Influent Flow Monitoring at Wastewater Treatment Plant

Influent Flow Monitoring
Figure 1: Signature flow meter  with LaserFlow
sensor sheltered in weather enclosure.
Four Teledyne ISCO Signature Flow Meters, each configured with 360 LaserFlow sensors, were installed at the inlet of a very large wastewater treatment plant (WWTP). This flow monitoring technology provided a unique solution for the challenging flow conditions at this site. Non-contact Doppler laser technology was chosen by the user for their continuous and maintenance free flow monitoring.

Inlet Section Overview

Flow monitoring in the wastewater treatment process is key for verifying performance of the plant as a whole, as well as its individual processing sections. Due to the enormity of the plant’s processing capacity sewage streams are transferred to the plant through different main sewers, which merge into four rectangular inlet channels, each with a width of 1.5 m. At this location, the Signature flow meters and their non-contact LaserFlow sensors were installed over each of four inlet channels and sheltered in all-weather enclosures (Figure1).

Influent Flow Monitoring
Figure 2: Multi-point/Multi-depth velocity method.
Site Challenges

Sludge buildup at the bottom of the channels and high sediment concentration in the flow streams were the major problems for continuous flow rate measurement. The performance of submersible, continuous wave Doppler sensors, previously installed at the site, had been adversely affected by site conditions and required costly maintenance.

Finding the Solution with LaserFlow

The Teledyne Isco distributor recommended using the non-contact LaserFlow sensor at the site. The conditions at the bottom of the channels were less than ideal for traditional flow monitoring. Being placed over the channel LaserFlow overcomes this. First, the unit’s built-in ultra-sonic level transducer determines the stream’s level. This is done by emitting an ultrasonic pulse and measuring the time it takes for the echo to return from the stream’s surface. By using ultrasonic level measurement the sensor can calculate a subsurface point at which to focus an optical laser. The frequency shift (Doppler shifting) of the returned light from the laser is proportionate to the water’s velocity. LaserFlow is able to measure velocities at up to fifteen points below the water’s surface. Being able to measure at multiple points minimizes the effects of turbulence and eliminates the need for manual profiling. Above average results are achieved by producing a level measurement and an exceptionally accurate mean velocity reading.

Measuring Results and Feedback
Influent Flow Monitoring
Figure 3: Flow Rate Measuring Results for four
inlet channels in dry weather conditions.

Thanks to its non-contact technology for velocity and level measurement, the Signature configured with a LaserFlow was capable of providing consistent and continuous flow rate results (Figure 3).

The end-user was able to reduce costs of service by limiting site visits to periodic inspections of the LaserFlow without the need for stopping flow, entering into the manhole and/or cleaning the sensors.

For more information, contact Instrument Specialties, Inc. by calling  407-324-7800 or visiting