Measuring Gravity Sewer Flow Accurately

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1 Measuring Gravity Sewer Flow Accurately Albert Royster Standards Certification Education & Training Publishing Conferences & Exhibits 2016 ISA Water / Wastewater and Automatic Controls Symposium August 2-4, 2016 Orlando, Florida, USA

2 Presenter Albert Royster is a retired Environmental Specialist with Florida Department of Health. Headshot photo He is a dual drinking water/wastewater treatment plant plant operator with 30 years experience in wastewater treatment. Doctor Septic 2

3 Presentation Outline The Problem Goals and Objectives Identifying the Problem The Solution Conclusion 3

4 Accommodate the Flow Have you ever planned a meal or even a wedding to find out the amount of effort that goes into the process involves how much to prepare? You have to know how much stuff to make to be enough to accommodate those you plan to cater to. Count your party. List your guests to know how many. Write your guests to know if they plan to attend. What if you exceed your count? What if your count does not show up? 4

5 Accommodate the Flow The same goes for measuring gravity sewer flow. You need to know how much is going through the pipe so you will be prepared to properly manage and take care in treating the wastewater. You must know how much is to be treated; accommodate the flow. Being prepared will include episodes of inflow and infiltration that will increase daily flow, especially during wet weather events. Monitoring the sewer flow can indicate peak activity and system overloading 5

6 Wastewater systems have two design values Hydraulic Load (flow) Biological Load (waste strength) Daily design flow determined by flow per bedroom. Biological load based on average range of mg/l BOD5. 6

7 Flow and Loading After determining the flows and BOD5, Combine the two to determine the mass load. Determine the mass loading rate (lbs/day): GPD x BOD5 (mg/l) x = PPD BOD5 Calculating mass flow 200 (GPD) X 140 (BOD5) x = 0.23 lbs/day For soil loading: 0.23 / absorption rate ft2 =Lb./day/square foot Most published data assumes a residential BOD5 of 250 mg/l. 7

8 Waste strength and flow volume comparison Residential example: Groundwater Infiltration Condition Flow BOD5 lbs/day BOD5 Design Value Expected Value for family of four High Flows Groundwater Infiltration

9 We know the flow (OR DO WE) How accurate is our educated guess: Prescribed by an engineer Based on state code Based on previous water usage history Inflow & Infiltration affect daily flow Is the system hydraulic overloaded? Do daily flows exceed the design capacity? 9

10 Was the flow designed on: Meter Readings Organic Loading State code Flow based varies from state to state and from agency to agency Septic systems are commonly not sized on loading factors: BOD, TSS, etc. 10

11 Metered Water for Septic Repair Date Meter Read Gallons used 5/14/08 1,019,000 76,000 4/17/08 943,000 76,000 3/12/08 867,000 22,000 2/14/08 845,000 16,000 1/10/08 829,000 12,000 Water usage is critical. This averages 1342 GPD more than what a septic tank outlet filter is designed for. Probable cause: Irrigation line break 11

12 Example of more normal pattern Metered Water for Septic Repair Date Meter Read Gallons Used 5/14/08 117,000 13,000 4/17/08 104,000 7,000 3/12/08 97,000 5,000 2/14/08 92,000 3,000 1/10/08 89,000 2,000 Progressive usage: possible leaks 12

13 ESTIMATED SEWAGE FLOW Estimated flows designed from code or engineer thought were acceptable. Water usage records have been an acceptable way to calculate average daily flow where septic systems have been repaired. The importance of knowing anticipated sewer flow can gauge potential problems. 13

14 QUESTION Does the pipe always have to be full to measure its flow? Can a single waste stream can be measured without subtracting the mass flow from water used for filling the swimming pool or for irrigating the yard? 14

15 Home Water Use Survey Showers and Baths Toilet Flushes Showers Baths Tooth brushing Hand Dishwashing Automatic Dishwasher Laundry Other Indoor uses Lawn Watering Other outdoor uses 15

16 MASS FLOW The mass flow includes the usage from showers, baths, toilet flushes, tooth brushing, dishwashing, laundry, and other indoor uses. Lawn watering and other outdoor uses are also considered into the mass flow equation. Following charts derived from SJRWMD website: Home Water Use A Family Survey 16

17 Estimating Indoor Use 17

18 Estimating Indoor Flow 18

19 Estimating Indoor Flow 19

20 A Family Survey (Family of Four) Note: Three bedroom residence Tooth brushing: 12 GPD Toilet Flushing: 64 GPD No major outdoor use: Irrigation, wash dog/car Dishwasher: 2 GPD Dishes by Hand: 2 GPD Handwashing: 12 GPD Laundry: 24 GPD Bath 0 GPD Showers: 100 GPD Total 216 GPD Water Usage Records show avg GPD 20

21 Washing machine uses the most water per use OTHER could mean soaking feet or washing pets Indoor Water Usage 15% 30% 40% 10% 5% Toilet Bath & Shower Laundry Kitchen Other 21

22 Comparing Flows State to State Commercial Applications Airport per passenger no food service Florida 4 GPD Alabama 5 GPD Office per employee Florida 15 GPD Alabama 25 GPD Motel per bedroom Florida 100 GPD Alabama 120 GPD From Appendix A from Alabama State septic code and Ch 64-E, Florida Administrative Code 22

23 Comparing Flows State to State Theater seat FL 4 ALA 5 Restaurant FL 20/35/40/60 ALA 50 Shopping Center FL 100 per 1000 sq ft Shopping Center AL 200 per 1000 sq ft Hospitals per bed FL 200 (plus 5 per meal) AL 300 Nursing Home per bed FL 100 (plus 5 per meal) AL 200 Residential 2 bedroom FL 200 ALA

24 COMMERCIAL Systems serving high volume establishments, such as restaurants, convenience stores and service stations located near interstate type highways and similar high-traffic areas, require special sizing consideration due to expected above average sewage volume. Minimum estimated flows for these facilities shall be 3.0 times the volumes determined from the Table I figures. CHAPTER 64E (Footnote 2) 24

25 Daily Flows are affected by: Ice machines Dishwashers Coolers Sinks Floor drains Note: Is running water used to thaw food or ice? Are there are leaking plumbing fixtures? Are low flow fixtures in use? 25

26 Something missing from the equation Effluent filters reduce suspended solids Solids deflection device keeps solids in tank Systems offer more types of treatment Alternative (non-aggregate) types of drainfield media are commonly installed Septic tanks are made of corrosive-free material. Repairs are now permitted and inspected. Low Flow fixtures are now in use Baffled tanks provide more retention for treatment Automate sensors detect level of grease and scum There is something still missing

27 Measuring Sewage Flow THE PROBLEM Flow Measurement is a missing link in computing why septic systems may fail. Sewers may suffer potential overflow conditions when other problems are evident. Do we really know a way to justify when a septic or sewer system is in a state of hydraulic overload? 27

28 THE PROBLEM Daily flow can exceed the design capacity of the system, resulting in frequent sewer backups or puddling of sewage onto the ground surface. Sanitary sewer overflows are evident in cases where potential problems are compacted with additional flows. 28

29 Is the Designed Flow Accurate Septic codes in each state adopt a value for daily sewage flow. Is the value accurate enough to constitute reasoning or could a misdiagnose of the estimated sewage flow affect system design? A poorly designed system can lead to premature failure. QUESTION: Is this method reasonable? Case of 22 residents in one dwelling Case with 33 seats in sandwich shop Case with 60 seat full service restaurant that is never busy 29

30 How do you know the flow if it is not measured When a building served by sewer or an onsite septic system is not connected to a metered water system, verification of above normal flow cannot be proved unless the flow can be metered. 30

31 Using a flow metering device If in-line flow meters are used on drinking water systems, they should be available also for private water systems serving a residence or business. Using such a flow meter would register the mass flow used. As one septic tank contractor commented with interest: There would be no basis for an argument from the homeowner about water usage anymore. 31

32 Types of Meters on the Market Volume (in/out) Inferential (speed) Differential Pressure (Examples: V Cone, Venturi, Vortex, Orifice Plate) Electromagnetic Doppler Ultrasonic MagMeter Area Velocity Reading the flow: Direct Read or Pulse Read 32

33 Selected Technologies Magnetic meters need full pipes and area velocity meters need a minimum submergence of about 1/2 before they will even begin to read. Adding a flume device at the base of the pipe to accommodate an ultrasonic device may work in this application. The ultrasonic requires a minimum amount of flow to register. The flume provides the constant level required to read incoming flow. 33

34 Surcharge Flow Measurements can be inaccurate A surcharge condition is when the manhole is actually flooded and the item used to measure the flow is underwater. 34

35 IDENTIFYING THE PROBLEM Water usage records have been an acceptable way to calculate average daily flow where septic systems have been repaired. Water use consumption is used as a calculated item when billing sewer customers. Using this method may hint if hydraulic overloading has occurred and if this condition is an ongoing issue in system performance. 35

36 IDENTIFYING THE PROBLEM At present, this can only be calculated by (estimating) subtracting the water used for filling the swimming pool or for irrigating the yard from the mass flow. Wet weather events can affect daily flow and system performance if inflow or infiltration is suspected. 36

37 Monitoring the Flow Calculating the estimated flow on a sewer system can be impacted by inflow and infiltration (I&I) issues. Wet weather events add to the flow equation. The actual flow may be further impacted with wet weather events and its impact may be ignored. Recommend water conservation measures 37

38 WHAT ARE INFLOW & INFILTRATION? Inflow and Infiltration (I&I) is water that enters the septic or sewer system through cracked pipes, leaky manholes, or improperly connected storm drains, down spouts and pumps. Most inflow comes from stormwater and most infiltration comes from groundwater. Sewage forced out of laterals due to cracks plus inflow problems associated with wet weather events greatly impact the overall flow on a sewer collection system or sewer lateral leading to a septic tank. 38

39 Exfiltration, Inflow and Infiltration can affect sewer flow If there is a break in the sewer pipe If the sewer clean out cap is missing Possible leak from root intrusion Movement of above ground piping can make the joints susceptible to leaks (due to stress and shifting) 39

40 WHAT ARE THE SOURCES OF I & I? 40

41 LOCATE I&I PROBLEMS Flow Monitoring -- Flow meter(s) are installed in sections of pipe where I&I problem is suspected or qualitatively identified. Flow rates and flow volumes data are collected for periods of normal or base flows (dry days) and for days with rain events. Comparison of the flow data reveals the magnitude of the I&I problem. This can provide information on the hydraulic conditions of the sewer line. 41

42 POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY LIFT STATION: use an elapsed time clock to register the hours for run time for each pump in use. The pump operates x GPM. You may know the gallons per cycle. How many cycles did the pump engage? 42

43 Residential Infiltration Example A dosing pump w/ hour meter was used to calculate the flow (discharge to the drainfield) for the total number of cycles per day. Df Pump Water Meter Difference (GPD)

44 POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY One method available uses a pump control to leverage a simple pressure transducer technology for the enhancement of pump system performance. Using a embedded microcomputer in the pump controller and a float-less level transducer in the pump chamber, the Panel monitors liquid levels, controls pumping time intervals, and logs events in real time. 44

45 POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY Use a tipping bucket mechanism to measure flow. 45

POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY Install a modified Venturi flow tube design with strategically positioned pressure transducers to accurately and reliably measure flow under all

46 POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY Install a modified Venturi flow tube design with strategically positioned pressure transducers to accurately and reliably measure flow under all conditions - including transitional periods between open channel and full pipe. Translate pressure directly into flow. Eliminate errors introduced by level and velocity conversions and average velocity calculations. 46

47 POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY + or - 1% accuracy flow meter installed at the appropriate place in the inside water piping system. 47

48 POSSIBLE SOLUTIONS TO MEASURE FLOW ACCURATELY By transmitting an acoustic wave signal from a transducer towards a liquid being monitored, the reflected signal or echo is received by the transducer and processed. The time between transmission of the acoustic signal and reception of the echo is measured, and using the speed of sound through air, the distance from the transducer to the liquid level is calculated. Flow is then calculated from the level measurement and user entered properties of the channel or waste stream. 48

49 49

50 LEVEL DETECTOR METHOD Using fiber optic cable, it transmits a beam of light from an LED at the control panel in a remote transceiver down to the float, where the beam makes and breaks depending on the tilt of the float. When the transceiver detects the presence or absence of light, it activates a relay in the transceiver. The receiver in the control panel detects the presence or absence of light and operate a relay in the receiver. 50

51 Bubbler The bubbler unit uses an internal air compressor to force air from a bubble tube submerged in the flow stream. The depth of the flow is determined by measuring the pressure needed to force bubbles out of the line. The unit then converts this depth into flow rate. 51

52 Inline Flange Meter The inline flange meter uses ultrasonic transit time and Doppler with telemetry. 52

MORE OPTIONS Gravity lines transport sewage from the home just like they do in a gravity system, but at the street or property line, the sewage empties into a buried

53 MORE OPTIONS Gravity lines transport sewage from the home just like they do in a gravity system, but at the street or property line, the sewage empties into a buried valve pit. When 10 gal of wastewater accumulate in the pit, the valve opens automatically and differential air pressure propels the contents into the vacuum main. 53

54 THE SOLUTION Flow should be able to be measured accurately. Using a device in the gravity sewer line to measure the flow should provide a more accurate value compared to the estimated value of flow design for the system. The use of such a device would provide support during an event that a hydraulic overload condition is ongoing. Knowing this would allow the user to justify alternative methods to reduce water usage or to consider modifying the system to meet the true flow entering the system. 54

55 THE SOLUTION Measuring flows accurately can improve system performance and contribute to a longer lasting system if monitored. 55

56 CONCLUSION Being able to meter sewage flow will be a benefit to plumbers, septic utility groups and septic tank contractors that service onsite management programs. Metered sewage flow should not burden a mandated regulation upon every system in use. Metered sewage flow will offer a way to monitor those septic systems where hydraulic overloading is suspected. 56

57 CONCLUSION Monitor sewer collection systems experiencing above normal flows for any particular reason. It would benefit sewer utility groups and municipalities that invoice the user for consumption of wastewater generated. Alternative measures to conserve water could be addressed in those cases to prevent the occurrence of system overuse. 57

58 CONCLUSION The system user should be advised that flow measurement can benefit the overall management of system performance. Measuring flows accurately can contribute to a longer lasting system if monitored 58

59 Please Contact: Albert Royster Phone (352)

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