Advanced Wastewater Treatment

How Much Does a Sewage Treatment Plant Cost?

“How much does a sewage treatment plant cost?”

It depends…

One of the first questions we get asked, is “How much does a sewage treatment plant cost?” That’s a reasonable question. And we love answering it! That’s because our top-quality systems are also some of the least expensive on the market. Don’t believe us? Click the button below to get an estimate for your particular project and then shop around.

Every Aqua Tech system is custom designed around each project. Our sewage treatment plants must meet local design standards while serving the particularities of each application. Factors such as collection type, design flow, and disposal method all play into the system design. And the system design determines the price.

In asking, “How much does a sewage treatment plant cost,” it’s important to remember that size matters.

Wastewater treatment systems, like a lot of other products, are subject to the economy of scale. Price per gallon goes down as the system size goes up.

Like in the diagram, the effect is more pronounced as the system size gets smaller. A 2000 gallon per day system might cost 3x as much per gallon as a 20,000 gallon per day system which might cost 30% more per gallon than a 40,000 gallon per day system.

The economy of scale in this case means that smaller systems require the same planning, design, construction, installation and startup time as do the larger systems. So, if you ask, “How much does a sewage treatment plant cost?” We’ll first need to know, “How big?”

It’s also important to remember that not all sewage is created equal.

Commercial wastewater is typically higher strength than what comes out of your home. RV Parks, for instance can produce raw sewage with a BOD (biological oxygen demand) of nearly 1000 mg/L while concentrations in residential wastewater average around 250 mg/L. Higher strength wastewater requires more biofilm media, larger bioreactors, and bigger tanks to reach mandated effluent limits.

Location (location, location) affects wastewater system price.

Several local conditions such as fast perc rates, high water tables, high quality, or impaired waterways call for stringent treatment levels even for subsurface disposal.

The Chesapeake Bay for instance, has been designated by the EPA as an impaired waterway. That means wastewater discharge in its watershed must be treated to municipal wastewater treatment standards or better.

process flow diagram for an mbbr wastewater treatment plant treating to under 2.5 mg/L TN

This is a process flow diagram for a system to be installed in the Chesapeake Bay Watershed. It requires special appurtenances (add-ons) to ensure reduction of total nitrogen to under 2.5 mg/L.

process flow diagram for an mbbr wastewater treatment plant treating to under 2.5 mg/L TN

That’s a heckuva lot of reduction for a system discharging subsurface.

Sometimes location affects the way treated effluent must be disposed.

The soil in the eastern two-third of Texas, for instance, absorbs very poorly. TCEQ (Texas Commision on Environmental Quality) consequently mandates a soil application rate (SAR) of no more than .1 gallons per square foot per day for subsurface drip disposal systems. That means drip disposal outside the crosshatched counties on this map can cost three times as much as the national average.

TCEQ subsurface disposal guidance map.

Disposal method affects how much a sewage treatment plant will cost.

Aqua Tech’s wastewater treatment technology is so advanced that we also sell surface water discharge systems. With surface water discharge you can do away with a disposal system altogether. That means the system will need to treat to a higher level and include disinfection. But even with those additions, surface water discharge systems price out around 10% less than subsurface disposal systems in most cases.

wastewater treatment tank with integrated controls
The Southside School wastewater treatment reactor with UV disinfector.

Getting there can be half the savings.

The cost of a sewage treatment plant is only part of the overall cost of developing your sewer infrastructure. Sanitary sewers needed to convey the wastewater to the system can cost significantly more than the treatment and disposal systems together. Many Aqua Tech customers have found they can save a ton of money up front and over the long run with STEP Collection. And because STEP Collection eliminates the need for a large settling tank at the treatment works, it can save you money on the treatment system as well.

There’s no fast way to accurately answer, “How much does a sewage treatment plant cost.”

But we don’t mind doing the work to put a free estimate together. Just fill out and submit this form!

Biological Sewer Sludge Treatment and Reduction

Aqua Tech’s biological process carries out complete sewer sludge treatment eliminating the need for a clarifier.

This sewer sludge treatment is based on biofilm technology. Biofilm is a dense community of attached-growth microorganisms living on specially designed plastic media. Having direct contact with wastewater, biofilm absorbs and oxidizes pollutants thus providing treatment. Multiple biozones ensure that an appropriate biological system develops according to the nature of wastewater composition. It supports dynamic balance on its own both in mass and qualitative composition according to variations of wastewater parameters (within the range of optimal adaptation rates and allowable values of design loadings).

depiction of three layer biofilm on plastic media

Multi-Chamber Design

Multiple chambers in our bioreactor create a series of ecosystems in which the excess biomass is digested and mineralized in successive chambers by higher level microorganisms. This process converts organic sludge into carbon dioxide, water and inorganic elements.

Each chamber houses specialized media to host the required microorganisms.

Specialized Bio-Film Media

floating media for wastewater biofilm

The first chamber of the bioreactor houses a smooth-surface floating media. The smooth surface coupled with high turbulence in the first chamber prevents high biofilm accumulation on the media.

Sloughed biofilm travels into the next chamber to be consumed by protozoa inhabiting porous media (Bio-Chip).

Floating media for biological film wastewater treatment plant

The Bio-Chip media mitigates biofilm overgrowth as the chips rub against each other under aeration. These unfavorable conditions on the outside of the Bio-Chip cause microorganisms to inhabit primarily the protected interior of the media. Treatment in this chamber is provided by slow-growing bacteria such as ANAMMOX which produce negligible biomass.

wastewater treatment biological reactor static media

Subsequent chambers facilitate the development of a complete trophic system with all four trophic levels. This means that the amount of bacteria are controlled by Protozoa and Metazoans that consume any surplus bacterial biomass.

The last chamber utilizes static media and minimal aeration intensity to ensuring high efficiency adsorption and mineralization of any residual suspended matter.

Nota Bene:

The above described is the conceptual model or ideology of the bioreactors which does not change if a bioreactor has just two or three chambers. Thus, any our biological process is designed so that effluent biomass amount is within the required effluent limit for TSS.

The short answer is, “Yes.”

However, it’s not very common. While several apartment units might share a single large septic tank, they still each need enough lateral lines to treat their effluent. So, a single apartment building would need several acres of leach field. An apartment complex would need to devote over half the land to wastewater treatment.

Advanced wastewater systems are a better option for apartments outside the reach of sanitary sewers. Because they treat septic effluent in a biological reactor rather than in the ground, they can reduce the acreage needed for disposal.

Here’s an example of apartment complex wastewater treatment that works :

Aerial photo of an apartment complex with wastewater effluent drip field labeled to show size
Upon entering this apartment complex, you drive past the clubhouse and wind by a lush slope. Spoiler: it’s the wastewater drip field.

Here’s the satellite view for scale:

Satellite view of an apartment complex with wastewater drip field outlined.

If you’re making plans to develop property into apartments, give us a call. We can help you make the most of the space.

What is Eutrophication?

Eutrophication is plant overgrowth in domestic waterways.

green grass on water
Photo by cottonbro on

Wastewater contains nitrate and phosphorus which are nutrients that plants need to grow. Usually, nutrients are good things, but growing population density can result in too much of a good thing being deposited into streams, rivers, and other waterways. When this happens, plant life takes over – crowding out the habitats of fish and other aquatic life. As these plants die and rot, they can change water PH and bacterial levels.

To stop eutrophication, wastewater treatment systems need to greatly reduce or eliminate the amount of nitrate and phosphorus which they return to the watershed in their effluent. Governmental agencies set concentration maximums and enforce them through regular testing.

For the most part, nitrate and phosphorus can be reduced below regulatory thresholds through biological processes known as denitrification and mineralization. Advanced wastewater treatment systems use highly concentrated populations of beneficial bacteria to digest nitrate and phosphorus. The former is then released as nitrogen gas and the latter, collects in the tank as part of the sludge.

Even after advanced treatment, trace amounts of nitrate and phosphorus can frequently be found in wastewater effluent. Where mandated, further treatment can completely prevent even these from reaching the watershed.

If you’re in need of a wastewater system that will prevent eutrophication, let’s talk!

Wastewater systems in the US are sized based on the maximum number of gallons per day they can treat.

A 300-room hotel, for instance, might require a 50,000 gallon-per-day system. Depending on soil loading rate*, that system might need a 2 acre drip field for effluent disposal.

An installer walking inside a wastewater system drip field dosing tank.
Every component in our systems must account for design criteria.

Here are some factors that determine how many gallons per day your community septic or other wastewater system must be able to handle:

  • Capacity in gallons per day is determined by state and local design specifications.
  • These regulatory agencies calculate required treatment capacity in terms of maximum gallons used per person per day or maximum flow per bedroom per day, etc.
  • Commercial wastewater systems use more complex formulas that take their specific usage into account. The hotel mentioned above might need to account for 75 gallons per bed per day but might also have a restaurant and a bar attached for which another 12 gallons per seat per meal would have to be added.
  • Design criteria must also assume the level of pollution present within wastewater from different sources. Very dirty wastewater takes longer to treat which means systems must have higher capacity than what is released to give the system the time needed.

Here is an example of a design criteria matrix from an actual state regulatory agency:

An example design criteria table for wastewater system capacity in residential and commercial applications.
Design criteria differ based on locality.
  • Design criteria tables such as the one above provide a starting point to determine size, but in most cases, regulatory agencies grant variances based on actual flow and treatment level.
  • We at Aqua Tech will research the design criteria required for your project and budget around them. As the build gets closer, we reevaluate your treatment needs and work with civil engineers and regulatory authorities to ensure regulatory compliance without excess expense.

Bottom line: Use this table to get a rough estimate. When you’re ready, let’s talk and get more specific.

*Soils differ in how much moisture they can absorb per hour. Very dense soil might only be able to absorb one tenth of a gallon per square foot every hour while porous soil can absorb almost a full gallon per square foot. Soil absorption per hour is called its “loading rate.” The higher the loading rate the smaller the drip field needed.

Secondary wastewater treatment uses natural biological processes to protect the environment from contaminants in sewage.

Wastewater poses several threats to the environment. Microorganisms use oxygen to digest the organic matter in sewage. The rate of this digestion can be measured as Biological Oxygen Demand (BOD). Water with high BOD can deplete dissolved oxygen in waterways thereby suffocating wildlife.

septic tank cutaway
A common septic tank design

Septic tanks use gravity to settle out around 70% of wastewater solids. This settling is called “primary treatment.” The other 30% of solids remain in the wastewater and flow out into the environment. We measure this component of wastewater as total suspended solids (TSS). Primary treatment achieves only a 30% reduction in BOD. While better than nothing, septic systems discharge contaminated wastewater into the environment via a drain field. Larger flows, higher strength wastewater, or poor site conditions can require further treatment to protect the environment.

Enter the secondary wastewater treatment system.

While technologies vary, all secondary wastewater treatment systems use oxygen to accelerate the bacterial consumption of organics. Aqua Tech recommends and sells MBBR (moving bed biofilm reactors). MBBR technology is the most recent innovation in wastewater treatment systems. These biological reactors can treat to a high standard with virtually no operational time or recurring costs. And our MBBR’s are the best on the market.

All MBBR’s host a bacterial slime layer on a plastic media of some kind. Wastewater treatment takes place where that slime layer contacts the contaminated sewer water.

the bacterial slime or “biofilm” is actually three layers each hosting a different type of bacteria

Systems with more contact area treat more efficiently. Our MBBR’s use ultra-high density biofilm media to host up to 5000 M2 of contact area for every 1 M3 of reactor space. That means our treatment reactors can do a ton of work in very little space. And smaller reactors are cheaper reactors.

7000 gallons per day of treatment capacity in this tiny box!

Through secondary treatment BOD and TSS are normally reduced by at least 85%. Our systems can reduce them by 99%.

But BOD and TSS aren’t the only potential environmental hazards in wastewater.

Nutrients like nitrogen and phosphorus can choke waterways and pollute drinking water. Nutrient reduction in wastewater is called “tertiary treatment.”

Our high-density biofilm media performs tertiary treatment simultaneous with secondary treatment. A recently discovered species of bacteria metabolizes the most basic nitrogen compounds, into nitrogen and oxygen gas. The Annamox bacteria can’t grow in every kind of wastewater technology, though. Their long lifecycle requires a protected habitat for them to grow and reproduce in sufficient numbers to mitigate total nitrogen. Our proprietary “biochips” provide protected pockets for Annamox to live and do their work. After about a year, our BioTank reactors can produce effluent discharge under 10 mg/L in total nitrogen with only oxygen.

infographic of nitrification and denitrification in wastewater
Conversion of ammonia to nitrate and nitrate to nitrogen gas in wastewater.

So our secondary wastewater treatment systems really provide tertiary results.

Wanna know more about wastewater or how we can take care of it for you?

What are the 3 Stages of Wastewater Treatment?

Wastewater can be treated in up to three stages generally known as primary, secondary, and tertiary treatment. Here’s what’s involved in each of these stages:

  • Primary Treatment

    In this stage, heavy solids and grease are separated from the raw sewage through gravity and buoyancy respectively. A conventional septic tank is an example of primary treatment.

  • Secondary Treatment

    The wastewater that leaves a septic tank or other primary treatment apparatus is still pretty contaminated with suspended solids and toxic chemicals such as ammonia. Secondary treatment systems use oxygen to facilitate natural digestion of contaminants by micro organisms already present in the wastewater. All municipal systems use secondary treatment.

  • Tertiary Treatment

    Even though much cleaner, water leaving secondary treatment can still pose somewhat of a threat to the environment. To ensure complete protection of aquifers and watersheds, wastewater effluent can enter a third treatment stage. Tertiary treatment usually involves some sort of natural or chemical filtration/sanitization. Examples of tertiary treatment are constructed wetlands or drip irrigation fields.

Our systems use all three stages of wastewater treatment to equip you for responsible growth. Let us show you how!

What does Advanced Wastewater Treatment involve?

Short answer:

“Advanced” doesn’t necessarily imply a particular type of technology so much as it refers to a degree of treatment. If the effluent leaving a system meets stringent criteria it’s said to have undergone advanced treatment.

Longer answer – Advanced treatment systems:

  • Use new technologies to accelerate biological consumption of organic contaminants in wastewater.
  • Remove toxic ammonia through nitrification.
  • Mitigate eutrophication of waterways by reducing nitrogen and phosphorus through Biological Nutrient Removal (BNR).
  • Sometimes introduce coagulants which settle nutrients and suspended solids through flocculation.
  • Occasionally feature chlorinators or UV arrays to sanitize effluent.
  • Rarely apply carbon filters to remove residual contaminants through adsorption.

Aqua Tech can design and build an advanced treatment system for nearly any situation.