How Much Do Anaerobic Wastewater Treatment Systems Cost?

Anaerobic wastewater treatment is a type of biological treatment that is typically used for treating waste streams with high concentrations of organic contaminants. If you are exploring wastewater treatment options for your facility, you may be wondering “how much do anaerobic wastewater treatment systems cost?”

The short answer is that the cost of anaerobic treatment systems can vary significantly depending upon the specific types of technologies chosen, as well as the scale of the installation. In this article, we’ll explore the key cost drivers of anaerobic systems, as well as their capacity for generating cost savings.

What’s included in an anaerobic wastewater treatment system?

Anaerobic treatment systems can take a variety of forms and can include configurations for batch or continuous treatment cycles. System components will vary depending upon which type of anaerobic technology is chosen, though common components include:

• Grit chamber or screens for removal of large particles.
• Sedimentation tanks for separating solids from liquid phases.
• Bioreactor/digester (e.g. lagoon, pond, tank, basin, or other receptacle).
• Acidification tank (often a stand-alone component in multi-stage bioreactor setups).
• Peripherals, including pumps, piping, valves, skids, fans, and thermal control systems.
• Biogas handling/processing system, including collection, treatment, flare, CHP energy reuse.
• Chemical pumps for maintaining pH and nutrient levels to sustain the anaerobic biomass.

Anaerobic treatment systems can include some or all of these components and may also include additional pre- and posttreatment technologies.

The main cost factors of an anaerobic wastewater treatment system

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

• What are the system capacity requirements?
• What cost offsets may be generated by the system?

System capacity

System capacity is a measure of how much wastewater a system is able to process in a given period of time. Anaerobic systems can be designed to suit a variety of small-, mid- and large-scale wastewater treatment needs. Generally speaking, capital and operational costs are proportional to system capacity. Facilities that need to process large volumes of wastewater will likely need to invest in larger bioreactor units, and/or may require multiple bioreactors, both of which will increase upfront costs.

Additionally, because the rate of anaerobic treatment also increases with temperature, facilities can increase capacity by opting for systems designed to maintain warmer temperatures. For this reason, anaerobic treatment processes are typically classed into three categories according to operating temperature, with psychrophilic at the low end (0-15^oC), mesophilic in the mid-range (15-45^oC), and thermophilic being the highest range (above 50^oC). In general, the warmer the operating temperature, the higher the cost, as facilities must install and run heat generation or heat recycling equipment to maintain proper operating temperatures in the bioreactor unit.

Cost offsets

Anaerobic wastewater treatment generates a couple of valuable byproducts—this includes methane biogas, which can be sold or used for electrical generation; and in the case of anaerobic solids digestion, a liquid or solid digestate, which can be stabilized (reducing odors and pathogens), and then sold as fertilizer. Sale and/or use of byproducts generated by anaerobic treatment can help to offset capital and operational costs.

When choosing an appropriate anaerobic wastewater treatment system, it is worthwhile to consider plans for sale or use of biofuel and fertilizer byproducts. Doing so can help you to narrow down which anaerobic technologies will best suit your needs. In batch-type anaerobic digesters, for example, wastewater solids are pumped into the digester and allowed to remain for anywhere from a few days to a few months. In a continuous-cycle system (such as UASBs, EGSBs and AFs), on the other hand, the anaerobic treatment process is sustained through regular additions of organic matter and removal of effluent and byproducts, resulting in more consistent, systematic production of biogas.

Anaerobic treatment systems can also be incorporated as part of a larger biological wastewater treatment train, typically for initial treatment of streams with high concentrations of organics ahead of aerobic treatment. Adding an anaerobic pre-treatment system will entail additional capital cost, though it can greatly reduce operational costs of downstream aerobic treatment in the long run.

Important factors to consider when pricing anaerobic wastewater treatment systems

These factors also play an important role in the total cost of an anaerobic treatment system, and should be taken into account when pricing solution designs to meet the needs of your facility:

• Feed variability. Wastewater stream variability can put stress on anaerobic digesters, causing them to function less efficiently or predictably. If severe enough, fluctuations in stream constituents, pH, temperature, and concentration can even damage the biomass. While adding pre-treatment steps, such as physical screening, blending, and/or thermal treatment can add cost to a system design, they can be worth it by ensuring predictability and efficiency in treatment cycles. While it may add to the total cost of a new system, conducting proper testing can help to avoid future problems.
• Space requirements. For facilities with limited physical space, it may be worthwhile to invest in more compact anaerobic treatment technology, such as expanded granular sludge blanket (EGSB) reactors or anaerobic filter (AF) reactors using fixed-bed media to support biofilms.
• Operation costs. The operational costs of anaerobic systems can vary depending upon how much effort is needed to sustain optimal process conditions, such as temperature and pH. Anaerobic lagoons, for example, entail little operational cost but require a large footprint and long retention period. On the other hand, systems with enclosed reactor tanks, such as UASBs and EGSBs require closer monitoring and maintenance.
• Other possible costs and fees. Installing and running an anaerobic wastewater treatment system can include various other costs, including taxes, utilities, design, engineering, special anaerobic seed for inoculation, testing, and discharge fees.

The bottom line

There are many types and configurations of anaerobic wastewater treatment systems, and each may vary significantly depending on the particularities of a given installation. Below, we’ve provided some general cost estimates by system type, inclusive of all necessary design, engineering, equipment, and installation; startup is not included.

For design basis, assume 500,000 gpd flow at 10,000 mg/L BOD₅ and 20-25^oC:

• Upflow Anaerobic Sludge Blanket (UASB) bioreactors: In general, for the given basis of design, the UASB system would be two UASBs, 43’x24’ (DxH) each, field-erected, with 20-hour retention time to remove 80% BOD, and will run about $5.0M ± 25% installed.
• Expanded Granular Sludge Blanket (EGSB) bioreactor: for the given basis of design, the EGSB system would be one EGSB, again 43’x24’ (DxH), field-erected, with 10-hour retention time to remove 85% BOD, and will run about $3.7M ± 25% installed.
• Anaerobic Filter (AF) bioreactors: for the given design basis, the AF system would be two AFs, 36’x24’ (DxH) each, field-erected, with 15-hour residence time to remove approximately 85-90% BOD, and will cost around $4.4M ± 25% installed.
• Anaerobic ponds and lagoons: For this design basis expect a 3-acre anaerobic lagoon, 4 m deep, with 25 day detention time to remove 60% BOD. The cost is highly site-specific and subject to applicable regulations, cost to acquire land, earthworks, excavation, liner, and required service facilities. Anaerobic lagoons tend to be low cost to construct and operate, but they will need periodic sludge removal and disposal.

For any anaerobic wastewater treatment system, such as complex or concentrated streams, higher system capacity, and higher effluent quality standards will all result in higher capital costs. Additionally, since anaerobic treatment systems are usually just one part within a larger wastewater treatment system (WWTS), it is also important to consider how addition of an anaerobic system will affect WWTS cost as a whole when evaluating biological treatment options.