How much electricity does a factory or township sewage treatment plant use per kilolitre, and what CO2 is that?
Divide the STP's electricity for a period by the kilolitres it treated, then multiply by 0.710 kg CO2 per kWh. At 0.5 kWh per kL, for example, that is about 0.36 kg CO2 per kL. Technology, load and blower control drive the number, so measure your own plant rather than borrow a figure.
Where an STP uses power
- Aeration blowers: usually the largest single load in activated sludge, SBR and MBBR plants, because they run most of the day.
- Pumps: raw sewage lift, sludge recirculation, filter feed and treated water transfer.
- Mixers, decanters and dosing pumps.
- Membrane plants (MBR): extra blower air to scour the membranes and permeate pumps, which is why they draw more power per kL than conventional aeration.
- Tertiary treatment: pressure sand filters, carbon filters, UV or ozone if the treated water is reused.
How to measure kWh per kL
- Fit an energy meter on the STP feeder. Without one, read each motor's running current with a clamp meter and log its run hours from the panel.
- Read the treated water flow meter at the outlet for the same days.
- kWh per kL = STP kWh / treated kL. Use at least a month, because flow swings with occupancy and shifts.
- Do not use nameplate kW times hours. Blowers and pumps rarely run at full load, so nameplate overstates.
Turning it into CO2 and putting it in the right scope
If you own or control the STP, its grid electricity is already inside your Scope 2 at 0.710 kg CO2 per kWh. Reporting kWh per kL does not add emissions; it shows where they sit. Diesel for a backup generator at the STP is Scope 1.
Treatment itself can release methane and nitrous oxide, mainly from anaerobic zones and sludge handling. The IPCC 2006 Guidelines, Volume 5, Chapter 6 give the method. Count those separately from electricity, in CO2e with a named GWP set.
Why the figure drifts and what to check
- Underloaded plants: a township STP built for full occupancy but running at 40% flow still runs its blowers, so kWh per kL rises.
- Fixed-speed blowers: dissolved oxygen above what the process needs wastes power. A DO sensor with a VFD lets the blower slow down.
- Clogged diffusers raise blower pressure and power.
- Compare your figure with the design basis report from the plant supplier, which states the expected power for the technology.
Worked example: one day at a 1,000 kL per day STP (readings assumed)
- Blowers: 2 running at a measured 12 kW each for 22 hours = 528 kWh
- Raw sewage pump: 6 kW for 10 hours = 60 kWh
- Filter feed pump: 4.5 kW for 16 hours = 72 kWh
- Dosing, mixers and lighting: 20 kWh
- Total: 528 + 60 + 72 + 20 = 680 kWh for 1,000 kL treated
- Intensity: 680 / 1,000 = 0.68 kWh per kL
- CO2: 0.68 x 0.710 = 0.48 kg CO2 per kL; 680 x 0.710 = 482.8 kg CO2 a day
These are example readings, not a typical value for any STP technology. Use your own feeder meter and flow meter.
What Senseible does here
Senseible reads the units on your electricity bill and applies 0.710 kg CO2 per kWh, so the STP's power is already in your Scope 2. A sub-meter reading or blower log lets you show the STP's share as kWh per kL alongside it.
- ZLD plant energy and CO2 per kL
- Methane from ETP wastewater
- VFD savings on pumps and fans
- Water intensity for BRSR
Sources: CEA CO2 Baseline Database, version 21.0, BEE Guide Book 3, Energy Efficiency in Electrical Utilities (pumps, fans and blowers), 2006 IPCC Guidelines, Volume 5, Chapter 6, Wastewater Treatment and Discharge
Last reviewed 2026-10-19.