How Much Energy Does a Sewage Treatment Plant Use?

A domestic sewage treatment plant like GRAF UK’s One2Clean uses very little electricity because the compressor only aerates for around 10.5 hours a day rather than running continuously. Typical sewage treatment plant energy usage on a small domestic unit starts from 0.63 kWh per day, which is comparable to leaving a light bulb switched on. This intermittent operation, controlled automatically by the system’s panel, is what keeps running costs low while still treating wastewater to a high standard.

How Do One2Clean and OneAdvanced Operate Each Day?

Both the One2Clean and OneAdvanced systems use a sequencing batch reactor (SBR) process to treat wastewater in cycles rather than continuously. Incoming sewage is collected and allowed to settle, then an aeration phase injects oxygen into the water so that beneficial bacteria can break down pollutants, before the water settles again so clean effluent can be drawn off. In larger commercial SBR systems such as the OneAdvanced, any remaining sludge is returned to the primary chamber as part of the cycle. The smaller One2Clean skips this step, keeping the process streamlined for household use.

The air compressor, which delivers oxygen to the bacteria, does not run around the clock. It operates intermittently under the control of the system’s panel, typically running for about 10.5 hours in total across the day rather than continuously. This cuts sewage treatment plant energy usage by roughly 50% compared with older treatment systems that run non-stop. For most One2Clean owners this means a morning and evening treatment cycle, often starting around 7am and 7pm, which lines up with typical household water use after overnight and after the daytime.

There are no moving mechanical parts inside the tank itself and no submerged electrical components, so the air pump and control panel sit externally or in a dedicated housing, which keeps maintenance straightforward. The standard air compressors run from as little as 36 decibels, so most owners barely notice the unit during daily life, and the compressor can also be housed in an outdoor cabinet or outbuilding for extra sound insulation.

Can I Turn My Treatment Plant Off to Save Energy?

No. Even though the compressor is not running constantly, the control panel needs to complete its timed cycles every day to keep the bacterial ecosystem inside the tank healthy. These microbes need regular oxygenation, and switching the system off for extended periods, even overnight, risks starving them of oxygen. Without that oxygen, the tank can turn septic and treatment performance drops.

The potential savings from manually switching the system off are minimal in any case. With daily sewage treatment plant energy usage already comparable to an LED bulb running continuously, the cost is typically well under £1 of electricity per week for most UK households, according to typical Energy Saving Trust household appliance benchmarks. Stopping and restarting the plant can do more harm than good: halted aeration allows waste to sit unprocessed, which can cause odours or push effluent quality below the standards set out by British Water, the UK trade association for on-site wastewater treatment. Leaving the system running is the simplest way to protect both performance and compliance.

Is It Normal for the Compressor to Turn On and Off?

Yes, this on and off cycling is exactly how the system achieves its efficiency, and it is not a fault. The controller activates the air pump during the aeration portions of the cycle, for example for a few hours after 7am and after 7pm, then switches it off during the settling phases when aeration is not needed. Across a full day, the compressor is typically active for roughly 10.5 hours in total, though this can vary slightly depending on the model and settings.

The pause between active periods is the settling or clarification stage, when the wastewater that was just aerated sits undisturbed so that solids can separate out and clarified water can rise to the top for discharge. This cyclical operation reduces wear on the compressor, which is the main mechanical component in the system, helping to defer replacement costs as well as keeping noise to a minimum. The only scenario worth flagging to your installer is if the compressor never switches on, or never switches off, since either pattern could indicate a fault.

Can I Change the Aeration Schedule to Cut Costs Further?

It is best to stick with the factory-set schedule unless a manufacturer-supported change is genuinely needed. The One2Clean and OneAdvanced controllers are pre-configured around typical daily flow patterns, and running one cycle in the morning and one in the evening ensures incoming sewage does not sit untreated for long. Shifting all aeration to overnight hours, for instance to make use of off-peak electricity rates, would leave daytime wastewater untended until evening, which can lead to septicity or odour issues, particularly in warmer weather.

Advanced OneAdvanced systems do offer a holiday mode and under-loading calibration for scenarios such as a holiday home left empty for weeks, adjusting cycle frequency or duration to keep the biology stable rather than simply moving aeration to night hours. For a typical primary residence, though, the standard 10.5-hour daily cycle already keeps sewage treatment plant energy usage low, so there is little financial benefit to forcing an overnight-only pattern, especially given how quiet the units already are.

Can I Leave the System Running While I’m on Holiday?

Yes, and you should. One of the main advantages of a modern sewage treatment plant is that it runs autonomously with very little supervision. Keeping the system powered on while you’re away means the controller continues its normal cycles, and because sewage treatment plant energy usage is so low, it will barely affect your electricity bill during that time. More importantly, allowing the system to keep running through its cycles keeps the bacterial culture in the tank alive and healthy, even if little or no new wastewater is entering the system while the property is empty.

Turning the system off while away risks the opposite outcome: stagnant conditions can cause the biology to go dormant or die off, leading to odours and poor treatment performance once the system restarts, with some delay before it re-establishes equilibrium. For larger or commercial installations, a holiday mode feature can dial back aeration during anticipated low-use periods, and some advanced systems include automatic carbon dosing to feed the bacteria if normal sewage flow stops for an extended time. For most homeowners going away for a few weeks, no action is required beyond making sure routine servicing and desludging are up to date before you leave.

How Do UK Seasons Affect a Sewage Treatment Plant’s Energy Usage?

One2Clean and OneAdvanced are designed to handle the UK climate year-round without needing seasonal adjustment. Because the tank is buried underground, it is naturally insulated from extreme cold, and the water inside typically stays well above 0°C even when air temperatures drop below freezing, partly due to the warmth of incoming household water. Bacterial activity does slow in cold conditions, but performance testing for these systems is carried out at 12°C to reflect realistic UK operating conditions, in line with treatment standards referenced by the Environment Agency.

In summer, biological activity can increase slightly as warmth boosts bacterial metabolism, and the system continues operating normally provided usage patterns stay consistent. Heavy rainfall is not a direct issue for the sealed treatment tank itself, since surface water should never enter the system, though prolonged wet weather or high groundwater can slow percolation through a soakaway or drainage field. A properly designed drainage field should still cope with normal British rainfall patterns, and keeping up with annual desludging and servicing gives the most buffer against any seasonal strain. Seasonal properties can also benefit from the OneAdvanced’s under-load calibration or carbon dosing modules, which keep the biology ticking over during long periods of low occupancy.

Owning a GRAF One2Clean or OneAdvanced sewage treatment plant means letting a low-maintenance system run exactly as it’s programmed, rather than trying to manage it day to day. The roughly 10.5-hour daily aeration cycle keeps sewage treatment plant energy usage to a minimum while still delivering effective treatment, whether the property is occupied, empty for a fortnight, or moving between seasons. The on and off cycling of the compressor is a sign the SBR process is working correctly, not a fault to troubleshoot, and the only real maintenance requirement is an annual service and desludge, much like servicing a boiler or car.

In essence, the One2Clean and OneAdvanced make sewage treatment “set it and forget it” for homeowners, delivering reliable performance for the long term. If you’re considering one of these systems for your property or have more questions about their use, feel free to reach out to our team at GRAF UK. We’re always happy to help you understand how our products can fit your needs and keep your home sustainable and compliant.