Wastewater treatment method and membrane bioreactor having mixed liquor and air conduits in a filtration tank

1. A method of biologically treating wastewater are a membrane bioreactor, comprising:

a. directing an influent stream of wastewater into a biological treatment tank and biologically treating the wastewater and forming mixed liquor in the treatment tank;

b. transferring the mixed liquor from the treatment tank to a downstream filtration tank;

c. submerging one or more membrane modules in mixed liquor contained within the filtration tank;

d. positioning the one or more membrane modules in the filtration tank such that the membrane modules occupy substantially the entirety of the cross-sectional area of the filtration tank;

e. transferring the mixed liquor from the treatment tank to the filtration tank including pumping mixed liquor from the treatment tank into one or more mixed liquor conduits extending through the filtration tank underneath the one or more membrane modules;

f. directing mixed liquor from the one or more mixed liquor conduits through orifices formed in an outer wall of the one or more mixed liquor conduits;

g. after passing through the orifices in the mixed liquor conduits, the mixed liquor moves vertically through the filtration tank and through the one or more membrane modules in the filtration tank;

h. constraining the flow of vertically moving mixed liquor in the filtration tank such that substantially the entire flow of vertically moving mixed liquor in the filtration tank is constrained to move through the one or more membrane modules;

i. as the mixed liquor moves vertically through the one or more membrane modules, passing a first portion of the mixed liquor through individual membrane filters forming a part of the one or more membrane modules to produce a permeate;

j. directing the permeate from the individual membrane filters and from the filtration tank;

k. recycling a second portion of the mixed liquor from the filtration tank to the treatment tank after the second portion of the mixed liquor has passed through the one or more membrane modules;

l. wherein at least 50% of the mixed liquor passing into the filtration tank is recycled to the treatment tank; and

m. dispersing air from openings in one or more air conduits extending through the filtration tank underneath the membrane modules such that both the air and mixed liquor move upwardly through the membrane modules.

2. The method of claim 1 wherein the one or more mixed liquor conduits are disposed below the one or more air conduits, and both the one or more mixed liquor conduits and the one or more air conduits are disposed below the membrane modules.

3. The method of claim 2 including utilizing the upwardly flowing mixed liquor in the filtration tank to generally uniformly distribute the upwardly moving air.

4. The method of claim 2 including utilizing the upwardly flowing mixed liquor in the filtration tank to generally uniformly distribute the upwardly moving air in the filtration tank such that the air is generally uniformly distributed across substantially the entire cross-sectional area of the one or more membrane modules.

5. The method of claim 1 wherein the one or more air conduits include first and second sets of air conduits; and wherein the one or more mixed liquor conduits include at least two spaced apart conduits extending through the filtration tank with each mixed liquor conduit having an array of the orifices formed therein to permit mixed liquor to be dispersed from the mixed liquor conduits throughout the filtration tank.

6. The method of claim 5 including directing air to the first and second sets of air conduits in an alternating pattern such that during one period of time air is dispersed by the first set of air conduits and not the second set of air conduits and in another period of time air is dispersed by the second set of air conduits and not the first set of air conduits.

7. The method of claim 1 including placing a seal around the one or more membrane modules such that the seal lies between the one or more membrane modules and the filtration tank.

8. The method of claim 1 wherein both the treatment tank and the filtration tank include a length and a width, and wherein the length of the filtration tank is less than the length of the treatment tank; and wherein the length of the filtration tank is substantially less than the width of the filtration tank.

9. The method of claim 1 including stacking a series of membrane modules one over the other in the filtration tank such that the stacked membrane modules occupy substantially the entire cross-sectional area of the filtration tank.

10. The method of claim 1 wherein each of the one or more membrane modules includes an array of out-to-in membrane filters, and wherein the mixed liquor enters the membrane filters from an outside area and passes into an interior area of the membrane filters as the permeate.

11. The method of claim 1 wherein the mixed liquor passing through the one or more membrane modules but not filtered is referred to as a non-permeate stream; and wherein the method includes restricting the movement of the non-permeate stream so as to substantially preclude the recirculation of the non-permeate stream back through the one or more membrane modules prior to the non-permeate stream being recirculated back to the treatment tank.

12. A membrane bioreactor wastewater treatment system for treating wastewater, comprising:

a. a wastewater treatment tank for receiving wastewater influent and biologically treating the wastewater in the wastewater treatment tank to form mixed liquor;

b. a filtration tank disposed downstream from the wastewater treatment tank for receiving mixed liquor treated in the wastewater treatment tank;

c. one or more membrane filtration modules disposed in the filtration tank and adapted to be submerged in the mixed liquor contained therein, and wherein the one or more membrane filtration modules filter at least some of the mixed liquor in the filtration tank to produce a permeate;

d. each membrane module including an array of membrane filters adapted to be submerged in the mixed liquor within the filtration tank;

e. the filtration tank and the one or more membrane modules sized relative to each other such that the one or more membrane modules occupies substantially the entire cross-sectional area of the filtration tank such that substantially all the mixed liquor passing through the filtration tank is constrained to move through the one and more membrane filtration modules;

f. one or more permeate lines operatively connected to the one or more membrane modules in the filtration tank for directing permeate from the filtration tank;

g. a recycle outlet for recycling mixed liquor from the filtration tank to the treatment tank;

h. wherein the membrane bioreactor wastewater treatment system is adapted to recycle back to the treatment tank at least 50% of the mixed liquor directed from the treatment tank to the filtration tank;

i. one or more mixed liquor conduits extending through a portion of the filtration tank, each mixed liquor conduit including an outer wall and disposed below the one or more of the membrane modules and including a series of orifices formed in the outer wall through which mixed liquor is dispersed into the filtration tank;

j. one or more mixed liquor transfer conduits for directing mixed liquor from the treatment tank to the one or more mixed liquor conduits;

k. one or more pumps for pumping mixed liquor from the treatment tank, through the one or more mixed liquor transfer conduits into the one or more mixed liquor conduits;

l. one or more air conduits for dispensing air into the filtration tanks and extending through the filtration tank and disposed below the one or more membrane filtration modules;

m. each air conduit having an array of orifices formed in an outer wall thereof for dispersing air into the filtration tank; and

n. a source of compressed air for supplying air to the air conduits.

13. The membrane bioreactor system of claim 12 wherein the filtration tank includes a bottom and wherein the one or more membrane modules are elevated relative to the bottom of the filtration tank so as to define an open space between the one or more membrane modules and the bottom of the filtration tank; and wherein both the one or more mixed liquor conduits and the one or more air conduits are disposed in the open space below the one or more membrane modules and wherein the one or more air conduits are disposed above the one or more mixed liquor conduits.

14. The membrane bioreactor system of claim 13 wherein the filtration tank is elongated and includes a width and a length and wherein the width is greater than the length.

15. The membrane bioreactor system of claim 12 wherein the one or more air conduits include first and second sets of air conduits, and wherein air is provided to the first and second sets of air conduits in alternating fashion such that in one period of time air is supplied to the first set of air conduits and not the second set of air conduits and in another period of time there is supplied to the second set of air conduits and not the first set of air conduits.

16. The membrane bioreactor system of claim 12 including a seal surrounding the one or more membrane modules and disposed generally between the filtration tank and the one or more membrane modules.

17. The membrane bioreactor system of claim 12 wherein the mixed liquor conduits include two spaced apart mixed liquor conduits, and wherein mixed liquor is fed into each mixed liquor conduit at two spaced apart locations.

18. The membrane bioreactor system of claim 12 wherein the orifices formed in the outer wall of the one or more mixed liquor conduits vary in size along the length of the respective mixed liquor conduits.

19. The membrane bioreactor system of claim 12 wherein the one or more mixed liquor conduits are disposed below the one or more air conduits in the filtration tank; and

wherein the mixed liquor conduits and the air conduits are oriented with respect to each other such that the mixed liquor flowing upwardly from the one or more mixed liquor conduits tends to uniformly distribute air moving upwardly from the one or more air conduits across the cross-sectional area of the filtration tank.