APPARATUS AND METHOD FOR INCREASING HYDRAULIC CAPACITY OF A GRAVITY SEWER

Abstract

A method for increasing hydraulic capacity of a gravity sewer system includes installing a receiving structure within or proximate to at least a portion of the gravity sewer system. The receiving structure has at least one fluid inlet opening, at least one liquid outlet opening, and at least one gas outlet opening. The method further includes evacuating at least some of any gas within the receiving structure through the at least one gas outlet opening to create a vacuum within the receiving structure, receiving a flow of at least liquid through the at least one fluid inlet opening of the receiving structure and into the receiving structure, and discharging at least some of the liquid from the receiving structure through the at least one liquid outlet opening of the receiving structure.

Description

BACKGROUND OF THE INVENTION

The present invention is directed generally to an apparatus and method for increasing the hydraulic capacity of a sewer system. More particularly, the present invention is directed to a receiving structure positioned within or proximate to a gravity sewer system for increasing the hydraulic capacity of the sewer system during a period in which the gravity-flow capacity of the sewer system would otherwise be exceeded.

Combined sewer systems were the “state-of-the-art” during the early 20th century. In addition to the collection and transport of municipal wastewater, these combined sewers were designed for stormwater flows as well—therefore the term “combined.” The design of combined sewer systems included “overflow structures.” When a wet weather event (for example, a storm, heavy rain or snowmelt) created stormwater flows which exceeded the design capacity (i.e., hydraulic capacity) of the combined sewer system, the excess flow (i.e., the combined sewer overflow “CSO”) would be intentionally diverted to nearby surface water via these overflow structures.

Later in the 20th century, the “state-of-the-art” shifted to the design and construction of separate sewers—individual sewer systems for municipal wastewater and stormwater. The design capacity of the sanitary sewer was intended to collect and transport municipal wastewater from the service area. Experience has shown that unintended water from non-municipal sources (i.e., stormwater) also enters the sanitary sewers. During wet weather events these excessive flows create sanitary sewer overflows (“SSO”) at locations which were not intentionally designed to accommodate such overflows.

The current approach taken by the United States Environmental Protection Agency (“USEPA”) to deal with the issue of CSO and SSO environmental impacts is based on legally-binding “Consent Decree” agreements between the USEPA and the sewer system entity—typically a municipal government or agency. The individually-negotiated Consent Decrees include a scope-of-work and schedule intended to reduce the frequency and volume of CSO during wet weather events.

The scope-of-work includes an assessment and evaluation of technically-feasible alternatives. Where increased hydraulic capacity is needed in order to reduce the frequency and volume of overflows, the typical alternatives often considered are parallel sewers and/or tunnels. Such alternatives are often very expensive solutions to deal with short-duration problems created by only a few wet weather events annually.

Therefore, it would be desirable to create an apparatus and method that alleviates or overcomes the above-described disadvantages of conventional sewer systems. More specifically, it would be desirable to create an attachment or addition to gravity sewer systems that—when necessary or desired—increases the hydraulic capacity of the sewer system, which is preferably an established or existing gravity sewer system. The present invention accomplishes the above objectives.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, a preferred embodiment of the present invention provides a system and method for increasing the hydraulic capacity of a gravity sewer. A “receiving structure” of the present invention is constructed at a downstream end of a section of sewer which is in need of additional capacity. When the receiving structure is caused to have an internal pressure less than atmospheric pressure, the hydraulic gradient of the section of sewer is increased; and, thereby its hydraulic capacity can be increased and controlled.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustration, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a schematic view, partially in cross-section, of two sections of a gravity sewer with sewer pipe or conduit between adjacent manholes. The first sewer pipe 12 is relatively flat; and, the second sewer pipe 16 is relatively steep. At full-flow, the hydraulic gradients (14a and 14b) are parallel to the slope of each sewer pipe. While normally depicted above the sewer pipe, in this figure the hydraulic gradient is intentionally shown beneath the sewer pipe in order to more clearly demonstrate the effect of the present invention.

FIG. 2 is a schematic view, partially in cross-section, of the first and second sewer pipes of FIG. 1 plus a receiving structure (10). Also, at least one vacuum device 26 is connected to gas outlet opening 22 of receiving structure 10. While normally depicted above the sewer pipes, in this figure the overall hydraulic gradient 14c is intentionally shown beneath the sewer pipes in order to more clearly demonstrate the effect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenience only and is not limiting. The words “left,” “top,” “up” and down,” and derivatives thereof, designate directions in the drawings to which reference is made. Unless specifically set forth herein, the terms “a,” “an” and “the” are not limited to one element, but instead should be read as meaning “at least one.” The terminology includes the words noted above, derivatives thereof and words of similar import.

Referring to the drawings, the first sewer pipe 12 of FIG. 1 has a maximum hydraulic capacity at full flow of a liquid, such as water, which is determined by its size and material-of-construction and its hydraulic gradient 14a. Likewise, the second sewer pipe 16 of FIG. 1 has a maximum hydraulic capacity at full flow of a liquid, such as water, which is determined by its size and material-of-construction and its hydraulic gradient 14b. It is preferred that the second sewer pipe 16 will have a full-flow hydraulic capacity which is greater than the first sewer pipe 12.

Flows in excess of the maximum hydraulic capacity of first sewer pipe 12 will back-up and cause overflow conditions upstream (i.e., to the left in FIG. 1) of first sewer pipe 12.

Referring to the drawings, FIG. 2 shows a downstream end of first sewer pipe 12 of FIG. 1 connected to a receiving structure 10 as is the upstream end of second sewer pipe 16 of FIG. 1. Except for these connections and outlet opening 22 to vacuum device 26, the receiving structure 10 is otherwise preferably a completely enclosed system or container; but, the present invention is not so limited

The air within receiving structure 10 is caused by vacuum device 26 to have an internal vacuum [the air pressure (“Pair”) is less than atmospheric pressure]. The equipment and controls for these vacuum wastewater systems are well known by those skilled in the art, and further description thereof is not necessary for a full and complete understanding of the present invention. Atmospheric pressure at sea level is approximately 14.7 psi which is approximately equivalent to 34 feet w.c. (water column). In other words, for example, a column of water 34 feet high would create a pressure of approximately 14.7 psi at the base of the column.

While a perfect vacuum is impractical for actual operation, if the air within receiving structure 10 was eliminated in order to create a perfect vacuum, the hydraulic gradient 14a at the downstream end of first sewer pipe 12 in FIG. 1 would be lowered by approximately 34 feet.

In actual practice, the design and operation of the present invention will be site-specific and dependent upon creating the increased hydraulic capacity desired. In actual practice, it will be practical to operate so that the air pressure within the receiving structure 10 is caused to be in-the-range-of approximately 6/7 to 3/7 of atmospheric pressure thereby lowering the hydraulic gradient at the downstream end of first sewer pipe 12 by approximately 5-20 feet and thereby substantially increasing the hydraulic capacity of first sewer pipe 12 when compared with its full-flow gravity capacity.

As shown in FIG. 2, at the upstream end of second sewer pipe 16 the hydraulic gradient 14c is also lowered by the same amount as it is the at the downstream end of first sewer pipe 12. This decreases the hydraulic capacity of the second sewer pipe 16 (when compared to its full-flow gravity capacity) while still having a hydraulic capacity equal or exceeding the increased hydraulic capacity of first sewer pipe 12. Importantly, the result is to create an overall hydraulic gradient 14c which is greater than the gravity-flow hydraulic gradient 14a of first sewer pipe 12 thereby creating a reduction in the frequency of overflows upstream of first sewer 12.

Further, in “flat-to-steep” situations such as shown on FIG. 1 and FIG. 2, the increased hydraulic capacity in first sewer pipe 12 is accomplished without a pump or other liquid evacuation device included among the apparatus. Avoiding pumps or other liquid evacuation devices associated with receiving structure 10 obviates the need for dealing with (via screens or similar devices) large objects commonly found in the stormwater component of combined sewer flows. This also eliminates the need for additional equipment, operation and maintenance requirements for redundancy, back-up power, controls, etc, associated with such pumps or other liquid evacuation devices.

Another “flat-to-steep” situation can be found in combined sewer system projects which include tunnels. Relatively flat consolidation sewers intercept flow at CSO locations and transport flow to (steep) tunnel drop shafts.

It is important to note that a preferred use of the present invention is to temporarily increase the hydraulic capacity of first sewer pipe 12—perhaps for only a few hours during each of only a few wet weather events per year. Furthermore, the increase in hydraulic capacity is preferably widely adjustable (by selectively, for example, controlling the vacuum level in the receiving structure 10) and can be tailored to match the conditions created by specific wet weather events when they occur. The capital and operating cost savings possible through the use of the present invention are thought to be very significant when compared to the very expensive alternatives of parallel sewers and/or tunnels for the reduction of CSO and SSO frequency and volume.

As understood by those skilled in the art, an existing first sewer pipe 12 and/or an existing second sewer pipe 16 such as constructed years ago, for example, could be modified, adjusted and/or retrofitted to accommodate or attach to one or more receiving structures 10, which could be in series or in parallel.

Finally, it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad invention concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present invention.

Claims

1. A method for increasing hydraulic capacity of a gravity sewer system, the method comprising: installing a receiving structure within or proximate to at least a portion of the gravity sewer system, the receiving structure having at least one fluid inlet opening, at least one liquid outlet opening, and at least one gas outlet opening;evacuating at least some of any gas within the receiving structure through the at least one gas outlet opening to create a vacuum within the receiving structure;receiving a flow of at least liquid through the at least one fluid inlet opening of the receiving structure and into the receiving structure; anddischarging at least some of the liquid from the receiving structure through the at least one liquid outlet opening of the receiving structure.

2. An apparatus for increasing hydraulic capacity of a gravity sewer system, the apparatus comprising: a receiving structure operatively connected to the gravity sewer system, the receiving structure including: at least one fluid inlet opening operatively connected to an upstream section of the gravity sewer system;at least one liquid outlet opening operatively connected to a downstream section of the gravity sewer system; andat least one gas outlet opening;at least one vacuum device operatively connected to the at least one gas outlet opening of the receiving structure; andwith no liquid evacuation device operatively connected to the at least one liquid outlet opening.