Aerobic wastewater treatment is a type of biological treatment that can be efficiently leveraged for a variety of organics removal applications. If you are exploring biological treatment options for your facility, you may be wondering “how much do aerobic wastewater treatment systems cost?”

Since aerobic wastewater treatment systems come in a variety of forms, cost can vary greatly. Here, we’ll take a look at the key factors that determine the cost of aerobic systems, and how they can be effectively used within a larger wastewater treatment train.

What’s included in an aerobic wastewater treatment system?

There are several types of aerobic wastewater treatment systems, each of which makes use of a different set of technologies. Therefore, the components of an aerobic wastewater treatment system can vary significantly depending upon the type of system chosen.

Components that are common across various aerobic systems include:

• • • Clarifiers for removal of suspended solids.
    • Aeration tanks, blowers, compressors, and/or mixers for maintaining oxygen levels in the wastewater.
    • Bioreactors (including tanks, ponds, or other receptacles) where aerobic microorganisms perform the work of digesting organic contaminants.
    • Multimedia filtration media and retention units are used in fixed-bed bioreactors, biological trickling filters, and moving bed bioreactors (MBRs).
    • Filter presses for sludge dewatering in MBRs.
    • Settling tanks for flocculation in activated sludge systems.
    • Peripherals, including pumps, piping, valves, and skids.
    • Chemical pumps for maintaining pH and nutrient levels to sustain the biomass.

While these represent some of the more typical technologies found in an aerobic treatment system, the exact components used can be varied to suit specific applications and system designs.

The main cost factors of an aerobic water treatment system

The cost of an aerobic wastewater treatment system is determined by a few of key factors, including:

• • • What are the system flow rate requirements?
    • What is the quality of the water entering the aerobic treatment system?
    • Effluent discharge requirements

System flow rate

Flow rate is an indication of the capacity of a wastewater treatment system. Usually measured in gallons per minute (GPM) or gallons per day (GPD), system flow rates indicate how much wastewater a system is able to process in a given period of time. For almost any wastewater treatment system, the higher the system flow rate, the higher the capital cost, although the costs of high-capacity systems can be mitigated by choosing aerobic treatment technologies suited for large wastewater volumes, such as traditional activated sludge systems and biological trickling filters.

Water quality and characteristics

A critical consideration is the character of the waste stream to be treated. Understanding what organic contaminants and nutrients are present in the stream, and at what concentrations, can help to narrow down the field of aerobic treatment technologies appropriate to your facility’s needs. Streams with relatively low biochemical oxygen demand (BOD) and/or chemical oxygen demand (COD) can be efficiently treated by activated sludge and biological trickling filtration systems, while streams with medium to high BOD/COD may be more cost-effectively treated by fixed-bed, moving-bed, or membrane bioreactors. For streams with complex combinations organic contaminants, fixed-bed bioreactors may offer capital cost advantages, as they can be designed with multiple chambers to accommodate various types of biofilm media for comprehensive organics treatment in a relatively small footprint.

Important factors to consider when pricing aerobic wastewater treatment systems

These factors also play an important role in the total cost of an aerobic treatment system, and should be considered in the design of a system to fit the needs of your facility:

• • • Space requirements. If physical space is valuable at your facility, then it may make sense to invest in aerobic treatment systems that have a smaller footprint—even if they come at higher capital or operating costs. While tight space constraints can mean that traditional activated sludge systems are off the table, for example, there are several other aerobic treatment technologies that occupy a compact footprint. These include moving-bed bioreactors and membrane bioreactors, as well as fixed-bed bioreactors, which offer the smallest footprint of all.
    • Operation costs. Maintenance and operation costs for aerobic wastewater treatment can vary significantly from one technology to the next depending upon the chemicals, equipment, and labor needed to sustain the system. Activated sludge and biological trickling systems tend to rank among the lowest in terms of operational costs comparative to other aerobic technologies, though their large footprint generally relegate their use primarily to municipal and sewer applications. On the other end of the spectrum, membrane bioreactors tend to have some of the highest operational costs comparative to other aerobic technologies, though their small footprint and high quality effluent output can offset its high maintenance costs.
    • Post-treatment and disposal costs. Different aerobic treatment technologies create varying amounts of sludge or slurry as a waste product. The characteristics and amount of sludge produced are an important consideration, as post-treatment and disposal costs can account for up to half the cost of the entire biological wastewater treatment system. Among aerobic treatment technologies, activated sludge systems produce the largest volumes of sludge, while fixed-bed bioreactors produce the lowest amounts of sludge of any aerobic system. Moving bed bioreactors can also be a cost-effective choice for reducing sludge disposal costs, as these produce a slurry waste stream that can be compressed and disposed as solid waste.
    • Other possible costs and fees. Implementing an aerobic wastewater treatment system can include other costs and fees, such as taxes, utilities, design, engineering, and testing costs. These costs should be taken into account when evaluating potential biological treatment systems.

The bottom line

There are several types of industrial aerobic wastewater treatment systems, each having variant capital and operating costs. On average, expect a 175,000 GPD fixed-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. 

For any aerobic biological treatment system, factors such as complex or concentrated streams, higher system capacity, and higher effluent quality standards will all contribute to higher capital costs. Additionally, since aerobic treatment systems are usually just one part within a larger wastewater treatment system (WWTS), it is also important to consider impacts on the WWTS cost as a whole when evaluating potential aerobic treatment options.

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