Trade waste flow metering

The most appropriate way to determine the trade waste effluent volume is by use of one of the following:

• An appropriately sized trade waste effluent flow meter.
• A sub water meter on the incoming process water line where all or a percentage is used or
• Taking a percentage of the site’s incoming water as measured by the property water meter.

Advice on the appropriate type of metering for your business can be obtained by contacting tradewaste@watercorporation.com.au

Regardless of the type of metering, meters must be located in accessible and safe areas to facilitate reading by Water Corporation.

Trade waste effluent flow meters

Trade waste effluent flow meters are to be electromagnetic flow meters that are appropriately sized for the trade waste discharge flow rate and volume of the business. They must also be able to be verified and calibrated.

Specifications for trade waste effluent flow meters

All trade waste effluent meters 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.
• Positioning of flow meter display: The display must be in a position:
  • No greater than 1500mm from ground level
  • Easily accessible by the meter reader
  • Does not pose an occupational, health and safety risk for the meter reader
  • Is protected from direct sunlight
• External output plug: The flow meter must have an Amphenol 6 pin output plug (part number MS 3102E14S-6P) with dust cover (part number MS 25043-14). The plug is to be located above ground and within 2 metres of the sample point and:
  • The output plug 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 be installed in situations where the effluent is pumped to sewer unless the following criteria can be achieved.
• Electromagnetic flow meters on gravity fed lines must have the 'low flow' setting enabled.
• 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).
• 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.

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. Water Corporation recommends that verification checks are done annually. Each time the meter is checked, a Trade Waste Monitoring System Verification Report is to be supplied to us.

Maintenance of trade waste 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 us within 7 days of occurrence.

Flow records for trade waste 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 effluent flow meters or sub water meters

Customer responsibilities

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

• Advise Water Corporation of the date and time of failure and the last meter reading (if available).
• Contact the manufacturer, or supplier, to have the meter serviced or replaced by an appropriately qualified technician. This must be performed within 1 week of the fault being recognised.
• Advise Water Corporation of the date the meter is back in operation or replaced and the initial meter reading.

Estimating volumes

• Water Corporation will estimate the volume discharged to sewer during the period the meter is out of operation using best available information, usually historical data. This estimate will be used for billing purposes.
• Where there is failure 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

• Where there is failure to install a sub water or trade waste effluent flow meter or repair/replace an existing failed meter, Water Corporation 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.