Denitrification biofilter device and method for treating wastewater

Abstract

A denitrification biofilter device, including: a regulating pool, a reactor body, a water tank, a first doser, a second doser, a backwash pump, a water inlet pump, and a blower. The regulating pool includes a raw water inlet and a water outlet. The reactor body includes a uniform water distributor, a filler layer, a buffer layer, a filter layer, a supporting layer, a filler supporting plate, a backwash water outlet, a treated water outlet, and a backwash water inlet. The treated water outlet and the backwash water inlet are disposed at the bottom of the reactor body and are connected to the water tank via pipes. The filler layer is filled with zeolites having a grain size of between 4 and 8 mm, a density of between 1.9 and 2.6 g/cm.sup.3, a porosity greater or equal to 48%, and a specific surface area of between 570 and 670 m.sup.2/g.

Claims

1. A device, comprising: a) a regulating pool, the regulating pool comprising a first inlet and a first outlet; b) a reactor body, the reactor body comprising a uniform water distributor, a filler layer, a buffer layer, a filter layer, a supporting layer, a filler supporting plate, a second outlet, a third outlet, and a second inlet; c) a water tank; d) a first doser, the first doser comprising a dosing tube; e) a second doser; f) a backwash pump; g) a water inlet pump; and h) a blower; wherein the dosing tube is extended into the regulating pool; the first outlet of the regulating pool is connected to the water inlet pump and a top of the reactor body via pipes; the reactor body is in a cylinder structure; the uniform water distributor, the filler layer, the filler supporting plate, the buffer layer, the filter layer, and the supporting layer are disposed inside the reactor body from top to bottom in that order; the filler layer is disposed in an upper portion of the reactor body; the buffer layer is disposed in a middle portion of the reactor body; the filter layer is disposed in a lower portion of the reactor body; the filler layer comprises nitrifying bacteria; the filter layer comprises denitrifying bacteria; the filler supporting plate is disposed between the filler layer and the buffer layer; a plurality of curved holes is disposed at a periphery of the filler supporting plate; the second outlet is disposed on a sidewall of the buffer layer; the third outlet and the second inlet are disposed at a bottom of the reactor body and are connected to the water tank via pipes, respectively; the backwash pump is disposed on a pipe between the second inlet and the water tank; the second doser is connected to the sidewall of the buffer layer via a pipe; the filler layer is filled with zeolites having a grain size of between 4 and 8 mm, a density of between 1.9 and 2.6 g/cm.sup.3, a porosity of more than or equal to 48%, and a specific surface area of between 570 and 670 m.sup.2/g; and when in use, wastewater comprising ammonium is introduced into the filler layer, and ammonium is converted to nitrate and nitrite by the nitrifying bacteria via a nitrification process; the wastewater from the filler layer flows into the buffer layer and then to the filter layer; and a source of carbon is added into the buffer layer via the second doser and is then consumed by the denitrifying bacteria in the filter layer, and nitrate and nitrite are reduced into nitrogen by the denitrifying bacteria via a denitrification process.

2. The device of claim 1, wherein the uniform water distributor comprises: a main pipe, branch pipes, and water distributing holes; and the water distributing holes having equal diameters are evenly disposed at equal intervals at a lower side of each branch pipe.

3. The device of claim 1, wherein the supporting layer is filled with pebbles, each pebble has a grain size of between 2 and 6 mm and a density of 2.65 g/cm.sup.3.

4. The device of claim 1, wherein the filter layer is filled with sea sand having a grain size of between 2 and 3 mm.

5. The device of claim 1, wherein four curved holes are disposed on a periphery of the filler supporting plate contacting with an inner wall of the reactor body; and each of the curved holes has a radian of 1.05 rad and a width of 4 mm.

6. The device of claim 1, wherein the source of carbon comprises sodium acetate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described hereinbelow with reference to the accompanying drawings, in which:

(2) FIG. 1 is a structure diagram of a denitrification biofilter device in accordance with one embodiment of the invention;

(3) FIG. 2 is a structure diagram of a filler supporting plate in accordance with one embodiment of the invention; and

(4) FIG. 3 is a cross-sectional view taken from line A-A of FIG. 2.

(5) As In the drawings, the following numbers are used: 1. Regulating pool; 2. First doser; 3. Second doser; 4. Uniform water distributor; 5. Filler layer; 6. Backwash water outlet; 7. Buffer layer; 8. Filter layer; 9. Supporting layer; 10. Backwash pump; 11. Water inlet pump; 12. Filler supporting plate; 13. Reactor body; 14. Water tank; 15. Blower; and 16. Curved holes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) For further illustrating the invention, experiments detailing a denitrification biofilter device and a method for treating wastewater are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

(7) As shown in FIG. 1, a denitrification biofilter device comprises: a regulating pool 1, a reactor body 13, and a water tank 14, a first doser 2, a second doser 3, a backwash pump 10, a water inlet pump 11, and a blower 15. The first doser 2 is provided with a dosing tube and the dosing tube is extended into the regulating pool 1. The regulating pool 1 comprises a raw water inlet and a water outlet. The water outlet of the regulating pool 1 is connected with the water inlet pump 11 and a top of the reactor body 13 in sequence via pipes. The reactor body 13 is in a cylinder structure. A uniform water distributor 4, a filler layer 5, a buffer layer 7, a filter layer 8, and a supporting layer 9 are disposed from top to bottom inside the reactor body 13. A filler supporting plate 12 is disposed between the filler layer 5 and the buffer layer 7. A backwash water outlet 6 is disposed on a sidewall of the buffer layer 7. A treated water outlet and a backwash water inlet are disposed at a bottom of the reactor body 13, and the treated water outlet and the backwash water inlet are connected to the water tank 14 via pipes. The backwash pump 10 is disposed on a pipe between the backwash water inlet and the water tank 14. The second doser 3 is connected to the sidewall of the buffer layer 7 via a pipe. The filler layer 5 is filled with zeolites, and each zeolite having a grain size of between 4 and 8 mm, a density of between 1.9 and 2.6 g/cm.sup.3, a porosity of more than or equal to 48%, and a specific surface area of between 570 and 670 m.sup.2/g. The uniform water distributor 4 comprises: a main pipe, branch pipes, and water distributing holes. 15 water distributing holes having equal diameters are evenly distributed at equal intervals on a lower side of each branch pipe. The supporting layer 9 is filled with pebbles, and each pebble has a grain size of between 2 and 6 mm and a density of 2.65 g/cm.sup.3. The filter layer 8 is filled with sea sand having a grain size of between 2 and 3 mm. A center of the filler supporting plate 12 is designed in the absence of holes. Four curved holes 16 are disposed on a periphery of the filler supporting plate 12 contacting with the inner wall of the reactor body 13. Each of the curved holes 16 has a radian of 1.05 rad and a width of 4 mm. A distance between a center position of each curved hole 16 and an inner wall of the reactor body 13 is 0.5 mm, and the four curved holes 16 are uniformly distributed in relative to the center of the filler supporting plate 12. Such shape design enables the downwardly flowing wastewater to pass through the curved holes in the form of a laminar flow along the inner wall of the reactor body 13 to enter the buffer layer, thereby avoiding water whirlpool that occurs in the conventional water flowing holes and preventing the oxygen in the air from entering the water. The denitrification biofilter is constantly fed with water by the water inlet pump. The constant water level operation is capable of decreasing the cascade and avoiding the production of the dissolved oxygen.

(8) A method for treating wastewater is conducted as follows:

(9) 1) Wastewater to be treated is introduced into the regulating pool 1. The first doser 2 is opened, and an ammonium chloride solution is added to the regulating pool 1 via the first doser 2 to enable a concentration of ammonia nitrogen to be 1.60.3 mg/L. A removal rate of ammonia nitrogen after 22 days treatment exceeds 76% and a concentration of ammonia nitrogen is stable. After that, the first doser 2 is closed. When the concentration of ammonia nitrogen of the influent is 0.78 mg/L, the filler layer 5 is capable of decreasing the dissolved oxygen of the influent from 6.70 mg/L to 4.15 mg/L.

(10) 2) The water inlet pump 11 is started, the water passes through the uniform water distributor 4 to enter the filler layer 5 where NH.sub.4.sup.+N of the influent is absorbed by the zeolites, nitrification of the nitrification bacteria occurs using NH.sub.4.sup.+N and the dissolved water, and NH.sub.4.sup.+N is converted into nitrate nitrogen and nitrite nitrogen.

(11) 3) The water flowing out of the filler layer 5 passes through curved holes of the filler supporting plate 12 along the sidewall of the reactor body to enter the buffer layer 7 and then to flow directly into the filter layer 8. Meanwhile, the second doser 3 is operated to add sodium acetate to the buffer layer 7 as an external carbon source. The external carbon source and the original BOD in the wastewater serve as the organic carbon source for the denitrification bacteria in the filter layer 8 to reduce nitrite and nitrate into nitrogen. After 12 days treatment, the removal rate of the nitrate nitrogen in the filter layer 8 reaches 84% and is stabilized.

(12) 4) The water after being treated by the filter layer 8 passes through the supporting layer 9 and enters the water tank 14.

(13) 5) One part of the water in the water tank 14 is used to backwash the filter layer 8 when the backwash pump 10 is opened, the water/gas simultaneously backwash the filter layer 8 for 3 min with a water intensity of 8 L/(s.Math.m.sup.2) and a gas intensity of 14 L/(s.Math.m.sup.2). The remaining water reaching the standard is discharged.

(14) The filler layer is able to effectively decrease the inhibition effect of the dissolved oxygen on the denitrification, so that the external carbon-nitrogen ratio is decreased from C/N=3 to C/N=1.86 on the premise of a constant total nitrogen concentration.

(15) The device having a hydraulic loading of 2 m.sup.3/(m.sup.2h) and an external carbon-nitrogen ratio of C/N=1.86 is utilized, and changes in water quality before and after treatment are as follows:

(16) TABLE-US-00001 NH.sub.3N NO.sub.3N NO.sub.2N TN SS TP COD (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) Before 0.78 8.50 0.0083 9.67 7.8 0.23 33.56 treatment After 0.20 1.06 0.023 1.39 1.5 0.07 28.16 treatment

(17) When the hydraulic loading is increased to 4 m.sup.3/(m.sup.2h), the total nitrogen of the effluent is 2.62 mg/L, which still satisfies the total nitrogen of the effluent <3 mg/L.

(18) Because of the strong absorption effect of the zeolite on NH.sub.4.sup.+N, the total nitrogen of the effluent of the denitrification biofilter is still stabilized within 3 mg/L even when the secondary effluent from the sewage is unstable and ammonia nitrogen loading is increased to 5 mg/L.

(19) While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.