Measuring Gravity Sewer Flow Accurately

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Measuring Gravity

Sewer Flow Accurately

Albert Royster

2016 ISA Water / Wastewater and Automatic Controls Symposium

August 2-4, 2016 – Orlando, Florida, USA

2016 ISA WWAC Symposium

Aug 2-4, 2016 – Orlando, Florida, USA 2

Presenter

• Albert Royster is a retired Environmental

Specialist with Florida Department of Health.

He is a dual drinking water/wastewater treatment plant

plant operator with 30 years experience in

wastewater treatment.

Doctor Septic

Headshot

photo



Presentation Outline

• The Problem

• Goals and Objectives

• Identifying the Problem

• The Solution

• Conclusion



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?


Aug 2-4, 2016 – Orlando, Florida, USA

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



Wastewater systems have two design values

6

• Hydraulic Load (flow)

• Biological Load (waste strength)

• Daily design flow determined by flow per bedroom.

• Biological load based on average range of 110-250 mg/l BOD5.



Flow and Loading

7

• 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 0.00000834 =

PPD BOD5

Calculating mass flow

200 (GPD) X 140 (BOD5) x 0.00000834 =

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.



Waste strength and flow volume comparison

8

Residential example: Groundwater Infiltration

Condition Flow BOD5 lbs/day BOD5

Design Value 450 250 0.94

Expected Value for family of four

200 140 0.23

High Flows 675 90 0.51

Groundwater Infiltration

1980 70 1.16



We know the flow (OR DO WE)

9

• 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?



Was the flow designed on:

10

• 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.



Metered Water for Septic Repair

11

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



Example of more normal pattern

Metered Water for Septic Repair

12

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



ESTIMATED SEWAGE FLOW

13

• 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.



QUESTION

14

• 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?



Home Water Use Survey

15

• Showers and Baths • Toilet Flushes • Showers • Baths • Tooth brushing • Hand Dishwashing • Automatic Dishwasher • Laundry • Other Indoor uses • Lawn Watering • Other outdoor uses



MASS FLOW

16

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 www.sjrwmd.com/floridaswater/conservation/survey.html

http://www.sjrwmd.com/floridaswater/conservation/survey.html



Estimating Indoor Use

17



Estimating Indoor Flow

18



Estimating Indoor Flow

19



–A Family Survey (Family of Four) Note: Three bedroom residence

20

• Tooth brushing: 12 GPD Dishwasher: 2 GPD

• Toilet Flushing: 64 GPD Dishes by Hand: 2 GPD

• No major outdoor use: Handwashing: 12 GPD

• Irrigation, wash dog/car

Laundry: 24 GPD

Bath 0 GPD

Showers: 100 GPD

Total 216 GPD

Water Usage Records show

avg 180-220 GPD



Washing machine uses the most water per use

OTHER could mean soaking feet or washing pets

21

Indoor Water Usage

40%

30%

15%

10%5%

Toilet

Bath & Shower

Laundry

Kitchen

Other



Comparing Flows State to State

22

• 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



Comparing Flows State to State

23

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 300



COMMERCIAL

24

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-6.008 (Footnote 2)



Daily Flows are affected by:

25

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?



Something missing from the equation

26

• 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. . . . .



Measuring Sewage Flow

27

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?



THE PROBLEM

28

• 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.



Is the Designed Flow Accurate

29

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



How do you know the flow if it is not

measured

30

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.



Using a flow metering device

31

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.”



Types of Meters on the Market

32

• 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



Selected Technologies

33

• 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.



Surcharge Flow Measurements can

be inaccurate

34

A surcharge condition is when the manhole is actually

flooded and the item used to measure the flow is

underwater.



IDENTIFYING THE PROBLEM

35

• 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.



IDENTIFYING THE PROBLEM

36

• 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.



Monitoring the Flow

37

• 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



WHAT ARE INFLOW & INFILTRATION?

38

• 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.



Exfiltration, Inflow and Infiltration

can affect sewer flow

39

• 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)



WHAT ARE THE SOURCES OF I & I ?

40



LOCATE I&I PROBLEMS

41

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.



POSSIBLE SOLUTIONS TO MEASURE FLOW

ACCURATELY

42

• 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?



Residential Infiltration Example

43

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)

429 374 55

675 344 331

675 214 461

1980 240 1740




ACCURATELY

44

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.




ACCURATELY

45

Use a tipping bucket mechanism to measure flow.




ACCURATELY

46

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.




ACCURATELY

47

+ or - 1% accuracy flow meter installed at the

appropriate place in the inside water piping

system.




ACCURATELY

48

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.





LEVEL DETECTOR METHOD

50

• 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.



Bubbler

51

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.



Inline Flange Meter

52

The inline flange meter uses ultrasonic transit time and

Doppler with telemetry.



MORE OPTIONS

53

• 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.



THE SOLUTION

54

• 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.



THE SOLUTION

55

• Measuring flows accurately can improve system

performance and contribute to a longer lasting system

if monitored.



CONCLUSION

56

• 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.



CONCLUSION

57

• 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.



CONCLUSION

58

• 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



Please Contact:

59

Albert Royster

E-Mail: [email protected]

Phone (352) 361-1646

mailto:[email protected]

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Measuring Gravity Sewer Flow Accurately

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