7 Ways to Reduce FOG in POTW

How Fats, Oils, and Grease Affect Wastewater Collection Systems

Excess fats, oils, and grease (FOG) discharged into wastewater collection systems can create serious operational problems for Publicly Owned Treatment Works (POTWs).

FOG can accumulate inside sewer lines, restrict wastewater flow, and contribute to blockages. Over time, these obstructions may increase the risk of sewer backups and overflow events.

Depending on the design of the collection system, blocked or overloaded sewer lines can contribute to:

Environmental Risks of Sewer Overflows

During an SSO or CSO event, untreated or partially treated wastewater may enter surface waters, waterways, and other sensitive environmental areas.

These discharges can introduce bacteria, nutrients, organic matter, and other contaminants into the environment, creating concerns for:

  • Surface water quality
  • Public health
  • Aquatic ecosystems
  • Drinking water sources
  • Regulatory compliance

Preventing FOG accumulation is therefore an important part of maintaining reliable wastewater collection and treatment systems.

FOG Management and Clean Water Act Compliance

Wastewater utilities are responsible for maintaining their collection systems and reducing the risk of preventable sewer overflows.

Violations of environmental requirements, including unauthorized sewer overflows or exceeding NPDES permit limits, may result in enforcement actions, additional monitoring requirements, and potential EPA penalties.

For this reason, wastewater service providers actively manage FOG and other materials that can contribute to sewer blockages, overflows, and wastewater treatment problems.

Effective FOG management can help protect collection system performance, reduce maintenance demands, and support long-term environmental compliance.

Figure 1. The above picture is a pipe with FOG blockage.  Fats, oils and grease are usually disposed of improperly in the kitchen. Image retrieved from https://www.wsud.us/sewer/page/fats-oil-and-grease-fog

How FOG Affects Wastewater Treatment Plant Performance

High concentrations of fats, oils, and grease (FOG) can reduce the efficiency of wastewater treatment plants.

Excess fatty organic material can interfere with the microbial communities responsible for biological solids removal, nutrient removal, and overall wastewater treatment. When biological treatment becomes less effective, facilities may have difficulty maintaining consistent effluent quality.

Wastewater treatment plants must meet the requirements established by their National Pollutant Discharge Elimination System (NPDES) permits. Facilities that discharge effluent exceeding permitted limits may face regulatory action and potential penalties.

Environmental Impacts of FOG

When excess nutrients, suspended solids, and other pollutants are discharged into surface waters, they can negatively affect:

  • Aquatic ecosystems
  • Surface water quality
  • Drinking water sources
  • Recreational waters
  • Regulatory compliance

FOG-related problems can also increase maintenance costs and create significant operational challenges for Publicly Owned Treatment Works (POTWs).

For these reasons, wastewater managers have a strong incentive to prevent, reduce, and manage FOG throughout their collection and treatment systems.

The following sections outline seven strategies for managing FOG in wastewater systems.

1. Prevent FOG from Entering the Wastewater System

One of the most effective ways to reduce FOG-related sewer blockages is to prevent excessive fats, oils, and grease from entering the collection system in the first place.

Wastewater utilities can accomplish this through:

  • Industrial and commercial pretreatment programs
  • FOG discharge limits
  • Grease interceptor requirements
  • Routine inspections
  • Community education
  • Proper cooking oil and grease disposal programs

Pretreatment Programs for Commercial and Industrial FOG

The National Pretreatment Program helps POTWs manage pollutants entering wastewater collection and treatment systems from industrial and commercial sources.

Establishing and enforcing local FOG limits can help reduce grease discharges from:

  • Restaurants and food service establishments
  • Commercial kitchens
  • Food processing facilities
  • Meat and protein processing operations
  • Other high-strength wastewater sources

Pretreatment programs can be especially important for smaller wastewater utilities that may have limited treatment capacity when receiving concentrated industrial discharges.

Reducing FOG before it enters the sewer system can also help lower the risk of sanitary sewer overflows (SSOs), combined sewer overflows (CSOs), and collection system blockages.

Managing Residential FOG

Residential FOG is more difficult to control because it enters the wastewater system from many individual homes.

Cooking oils, fats, and grease are still commonly poured down household drains. Once cooled, these materials can accumulate inside pipes and contribute to sewer blockages.

Public education can help residents understand why cooking grease should not be disposed of through sinks or drains.

Benefits of FOG Prevention

Pretreatment and community education programs can:

  • Reduce the amount of FOG entering sewer systems
  • Lower the risk of sewer blockages
  • Improve collection system reliability
  • Reduce maintenance requirements
  • Improve community understanding of proper grease disposal

Limitations of FOG Prevention

Developing and enforcing a successful pretreatment program can require significant staff time and resources.

Smaller municipalities may have limited personnel available to monitor restaurants, industrial facilities, and other FOG-generating sources.

Changing long-established residential grease disposal habits can also take time and require ongoing public education.

2. Biological FOG Treatment and Bioaugmentation

Biological treatment, or bioaugmentation, uses microorganisms capable of metabolizing fats, oils, and grease.

These grease-degrading microorganisms produce enzymes that help break down complex fatty materials into smaller compounds that can be used as energy and nutrients.

Adding selected microbial populations to wastewater collection systems can help support the biological degradation of accumulated grease.

Benefits of Biological FOG Treatment

Bioaugmentation provides a biological approach to FOG reduction in wastewater collection systems.

Increasing populations of grease-degrading microorganisms may help:

  • Break down accumulated fatty deposits
  • Reduce FOG buildup in sewer lines
  • Support wastewater flow
  • Reduce collection system maintenance
  • Lower the risk of grease-related blockages

As microorganisms metabolize organic material, FOG is converted into microbial biomass and simpler metabolic byproducts.

Once an active microbial community becomes established, maintenance applications can help support continued biological treatment.

Biological FOG treatment can also offer an advantage over some chemical approaches because it works through microbial degradation rather than relying primarily on chemicals that alter the physical properties of grease.

Limitations of Biological FOG Treatment

Bioaugmentation depends on living microorganisms, so treatment generally requires time for the microbial population to become established and actively degrade accumulated grease.

For severe or immediate blockages, biological treatment may not work as quickly as mechanical cleaning, jetting, vacuuming, or manual removal.

3. Jet, Vacuum, and Combination Trucks

Mechanical cleaning is another common method for removing FOG blockages from wastewater collection systems.

Utilities frequently use jet, vacuum, and combination trucks to remove grease, sludge, debris, and other materials from sewer lines.

Jet Trucks

Jet trucks use high-pressure water to remove grease deposits, debris, and other obstructions from sewer pipes.

In heavily affected areas, additional cleaning agents may sometimes be used as part of the sewer maintenance process.

Vacuum Trucks

Vacuum trucks use powerful pumps to remove sludge, grease, wastewater, and debris from sewer lines.

The collected material is transferred into an onboard storage tank for transportation and proper disposal.

Combination Trucks

Combination trucks provide both high-pressure jetting and vacuum capabilities.

These vehicles can break apart FOG deposits with pressurized water and then vacuum the loosened grease, sludge, and debris into a holding tank.

This approach allows wastewater utilities to clean sewer lines and remove accumulated material during the same maintenance operation.

Figure 2. Jet vac trucks are dual purpose trucks with pumping and jetting capabilities utilized to extract sludge from a location (often underground) into the tank of the truck. Image retrieved from https://www.colorado.gov/pacific/cityofyuma/wastewater

Benefits of Jet, Vacuum, and Combination Trucks

Jet, vacuum, and combination trucks can be highly effective when FOG blockages require immediate removal to help prevent sanitary sewer overflows (SSOs) and combined sewer overflows (CSOs).

These vehicles are commonly used to clean wastewater collection lines and remove accumulated grease, sludge, and debris.

Combination trucks are especially useful because they can both dislodge and collect FOG at the source of the blockage, reducing the amount of manual cleanup required.

Key Benefits

  • Rapid removal of severe FOG blockages
  • Effective sewer line cleaning
  • Reduced risk of SSO and CSO events
  • Removal and collection of grease, sludge, and debris
  • Lower manual labor requirements when using combination trucks

Limitations of Jet, Vacuum, and Combination Trucks

Standard jet trucks without vacuum capabilities can dislodge FOG deposits without removing them from the collection system.

Once loosened, the grease may travel downstream toward the wastewater treatment plant. Utilities may therefore need additional screening or collection procedures to prevent large FOG deposits from entering the treatment process.

Vacuum trucks can remove and collect accumulated grease, but they may be less effective than high-pressure jetting for breaking apart difficult sewer blockages.

Jet, vacuum, and combination trucks can also be expensive to purchase, operate, and maintain. These costs may be difficult for smaller Publicly Owned Treatment Works (POTWs) to manage.

Mechanical cleaning is effective for immediate FOG removal, but it does not address the underlying causes of recurring grease accumulation. For this reason, it is often best used as part of a broader FOG management strategy.

4. Citrus Degreasing Products

Citrus-based degreasers are another option for managing fats, oils, and grease in wastewater collection systems.

These products can dissolve and emulsify FOG, allowing grease deposits to mix with wastewater and move through collection lines.

By breaking apart accumulated grease, citrus degreasers can help restore wastewater flow through affected sewer pipes.

Benefits of Citrus Degreasers

Citrus-based products are often marketed as alternatives to harsher chemical degreasers.

Many formulations are biodegradable and can act quickly on accumulated grease.

Potential benefits include:

  • Rapid breakdown of FOG deposits
  • Improved wastewater flow
  • Fast response during grease-related sewer blockages
  • Easier removal of accumulated grease from collection lines

Their fast-acting properties can make citrus degreasers useful when wastewater utilities need to respond quickly to a developing sewer blockage.

Limitations of Citrus Degreasers

One concern with emulsifying grease is that the FOG may be moved downstream rather than permanently removed from the wastewater system.

High FOG loads entering the treatment plant can interfere with the microbial communities responsible for biological oxygen demand (BOD) removal and nutrient treatment.

Emulsions may also become unstable over time. As oils begin to separate from the wastewater, grease can redeposit in downstream pipes, pumps, or treatment equipment.

As a result, citrus degreasers may provide short-term relief from a blockage without fully addressing long-term FOG accumulation.

5. Chemical Degreasing Agents

Some POTWs use chemical degreasing agents to break down or liquefy FOG deposits within wastewater collection systems.

These chemicals react with accumulated grease and help move the material into the wastewater stream.

Chemical degreasers may be applied using:

  • High-pressure sewer jetting equipment
  • Chemical dosing pumps
  • Direct manual application

In some cases, degreasing agents are combined with high-pressure jetting to help remove heavy grease deposits from sewer lines.

While chemical treatments can provide rapid FOG removal, utilities should also consider how the dissolved or emulsified grease may affect downstream wastewater treatment processes.

Figure 3. Chemical degreasers are often used to dissolve fats, oils and grease in wastewater collection systems. Image retrieved from http://www.guardianchem.ca/

Benefits of Chemical Degreasers

Chemical degreasers can provide a fast and effective method for removing fats, oils, and grease (FOG) from wastewater collection systems.

During severe grease blockages, chemical treatment may help restore wastewater flow and reduce the risk of sanitary sewer overflows (SSOs) or combined sewer overflows (CSOs).

Key Benefits

  • Rapid treatment of severe FOG blockages
  • Fast restoration of wastewater flow
  • Useful during time-sensitive sewer maintenance situations
  • Can be combined with high-pressure jetting

Limitations of Chemical Degreasers

Chemical degreasers can affect the biological processes used at downstream wastewater treatment facilities.

When introduced into wastewater, these products may change pH, chemical composition, or other environmental conditions that influence microbial activity.

Changes in wastewater chemistry can reduce the activity of microorganisms responsible for BOD removal, nutrient removal, and biological treatment.

Wastewater toxicity can also suppress microbial growth and disrupt treatment performance.

Potential Effects on Activated Sludge

Changes in wastewater conditions may alter the balance of microorganisms within an activated sludge system.

Certain filamentous bacteria can tolerate a wider range of operating conditions than other treatment organisms. If environmental conditions favor filamentous growth, these bacteria may become more abundant.

Excessive filamentous bacteria can contribute to:

  • Poor sludge settling
  • Excessive foaming
  • Solids carryover
  • Reduced treatment efficiency
  • Increased operational challenges

For these reasons, wastewater utilities should consider potential downstream impacts when selecting and applying chemical FOG treatments.

6. Manual FOG Removal

Some Publicly Owned Treatment Works (POTWs) manually remove accumulated FOG from lift stations, manholes, and other accessible areas of the wastewater collection system.

When biological or chemical treatments are not appropriate or have not adequately removed grease deposits, maintenance crews may physically scrape, collect, or remove the accumulated material.

Benefits of Manual FOG Removal

Manual removal does not require specialized chemical treatment products or large mechanical cleaning equipment.

Removing grease directly from the collection system can also prevent accumulated FOG from traveling downstream and creating problems at the wastewater treatment plant.

Key Benefits

  • Direct removal of accumulated grease
  • Limited equipment requirements
  • Prevents some FOG from entering downstream treatment processes
  • Useful in accessible problem areas

Limitations of Manual FOG Removal

Manual grease removal can be labor-intensive and expensive.

Its effectiveness is also limited by the accessibility of the sewer system and the safety requirements associated with wastewater collection infrastructure.

Confined spaces and other hazardous environments require proper procedures, training, and equipment before workers can safely perform maintenance.

7. FOG Removal Technology

Advances in FOG removal technology have provided wastewater facilities with several mechanical options for separating fats, oils, and grease from wastewater.

Common technologies include:

Grease Skimmers

Grease skimmers are designed to remove floating FOG from wastewater.

Many systems use belts or conveyor mechanisms made from materials that attract oils and grease while allowing water to remain in the treatment stream.

The collected FOG is then separated and stored for disposal or possible reuse.

Dissolved Air Flotation Systems

Dissolved air flotation (DAF) systems separate FOG and suspended solids from wastewater using fine air bubbles.

In a typical DAF process, recycled wastewater is pressurized with air and introduced into a flotation tank containing untreated wastewater.

When the pressure is released, small air bubbles form and attach to grease and suspended solids. These materials rise to the surface, where they can be skimmed and removed from the wastewater.

The separated FOG may then be disposed of or, where appropriate, recovered for another use.

Gravity Grease Traps

Gravity grease traps separate FOG by allowing wastewater to remain in a holding chamber long enough for grease to rise to the surface.

The accumulated FOG is retained in the unit while wastewater continues through the collection or treatment system.

Regular cleaning is required to maintain effective grease separation.

Figure 4. A wastewater worker holds an accumulation of non-flushable material recovered from a treatment system.

Benefits of Mechanical FOG Removal

Mechanical grease separation can be effective for both food processing wastewater and municipal wastewater treatment.

FOG removal equipment is available for facilities of different sizes and treatment capacities.

Potential benefits include:

  • Physical removal of grease from wastewater
  • Reduced FOG loading on downstream treatment processes
  • Application at both small and large facilities
  • Recovery of grease for potential reuse
  • Reduced accumulation in wastewater infrastructure

In some applications, collected grease may have value as a feedstock for energy recovery or other processing.

Limitations of Mechanical FOG Removal

Mechanical FOG removal systems require regular maintenance, cleaning, and replacement of worn components.

These requirements can increase operating and labor costs.

Depending on the technology used, effective treatment may also require:

  • Wastewater recirculation
  • Chemical conditioning
  • Flow equalization
  • pH adjustment
  • Additional pretreatment equipment

Facilities should consider capital costs, maintenance requirements, flow conditions, and wastewater characteristics when selecting a mechanical FOG removal system.

Further Considerations for FOG Management

Unmanaged fats, oils, and grease remain a persistent challenge for wastewater utilities.

Preventing excessive FOG discharges through pretreatment programs and public education should be an important part of every wastewater utility's management strategy.

Beyond prevention, the most appropriate treatment method depends on factors such as:

  • Collection system design
  • Severity of the FOG problem
  • Available budget
  • Treatment objectives
  • Required response time
  • Facility size
  • Downstream treatment processes

In many cases, the most effective FOG management strategy combines prevention, biological treatment, mechanical removal, and routine collection system maintenance.

Recovering and Reusing Collected FOG

Mechanically collected FOG may also have potential value when it can be safely recovered and processed.

Wastewater grease can be used as an organic feedstock in anaerobic digestion to support biogas and biofuel production.

Depending on local regulations and processing requirements, recovered fats and oils may also be used as feedstocks for other industrial applications.

Recovering usable materials can help turn some FOG management programs from a disposal expense into a potential resource-recovery opportunity.

Key Takeaways for Wastewater FOG Management

  • Small POTWs should consider pretreatment programs to help manage FOG discharges from restaurants, food processors, and industrial sources.
  • Community education can reduce FOG at the source by encouraging proper grease disposal.
  • Bioaugmentation can support biological FOG degradation within collection systems.
  • Jet, vacuum, and combination trucks provide rapid mechanical removal of severe grease blockages.
  • Citrus and chemical degreasers can act quickly, but their potential effects on downstream wastewater treatment should be considered.
  • Mechanical FOG removal technologies are available for a wide range of facility sizes and applications.
  • Recovered FOG may have beneficial reuse opportunities, including anaerobic digestion and energy recovery.

Additional FOG Resources

For more information about FOG prevention, wastewater pretreatment, and grease management, visit:

National Pretreatment Program – Food Service Establishments

Review of Fats, Oils, and Grease in Wastewater Systems

Lydia Kimball