Flow metering

The most appropriate method/instrument to measure a trade waste wastewater volume is based on a number of factors. Find out more here.

The most appropriate method/instrument to measure a trade waste effluent volume is based on a number of factors. The flow can be measured by any of the following:

  • an approved effluent flow meter
  • a sub-water meter on the process water incoming line
  • a percentage of the mains incoming water meter.

Advice on the appropriate type of metering for your business can be obtained by contacting our Commercial and Industrial Services section.

Electromagnetic flow meters are greatly to be preferred in most cases where an effluent flow meter is required. Ultrasonic meters are often problematic in measuring trade waste flows as they are subject to interference by floating solids or foam, solids clogging V notch weirs, solids accumulating upstream of weirs, and sensors being knocked out of alignment. 

The installation of an effluent meter other than an electromagnetic flow meter should be avoided unless it is clearly established that an alternative meter is justified.

Specifications for effluent flow meters

All trade waste meters are to employ electromagnetic flow sensors or ultrasonic sensors and are to comply with the following requirements:

  • Accuracy: The accuracy is to be plus or minus 2% of actual flow at the lowest typical flows. The basis of sizing is to be stated in the documentation.
  • Power supply: The power supply is to be provided by a separate dedicated circuit and is to be wired through an on/off switch to the meter. Any on/off switch is to be secured (locked) to prevent unauthorised use.
  • Flow meter totaliser: A flow meter totaliser must have a visual display with a minimum of six (6) digits, displaying in kilolitres. The display can be mechanical or LCD, with battery backup and password protection. The totaliser display is to be clearly marked with ‘Display in whole kilolitres’.
  • Instantaneous flow rate display: The display must be in digital format showing instantaneous flow rate in litres per second, with a minimum indication of 1 decimal point. The indicator is to be clearly marked as displaying in litres per second.
  • External output plug: There is to be an Amphenol 6 pin output plug (part number MS 3102E14S-6P) with dust cover (part number MS 25043-14) from the flow meter. The plug is to be located above ground and within 2 metres of the sample point.
    • The output pulse is to be set at one (1) pulse per 100 litres.
    • The plug is to be wired as follows:
      • Pin A + Pulse output (voltage free)
      • Pin C - Pulse output (voltage free)
    • If no chart recorder is required a 4-20 mA output signal must be available at points E and F on the pulse plug, as follows:
      • Pin E + Analogue output (4-20 mA)
      • Pin F - Analogue output (4-20 mA).

Additional specifications for electromagnetic flow meters

  • Pumped discharge requirement – electromagnetic flow meters shall only be installed in situations where the effluent is pumped to sewer unless the following criteria can be achieved.

  • Electromagnetic flow meters must be sized, so that the meter maximum flow rate is equal to twice the flow rate allowed by Water Corporation. This meter maximum flow rate must be equal to a minimum linear flow through the meter, of 3 meters per second. This is to ensure acceptable accuracy at near zero flow conditions. A line sized meter is not to be used unless the linear flow rate through the meter at meter maximum flow (full scale) is equal to a minimum linear velocity of 3 meters per second. Where flows are extremely low, a pumping system must be employed to ensure a steady measurable flow.

  • Isolating valve – an isolating valve must be installed upstream of the meter for maintenance purposes (this is not required if a pumped discharge is used).

  • Installation – the pipe work in to, and out of, an electromagnetic flow meter must be designed using pipe bends to ensure the meter tube remains full at all times as detailed in Typical drawing HX33-20-00 – trade waste monitoring point.

  • Flow disturbance – the meter is to be installed a minimum of 5 diameters downstream and 5 diameters upstream of any flow disturbance in the discharge line.

  • Conductivity – the conductivity of the process liquid is to be a minimum of 20 micro Siemens per centimetre (μS/cm).

  • Calibration, commissioning and verification – the meter must be commissioned by an approved company at the time of installation. Frequency of subsequent verification is to be appropriate to the application, to ensure accuracy remains within Water Corporation’s requirements. Each time the meter is checked, a Trade Waste Monitoring System Commissioning Report F 1-8-2 is to be supplied to Water Corporation.

  • Inspection and maintenance – meters are to be installed such that they are able to be inspected, at least annually, and are not to be installed where they will, or may, be submerged. Installation should also facilitate meter removal for repair and recalibration.

Additional specifications for ultrasonic (V-notch open weir type) flow meters

  • Meter size: V notch open weir ultrasonic flow meters must be sized such that the meter maximum flow rate is equal to twice the flow rate allowed by Water Corporation. This meter maximum flow rate must give a minimum height across the V notch of 100 mm.
  • Flow pit: The flow pit must conform to British Standard 3680 Part 4A (1965).
  • Installation: The V notch is to be installed in accordance with the theory of hydromechanics.
  • Temperature compensation: The sensor must have temperature compensation unless the manufacturer can guarantee that in its absence, the meter can achieve 2% accuracy over the expected range of flows for the application.
  • Calibration, commissioning and verification: The meter must be commissioned by an approved company at the time of installation and subsequently verified, at a frequency recommended by the manufacturer or supplier. The frequency is to be appropriate to the application to ensure accuracy remains within Water Corporation’s requirements. Each time the meter has maintenance done a Trade Waste Monitoring System Commissioning Report is to be supplied to Water Corporation. Where the meter is not calibrated in situ, verification must be confirmed once the meter is reinstalled.

Maintenance of effluent flow meters

The meter is to be maintained in accordance with the manufacturer's requirements and is to be inspected, cleaned and repaired as necessary by a service provider approved by the manufacturer. The details of all work performed shall be supplied to Water Corporation within 7 days of occurrence.

Flow records for effluent flow meters

For most businesses, there is a direct relationship between water consumption and effluent volumes. It is recommended that weekly readings of water consumption and effluent volumes be made and the ratio of effluent to water consumption calculated. This will help prompt identification of leaks, excessive water use per unit of production, and meter malfunctions.

Failure of trade waste meters

Customer responsibilities

If the trade waste meter indicates unusual readings or ceases to operate, the customer will:

  • advise us of the date and time of failure and the last meter reading (if available)
  • contact the manufacturer, or supplier, and request to have the meter serviced by an appropriately qualified technician (this must be done within 1 week of the fault being recognised)
  • advise us of the date when the meter is back in operation or replaced and advise of the initial meter reading.

Estimating volumes

  • We will estimate the volume discharged to sewer during the period when the meter is out of operation using best available information, usually historical data. This estimate will be used for billing purposes.
  • Where the customer fails to take reasonable and timely action to have the meter repaired, or replaced, the estimate will be based on the upper value of appropriate historical data.

Customers for whom chargeable trade waste quality is lower than business domestic waste

  • If the customer fails to install a trade waste meter or fails to repair or replace an existing failed trade waste meter, we may charge the trade waste volume as commercial sewerage charges. 
  • The non-residential discharge factor will be re-set to include both trade and non-residential domestic volumes.

More information

Trade waste monitoring system commissioning report

Trade waste monitoring point typical drawing (HX33-20-00)

More information

Email us at: tradewaste@watercorporation.com.au


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