Abstract:
Reductions in energy consumption and maintenance requirements for operating a wastewater treatment plant are achieved by controlling the operation of pumps at pump stations along a force main in a systematic fashion. The operation of the pumps is controlled to manage the flow of wastewater along the force main to minimize energy consumption, to eliminate sediment, to manage peak pressures encountered by smaller pumps and to avoid septic conditions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional application Ser. No. 60/870,862, filed on Dec. 20, 2006, entitled “Wastewater Collection Flow Management System” the contents of which are hereby incorporated into this application by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to wastewater collections systems for wastewater treatment plants, and is particularly directed to pump management, wastewater treatment plant inflow management, sediment elimination, pressure management and septic elimination in wastewater collection systems, wherein an improvement to the operation of wastewater collection systems is made by modulating the operation of the pumping stations systematically, rather than allowing pumps to operate independently. 
     2. Description of the Prior Art 
     In a wastewater collection service area, many pump stations often pump wastewater to a treatment facility or to a master pump station through a force main. Force mains are used to move wastewater under pressure, typically over terrain that is not conducive to gravity flow. A typical wastewater pump station may house two, three or more pumps. The number and size of the pumps at each station are determined by the amount of wastewater inflow to that site and by amount of storage capacity in a wet well. There is normally no coordination of activity between pumping stations. Pump operations at a given wastewater pump station are typically controlled locally. When the influent in the wet well at a pumping station reaches a certain predetermined level, a sensor triggers the “lead” (or first) pump to start. If the pump&#39;s action is not sufficient to handle the inflow of sewage, additional, or “lag” pumps, are called into service. When the wet well level lowers to the desired level, another sensor causes the pump(s) to turn off. 
     Most wastewater is generated during two or three peak periods of daily activity, mostly in the morning when families are rising for the day and in the early evening when families are returning home from work and school. Throughout the operating day, but especially during these peak periods, it is normal for many stations to pump simultaneously into the same force main since there is no coordination between pumping stations. The more stations that pump at one time, the higher the head pressure in the force main becomes. Pumps cannot pump efficiently when pumping against higher pressures—smaller pumps may not be able to pump at all when more powerful pumps are dominating the force main—causing pumps to run longer in order to accomplish their purpose. This condition results in drastically higher energy costs, increased wear and tear on pumps and mains and a greater likelihood of failures that cause sewage spills. Conversely, there are also many periods during which no pumps are running. When wastewater generation is at the lowest volume, in the middle of the night or, perhaps at mid-morning or mid-afternoon, the majority of pumping stations are frequently dormant. 
     Wastewater treatment plants are designed and sized one of two ways: either to accommodate estimated daily total inflows, or to serve peak demands on the system. Plants designed to accommodate a daily average inflow run the risk of being incapable of handling those few peak hours of the day when most of the inflow occurs. Those designed to accommodate the peak inflow hours sit idle for most of a twenty-four hour period, since the peak inflows only occur during a few hours of the operational day. Failure to provide sufficient capacity will likely result in pretreatment spills, damage to infrastructure with attending high repair costs and loss of service to customers and damage to customer property. This consequence forces careful sizing to accommodate the long-term estimate of peak loading. The daily capacity of the infrastructure to treat wastewater may be supplemented by surge tanks either in the initial design or as an addition to the existing infrastructure. In either case, the infrastructure and surge tanks are quite costly and add to on-going maintenance costs. 
     Very frequently, wastewater treatment plants are sized based on estimated daily total inflows and are measured in terms of (millions) of gallons per day. When, over a period of years, population increases exceed long-term plans, the addition of surge tanks to temporarily store the unmanageable inflow is necessary to prevent overflows at the plant&#39;s headworks, the point of inflow into the plant. Later, during lower flow times, surge tank contents may be processed through the treatment system. Surge tanks provide temporary storage at the wastewater treatment plant to accommodate the wastewater plant&#39;s processing rate, but do not lessen flow into the infrastructure. 
     Wastewater collection systems have pump stations distributed throughout the service area that arbitrarily pump wastewater to the treatment plants. But these pumps only respond to local conditions and are activated by local level sensors without regard to events or conditions elsewhere. As a result, during peak activity hours, e.g., from 6 AM to 8 AM and from 5 PM to 7 PM, these pump stations operate more frequently, thereby raising the inflow into the plant, frequently surpassing the plant&#39;s processing capability. It should be noted that these high inflow periods normally occur between periods during which there is very little, if any, flow into the wastewater treatment plant. The result is normally a need for a higher design margin and/or earlier system expansion. 
     Another consequence of unmanaged flow is reduced efficiency in managing the biological treatment material at the wastewater treatment plant. The most efficient biomass management requires a relatively constant flow rate so that bacteria used in processing can effectively interact with the influent waste. High or irregular flow rates lessen the efficiency of the treatment system and the quality of the treated effluent. 
     Sewer mains are frequently sized to take into account future growth in a wastewater collection service area, but it is not unusual for years to pass before the volume of wastewater reaches the level for which the system was designed. During this time, the utility may experience maintenance problems if the volume of wastewater through the main is not sufficient to carry with it solids and silt. If the flow of wastewater is so small relative to the pipe size that it fails to reach a velocity known as ‘scour speed’, solids will fall out of the liquid and accumulate in the bottom of the sewage mains. When this occurs, expensive specialty vehicles typically known as vacuum trucks are employed to clean out sediment that accumulates in the sewage system. 
     PROBLEMS OF THE PRIOR ART 
     Wastewater collection and treatment systems often operate under conditions in which pumps operate inefficiently, causing increased energy cost and wear and tear on costly equipment. Further, peak flows into the treatment plant result in accidental spillages and impede the operational efficiency of the biological treatment processes utilized in the treatment plant. Further, there are times when flow is inadequate to keep the force mains free of sediment, requiring the use of expensive special purpose trucks. In addition, the operational requirements of the various force main sometimes allows small pumps to run at the same time as larger pumps thereby causing the smaller pumps to operate against the higher pressure from the larger pumps resulting in considerable inefficiency in the operation of the smaller pumps. Also, existing systems frequently encounter situations where the wet wells to do not get pumped down sufficiently and they therefore begin to generate septic conditions with the accompanying unpleasant smells. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, these and other problems associated with the operation and maintenance of wastewater collections systems for wastewater treatment plants, are successfully addressed by apparatus and techniques for pump management, wherein the operation of wastewater collection systems is based upon modulating the operation of the pumping stations systematically, rather than allowing pumps to operate independently. 
     One aspect of the invention employs a Wastewater Collection Flow Management System that incorporates (selectively or collectively) five techniques that improve wastewater collection and treatment operations. These steps include: 1—PUMP MANAGEMENT that provides for increased pump efficiency, which reduces energy costs and wear and tear on costly equipment; 2—FLOW MANAGEMENT for controlling the rate at which wastewater enters the wastewater treatment plant, reducing accidental spillages, diminishing the need for additional construction and improving the efficiency of the biological treatment process; 3—SEDIMENT ELIMINATION for keeping sewage mains free of sediment to maximize flow capability and saving the expense of alternative methods of sewage main cleaning; 4—PRESSURE MANAGEMENT for comprising operating efficiency by allowing small pumps to run only when a larger pump is not running so that the smaller pumps do not pump into a main which has a higher pressure than is optimal for the smaller pumps; and 5—SEPTIC ELIMINATION for ensuring that wet wells get pumped down enough that septic conditions do not occur or are minimized. These steps are combined to drastically reduce a water utility&#39;s energy expenditures, reduce maintenance and repair costs and reduce the need and expense of special equipment and additional infrastructure construction. 
     The invention is designed to overcome the problems of the prior art as indicated below. 
     One embodiment of the invention is directed to a method of operating a plurality of pump stations feeding a wastewater treatment facility. The method may include the step of controlling the operation of pump stations in a systematic fashion from a central location. 
     The step of controlling the operation of pump stations in a systematic fashion comprises may include activating pumps at pump stations on a force main in an order of priority based on capacity of a wet wells and intake volumes at the pump stations. 
     The step of controlling the operation of pump stations in a systematic fashion may alternately comprises activating pumps at pump stations on a force main in order of distance from a treatment facility from farthest to nearest. 
     The wet wells of pumps on a force main may be pumped down prior to the start of a peak flow period. 
     The step of controlling the operation of pump stations in a systematic fashion may comprises the steps of allowing the wet wells of one or more pump stations to fill to a secondary lead level, and activating a sufficient number of pumps at one or more pump stations to pump down the wet wells at a rate sufficient to cause flow in the force main to exceed a scour speed for the force main, to thereby flush the force main. 
     The step of controlling the operation of pump stations in a systematic fashion may also comprises the steps of notifying the central location from each pump station of the status of the wet well and the identity of any pumps running, receiving a command from the central location, if any relatively small pump is running on a force main, to increase the threshold level of activation for wet wells associated with relatively larger pumps on that force main: and info relatively smaller pumps are operating, receiving a command from the central location to activate larger pumps at full pressure output, so that no relatively smaller pumps are operating on a force main at the same time that a larger pump is running on that force main. 
     The step of controlling the operation of pump stations in a systematic fashion may still further comprises the steps of; identifying pump stations on a force main that do not pump wet wells at said pump station down to the lowest level at least twice a day; and, for each pump station identified, activate one or more pumps twice a day to reduce levels in the wet wells to a point where septic conditions are minimized. 
     The invention is also directed to a wastewater treatment system comprising a wastewater treatment facility, a plurality of force mains connecting a plurality of pump stations, each having a wet well, to said wastewater treatment facility, a plurality of communication transceivers at a corresponding plurality of pump stations for notifying a central station of information about the operation of a pump station, and a central communication station for receiving information from said plurality of transceivers and for sending information to said transceivers to control the operation of the pump stations in a systematic fashion. 
     The system may also include information for activating pumps at pump stations on a force main in an order of priority based on capacity of a wet wells and intake volumes at said pump stations. 
     The information sent to the transceivers to control the operation of pump stations in a systematic fashion may comprise information for activating pumps at pump stations on a force main in order of distance from a treatment facility from farthest to nearest. 
     The information sent may causes wet wells of pumps on a force main to be pumped down prior to the start of a peak flow period. 
     The information sent to the transceivers to control the operation of pump stations in a systematic fashion may comprises information causing the wet wells of one or more pump stations to fill to a secondary lead level, and information for activating a sufficient number of pumps at one or more pump stations to pump down the wet wells at a rate sufficient to cause flow in the force main to exceed a scour speed for the force main, to thereby flush the force main. 
     The transceivers of each pump station may notify the central location of the status of the wet well and the identity of any pumps running, and the central location sends information to said transceivers, if any relatively small pump is running on a force main, to increase the threshold level of activation for wet wells associated with relatively larger pumps on that force main and if no relatively smaller pumps are operating sending information to activate larger pumps at full pressure output, so that no relatively smaller pumps are operating on a force main at the same time that a larger pump is running on that force main. 
     The information sent to the transceivers to control the operation of pump stations in a systematic fashion may comprise the steps of identifying at a central location, using information received from said transceivers, pump stations on a force main that do not pump wet wells at said pump station down to the lowest level at least twice a day and, for each pump station identified, activating one or more pumps twice a day to reduce levels in the wet wells to a point where septic conditions are minimized. 
     The invention may further include a method of reducing energy used in operation of a wastewater treatment plant. The method may include the steps of pumping down wet wells of pump stations on a force main prior to the beginning of a peak flow period. 
     The step of pumping down wet wells of pump stations on a force main prior to the beginning of a peak flow period may include activating pumps at pump stations on a force main in order of distance from a treatment facility from farthest to nearest. 
     The invention may still further include a method of reducing maintenance requirement on pumps of a pump station having transceivers on it force main feeding a wastewater treatment facility. The method may comprise the steps of causing transceivers of each pump station to notify a central location of the status of the wet well and the identity of any pumps running, and causing the central location to send information to said transceivers, if any relatively small pump is running on a force main, to increase the threshold level of activation for wet wells associated with relatively larger pumps on that force main and if no relatively smaller pumps are operating sending information to activate larger pumps at full pressure output, so that no relatively smaller pumps are operating on a force main at the same time that a larger pump is running on that force main. 
     The invention may still further include a computer program product comprising: a computer readable memory medium, computer controlling instructions stored on the computer readable memory medium. The instructions may include instructions for controlling the operation of pump stations on one or more force mains of a wastewater treatment facility in a systematic fashion. 
     The computer controlling instructions stored on the computer readable memory medium may further comprise instructions for pumping down the wet wells of pumps on a force main prior to the start of a peak flow period for that force main. 
     The computer controlling instructions stored on the computer readable memory medium may further comprise instructions for notifying the central location from each pump station of the status of the wet well and the identity of any pumps running, receiving a command from the central location, if any relatively small pump is running on a force main, to increase the threshold level of activation for wet wells associated with relatively larger pumps on that force main; and info relatively smaller pumps are operating, receiving a command from the central location to activate larger pumps at full pressure output, so that no relatively smaller pumps are operating on a force main at the same time that a larger pump is running on that force main. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating how a plurality of pump stations communicate with a central server in a wastewater treatment system in accordance with one aspect of the invention. 
         FIG. 2A  is a block diagram of an exemplary pump station in accordance with one aspect of the invention. 
         FIG. 2B  is a diagram showing a typical level sensor arrangements in a wet well as used in the prior art. 
         FIG. 2C  is a diagram showing a level sensor arrangement in a wet well in accordance with one aspect of the invention. 
         FIG. 3  illustrates an example of how a plurality of pump stations are interconnected to a wastewater treatment plant using force mains. 
         FIG. 4  is a flow chart of a pump management process using pump priorities in accordance with one aspect of the invention. 
         FIG. 5  is a flow chart of a flow management process in accordance with one aspect of the invention. 
         FIG. 6A  illustrates flow volumes as a function of time of day without the use of the flow management aspects of the invention. 
         FIG. 6B  illustrates flow volumes as a function of time of day with the use of the flow management aspects of the invention. 
         FIG. 7  is a graph showing the number of pumps running as a function of time of day without flow management. 
         FIG. 8  is a graph showing the number of pumps running as a function of time of day using flow management in accordance with one aspect of the invention. 
         FIG. 9  is a flow chart of a process for sediment elimination in accordance with one aspect of the invention. 
         FIG. 10  is a diagram of a wet well in accordance with one aspect of the invention showing use of secondary lead level detection for sediment elimination. 
         FIG. 11  is a flow chart of a process for pressure management in accordance with one aspect of the invention. 
         FIG. 12  is a flow chart of a process for septic elimination in accordance with one aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram illustrating how a plurality of pump stations communicate with a central server in a wastewater treatment system in accordance with one aspect of the invention. A central station  100  includes a base station  101 , preferably including an XGMI Cognitive Radio for communicating with remotely located pump stations. Commands are sent to the pump stations over the base station radio and are generated by a server process running, preferably, on a DFS hyper SCADA server  102 . The server is controlled by system control software  103  described more hereinafter 
     A plurality of stations  110 -A through  110 -N communicate with the central base station using, preferably, radio links. Almost any type of communication link is possible when designing a system to utilize the benefits of the disclosed invention. These can include microwave, optical (e.g. laser), wireline, optical fiber, microwave communication links and the like. Preferably, however, radio communication links are used in this invention. Each pump station  110 -A through  110 -N is equipped with an XGM1 Cognitive Radio  111  (data version) for transmitting and receiving information from the central. 
     The radio  111  interfaces to a programmable logic controller  113  utilizing telemetry control unit  112 . Preferably, telemetry control unit is a Data Flow System TAC Pack and the programmable logic controller is a Data Flow System PLC 033. A plurality of well level sensors  114  are located within the wet well and provide information to the programmable logic controller  113  which includes ladder logic functionality to determine which pump should be activated, depending upon the level of liquid within the wet welL The ladder logic then activates the appropriate pumps using respective pump control circuitry, such as relays as illustrated, for example, in block  115 . 
       FIG. 2A  is a block diagram of an exemplary pump station in accordance with one aspect of the invention. A plurality of pumps  200 A through  200 C serve to empty a wet well  210  depending upon the level determined by the well sensor inputs  114 . The well sensor inputs feed ladder logic  116  which then determine which pumps to activate, depending upon the levels sensed by the sensors and upon information received from the central via radio unit  110 , telemetry control unit  112  and programmable logic  113 . When one or more pumps are turned on, the liquid in the wet well is pumped through pipes into the force main  300  to begin its travel to the wastewater treatment plant. 
       FIG. 2B  is a diagram showing a typical level sensor arrangement in a wet well as used in the prior art. As show in  FIG. 2B  there are four sensors. From bottom to top, the first is a sensor indicating that the liquid is at an appropriate level and all pumps are turned off. The second causes the lead pump start to be triggered when the liquid in the well rises to the level indicated. It is the level at which the first pump begins to pump into the force main. Yet higher up the wet well is a lag pump start which is utilized to activate one or more additional pumps when the level reaches that sensor. Finally, there is a high well (alarm) sensor which indicates that over flow is threatened and appropriate action should be taken. 
       FIG. 2C  is a diagram showing a level sensor arrangement in a wet well as used in accordance with one aspect of the invention. In addition to the sensor levels described in conjunction with  FIG. 2B , there is a secondary lead level which is utilized as described more hereinafter. 
       FIG. 3  illustrates an example of how a plurality of pump stations  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  is interconnected to a wastewater treatment plant using force mains. The size of the individual symbol utilized for the pump stations  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  shown feeding the wastewater treatment plant is indicative of the relative capacity of the wet well and the pumps associated with the pump station. The numerals associated with the various pump stations  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  are used in later discussions of the invention. 
       FIG. 4  is a flow chart of a pump management process using pump priorities in accordance with one aspect of the invention. As shown in  FIG. 4 , a priority is assigned to each pump station on a main based on the storage capacity of the wet well and intake volumes ( 400 ). All pump stations notify the central station of the status of the wet well and whether any pump is running ( 410 ). The central activates or authorizes activation of pumps at a pump station in order of pump station priority ( 420 ). Finally, the central station optionally notifies pump stations if pumps of a higher priority pump station are operating on the same main ( 430 ). 
     This first, PUMP MANAGEMENT aspect of the invention synchronizes the operations of remote wastewater pumping stations that feed a common pressurized sewage main (force main). The goals of PUMP MANAGEMENT are to eliminate conditions during which multiple pump stations need to pump simultaneously and to reduce the periods during which no pump is running. PUMP MANAGEMENT provides a mechanism by which busier pump stations, those that historically have either a higher rate of influent or a comparatively smaller storage capacity and tend to have a more critical need to pump, are given priority over those with a lower demand. This priority-based PUMP MANAGEMENT control mechanism tends to minimize the immediate peak flow level in the wastewater collection system since pump stations with a lesser need for immediate pumping are delayed until higher priority pumps have completed their pumping cycles. As the higher-priority pump stations&#39; demand diminishes, other stations are enabled to operate their pumps, according to their descending priority. 
     Since pumping stations normally operate independently, using local wet well level sensors to trigger pumps when wet wells reach a prescribed level, it is not unusual for many of the pumping stations to pump simultaneously into a common force main during high usage periods. When this occurs, pumps must work against increased head pressure in the force main. The result is that more powerful pumps must pump longer in order to overcome the head pressure and complete their tasks of emptying their respective wet wells. Smaller pumps frequently spin uselessly, since they are unable to generate enough power to overcome the head pressure encountered during high usage periods. (Also, during low usage hours, it is not unusual for no pumps using a common main to pump, leaving the force main and the system idle.) This condition causes two main problems. First, it greatly increases the already very high energy cost associated with operating a wastewater collection system, which is frequently the highest ongoing budget item absorbed by water utilities. Second, this ineffective mode of operation causes pumps to run longer and against more resistance, resulting in greatly increased maintenance and repair costs associated with maintaining wastewater pumping stations. 
     The object of PUMP MANAGEMENT is to reduce the number of pumps operating simultaneously, resulting in more efficient, lower cost operations, and to better utilize the pumping system during those quiet hours when no pumps are running. The control mechanism utilizes a remote monitoring and control system called a supervisory control and data acquisition (SCADA) system. Pumping stations are prioritized using historical and physical data regarding the sites. An additional wet well level criterion, ‘Secondary Lead’ is added to the typical level indications, which are normally, ‘Off’, ‘Lead (pump)’, ‘Lag (secondary pump)’, and ‘High Level’ alarm ( FIG. 1 ). The ‘Lead’ sensor position is lowered close to the ‘Off’ position and the new, ‘Secondary Lead’ sensor is positioned higher in the wet well, but not higher than the ‘Lag’ position, to allow for additional storage in the wet well before a pump is called to run ( FIG. 2C ). 
     Each local pump control system includes an output to the SCADA system that indicates if any pump is running. In addition, each pump control includes an input point that allows the central SCADA software to inform the site if a higher priority site is pumping. 
     In operation, when a pump station wet well reaches its normal ‘lead pump on’ level, the site is only permitted to begin pumping if no higher priority site is currently pumping. The pump station remains dormant until either no higher priority pump along the force main is running or until the secondary lead level is reached in the wet well. At that point, the site is permitted to pump even if a higher priority site is pumping in order to avoid an overflow/spill. If the SCADA system signals the pump station that no higher priority site is operating, the pump station is permitted to operate normally, using the regular ‘lead’ pump level, and the secondary lead sensor is ignored. 
     This system substantially eliminates periods during which more than one pump is running. Pumps do not have to work against high head pressures. As a result, the pumps operate more efficiently, using less power and completing their tasks more quickly. In addition, since the system causes the pump station operations to spread out in time, the lower priority pump sites begin to run more frequently during the low usage hours. 
       FIG. 5  is a flow chart of a flow management process in accordance with one aspect of the invention. The peak and slack periods for flow on a force main are identified at block  500 . Typically, the peak and flow periods are associated with certain times of the day. For example, one would expect a peak flow period in the morning as people arise from the night and prepare themselves for the day. Water usage and waste flow increase at those times, because people tend to follow the same daily cycle of activities. 
     The pump stations on a particular force main are ordered by distance from a treatment plant ( 510 ) as illustrated, for example, with the numbers shown in  FIG. 3 . As shown in  FIG. 3 , the pumps are assigned numbers starting from the outermost pump station on a force main and increasing along the force main toward the wastewater treatment plant. 
     Prior to a peak period of usage, the pump stations are ordered to pump down the wet well in an order that begins from the farthest to the nearest as illustrated, for example, at block  520 . This means that when a peak period begins, each of the wet wells of the pump stations have been substantially emptied to the extent needed to absorb an increase of flow beyond the capacity of the pump stations to handle currently. 
     Optionally, control of the pumping of the pump stations closest to the treatment plant may be arranged so that they don&#39;t pump simultaneously (block  530 ) at full force which might overload the ability of the treatment plant to process the flow. 
       FIG. 6A  illustrates flow volumes as a function of time of day without the use of flow management described in conjunction with  FIG. 5 . 
       FIG. 6B  illustrates flow volumes as a function of time of day with the use of flow management in accordance with the invention. One can see that the peak flows of  FIG. 6B  are much less than the peak flows of  FIG. 6A . One can also see that the minimums of flow occur at a higher level than occur in  FIG. 6A . The results from pumping down the wet wells prior to the peak period, results in lower peak usage but the excess flow that would have been handled at a peak time is averaged over other periods. 
       FIG. 7  is a graph showing the number of pumps running as a function of time of day without flow management. In this figure, the peak number of pumps running is 6 with 9 periods occurring during the day during which five pumps or more are simultaneously running. 
       FIG. 8  is a graph showing the number of pumps running as a function of time of day using flow management in accordance with one aspect of the invention. With flow management in place, the peak number of pumps running at any point in time is 3, rather than 6 when flow management in accordance with the invention was not utilized. Further, during those periods in which only one pump was running, one can see from the substantially black areas, that there are periods during which there are very few intervals during which no pump is running. Thus, there are many fewer intervals during which more than one pump is running and there are fewer intervals during which no pumps are running. Note also that the peak time intervals are somewhat shifted in the graph of  FIG. 8  from the peak time interval shown in  FIG. 7 . This can be accounted for by the fact that the emptied wet wells have more time to fill before a pump is required to move their contents. 
       FIG. 9  is a flow chart of a process for sediment elimination in accordance with one aspect of the invention. In this case, at one or more pump stations along a force main, one allows the wet wells to fill to, in this example, a secondary lead level ( 900 ). 
     When the wet well is filled to the secondary lead level, one activates a sufficient number of pumps at one or more pump stations to pump down the wet wells at a rate sufficient to cause flow in the force main to exceed the scour speed and to therefore flush the main ( 910 ). In this manner, sediment occurring along a force main can be flushed out without the intervention of a vacuum truck or other external mechanism. 
       FIG. 10  is a diagram of a wet well in accordance with one aspect of the invention showing use of secondary lead level detection for sediment elimination. As noted above, when the secondary lead level is reached, pumps will be turned on to produce a flow which will result in a sufficient flow to flush sediment from the main. 
       FIG. 11  is a flow chart of a process for pressure management in accordance with one aspect of the invention. In this approach, pumps at each pump station servicing a particular force main are characterized by pumping capacity (size) ( 1100 ). All pump stations notify the central station of the status of their wet well and of the identity of any pumps running ( 1110 ). If any relatively small pump is running on a force main, the central will order the threshold level of activation for wet wells associated with larger pumps on that force main to rise (e.g. to a secondary lead level) ( 1120 ) so they do not activate and adversely affect the pumping efficiency of the relatively small pump. 
     If no relatively smaller pumps are operating, the central can activate the larger pumps to operate at full pressure output. In this way, relatively small pumps may not attempt to operate during periods when the larger pumps are operating at full pressure output, which would negate the capabilities of the smaller pumps to efficiently transfer fluid to the force main (see block  1130 ). 
       FIG. 12  is a flow chart of a process for septic elimination in accordance with one aspect of the invention. To avoid septic conditions, pump stations that do not pump down to the lowest level of a wet well at least twice a day are identified (see block  1200 ). For each such pump station, one or more pumps at that pump station will be activated twice a day to reduce the level in the wet well to a point where septic conditions are eliminated or at least minimized (see block  1210 ). This technique is particularly useful when a large force main has been installed to accommodate planned future development, but the current needs utilize only a small portion of the capacity 
     While various embodiments of the present invention have been illustrated herein in detail, it should be apparent that modifications and adaptations to those embodiments may occur to those skilled in the art without departing from the scope of the present invention as set forth in the following claims.