How Much Do Biological Wastewater Treatment Systems Cost?

Biological wastewater treatment systems are commonly deployed for industrial streams with high concentrations of organic contaminants, such as waste streams produced by food, beverage, chemical manufacturing, refining and petrochemical, mining and leachates, textile and industrial laundering, and municipal waste treatment industries. Biological wastewater treatment can be an efficient and cost-effective choice over surcharge payments to local sewer districts or other treatment processes like chemical and thermal oxidation.

When facilities begin looking into biological treatment options, the question “how much do biological wastewater treatment systems cost?” usually ranks near the top of the list. While the short answer is that costs can depend on a number of factors, the following article will explore the key aspects that determine the cost of biological wastewater treatment systems and provide some ballpark estimates for typical systems.

What’s included in a biological wastewater treatment system?

Biological treatment units are typically part of a larger wastewater treatment system (WWTS). In addition to biological treatment, a WWTS can include primary treatment for solids and oil removal, and tertiary treatment components for solids separation and further effluent purification. The costs of the biological treatment component and the larger WWTS train are interrelated, so it’s worthwhile to not only evaluate the cost of a biological treatment system on its own, but also to understand WWTS costs as a whole.

The specific equipment used in a biological WWTS will depend upon whether aerobic, anoxic, and/or anaerobic types of treatment are needed, as well as other factors. Common components include:

• • • Clarifiers or Dissolved Air Floatation (DAF) units for removal of suspended solids by sedimentation, flocculation, or coagulation.
    • Oil water separators (OWS) for removal of free-phase oils
    • Bioreactor units (including aeration tanks, fixed-beds, moving beds, trickling filters) where microorganisms can break down organic contaminants.
    • Microfiltration and ultrafiltration membrane units for removing biosolids in membrane bioreactor systems (MBRs).
    • Multimedia filtration units for polishing treated effluent after aerobic and anaerobic biosystems.
    • Chemical pumps for maintaining pH and adding nutrients to sustain the biomass.
    • Centrifuges and belt or plate-and-frame filter presses for sludge dewatering.
    • Peripherals, including pumps, blowers, controls, instrumentation, piping, valves, and skids.

There is often flexibility in the use of these and other technologies in fulfilling a given wastewater treatment need. Conducting a wastewater treatability study can significantly help narrow down the best approach for your facility.

The main cost factors of an industrial water treatment system

There are three main factors that determine the cost of a biological wastewater treatment system:

• • • What are the system capacity requirements? In other words, what volume of wastewater will need to be processed in a given period of time?
    • What are the characteristics of the waste stream to be treated, such as types and concentration of organic contaminants present?
    • What is the target level of quality for the effluent stream? Or put another way, where does the treated water discharge to, and therefore how low do we need to go?

System capacity

Usually measured in gallons per minute (GPM), gallons per day (GPD), and/or million gallons per day (MGD) system flow rates indicate how much wastewater a system is able to process, and how quickly. For most biological WWTSs, lower capacity means lower capital costs, although the degree to which flow rates impact cost may vary depending upon the type of biological treatment system chosen. An accurate measure of system capacity (design flow rate) requirements will not only narrow down the field of appropriate biological wastewater treatment technologies but will also help you to obtain accurate cost estimates.

Waste stream characteristics

A big factor in the cost of biological wastewater treatment systems is the character of the stream to be treated. This can include the types of organic and inorganic contaminants present, solids present, the concentration of the contaminants, and the degree of variability to the types and concentrations of constituents present. For streams with a high concentration of organic contaminants, for example, it is likely that a facility will use a combination of aerobic and anaerobic biological treatment systems. While adding an anaerobic component to a biological treatment train can increase the capital investment, it can significantly lower operational costs in the long run.

Additionally, since biological treatment systems rely on a living biomass to perform the work of breaking down organic contaminants, they are susceptible to variability in terms of seasonal temperatures, as well as changes to the pH and salinity of the stream. If stream or condition variability is a concern, there may be additional costs involved (such as equalization, pH and/or temperature control) in the biological treatment system design and components.

Effluent quality

Compliance with regulatory discharge standards is critical to avoiding costly fines and other consequences. Biological wastewater treatment systems provide a variety of solutions to help meet effluent volume and quality goals. Choosing an activated sludge system, for example, will have the benefit of low capital costs, but with drawbacks of larger footprint and generating greater volumes of waste sludge comparative to other types of biological wastewater treatment, such as fixed film and trickling filter technologies. Understanding the contaminant target thresholds, discharge volume limits, and discharge treatment options for your facility can help to ensure that you choose the right biological treatment technologies and design to meet your needs.

Other important factors to consider when pricing biological wastewater treatment systems

• • • Space requirements. The size of your wastewater treatment system and your plant location are often important considerations. If physical space is valuable at your plant, it may make more financial sense to invest in biological technologies with a compact footprint—even if they come with a higher capital or operational cost. This can include opting for fixed-bed bioreactors (FBBRs) and moving bed bioreactors (MBBRs) over systems with a larger footprint, such as activated sludge basins or stabilization ponds.
    • Operation costs. Operational costs for biological wastewater treatment can vary substantially from one technology to the next. You’ll need to balance initial versus long-term cost investment, with all the costs of chemicals, electricity, labor, equipment maintenance, and other factors involved in maintaining and operating your system through its life cycle. While many aerobic biological treatment technologies require relatively little maintenance, specialized needs, like treating chlorinated wastes, for example, may demand that a facility choose an anaerobic pretreatment before aerobic polish biosystems—even if it comes with higher capital and operating costs.
    • Sludge management costs. As much as half the cost of biological wastewater treatment system can be attributed to solids handling and disposal of resulting sludge. These costs can arise from solids generated during primary treatment and/or dewatering processes used to reduce final sludge volumes, as well as energy, equipment, and operational costs associated with pumping, transporting, and disposing of sludge. Depending upon the needs and priorities of your facility, it may be worthwhile to add an anaerobic pre-treatment biosystem to your train to reduce sludge generation. Alternatively, it may be wiser to invest in a fixed-film FBBR or MBBR technologies that generate less waste sludge comparative to a traditional activated sludge system.
    • Other possible costs and fees. There can be a range of other hidden costs and fees when purchasing a biological wastewater treatment system, including design and detailed engineering, civil and mechanical site work, installation and/or construction costs, utility supply or upgrade, permitting, taxes, start-up and testing costs. Understanding the full cost of a biological solution can help to ensure that you make the best financial decision for your facility.

While not exhaustive, these factors provide a good starting point for discussing cost-effective alternatives as you explore biological treatment technologies with system engineers or manufacturers.

The bottom line

Biological wastewater treatment systems comprise several different types of technologies, and are often combined with one another and/or other treatment or separation technologies. The cost of a biological treatment system can vary significantly due to these factors, with smaller systems starting as low as $250,000 (key mechanical equipment; add 50-75% for install), while high-capacity systems can easily exceed $5M (field-erect, install included). While an accurate estimate of biological WWTS cost is virtually impossible without accounting for the unique characteristics and flows of the facility, we’ve compiled general cost guidelines below:

Aerobic wastewater treatment systems

There are several types of industrial aerobic wastewater treatment systems, each having variant capital and operating costs. On average, expect a 175,000 GPDfixed-bed bioreactor (FBBR) system with 4,000 mg/L BOD (i.e., treating 2,600 kg/day BOD with 90% removal) to carry a capital cost around $2.5M, (includes engineering, key and auxiliary equipment, installation, and startup) with operating costs approximately $5.00 per 1000 gallon treated.

By comparison to FBBRs, MBBRs typically have lower capital costs (approximately 20% less) but higher operating costs (approximately 25% higher, or $6.25 per 1000 gal treated), due to power requirements for mixing air and higher solids).

Also in comparison to FBBRs, MBRs typically have very similar capital costs (smaller size but higher auxiliary costs with the membrane system), but have significantly higher operating costs (double, or approximately $10 per 1000 gal treated) due to more chemicals, membrane maintenance, labor, and membrane replacement. 

Anaerobic wastewater treatment systems

Anaerobic treatment systems for industrial applications are typically UASBs (> 60%) or anaerobic filters, are very temperature-sensitive, and require high BOD influent levels to maintain complete microbial populations.  In addition, anaerobic process removals are not high enough to meet secondary treatment standards, so as a result, aerobic posttreatment must be provided for most applications, along with gas collection and treatment equipment to control odors.

As a result, anaerobic treatment systems carry higher capital costs compared to most of their aerobic counterparts. For the process conditions laid out above for aerobic systems (i.e., treating 2,600 kg/day BOD with 90% removal), the fully-installed anaerobic system with aerobic polish will have twice the foot print and run between $3M and $4M.

Operationally, anaerobic systems typically have lower chemical and energy costs (with possible energy recovery if utilizing the biogas), and lower solids production with associated lower solids disposal costs.  As a result, operating costs of anaerobic treatment systems are approximately $3 to $4 per 1000 gallon treated.

For any biological treatment system, more complex or concentrated streams, higher system capacity, and higher effluent quality standards will all drive the system cost upward.

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