Aeration Energy

Energy Savings Program

Axbold runs an energy savings program for sites where two conditions coincide: a high electricity tariff, and a large conventional aeration installation that runs more or less continuously. Twelve months of interval data, an oxygen and mixing balance and a metered proof period establish the saving before any of it is billed.

  • Plant and process engineers
  • Utilities and energy managers
  • Sustainability and Scope 2 reporting leads
  • Finance and controlling teams
  • Public works directors
  • County engineers
Request an assessment See whether your site qualifies

The problem

The Largest Load, Unmeasured

Aeration is typically the largest single electrical load in a biological wastewater treatment plant, and on sites treating high-strength organic wastewater it runs hard. Where that plant sits on an expensive industrial tariff, the aeration line becomes one of the largest controllable costs on the site — controllable in the narrow sense only, because the fleet is usually oversized, fixed-speed and running more or less continuously, which is the configuration that carries the least operating risk.

What that load actually costs, and what it actually delivers, is usually unmeasured. Aerator nameplate horsepower converted to kilowatts is a connected figure, not the metered demand the site is billed on, and the two diverge for two reasons a spreadsheet cannot supply: the whole fleet is rarely running in the interval that sets the site's peak, and billing demand is an averaged interval maximum rather than an instantaneous sum of everything installed. Interval data settles both. The duty cycle is rarely what people assume either, because a plant described as seasonal often runs its aeration year-round with fewer units energized rather than each unit turned down — a fixed-speed aerator has no partial load, it is on or off. That distinction matters twice over: what can be displaced is a whole number of units, and what the demand saving is worth depends on which units were running in the interval that set the peak.

The third unknown is the incumbent's aeration efficiency — mass of oxygen delivered per kilowatt-hour, corrected from a standard rating to what a given aerator achieves in a given pond, at that pond's temperature, salinity, solids, surfactant load and operating dissolved oxygen concentration. It is almost never metered, and the published bands for field-corrected aeration efficiency are wide enough that the top and the bottom of the band point to different decisions. So Axbold does not publish a savings percentage. A percentage quoted before the interval data has been read is arithmetic on the wrong inputs. The saving is established by measurement, which is why the assessment comes first, run through the consulting, testing and data services built into every Axbold program.

  • Aeration is typically the largest single electrical load in a biological treatment plant
  • Nameplate horsepower is a connected figure; the bill is written against metered demand
  • Run hours by unit have to be built from the operating record, not assumed
  • Fixed-speed fleets are on or off; the only turndown available is switching whole units out
  • Field-corrected aeration efficiency, oxygen per kilowatt-hour, is almost never metered and the published bands are wide
  • A large industrial bill has two components, and only one of them is kilowatt-hours
Illustration of an Axbold Guardian on the lined wastewater pond of a California food-processing plant, with orchards and vineyards beyond

How it works

Oxygen Transfer, Not Circulation

The Axbold Guardian infuses gas as nanobubbles averaging 76 nm, at 220 million per mL, with 90% mass transfer into the fluid at 171.9 LPM (45.4 GPM). That last figure is a device figure for gas dissolved at the platform: it is not a basin oxygen transfer efficiency, it is not comparable to a diffuser rating, and it is not corrected for the temperature, salinity, solids and surfactant load of a given basin. Axbold applies the same field correction to its own platform that it applies to the incumbent. By mass a platform delivers 222 grams per minute of air, or 245 grams per minute of oxygen subject to generation capability, and the gap between those two feeds is why some basins only close the oxygen balance on a generated oxygen feed — which draws its own power, netted with the platform's.

The fleets this program addresses are mechanical surface and floating aerators in lagoons and basins. Fine-bubble diffused aeration with working blower turndown is a different and generally better behaved machine, and a plant already running one is usually not a candidate. A surface aerator does two jobs: it transfers oxygen, and it moves water. Axbold nanobubbles are electrically charged, highly pressurized and can stay in solution for months rather than rising and venting within seconds, so they do the first extremely well and do not do the second — a bubble with no buoyancy does not drive a current. Oxygen is held down the water column at the platform rather than lost to the surface, but distributing it across a basin is a transport question rather than a transfer one, and without a current a platform holds dissolved oxygen in its own zone of influence and no further. Platform count and placement therefore follow the basin's existing circulation as well as its oxygen demand, and a one-for-one swap of an aeration fleet is not generally defensible.

The energy case does not rest on beating a well-run conventional aerator on oxygen delivered per kilowatt-hour. It rests on fleets that are oversized for the load they carry, fixed-speed with no turndown, and running continuously on a tariff that bills peak kilowatts as well as kilowatt-hours. It is also a case about how cost scales: a fixed-speed fleet answers a heavier load by running longer, and a Guardian fleet sized from the oxygen balance does not. Said plainly, the saving is the oversizing, converted into a smaller bill. It is not an efficiency gain and it is not free — a fleet sized to the actual oxygen demand carries less spare capacity than one sized well above it, and how much margin a basin can give up in its worst month rather than its average one is the substance of the oxygen balance. Where a site's margin is already thin, that balance says so, and the recommendation is a water security program rather than an energy one.

  • 220 million nanobubbles per mL at an average of 76 nm, NanoSight measured
  • 90% mass transfer into the fluid at 171.9 LPM (45.4 GPM) of gas, measured at the platform rather than across a basin
  • 222 grams per minute of air, or 245 grams per minute of oxygen subject to generation capability, per platform
  • Fleet count follows the basin's oxygen demand against that delivery rate, not a kilowatt ratio
  • No bulk circulation: a bubble that does not rise does not drive a current, so each platform has a zone of influence
  • Mixing is assessed separately from oxygen, because they are separate duties

Deployment modes

Three honest outcomes, and one of them costs energy

01

Full Displacement

Incumbent fleet retired

The incumbent aerators are shut down and come off the load entirely. This is only defensible where bulk circulation is provided by something else, or where the basin does not depend on the aerators for it, which is why the mixing question is settled during the assessment rather than in a proposal. The mixing test is applied forward as well as at the point of retirement: solids the aerators were holding in suspension will settle once they stop, and a growing benthic layer raises sediment oxygen demand over the following seasons, so the balance has to still close against the sediment demand the retirement itself creates. Where it holds, both components of the bill move.

02

Hybrid

Part of the fleet retained for mixing

Part of the incumbent fleet stays in service for bulk circulation and the rest is retired. The retained units keep transferring oxygen while they mix, so their output is credited in the oxygen balance and the Guardian fleet is sized only for the remainder; sizing it for the whole duty would buy oxygen the basin is already getting and add demand for nothing. In practice this is the common answer, and it is the one the physics usually produces. How much smaller the saving is depends on the basin rather than on preference: bulk circulation and solids suspension carry their own power requirement, and that requirement sets a floor on what can be retired — on some basins the floor is a modest share of the fleet, on others it is most of it and there is little to retire. The assessment computes the floor before any saving is discussed, and whatever is left survives contact with a submeter.

03

Supplemental

Nothing retired; consumption rises

Guardians are added and nothing is switched off. Energy consumption goes up. The return here is water quality, compliance headroom or process capacity rather than an energy saving, and Axbold will not sell it as one; a site in this position is buying water quality on a Proactive program, which costs electricity rather than saving it.

Where the program runs

Two markets, two operator types

California

Food and agricultural processors

Processors running on-site biological treatment of high-strength organic wastewater, on large industrial schedules, are the clearest fit in the state. On PG&E Schedule B-20, service at 1,000 kW and above, the bill has two parts that both matter, and a continuously run aeration load pays into both of them every month of the year. That is the condition this program is built for.

Hawaii

County and state facility operators

Hawaii has among the highest electricity prices in the United States, but its industrial wastewater largely does not sit in aerated lagoons — it goes to a county sewer, to an injection well, or back onto the land. The crude, oversized, fixed-speed aeration this program is built for sits mostly in county and state-operated facilities, and that is where the Hawaii energy program is aimed. Public water bodies such as ditch and drainage systems are a separate case: they carry dissolved oxygen deficits in assets no private operator owns, and with no incumbent electrical load to displace there is no energy saving to share, so that is a remediation program with a different funding shape. A shared-savings agreement with a public agency also runs into procurement and appropriation constraints, which shape the contract before the engineering does.

The assessment

How the number gets established

  1. 01

    Twelve Months Of Interval Data

    Twelve months of interval data and utility bills come first, because they settle the real demand profile, the run hours by unit and the tariff the site is actually on. The matching process record comes with them — influent flow, organic and solids loading, ammonia, basin temperature, dissolved oxygen and permit limits — because nothing downstream of that is defensible without both.

  2. 02

    Oxygen And Mixing Balance

    What the water demands — organic load, sediment oxygen demand, and nitrification, which adds substantially to the oxygen required and raises the dissolved oxygen the basin has to hold — is set against what the incumbent delivers and what a Guardian fleet could deliver. Sediment oxygen demand is assessed both as it stands and as the proposed configuration would change it, and mixing is checked separately from oxygen, because only one of the two is a nanobubble problem.

  3. 03

    Sizing From Oxygen, Not Kilowatts

    The fleet is sized from the oxygen balance rather than from a kilowatt-for-kilowatt ratio against the incumbent, because sizing on a kilowatt ratio carries one site's oversizing forward to the next site, where it does not hold. The redundancy basis is set here as well, alongside the unit count, rather than after commissioning.

  4. 04

    A Proof Period

    The fleet runs against submetering before any saving is billed. Where the incumbent cannot safely be shut down on an unproven system it runs in parallel first and site load goes up for that period, but a parallel run only establishes that the Guardian fleet can hold dissolved oxygen, not that it can hold it instead of the incumbent; a staged step-down of incumbent units is what the proof period is for. The step-down runs against a written protocol — continuous dissolved oxygen monitoring at the critical location, a defined hold threshold, a defined abort trigger that returns incumbent units to service, and effluent sampling through the transition — and the protocol, the thresholds and where compliance exposure sits are agreed before the first unit is switched off. The period is set against the site's own cycle rather than a fixed calendar, because a trial that observes one season verifies one season and the rest is modeled.

  5. 05

    Measurement And Verification

    Revenue-grade submetering goes on both aeration loads rather than one, the Axbold fleet and the incumbent fleet, so a retirement is measured rather than inferred. Those meters are read against a baseline built from the site's own pre-retrofit interval data, under a measurement and verification protocol named in the agreement, with the independent variables, the adjustment model and the non-routine adjustment rules agreed in writing before the baseline period closes. Both components are verified, energy and demand, because a saving written in kilowatt-hours alone accounts for only part of the bill.

Qualifying a site

Where this works, and where it does not

A strong fit

  • Aeration that runs more or less continuously, on a large industrial tariff carrying a demand component
  • Oversized, fixed-speed mechanical aerator fleets in lagoons or basins, with little or no turndown
  • Basins where bulk circulation comes from something other than the aerators, or is not required
  • Sites that can produce twelve months of interval data and utility bills together with the matching process record — influent flow, BOD or COD, TSS, ammonia and TKN, basin temperature, dissolved oxygen readings, effluent permit limits, aerator make, rating and run hours by unit, and a sediment survey where settled solids are likely to carry their own oxygen demand
  • Sites able to provide a point of electrical connection with capacity for the fleet and basin access for installation, and prepared to run a metered proof period before any saving is billed

The wrong conversation

  • A site already failing its dissolved oxygen limit with the whole fleet running, or one that meets its limits only in its worst month: there is no aeration headroom to give back, and the conversation there is an Emergent project rather than an energy program
  • A plant whose binding constraint is ammonia rather than dissolved oxygen: nitrification adds substantially to the oxygen demand and raises the dissolved oxygen the basin has to hold, and apparent oversizing usually disappears against it
  • Fine-bubble diffused aeration with working blower turndown, aeration already running at low duty or already under variable-speed control, and suspended-growth basins where the aerators are the mixed-liquor mixers, because losing that mixing is a process failure rather than a smaller saving
  • Cheap power, or connected loads small enough that the measurement and verification work outweighs what is on the table

What you get

Measured First, Billed After

Nothing is billed by Axbold during the proof period, and there is no client capital at any point. Axbold funds, designs, installs, commissions, operates and maintains the fleet, title stays with Axbold, and replacement at end of life is Axbold's obligation rather than the client's. Axbold is paid from a share of verified savings. The site's own exposure during the proof period is the electricity it carries while an incumbent fleet runs in parallel, and that is sized before the trial starts rather than discovered on a bill. What the site provides beyond that is the interface: a point of electrical connection with capacity for the fleet, basin access and mounting, and cooperation on any permit modification the installation requires. Where that interface itself needs work, the scope and who carries it are settled in the assessment and written into the agreement rather than discovered during installation.

A large industrial electricity bill has a volumetric component billed per kilowatt-hour and a demand component billed per kilowatt of peak draw, and on PG&E's large industrial schedule the demand component is a large fraction of the all-in cost of a kilowatt. What continuous running changes is not the size of that share but the reliability of the saving: a kilowatt taken off a load that runs around the clock is taken off every interval, so it reduces energy in every hour and sets a lower peak in all twelve months rather than in the one or two the plant happened to run hard. A savings agreement written only in cents per kilowatt-hour structurally cannot capture that, so Axbold measures and contracts on both components.

The fleet's own consumption is netted in full, and the fleet means everything Axbold puts on the site's meter. Guardians running continuously to hold dissolved oxygen are a new billed demand in every month of the year; where the oxygen balance calls for a generated oxygen feed rather than natural air, that generation is a further continuous load, outside the platform's own consumption figure and netted alongside it; controls, submetering and any retained incumbent units are netted the same way. Netting demand is not arithmetic on annual figures. Demand is set in the intervals that produce each month's peak, and a continuously running Guardian fleet is present in every one of them while the retired units may not have been, so the demand saving is computed against the actual billing determinant in each month — which is also why the assessment reads twelve months of intervals rather than twelve monthly totals. Avoided kilowatt-hours are avoided Scope 2 emissions, and a client's own reporting can claim them. Organizations that need the physical assets on their own balance sheet are describing Embedded rather than this program.

  • No client capital; Axbold funds, designs, installs, commissions, operates and maintains the fleet, and the site provides the electrical connection and basin access
  • Title stays with Axbold, and end-of-life replacement is Axbold's obligation
  • Nothing is billed by Axbold during the proof period, and the report states which months were measured and which were modeled
  • Axbold is paid from a share of verified savings, with energy and demand contracted as the two separate bills they are
  • Everything Axbold puts on the site's meter is netted, gas generation included where the oxygen balance calls for it
  • Demand is netted interval by interval against the billing determinant, not as an annual subtraction

12 Months

Interval Data And Utility Bills

Read before any fleet is sized

2.7 kWh

Energy Consumption Per Platform

The Guardian on a natural air feed, per hour of continuous running; ozone and oxygen duty also need gas generation, which draws its own power and is netted alongside it

90%

Gas Mass Dissolved At The Platform

Device level, of 171.9 LPM (45.4 GPM) gas delivered. Not a basin oxygen transfer efficiency; the field figure comes from the site assessment

Request an assessment Guardian specifications

Related

The rest of the water

All solutions

The seven water problems Axbold treats, and how one capability covers all of them.

Service programs

Proactive, Emergent and Embedded — the three shapes a water security program takes.

Systems

Why treatment sits in the water rather than beside it, and what carries the duty.

Common questions

What percentage will we save?

Not before your site is measured, and three things are the reason. None of them is known in advance: your metered demand rather than your nameplate horsepower; your actual unit-hours rather than the duty cycle the plant is described by, because for a fixed-speed fleet the question is not how hard each aerator worked but how many of them ran, for how long, and which were running when each month's peak was set; and the field-corrected aeration efficiency of the aerators you already own, oxygen delivered per kilowatt-hour, which is almost never metered and sits inside a wide published band. Settling those takes twelve months of interval data and utility bills together with the matching process record — flow, organic and solids loading, ammonia, basin temperature, dissolved oxygen, permit limits, and aerator make, rating and run hours by unit. The assessment produces the number, and nothing is billed until submetering confirms it.

Can you replace our aeration fleet one for one?

Usually not, and Axbold says so early. A surface aerator transfers oxygen and moves water; the Guardian holds dissolved oxygen down the water column extremely well and does not induce bulk circulation, because a bubble with no buoyancy does not drive a current. Where mixing comes from something else, or the basin does not depend on the aerators for it, full displacement is on the table. Where it does not, the answer is a hybrid that keeps part of the incumbent fleet running for circulation, with the oxygen those retained units still transfer credited against what the Guardian fleet has to carry.

Who owns the equipment, and what lands on our balance sheet?

Axbold owns it, throughout. The distinction that matters on your side is that there is no capital request, no depreciation schedule and no end-of-life replacement budget; those sit with Axbold. What the site does carry is the electrical connection, basin access and any permit modification the installation needs, all scoped in the assessment rather than after it. Organizations that need the physical assets on their own balance sheet are describing Embedded, which is a different program shape over the same platform.

How is the saving verified?

Submetering goes on both aeration loads, the Axbold fleet and the incumbent, so a retirement is measured rather than inferred, and both are read against a baseline built from your own pre-retrofit interval data. The adjustment model and the non-routine adjustment rules are agreed in writing before the baseline period closes, which is the clause that decides who carries a process change or a throughput shift in year two. Energy and demand are settled separately, because a settlement written only in cents per kilowatt-hour structurally cannot capture a demand saving.

What happens if the proof period does not deliver?

Nothing is billed by Axbold during the proof period, so a trial that does not produce a saving does not produce an Axbold invoice. It is not costless. While the incumbent runs in parallel the site carries the extra electricity on its own meter, and a higher peak set during that period can carry forward under the demand provisions of a large industrial schedule; both are sized before the trial starts, and the trial is staged to avoid setting a new peak wherever the tariff allows. If the data says the site is a hybrid rather than a full displacement, or a shoulder-season deployment rather than a year-round one, that is what the report says.

What happens if a Guardian fails?

A fleet is more than one platform, so the loss of one unit is a share of the transfer rather than all of it, and the redundancy basis is set during sizing rather than after commissioning. Dissolved oxygen is monitored continuously at the critical location with alarming, and where the assessment calls for it retired incumbent units are left in place and re-energizable as fallback rather than removed from the site. Response cadence and any availability commitment sit in the program agreement, alongside the platform's own duty basis: two moving parts, a quarterly checkup capped at one hour, and a 10 year useful life. Talk with an expert about the redundancy basis a given basin needs.

Energy Savings Program

Send us twelve months of interval data

Utility bills and interval data settle the tariff, the demand profile and the duty cycle. That is the first thing we ask for, and it is the first thing that tells either of us whether this is worth pursuing.

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