the other anoxic tank is referred to as a second anoxic tank dividedly according to the flowing order of the inflow wastewater). In case that the suspension in the anaerobic tank (101) is directly introduced into the oxic tank (104), organic matter in the suspension consumes oxygen in the oxic tank (104) and therefore needs an aeration energy. Further, there exists the problem that the organic matter in the suspension which is useful in denitrification is directly consumed without being used in the denitrification. Accordingly, if the suspension in the anaerobic tank (101) allows to be introduced into the second anoxic tank (103) prior to introducing into the oxic tank (104), the cost of the aeration energy can be saved and the efficiency of deni¬ trification can also be increased. Also, the efficiency of denitrification is more improved by additionally installing a third internal circulation pipe (204) for connecting the oxic tank (104) and the second anoxic tank (103) each other and returning the nitrates thereto so that the nitrates produced in the oxic tank (104) can be retreated in the second anoxic tank (103) as well as the first anoxic tank (102). The third internal circulation pipe (204) may be installed to be branched from the second internal circulation pipe (203).

[59] In case of flow control of the apparatus shown in Fig. 5 when the COD/TKN ratio in the inflow water is high, the internal circulation rate from the oxic tank (104) to the first anoxic tank (102) depends on the concentration of nitrogen in the treated water because the organic matter necessary for denitrification in the first anoxic tank (102) is sufficient and the suspension transfer rate from the anaerobic tank (101) to the first anoxic tank (102) is controlled correspondingly to the above internal circulation rate. At this time, the suspension which was not transferred from the anaerobic tank (101) to the first anoxic tank (102) is introduced into the second anoxic tank (103). Meanwhile, in case that the COD/TKN ratio in the inflow water is low, the amount of the organic matter becomes low and thus the rate of the internal circulation from the oxic tank (104) to the first anoxic tank (102) is limited by the organic matter in the inflow water.

[60] As such, in case that COD/TKN ratio of the inflow water is low, the increase of the suspension transfer rate from the anaerobic tank (101) to the first anoxic tank (102) results in the correspondingly increased internal circulation rate from the oxic tank (104) to the first anoxic tank (102). However, because it is practically difficult as well as high expensive to transfer all suspension of the anaerobic tank (101) to the first anoxic tank (102) although the transferring rate of the suspension is highly maintained, a portion of the suspension is introduced into the second anoxic tank (103) which is the subsequent bioreactor. In the wastewater having a low COD/TKN ratio, if the organic matter of the anaerobic tank (101) is not used for denitrification, it becomes in¬ effective. Accordingly, by introducing in an internal circulation manner, nitrates are transferred to the second anoxic tank (103) corresponding to the organic matter of suspension transferred to the second anoxic tank (103), the denitrification rate becomes high and thus the aeration energy can be reduced. Herein, the internal circulation rate from the oxic tank (104) to the first anoxic tank (102) is referred to as a first internal circulation rate (internal circulation amount to a first anoxic tank / flowing amount of inflow water) and the internal circulation rate from oxic tank (104) to the second anoxic tank (103) is referred to as a second internal circulation rate (internal circulation amount to the second anoxic tank (103) / flowing amount of inflow water). As described above, the first internal circulation rate and the second internal circulation rate are generally controlled depending on the nitrogen concentration of treated water and the load of organic matte in inflow water. Particularly, the second internal circulation is controlled depending on the first internal circulation rate and the load of organic matter which was not transferred to the first anoxic tank (102). In the anaerobic tank (101), the suspension transfer rate is controlled depending on the load of nitrates in a returning sludge which is returned from settling tank (105) as well as the load of nitrates by the first internal circulation rate.

[61] Figure 7 schematically shows an other example of the biological wastewater treatment apparatus according to the present invention.

[62] The apparatus shown in Figure 7 according to the present invention has not the second internal circulation pipe (203) in Figure 5 and can prevent an interference due the overload or load fluctuation of nitrates which may be caused when both the suspension in the oxic tank (104) and the sludge in the settling tank (105) are transf erred to the first anoxic tank (102). Due to the apparatus, the first anoxic tank (102) receives only the load of nitrates by the sludge of the settling tank (105) and thus can stably denitrify nitrates within the sludge in the settling tank (105). Further, because the amount of organic matter necessary to denitrify nitrates is less required, the transferring rate of the suspension from the anaerobic tank (101) can be reduced. Also, because the suspension in the oxic tank (104) is returned to only the second anoxic tank (103) to which a portion of the suspension from the anaerobic tank (101) is transferred, nitrates contained therein is denitrified and thus phosphorus can be more completely and stably treated in the apparatus in Figure 7. In case of the apparatus shown in Figure 2 used in the conventional DNR process, because the denitrification in the DNR process occurs by an endogenous respiration which uses the organic matter of micro-organisms itself, the speed of denitrification by endogenous respiration is very low and thus it is necessary to increase the amount of micro-organisms in order to obtain a desired effect and consequently, to increase the volume of bioreactor. However, according to the apparatus shown in Figure 7, because the organic matter contained in the suspension in the anaerobic tank (101) through the first internal circulation pipe (202) is supplied to the first anoxic tank (102), nitrites can be denitrified more promptly and thus the increase in the volume of the bioreactor is not required.

[63] With respect to a control of the flowing amount in the apparatus of Figure 7, the transferring rate of suspension from the anaerobic tank (101) to the first anoxic tank (102) is defined depending on the load of nitrates within the returning sludge from the settling tank (105) to the first anoxic tank (102) and the second internal circulation rate from the oxic tank (104) to the second anoxic tank (103) is defined depending on the load of organic matter which was inflowed into the second anoxic tank (103), without being transferred to the first anoxic tank (102) depending on the transferring rate of suspension from the anaerobic tank (101) to the first anoxic tank (102).

[64] Figure 8 schematically shows another example of the biological wastewater treatment apparatus according to the present invention.

[65] The apparatus shown in Figure 8 according to the present invention has the first anoxic tank (102) and the anaerobic tank (101) exchanged in the arrangement order compared to that in Figure 5 and has a sludge-internal-circulating pipe (208) for returning the sludge of the first anoxic tank (102) to the anaerobic tank (101). According to the apparatus shown in Figure 8, because nitrates contained within the suspension in the oxic tank (104) as well as within the sludge in the settling tank (105) are denitrified in the first anoxic tank (102) and then returned to the anaerobic tank (101), the competition between PAO and denitrifying micro-organisms can be prevented, resulting in the increase of the removal efficiency of phosphorus. At this time, the internal circulation of sludge from the first anoxic tank (102) through the sludge-internal-circulating pipe (208) to the anaerobic tank (101) is accomplished by returning the suspension in the first anoxic tank (102) to the anaerobic tank (101), and the rate of the internal circulation of sludge (sludge internal circulating amount/flowing amount of inflow water) should be appropriately adjusted depending on the appropriate concentration (MLSS concentration) of micro-organisms in the anaerobic tank (101). Although the rate of sludge internal circulation should be increased in order to increase the MLSS concentration in the anaerobic tank (101), the increase of the rate of sludge internal circulation more than 500% is not preferable because the increase of the MLSS concentration is insignificant in such rate.

[66] Also, according to the apparatus of Figure 8, similar to the apparatuses shown in

Figures 5 and 7, the suspension in anaerobic tank (101) is transferred to the oxic tank (104) through the first anoxic tank (102) and the second anoxic tank (103) and thus the cost of the aeration energy can be reduced and the efficiency of denitrification can be increased.

[67] Herein, although the first internal circulation rate from the oxic tank (104) to the first anoxic tank (102) and the second internal circulation from the oxic tank (104) to the second anoxic tank (103) are generally controlled depending on the nitrogen con¬ centration of a treated water and the load of organic matter in inflow water, they can also be influenced by the load fluctuation of inflow nitrogen and inflow organic matter. As the general wastewater, if there is the load fluctuation of inflow nitrogen and inflow organic matter, the organic matter inflowed in the first anoxic tank (102) and nitrates not treated by nitrates load are inflowed from the first anoxic tank (102) to the anaerobic tank (101) and then it is resulted from the obstruction of phosporus treatment.

[68] Therefore, the first internal circulation rate to the first anoxic tank (102) is controlled to the extent that nitrates can be stably treated, and the second internal circulation rate to the second anoxic tank (103) is controlled so as to treat nitrates cor¬ responding to the non-treated organic load in the first anoxic tank (102).

[69] In connection with treatment of the wastewater using the apparatus according the p resent invention, hydraulic retention time of waste waters, MLSS concentration, suspension transfer rate, internal circulation rate (a first internal circulation rate), a second internal circulation rate, a sludge internal circulation rate and a sludge return rate in the anaerobic tank (101), the anoxic tank (the first anoxic tank (102), the second anoxic (103)), the oxic tank (104) and the settling tank (105) in case of the general treatment of waste waters using Figures 3, 5, 7 and 8 are shown in Table 1, re¬ spectively.

[70] Table 1

<71> <72> Under such conditions, in case that general sewages are treated using the apparatus according to the present invention, total nitrogen (TN) and total phosphorus (TP) are treated to the extent to 6~12mg/l and l~2mg/l, respectively and thus good efficiency of treatment can be obtained.

<73> The wastewater treatment apparatus according to the present invention may be applied with well-known apparatuses and methods, if necessary. That is, before introducing inflow waters into the anaerobic tank(lθl), it may be possible for the inflow waters to go through a screen for removing impurities in the wastewater, a grit chamber for removing sediments such as sands, an equalization tank for equalizing the flowing amount and the quality of water which are installed in front of the inflow pipe (201) or to go through a first settling tank for removing suspended solids.

<74> It is preferable that in the treatment apparatus according to the present invention, the first anoxic tank (102) and the second anoxic tank (103) have an appropriate mixing device for mixing and the oxic tank (104) has an oxygen or air supplying device for supplying oxygen to micro¬ organisms, respectively.

<75> Also, a submerged ultrafiltration membrane for solid-liquid separation from suspension may be installed into the oxic tank (104) of Figs.3, 5 and 8.

<76> Herein, by further installing a treated discharging pipe (206) and sludge discharging pipe (207) into the oxic tank (104), the settling tank (105) and the pipes connected discharging pipe (207)) can be removed to thereby increase the efficiency of space.

[77] Figures 4, 6 and 9 show that the submerged ultrafiltration membrane (301) is applied to the apparatuses shown in Figures 3, 5 and 8, respectively.

[78] The submerged ultrafiltration membrane (301) is a kind of a separating membrane, and its separation mechanism is absorptive with a screen filtering and if necessary, can be selectively used in the range of 1,000 ~ 2000 in molecular weight cutoff and of 0.1 -0.00 ID in micro pore.

[79] Also, its shape may be selected among a plate and frame type, a tubular type, a hollow fiber type and a spiral wound type, particularly it is preferable to use the plate and frame, tubular or hollow fiber type. A principle of treating wastewater using the submerged ultrafiltration membrane (301) is as follows:

[80] That is, the submerged ultrafiltration membrane (301) that was submerged in the oxic tank (104) adsorbs and filters the suspension inflowed into the oxic tank (104). Suspension is absorbed into the submerged ultrafiltration membrane (301) by an absorption pump (302) operated at generally less than 0.5kg/D, and the solid matter that did not pass through the submerged ultrafiltration membrane (301) remains in the oxic tank (104), while the filtered water is discharged as a treated water.

[81] The treated water absorbed by the absorption pump (302) is one that already passed through the submerged ultrafiltration membrane (301) and thus its degree of turbidity is very low.

[82] Discharging of the resiudal sludge is accomplished through a sludge discharging pipe (207) installed in the oxic tank (104) and an appropriate concentration of micro¬ organisms in the bioreactor which acts as a settling tank is maintained by the returning of suspension in the oxic tank (104) through the second internal circulation pipe (203).

[83] In case of use of the submerged ultrafiltration membrane (301), an additional cleaning device may be preferably installed, if necessary because foreign materials are attached or captured to the surface of the membrane or the micro pore.

[84] As such, if wastewaters are treated by the treating apparatus that uses the submerged ultrafiltration membrane (301), it is possible to obtain the SS reducing effect of treated water compared to the treatment apparatus using the settling tank, and the MLSS concentration in the bioreactor can be maintained highly.

[85] More specifically, in case of the method of treating biological nitrogen and phosphorus using the settling tank, SS in the treated water is 10~30mg/l, and MLSS l,000~4,000mg/l in general, whereas in case of the method of treating biological nitrogen and phosphorus using the submerged ultrafiltration membrane (301), SS in the treated water is less than 2mg/l and MLSS is about 2,000~8,000mg/l. As a result, the volume of bioreactor can be reduced to about to one half.

[86] Alternatively, it is possible to increase the concentration of micro-organisms by filling a flowing media (401) and a fixed media (408) in order to provide the oxic tank (104) in Figures 3, 5, 7 and 8 according to the present application with a space or surface for capturing micro-organisms and attaching thereto.

[87] Increase of the concentration of micro-organisms according to the multiplication and growth of micro-organisms in the flowing media (401) or fixed media (408) allows the effect that the volume and available building site area can be reduced to about 1/2 to 2/3.

[88] Also, given that the growing speed of nitrifying micro-organisms that causes a ni¬ trification in the oxic tank (104) is slow and that the nitrifying action at low temperature by the nitrifying micro-organisms is not easy, the stable holding of the nitrifying micro-organisms can achieve more efficient nitrifying effects.

[89] The size, shape, materials and the like of the flowing media (401) or fixed media

(408) being filled therein are not specifically limited. In case of the flowing media (401), media having a polyhedron shape such as cubic shape or circular of several mm to several cm may be filled selectively and in case of the fixed media (408), a media having a fiber shape of several tens cm to several m in length, a honeycombed shape, a plate shape or the like may be filled selectively.

[90] Also, materials of the flowing media (401) or fixed media (408) may be used by selecting any one of inorganic matters such as clays, sands, natural, artificial zeolite or the like; waste materials such as waste vinyl; synthetic resins such as polyethylene, polystyrene, polyamide and the like; and synthetic resins having activated charcoal annexed thereto.

[91] As such, in order to prevent the filled media from being separated and washed out from the oxic tank (104), in case of the flowing media (401), a device for rotating the media using the flow of suspension in the oxic tank (104), gravity and inertia power of the media may be installed as shown in Figure 10 or alternatively, the screen (407) may be installed into the oxic tank (104) as shown in Figure 11. In case of the fixed media (408), as shown in Figure 12, the oxic tank (104) may be filled with fiber-shape media having its upper end and lower end fixed to the frame, a honeycombed-shape or a plate-shape media fixed to a lattice-shape frame.

[92] In case that as shown in Figure 10, the oxic tank (104) is installed with an aeration device (405), rotation inducing plate (402) and the like in order to rotate media using the flow of suspension in the oxic tank (104) and the gravity and inertia power of media, a blocking plate (403) and separating plate (404) may be further installed in order to prevent the overflow of suspension including a flowing media (401).

[93] In case that some of suspension and flowing media (401) overflow the blocking plate (403), these are induced to the lower portion of the oxic tank by the gravity of them, separated from each other at the boundary of the blocking plate (403) by a rotating power of suspension and the gravity and inertia power of media and thus only the suspension is outflowed through the blocking plate (403). Therefore, the flowing media can be continuously recirculated within the oxic tank (104).

[94] Also, in case that the oxic tank (104) is installed with the screen (407) as shown in

Figure 11, a media circulation pipe (406) may be further installed for circulating the flowing media (401), and a circulation device, such as air lift pump, for the flowing media (401) in order to prevent the situation that flowing media (401) being con¬ centrated and gathered on the screen according to the flow of suspension containing the flowing media (401).

[95] When treating waste waters using the wastewater treating apparatus according to the present invention, in order to maintain COD/TKN and COD/TP in a predetermined ratio to thereby treat nitrogen and phosphorus more effectively, the anaerobic tank (101) and/or the first anoxic tank (102) are introduced with at least one species of external carbon sources selected from the groups consisted of an organic chemicals such as methanol, acetate, etc.; organic liquid wastes containing organic matter such as methanol, acetate, etc.; organic liquid wastes containing solid in great quantities such as night soil, sediment of septic tank, live stock waste water, food waste, etc.; raw sludge generated in a first settling tank in the wastewater treatment field; recirculated water such as supernatant from sludge concentration apparatus and digester, effluent from dehydrator in the wastewater treatment field; and acid fermentation products of the above organic liquid wastes and raw sludge.

[96] Particularly, because organic acid among COD is effective in order to treat phosphorus more effectively, the carbon source may be inflowed after converting organic liquid wastes, organic liquid wastes containing solid in great quantities, raw sludge generated in a first settling tank and the like to organic acids through anaerobic acid fermentation.

[97] If the anaerobic tank (101) is designated as the inflowing point of the external carbon source, the absorption amount of organic matter and the release amount of phosphorus by PAO can be increased and resultantly the efficiency of phosphorus treatment can be improved. If the first anoxic tank (102) is designated as the inflowing point of the external carbon source, this carbon source becomes an electron acceptor and thus nitrates are actively denitrified and the efficiency of nitrogen treatment is increased

[98]

Industrial Applicability

[99] According to the wastewater treating apparatus of the present invention, because the absorption of organic matter and release of phosphorus by PAO in the anaerobic tank are effectively achieved, the removal efficiency of phosphorus can be elevated, while the removal efficiency of nitrogen can be increased.

[100] Also, by using applying conventional ultrafiltration membrane and media with having the wastewater treating apparatus of the present invention as a basic con¬ struction, the high removal efficiency of nitrogen and phosphorus can be maintained and the volume and a required building area of the wastewater treating apparatus can be reduced.

[101]

Claims

[1] A wastewater treatment apparatus comprising a anoxic tank, an anaerobic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising: an inflow pipe for introducing waste waters into the anaerobic tank; a first internal circulation pipe for connecting the anaerobic tank and the anoxic tank and transferring a suspension in the anaerobic tank to the anoxic tank; a second internal circulation pipe for connecting the oxic tank and the anoxic tank and returning a suspension in the oxic tank to the anoxic tank; a returning sludge pipe for connecting the settling tank and the anoxic tank and returning a sludge in the settling tank to the anoxic tank; a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and a sludge discharging pipe serving as a passage for discharging sludge in the settling tank.

[2] A wastewater treatment apparatus comprising a first anoxic tank, an anaerobic tank, a second anoxic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising: an inflow pipe for introducing waste waters into the anaerobic tank; a first internal circulation pipe for connecting the anaerobic tank and the first anoxic tank and transferring a suspension in the anaerobic tank to the first anoxic tank; a second internal circulation pipe for connecting the oxic tank and the first anoxic tank and returning a suspension in the oxic tank to the first anoxic tank; a third internal circulation pipe for connecting the oxic tank and the second anoxic tank and returning a suspension in the oxic tank to the second anoxic tank; a returning sludge pipe for connecting the settling tank and the first anoxic tank and returning a sludge in the settling tank to the first anoxic tank; a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and a sludge discharging pipe serving as a passage for discharging sludge in the settling tank.

[3] A wastewater treatment apparatus comprising a first anoxic tank, an anaerobic tank, a second anoxic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising: an inflow pipe for introducing waste waters into the anaerobic tank; a first internal circulation pipe for connecting the anaerobic tank and the first anoxic tank and transferring a suspension in the anaerobic tank to the first anoxic tank; a third internal circulation pipe for connecting the oxic tank and the second anoxic tank and returning a suspension in the oxic tank to the second anoxic tank; a returning sludge pipe for connecting the settling tank and the first anoxic tank and returning a sludge in the settling tank to the first anoxic tank; a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and a sludge discharging pipe serving as a passage for discharging sludge in the settling tank.

[4] A wastewater treatment apparatus comprising an anaerobic tank, a first anoxic tank, a second anoxic tank, an oxic tank and a settling tank in serial and pipes for connecting them in serial, comprising: an inflow pipe for introducing waste waters into the anaerobic tank; a sludge internal circulation pipe for connecting the anaerobic tank and the first anoxic tank and returning a suspension in the first anoxic tank to the anaerobic tank; a second internal circulation pipe for connecting the oxic tank and the first anoxic tank and returning a suspension in the oxic tank to the first anoxic tank; a third internal circulation pipe for connecting the oxic tank and the second anoxic tank and returning a suspension in the oxic tank to the second anoxic tank; a returning sludge pipe for connecting the settling tank and the first anoxic tank and returning a sludge in the settling tank to the first anoxic tank; a treated water discharging pipe serving as a passage for discharging the treated water in the settling tank; and a sludge discharging pipe serving as a passage for discharging sludge in the settling tank.

[5] The wastewater treatment apparatus according to any one of claim 1, 2 or 4, wherein after removing the settling tank and the returning sludge pipe connected thereto, the treated water discharging pipe and the sludge discharging pipe instead thereof, a submerged ultrafiltration membrane is installed into the oxic tank and the treated water discharging pipe and the sludge discharging pipe are connected to the oxic tank.

[6] The wastewater treatment apparatus according to any one of claims 1 to 4, wherein a flowing media or a fixed media is additionally filled into the oxic tank.

[7] The wastewater treatment apparatus according to any one of claims 1 to 4, further comprising: in front of the inflow pipe, at least one device of a screen for removing impurities in the wastewater, an aeration tank for removing sediments such as sands, an equalization tank for equalizing the flowing amount and the quality of water and a first settling tank for removing suspended solids.

[8] The wastewater treatment apparatus according to any one of claims 1 to 4, wherein the anaerobic tank and/or the first anoxic tank are introduced with at least one species of external carbon source selected from the groups consisted of an organic chemicals such as methanol, acetate, etc.; organic liquid wastes containing organic matter such as methanol, acetate, etc.; organic liquid wastes containing solid in great quantities such as night soil, sediment of septic tank, live stock waste water, food waste, etc.; raw sludge generated in a first settling tank in the wastewater treatment field; recirculated water such as supernatant from sludge concentration apparatus and digester, effluent from dehydrator in the wastewater treatment field; and acid fermentation products of the above organic liquid wastes and raw sludge.