Zero excess sludge membrane bioreactor

• US 20050194310A1
• Filed: 03/01/2005
• Published: 09/08/2005
• Est. Priority Date: 03/03/2004
• Status: Active Grant

• Current Assignee: Chuan-Hong Xing, Kazuo Yamamoto
• Original Assignee: Chuan-Hong Xing, Kazuo Yamamoto
• Inventors: Xing, Chuan-Hong, Yamamoto, Kazuo
• Granted Patent: US 7,311,833 B2
• Time in Patent Office: Days
• US Class Current: 210/605
• CPC Class Codes: C02F 3/1268 Membrane bioreactor systems
• CPC Class Codes: C02F 3/2893 with biogas recycling
• CPC Class Codes: C02F 3/302 Nitrification and denitrification treatment C02F3/308 takes precedence
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage

Abstract

An inclined plate coupled membrane bioreactor for treating feed water having excessive level of nutrients in particular chemical oxygen demand and total nitrogen and suspended solids has an aerobic bioreactor for nitrification and aerobic biodegradation in which membranes are submerged for permeate extraction, and an anoxic bioreactor for denitrification within which the inclined plates are outfitted to confine as much anoxic sludge as possible. An air oxygenating and an air scouring are continuously provided to the aerobic bioreactor to maintain a desired aerobic environment and to mitigate membrane fouling while an intermittent air blowing is provided to the anoxic bioreactor to blow out gaseous content generated through denitrification and to rectify the uniformed flow along the inclined plates. The aerobic sludge is recycled to the lower compartment of anoxic bioreactor and the supernatant of anoxic bioreactor is collected as weir effluent and delivered to the downstream aerobic bioreactor. Permeate is intermittently extracted from the membranes by a suction pump. There is no excess sludge withdrawn from the inclined plate coupled membrane bioreactor throughout the experiment.

Claims

1. An inclined plate coupled membrane bioreactor comprising,

(a) an anoxic bioreactor (16) outfitted with required outlets and inlets for outgoing and incoming exchanges in the form of gas, liquid or solids;

(b) an aerobic bioreactor (17) outfitted with required outlets and inlets for outgoing and incoming exchanges in form of gas, liquid or solids;

(c) a single or an array of inclined plates (37) placed at the upper compartment (42);

(d) a single weir or a multiple weir system (25) in association with said anoxic bioreactor (16);

(e) a membrane or a bank of membranes (21) submerged into the aerobic sludge (50) either vertically or inclinedly to the bottom of said aerobic bioreactor (17).

2. The inclined plate coupled membrane bioreactor of claim 1 wherein the holed plate flow regulator or the like is optional and preferable at a hole (40) size of 5 mm up to 100 mm, and more typically at a hole size of 10 mm to 50 mm in diameter.

3. The inclined plate coupled membrane bioreactor of claim 1 wherein the slow agitator (39) or the like is optional and preferable in continuous operation at a speed of 10 rounds per minute to 1000 rounds per minute, more typically at a speed of 30 rounds per minute to 300 rounds per minute.

4. The inclined plate coupled membrane bioreactor of claim 1 wherein the ratio of aerobic bioreactor (17) to anoxic bioreactor (16) is preferable between 0.1 and 0.9 and more preferably between 0.3 and 0.6.

5. The inclined plate coupled membrane bioreactor of claim 1 wherein the ratio of the upper compartment (42) to the lower compartment (41) is preferable between 0.3 and 0.8 and more preferably between 0.4 and 0.6.

6. The inclined plate coupled membrane bioreactor of claim 1 wherein the angle of inclined plates is preferably movable between 30 degrees to 150 degrees. The inclined plates (37) typically move from the initial inclined angle (35) to its supplementary angle at a speed of 0.01 degree per second to 10 degree per second and at a frequency of once every 30 minutes to once every week, depending on the actual situation of anoxic sludge pileup at the foot of inclined plates (37).

7. A process for treating wastewater (1) in an inclined plate coupled membrane bioreactor comprising the steps of:

(a) feeding the wastewater (1), either directly or subject to mixing with the recycled aerobic sludge (50), into the lower compartment (42) of an anoxic bioreactor (16) where biological processes convert the wastewater (1) and the recycled aerobic sludge (50) from downstream aerobic bioreactor (17) into the mixed liquor or the anoxic sludge (43) in the absence of sufficient free oxygen; and

(b) providing a single or an array of inclined plates (37) at the upper compartment (42) of the bioreactor (16) to achieve the desired sedimentation of the said mixed liquor or the anoxic sludge (43) through a mechanism of offering larger sedimentation area and promoting the formation of counterflows between two adjacent plates (60, 61); and

(c) providing a weir (25) through which the top supernatant (48) of the anoxic sludge (43) is collected and transferred to the downstream aerobic bioreactor (17); and

(d) feeding the weir effluent (51) into an aerobic bioreactor (17) in which aerobic biological processes convert the weir effluent (51) into a mixed liquor or the aerobic sludge (50); and

(e) providing a single membrane or a bank of membranes (21) submerged in the said aerobic sludge (50) so that the hollow fiber membranes (21) can withdraw the permeate (13) from said aerobic sludge (50) to the membrane lumens (23) through the permeate line (19) under a substantial negative pressure; and

(f) providing both continuous air scouring bubbles (22) and air oxygenating bubbles (29) upwards to mitigate possible fouling of the membranes (21) and to maintain an aerobic microenvironment for the said aerobic sludge (50); and

(g) recycling the nitrate enriched aerobic sludge (50) to the lower compartment (41) via an inlet (3) at a designed recycle ratio for continuous denitrification.

8. The process of claim 7 wherein the intermittent air blowing to the anoxic bioreactor (16) is preferably provided at 0.1 m³-0.5 m³ normal air 20°

C. per square meter section area per minute for a 1 min-30 min ON and 10 min-120 min OFF cycle, and more typically, supplied at 0.1 m³-0.3 m³ normal air 20°

C. per square meter section area per minute for a 2 min-10 min ON and 30 min-60 min OFF cycle.

9. The process of claim 7 wherein the diffuser (33) employed for air blowing to the anoxic bioreactor (16) produces coarse bubbles having an average diameter of 1 mm to 50 mm, more preferably having a diameter range between 5 mm and 10 mm. The source of blowing air supply can be either fresh air or oxygen-depleted air (46) collected by a hood (18) suspended above the water surface (30) of the aerobic bioreactor (17).

10. The process of claim 7 wherein the weir effluent (51) is transferred to the downstream aerobic bioreactor (17) by either gravity flow or pressurized flow, depending on actual altitudinal collocation.

11. The process of claim 7 wherein the continuous air scouring to membranes (21) is provided at 0.1 m³-0.8 m³ normal air 20°

C. per square meter section area per minute and more typically, provided at 0.2 m³-0.5 m³ normal air 20°

C. per square meter section area per minute. The average bubble size has a preferable diameter between 1 mm and 50 mm, and more typically have an average between 5 mm and 10 mm.

12. The process of claim 7 wherein the membrane module (24) is submerged into the aerobic bioreactor (17) either vertically or inclinedly. An inclined orientation (e.g., 60 degree to 89 degree to the bioreactor bottom) is preferable to maximize the effectiveness of air scouring to hollow fiber membranes (21). Such an arrangement is more preferable for submerged Kubota plate membranes but not limited to.

13. The process of claim 7 wherein the aerobic bioreactor (17) has a HRT of 1.0 hour to 5 hours and more preferably 1.0 hour to 3 hours, and the anoxic bioreactor (16) has a HRT of 2.0 hours to 10 hours and more preferably 3 hours to 6 hours.

14. The process of claim 7 wherein the SRT is kept at infinitely long and no excess sludge is therefore withdrawn from both reactors according to the invention.