WASTEWATER TREATMENT WITH INDEPENDENTLY CONTROLLED AERATION AND MIXING

Abstract

Fine-bubble-producing aeration units and large-bubble-producing (or other mechanical) mixing units are interspersed with each other in a given body of water to be treated. The two different types of units are independently controlled to independently regulate degrees of aeration and mixing in the given body of water.

Claims

1. In a wastewater treatment facility having fine-bubble-producing aeration units and mixing units interspersed with each other in a given body of water, the method comprising: controlling a rate of fine-bubble production via the fine-bubble-producing aeration units; and independently controlling a rate of mixing of water in the body of water using the mixing units.

2. The method of claim 1, wherein the mixing units comprise large-bubble-producing mixing units and wherein fine-bubble-based aeration and large-bubble-based mixing are conducted at different times with respect to each other.

3. The method of claim 2, wherein the fine-bubble-producing aeration units and the large-bubble-producing mixing units are supplied with air from a common source of air and wherein rates of air delivery to the fine-bubble-producing aeration units and the large-bubble-producing mixing units are independently controlled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic plan view of an installation for independently controlling fine-bubble-producing aeration units and large-bubble-producing mixing units in accordance with this disclosure; and

[0012] FIGS. 2A and 2B are schematic side views of the installation illustrated in FIG. 1, illustrating operation in an aerobic mode and in an anaerobic mode, respectively.

DESCRIPTION OF EMBODIMENTS

[0013] An embodiment 10 configured to practice the claimed invention is illustrated in FIGS. 1, 2A, and 2B. The embodiment 10 may be, for example, a wastewater treatment lagoon system, including a first, primary cell 12 in which aerobic nitrification and anaerobic denitrification take place depending on the operational mode of the cell 12; and a second, downstream polishing or clarifying cell 14 in which further aerobic nitrification takes place.

[0014] The primary cell 12 has a multitude of air-injecting units distributed across the floor of the cell, preferably interspersed with each other. The air-injecting units include fine-bubble-producing aeration units 16, which oxygenate the water and drive aerobic nitrification, and large-bubble-producing mixing units 18, which primarily drive mixing or turnover of water within the system. (Although some of the oxygen in the air released into the water column by the large-bubble-producing mixing units 18 will dissolve into the water column, the degree of dissolution will be at least an order of magnitude less than the degree of dissolution of oxygen in the air released into the water column by the fine-bubble-producing aeration units 16.) On the other hand, the downstream polishing or clarifying cell 14 has only fine-bubble-producing aeration units 16 distributed across the floor of the cell.

[0015] Suitably, the fine-bubble-producing aeration units 16 may each consist of several (e.g., four to six) wand-type tube diffusers, which are well known in the art, attached to and extending radially from a central air-supply hub. Other types of devices such as frits, perforated airline tubing, etc. are known to those having skill in the art and may be used instead of or in addition to tube diffusers. On the other hand, the large-bubble-producing units 18 may each be constructed rather simply, e.g., from a short length of pipe such as PVC pipe extending from an air-supply base.

[0016] One air-supply system provides air to the fine-bubble-producing aeration units 16 in each of the cells 12 and 14, and another air-supply system provides air to the large-bubble-producing mixing units 18 in the cell 12. As illustrated in FIGS. 2A and 2B, each of 1) the air-supply systems that provide air to the fine-bubble-producing aeration units 16 in the cells 12 and 14; and 2) the air-supply system that provides air to the large-bubble-producing mixing units 18 in the cell 12 may receive air from a common, central blower 20, with the amount of air delivered to each of the separate air-supply systems being independently regulated, e.g., by separate flow-control devices 22 (valves or flow-regulators) positioned downstream of the central blower and upstream of the respective sets of air-injecting units. Alternatively, in a configuration that is not illustrated, each of the separate air-supply systems may receive air from its own dedicated, independently controllable blower/valve arrangement.

[0017] As further illustrated in FIG. 2A, when the wastewater-treatment system 10 is operating in an aerobic, nitrifying mode of water treatment, air is supplied to both the fine-bubble-producing aeration units 16 and the large-bubble-producing mixing units 18 within the primary cell 12. In accordance with the claimed invention, the respective rates at which air is provided to the fine-bubble-producing aeration units 16 and the large-bubble-producing mixing units 18, e.g., in the primary cell 12, are independently controlled so that the rate of fine-bubble production via the fine-bubble-producing aeration units 16 and the rate of large-bubble production via the large-bubble-producing mixing units 18 are independently controlled. After a period of nitrification within the primary cell 12which could be a fixed, predetermined period of time or a variable period of time that is as long as is required for all ammonia within the primary cell 12 to be reduced to nitrite and then to nitratepartially treated wastewater is transferred to the polishing or clarifying cell 14, where it is further processed aerobically using fine-bubble-producing aeration units 16.

[0018] Once the wastewater has been nitrified, the system 10 is operated in an anaerobic, denitrifying mode as illustrated in FIG. 2B. During operation in this mode, air is no longer supplied to the fine-bubble-producing aeration units 16 in the primary cell 12, but air continues to be supplied to the large-bubble-producing mixing units 18 on an as-needed basise.g., following an on/off cycleto turn over and mix the wastewater in the cell 12. Additionally, if desired, a portion of nitrified water can be fed back and supplied to the primary cell 12 from the polishing or clarifying cell 14 to foster denitrification in the primary cell 12. Doing so brings nitrified water that is high in nitrate to the front of the process, where denitrification can occur due to there being sufficient carbon (i.e. BOD) to drive down dissolved oxygen and give the denitrifying bacteria a source of food.

[0019] The foregoing description is of specific embodiments, and various modification to the disclosed embodiments will occur to those having skill in the art. For example, the illustrated embodiment uses large-bubble-producing mixing units to mix or turn over the water within the cell 12. However, mechanical mixing devices which use blades, vanes, impellers, or other stirring or pumping-type action can also be used, and the efficiency-maximizing, energy-saving benefits with respect to the cost to power such devices can still be obtained.

[0020] What is intended to be covered by Letters Patent is set forth in the following claims.