Instrument Selection for Wastewater Plant Upgrades

With tightening discharge standards, many wastewater treatment plants are being upgraded. Sensible instrument selection directly affects post-upgrade operational stability and energy consumption.

Influent flow metering

Influent carries heavy suspended solids and fibres — one of the most difficult media for flow measurement. Electromagnetic meters here need wear-resistant lining (polyurethane, for example) and fouling-resistant electrodes. Installation should allow at least 5D upstream and 3D downstream straight pipe, avoiding the turbulent zone at pump discharge.

Level by process stage

Conditions differ markedly between aeration, settling and sludge tanks. Aeration basins have foam and surface turbulence that disturb ultrasonics — radar is recommended. Settling tank surfaces are stable, so ultrasonics suffice. Sludge is viscous, favouring submersible pressure or capacitive measurement.

Dosing systems

Dosing rate directly drives operating cost. Small-bore electromagnetic or rotameter devices on the dosing line, combined with online water quality instruments, enable closed-loop control. Note that dosing chemicals are usually corrosive, so wetted materials must be selected accordingly.

Energy monitoring

Blowers are the largest energy consumers in a wastewater plant. Monitoring blower outlet flow and optimising aeration against dissolved-oxygen data typically yields 10–20% energy savings.