Wastewater Treatment Equipment: Screens, Clarifiers, Aeration and Dewatering

Quick Answer

A wastewater plant is a sequence of unit operations, and each stage exists to protect the next. Preliminary treatment removes what would damage equipment: coarse bar screens at 20-50 mm, fine screens at 2-6 mm, and grit removal sized to capture 95% of particles above 0.2 mm at about 0.3 m/s channel velocity. Primary clarification at surface overflow rates of roughly 30-50 m³/m²/day removes 50-70% of suspended solids and 25-40% of BOD by gravity alone. Secondary biological treatment oxidises dissolved organics — conventional activated sludge at 4-8 hours hydraulic retention and an F/M ratio of 0.2-0.5 kg BOD/kg MLSS/day, extended aeration at 18-36 hours, MBBR, SBR or MBR depending on footprint and effluent quality. Aeration is the dominant energy cost, typically 50-60% of plant electricity: fine-bubble membrane diffusers transfer 4-6% oxygen per metre of submergence against 1.5-2.5% for coarse bubble, which usually justifies their higher maintenance. Dewatering reduces sludge volume: gravity thickening to 2-6% dry solids, belt presses and screw presses to 15-25%, decanter centrifuges to 20-30%, and thermal drying beyond that. Getting the preliminary stages wrong destroys the equipment downstream — rag in a centrifuge and grit in a digester are the two most expensive consequences of saving money on screens.

A food processing plant in North Africa installed a 1,800 m³/day treatment plant. The design was competent. The budget was cut late in the project and the fine screen was deleted, leaving only a 50 mm coarse bar screen.

Within four months the plant had replaced three submersible mixers whose impellers were wrapped solid with rag and plastic film, rebuilt both sludge pumps, and had a decanter centrifuge out of service with a scored scroll and damaged conveyor flights. The aeration diffusers in the first zone were partially blinded by grease and fibre. Effluent quality was out of consent and the local regulator had issued a notice.

The deleted fine screen was quoted at 41,000 EUR. The first eighteen months of consequences cost approximately 260,000 EUR in parts, labour and regulatory exposure, and the screen was installed anyway in month nineteen.

Preliminary treatment is not a stage you optimise. It is the stage that determines whether everything downstream survives.

Preliminary Treatment

Bar screens

The first barrier. Removes rags, plastics, wood, textiles and anything else that would block or wrap rotating equipment.

Coarse screens — 20-50 mm bar spacing. Mechanically raked. Protect pumps and the works inlet.

Fine screens — 2-6 mm. Step screens, perforated plate band screens, drum screens or multi-rake screens. Remove the fibrous material that coarse screens pass and that causes most downstream damage.

Design rules that matter:

• Approach velocity through the screen: 0.6-1.2 m/s at peak flow. Below 0.3 m/s solids settle in the channel; above 1.2 m/s material is forced through the bars.
• Channel velocity upstream: minimum 0.3 m/s to keep grit moving.
• Head loss allowance: a clean screen may lose 50-150 mm, a blinded one far more. Channel freeboard and the upstream hydraulic profile must accommodate the blinded condition.
• Duty and standby screens, or a bypass channel with a manual screen. A single screen is a single point of plant failure.
• Screenings handling: a washer-compactor reduces screenings volume by 50-70% and removes faecal matter, cutting disposal cost and odour. Specified as a matter of course on municipal works and increasingly on industrial ones.

Fine screening at 2-3 mm is the single most cost-effective protection in a plant with membranes, centrifuges or submersible mixers. MBR plants require it — membrane manufacturers typically mandate 1-2 mm screening, and operating an MBR without it voids the warranty and destroys the modules.

Grit removal

Grit is sand, gravel, eggshell, coffee grounds, bone — inert, dense, abrasive material. It wears pumps and centrifuges, accumulates in digesters and channels, and reduces tank volume.

Types:

• Horizontal flow (velocity-controlled) channel — simple, relies on maintaining 0.3 m/s so organics stay suspended while grit settles. Needs a proportional weir or Parshall flume to hold velocity across the flow range.
• Aerated grit chamber — diffused air creates a spiral roll; grit falls out, organics stay suspended. Tolerant of flow variation, also provides some grease separation and pre-aeration. Larger and uses energy.
• Vortex grit chamber — a mechanically induced vortex separates grit into a central hopper. Compact and widely used in new works.
• Detritus tank — square settling tank with a raking mechanism.

Design target: capture 95% of particles larger than 0.2 mm with a specific gravity of 2.65. Many plants only capture down to 0.3 mm in practice, and the 0.2-0.3 mm fraction is enough to cause digester accumulation over years.

Grit washing and classification removes organics from the captured grit, cutting disposal volume and odour, and producing a material that can be landfilled or reused rather than handled as putrescible waste.

Grease and oil removal

Grease traps and skimming tanks for primary separation.

Dissolved air flotation (DAF) — air is dissolved into a recycle stream at 4-6 bar and released into the flotation tank, where microbubbles attach to oil, grease and light solids and float them to a skimmer. Hydraulic loading typically 5-12 m³/m²/h. Very effective: 90-95% removal of fats, oils and grease and 60-90% of suspended solids with coagulant and flocculant addition.

DAF is the standard pretreatment for food processing, dairy, meat, rendering, fish processing, edible oil and many chemical effluents. It removes the load that would otherwise overwhelm a biological stage, and the float is a concentrated stream that can often be recovered or digested.

Primary Treatment

Gravity settlement in a clarifier, removing settleable solids before the biological stage.

Design parameters:

• Surface overflow rate: 30-50 m³/m²/day at average flow, up to 80-120 at peak
• Hydraulic retention time: 1.5-2.5 hours
• Side water depth: 3-4.5 m
• Weir loading: below about 250 m³/m/day
• Sludge withdrawal: continuous or frequent; primary sludge goes anaerobic quickly and releases odour and dissolved organics back into the liquid stream

Typical removal: 50-70% suspended solids, 25-40% BOD.

Types: circular centre-feed with rotating scraper bridge, circular peripheral-feed, rectangular with chain-and-flight or travelling bridge collectors.

Chemically enhanced primary treatment (CEPT) — coagulant (ferric chloride, alum or PAC) plus polymer raises removal to 80-90% SS and 50-70% BOD. A very cost-effective way to debottleneck an overloaded biological stage or to meet a load reduction target without building more aeration. The penalty is substantially more primary sludge, which must be handled.

Lamella and inclined plate settlers multiply effective settling area within a given footprint by a factor of 5-10, at the cost of being sensitive to blockage and requiring good upstream screening. Valuable in retrofits and space-constrained sites.

Secondary (Biological) Treatment

Conventional activated sludge

Aeration basin with returned activated sludge, followed by a secondary clarifier.

• Hydraulic retention time: 4-8 h
• MLSS: 2,000-4,000 mg/L
• F/M ratio: 0.2-0.5 kg BOD/kg MLSS/day
• Sludge age (SRT): 4-10 days
• BOD removal: 85-95%

Extended aeration — HRT 18-36 h, MLSS 3,000-6,000 mg/L, F/M 0.05-0.15, SRT 20-40 days. Lower sludge production, more stable to load shock, better nitrification, simpler operation. Larger tanks and higher aeration energy per unit treated. The usual choice for small works and remote sites.

Nitrification requires SRT above roughly 8-10 days at 20°C and considerably more at lower temperatures, dissolved oxygen above 2 mg/L, alkalinity (about 7.1 mg CaCO₃ consumed per mg of ammonia oxidised — insufficient alkalinity stalls nitrification and crashes pH), and temperature above about 10°C for reliable performance.

Denitrification requires an anoxic zone with a carbon source and no oxygen. Modified Ludzack-Ettinger (MLE) puts the anoxic zone first and recycles nitrified mixed liquor to it; the 4-stage Bardenpho adds a second anoxic and re-aeration stage for lower total nitrogen. Denitrification recovers about 3.6 g of oxygen equivalent per gram of nitrate reduced and about half the alkalinity consumed in nitrification, so it reduces aeration energy and chemical cost as well as nitrogen.

Biological phosphorus removal requires an anaerobic selector zone ahead of the aeration where phosphorus-accumulating organisms take up volatile fatty acids, followed by aerobic uptake. A5-stage Bardenpho or UCT configuration. Chemical phosphorus removal with ferric or alum is simpler and more reliable but produces more sludge and operating cost.

Secondary clarifiers

• Surface overflow rate: 16-32 m³/m²/day
• Solids loading rate: 4-6 kg/m²/h
• Side water depth: 3.5-5 m — deeper is more robust against sludge blanket upset
• Return activated sludge capacity: 50-150% of average flow, variable speed

Secondary clarifier performance governs final effluent suspended solids and therefore consent compliance. Underdesigned clarifiers are the most common reason a biologically sound plant fails its consent.

MBBR and IFAS

Moving bed biofilm reactor (MBBR) — plastic carrier media kept in suspension by aeration or mixing, with biofilm growing on the protected internal surface. Typical protected surface area 350-800 m²/m³, carrier fill 30-60% of tank volume. No sludge return, no settling in the reactor, very tolerant of load variation and toxic shock.

Integrated fixed-film activated sludge (IFAS) — carriers added to a conventional activated sludge basin, increasing biomass without increasing MLSS. The standard way to upgrade an existing overloaded plant within its existing tanks, particularly to add nitrification capacity.

Media retention screens are critical: media loss through a failed screen is expensive and immediate.

Sequencing batch reactor (SBR)

One tank performing fill, react, settle, decant and idle in sequence. No separate clarifier, no RAS pumping, excellent process flexibility, and anoxic and aerobic phases achieved by control rather than by separate tanks. Needs reliable automation and a decanter mechanism, and flow equalisation or multiple basins for continuous inflow.

Membrane bioreactor (MBR)

Activated sludge with membrane separation replacing the secondary clarifier. Hollow fibre or flat sheet, immersed or external, typically 0.03-0.4 micron.

• MLSS 8,000-12,000 mg/L — far higher than clarifier-limited systems, so a much smaller footprint
• Effluent SS below 1 mg/L, turbidity below 0.2 NTU, substantial pathogen removal
• Effluent suitable for reuse with minimal further treatment
• Flux typically 15-30 LMH depending on membrane and temperature

MBR requirements that are frequently underestimated:

• 1-2 mm fine screening is mandatory. Hair and fibre braid onto hollow fibres and cannot be removed.
• Air scour and relaxation or backpulse cycles
• Periodic maintenance cleaning with hypochlorite and citric or oxalic acid, and recovery cleaning as needed
• Higher aeration energy, because high MLSS reduces oxygen transfer efficiency through the alpha factor
• Membrane replacement budget — typically 7-10 year life

MBR is the right answer where footprint is severely constrained, where reuse-quality effluent is required, or where the consent is tight enough that clarifier-based systems cannot reliably meet it.

Anaerobic treatment

For high-strength industrial effluent — brewery, distillery, food processing, pulp — anaerobic treatment converts organics to biogas rather than to sludge.

UASB (upflow anaerobic sludge blanket) — granular sludge bed, organic loading 4-12 kg COD/m³/day.

EGSB and IC reactors — higher upflow velocity, loading 15-35 kg COD/m³/day, very compact.

Anaerobic digesters (CSTR) — for sludge and for slurries not suited to granular systems.

Advantages: 70-90% COD removal, biogas at roughly 0.35 m³ CH₄ per kg COD removed, sludge production about one-tenth that of aerobic treatment, no aeration energy. Requires temperature control (mesophilic 35-38°C), is sensitive to pH, sulphide and toxicity, and almost always needs aerobic polishing to meet a discharge consent.

Aeration — Where the Energy Goes

Aeration is typically 50-60% of a wastewater plant's electricity consumption. Equipment choice and control here dominate operating cost.

Diffusers

Fine bubble diffusers in a 5 m deep tank reach standard oxygen transfer efficiency around 20-30%, against 8-12% for coarse bubble. That difference typically cuts aeration power by half or better, which on a plant of any size overwhelms the maintenance difference.

Coarse bubble still has its place: aerated grit chambers, channels, sludge holding tanks, aerobic digesters, and any duty where fouling or ragging would make fine bubble unmaintainable.

Alpha factor — the ratio of oxygen transfer in process water to clean water. Typically 0.4-0.7 for fine bubble in municipal activated sludge, falling with rising MLSS and with surfactant presence, and often 0.3-0.5 in MBR at high MLSS. Sizing blowers on standard (clean water) transfer rates without applying alpha, beta and theta corrections produces a chronically underaerated plant.

Blowers

Dissolved oxygen control with VFD blowers is the single largest energy saving available in most existing plants. Running blowers at constant output to satisfy peak demand while average demand is far lower commonly wastes 25-40% of aeration energy. A DO probe, a controller and VFDs typically pay back in 1-3 years.

Most-open-valve control adds a further layer: the controller trims header pressure so the most-open zone valve sits near fully open, minimising throttling loss across the whole air system.

Sludge Treatment

Sludge handling is often more than half the operating cost of a wastewater plant, and it is the stage most often under-designed.

Thickening

Stabilisation

Anaerobic digestion — mesophilic at 35-38°C, 15-25 day retention. Reduces volatile solids 40-55%, produces biogas at roughly 0.9-1.1 m³/kg VS destroyed at 60-65% methane, and produces a stabilised, far less odorous biosolid. On plants above roughly 20,000 population equivalent, the biogas usually justifies the capital.

Aerobic digestion — simpler, no gas handling, but consumes significant aeration energy and reduces volatile solids less. Suits small plants.

Lime stabilisation — raises pH above 12 to kill pathogens. Simple and fast, increases mass and volume, used where land application requires pathogen reduction.

Thermal hydrolysis — pressure-cooking sludge ahead of digestion, raising volatile solids destruction and allowing higher digester loading and better dewaterability. Capital-intensive, for large works.

Dewatering

Disposal cost drives dewatering selection. Going from 18% to 25% dry solids reduces cake mass by about 28%, so where disposal is charged by the tonne and the distance is long, the capital difference between a belt press and a centrifuge is often recovered quickly. Where disposal is cheap and local, a screw press's low energy and low maintenance usually wins.

Polymer is a major consumable. Dose, make-up concentration, ageing time and mixing energy all affect performance, and a poorly set polymer system can double consumption while delivering worse cake. Specify a proper polymer make-up unit with correct wetting, ageing and dilution rather than a drum and a dosing pump.

Disinfection

Chlorination (hypochlorite) — effective, cheap, residual persists. Forms disinfection by-products, and dechlorination is required before discharge to sensitive waters.

UV disinfection — no chemicals, no by-products, effective against chlorine-resistant protozoa. Dose typically 30-40 mJ/cm² for secondary effluent. Performance depends strongly on upstream suspended solids and on lamp sleeve cleanliness — a UV system on poor-quality effluent does not work, and automatic sleeve wipers are not optional.

Ozone — powerful oxidant, also reduces colour and micropollutants. Generated on site, high energy, requires off-gas destruction.

Peracetic acid — increasingly used where chlorine by-products are unacceptable and UV is impractical.

Common Specification Mistakes

1. Deleting or undersizing fine screening. The food plant example: a 41,000 EUR screen deleted, 260,000 EUR in downstream damage.

   Prevention: Specify 2-6 mm fine screening upstream of any plant with mixers, centrifuges or membranes, and 1-2 mm ahead of an MBR as a non-negotiable requirement.

2. Sizing blowers on standard oxygen transfer efficiency without alpha, beta and theta corrections. The plant is chronically underaerated and never meets its consent at design load.

   Prevention: Require field oxygen transfer calculations with site-specific alpha factor, process temperature and elevation, and state the assumed alpha on the datasheet.

3. No dissolved oxygen control. Blowers run flat out to cover peak demand while average demand is far lower.

   Prevention: Specify DO probes, VFD blowers and automatic control, with most-open-valve header pressure control on multi-zone plants.

4. Secondary clarifier sized on surface overflow rate only, ignoring solids loading rate. The blanket rises and solids carry over at peak load.

   Prevention: Check both surface overflow rate and solids loading rate at peak flow with peak RAS, and specify adequate side water depth — 4 m or more.

5. Nitrification specified without checking alkalinity and SRT. Nitrification consumes about 7.1 mg of alkalinity as CaCO₃ per mg of ammonia; low-alkalinity influent crashes pH and nitrification stops.

   Prevention: Calculate the alkalinity balance, provide alkalinity dosing if needed, and verify SRT is adequate at the minimum design temperature, not the average.

6. Grit removal designed for 0.3 mm rather than 0.2 mm. The fine fraction passes and accumulates in digesters and channels over years.

   Prevention: Specify 95% capture of 0.2 mm particles at specific gravity 2.65 across the design flow range, and include grit washing and classification.

7. No flow equalisation on an industrial effluent with batch discharges. The biology sees a shock load, the sludge deflocculates and the clarifier loses solids.

   Prevention: Provide a balancing tank sized against the actual discharge pattern, with mixing and often pH correction, upstream of the biological stage.

8. No DAF on a high-FOG industrial effluent. Grease blinds diffusers, coats media and causes filamentous bulking.

   Prevention: Specify DAF with coagulant and flocculant dosing ahead of biological treatment for food, dairy, meat, rendering and edible oil effluents.

9. Dewatering selected on capital cost without costing disposal. A few percent more dry solids has a large effect on haulage and gate-fee cost.

   Prevention: Model annual disposal cost at each achievable cake dryness, including haulage distance and gate fee, and compare against capital and operating cost over ten years.

10. UV disinfection on effluent with high suspended solids. UV transmittance collapses and the dose delivered is a fraction of the design value.

    Prevention: Verify upstream effluent quality, specify UV transmittance assumptions explicitly, include automatic sleeve cleaning, and consider tertiary filtration ahead of UV.

11. MBBR media retention screens undersized or poorly supported. Media escapes and is lost downstream.

    Prevention: Specify screen open area, approach velocity and structural support, and require a media recovery provision.

12. No standby on single-stream critical equipment. One screen, one blower or one dewatering unit with no backup means any failure is an immediate consent breach.

    Prevention: Specify duty and standby on screens, blowers, RAS pumps and dewatering, or a bypass that can be operated safely.

Supply from Kasko Makine

Kasko Demir Çelik Makine supplies wastewater treatment equipment for municipal and industrial plants:

Preliminary treatment

• Mechanically raked coarse bar screens, 20-50 mm
• Fine screens: step, band, drum, multi-rake and perforated plate, 1-6 mm
• Screenings washer-compactors and conveyors
• Vortex, aerated and horizontal-flow grit removal systems
• Grit classifiers, washers and pumps
• Grease traps, skimming tanks and scum removal equipment
• Dissolved air flotation units with saturation systems and chemical dosing

Clarification and separation

• Circular clarifiers with centre and peripheral drives, scraper bridges and suction mechanisms
• Rectangular clarifiers with chain-and-flight and travelling bridge collectors
• Lamella and inclined plate settlers
• Scum boxes, weirs, baffles and launders
• Coagulation and flocculation tanks with flash mixers and flocculators

Biological treatment

• Activated sludge packages, extended aeration and MLE/Bardenpho configurations
• MBBR and IFAS systems with carrier media and retention screens
• SBR systems with decanters and automation
• MBR systems with hollow fibre and flat sheet modules, air scour and CIP skids
• UASB, EGSB and anaerobic digester equipment
• Containerised and packaged plants for remote and small-flow sites

Aeration

• Fine bubble membrane disc and tube diffusers in EPDM, silicone and polyurethane
• Coarse bubble diffusers and aerated channel grids
• Diffuser grids, drop pipes, headers and supports in stainless and HDPE
• Surface aerators and jet aeration systems
• Blowers: positive displacement, multistage centrifugal, screw and high-speed turbo
• Blower packages with acoustic enclosures, VFDs, filters and silencers
• DO probes, controllers and most-open-valve control systems

Sludge treatment

• Gravity thickeners, gravity belt thickeners, rotary drum thickeners and DAF thickeners
• Anaerobic digester equipment: mixers, gas holders, heat exchangers, gas handling
• Belt filter presses, screw presses, rotary presses, decanter centrifuges and plate-and-frame filter presses
• Polymer make-up and dosing systems with correct wetting and ageing
• Sludge pumps: progressive cavity, rotary lobe and piston
• Cake conveyors, silos and loading equipment

Disinfection and tertiary

• UV systems with automatic sleeve cleaning
• Hypochlorite and peracetic acid dosing systems
• Ozone generators with off-gas destruction
• Sand, disc and drum tertiary filters

Associated supply

• Submersible, dry-well, progressive cavity and self-priming pumps
• Submersible and top-entry mixers
• Piping and valves in HDPE, PVC, stainless and carbon steel
• Penstocks, stop logs, weirs and flow measurement
• Instrumentation: flow, level, DO, pH, ORP, turbidity, suspended solids
• Tanks and vessels in carbon steel, stainless, GRP and bolted panel construction
• Odour control: biofilters, chemical scrubbers, activated carbon

Engineering support

Send design flow (average, peak hourly, peak daily), influent analysis (BOD, COD, SS, TKN, ammonia, total phosphorus, FOG, pH, temperature, alkalinity), discharge consent limits, available footprint and the local electricity tariff. We will return a treatment train with unit sizing, an aeration demand and blower selection with alpha factor stated, a sludge production and dewatering estimate, and an indicative operating cost breakdown so capital and operating trade-offs are visible.

Certification

Material certificates to EN 10204 3.1, welding procedure and welder qualification documentation, surface preparation and coating specifications with DFT records, hydrostatic and leak test certificates, factory acceptance test reports for packaged units, CE marking and PED documentation where applicable, and performance test procedures for clarifier and aeration equipment.

Logistics

Standard screens, diffusers and pumps generally ship in 4-8 weeks. Clarifier mechanisms and blower packages typically 10-16 weeks. MBR systems, centrifuges and complete packaged plants 14-24 weeks. Shipping from Istanbul by road to Europe, the Caucasus and Iraq, and by sea to Gulf, African and Asian destinations.

Send your flow data and influent analysis and we will return a treatment train with equipment sizing within five working days. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading: Water Series

• Boiler and Cooling Water Treatment
• Sewage and Wastewater Pumps
• Industrial Mixers and Agitators
• HDPE Pipes: Properties and Applications

Frequently Asked Questions

Q: What screening does a wastewater treatment plant need?
A: Coarse bar screens at 20 to 50 mm protect the inlet works and pumps, while fine screens at 2 to 6 mm remove the fibrous material that causes most downstream damage to mixers, pumps and centrifuges. Membrane bioreactors require 1 to 2 mm screening as a mandatory condition, because hair and fibre braid onto hollow fibre membranes and cannot be removed. Approach velocity should be 0.6 to 1.2 m/s at peak flow.

Q: What is the difference between fine bubble and coarse bubble aeration?
A: Fine bubble membrane diffusers transfer approximately 4 to 6% of oxygen per metre of submergence, reaching 20 to 30% standard transfer efficiency in a 5 metre tank, while coarse bubble diffusers achieve 1.5 to 2.5% per metre or 8 to 12% overall. Fine bubble typically halves aeration power but needs periodic cleaning and membrane replacement every 5 to 10 years. Coarse bubble remains correct for grit chambers, channels and sludge holding tanks.

Q: How do you size a secondary clarifier?
A: Check both hydraulic and solids loading. Surface overflow rate is typically 16 to 32 m³/m²/day and solids loading rate 4 to 6 kg/m²/h, both evaluated at peak flow with peak return activated sludge rate. Side water depth should be 3.5 to 5 metres, with deeper tanks far more robust against blanket upset. Sizing on overflow rate alone is the most common cause of solids carryover and consent failure.

Q: Which sludge dewatering equipment gives the driest cake?
A: Plate and frame filter presses reach 30 to 45% dry solids, decanter centrifuges and rotary presses 20 to 30%, and belt and screw presses 15 to 25%. Thermal drying exceeds 90% but uses very large amounts of energy. Selection should be made against disposal cost: moving from 18% to 25% dry solids cuts cake mass by about 28%, which repays capital quickly where haulage is long or gate fees are high.

Q: When should an MBR be used instead of a conventional clarifier?
A: MBR suits sites where footprint is severely constrained, where reuse-quality effluent is needed, or where the discharge consent is too tight for clarifier-based systems. It operates at 8,000 to 12,000 mg/L MLSS against 2,000 to 4,000 for conventional plants and produces effluent below 1 mg/L suspended solids. The costs are mandatory 1 to 2 mm screening, higher aeration energy from the reduced alpha factor, cleaning regimes and membrane replacement every 7 to 10 years.

Q: What does dissolved air flotation remove?
A: DAF dissolves air into a recycle stream at 4 to 6 bar and releases it into the flotation tank, where microbubbles attach to oil, grease and light solids and carry them to the surface for skimming. With coagulant and flocculant it removes 90 to 95% of fats, oils and grease and 60 to 90% of suspended solids. It is the standard pretreatment for food, dairy, meat, rendering, fish and edible oil effluents.

Q: How much of a wastewater plant's energy is used for aeration?
A: Aeration typically accounts for 50 to 60% of total plant electricity consumption, which makes blower selection and control the dominant operating cost decision. Fitting dissolved oxygen probes, variable frequency drives and automatic control to an existing plant running blowers at constant output commonly saves 25 to 40% of aeration energy, with payback usually within one to three years.