7 Ways FOG are Introduced into Publicly Owned Treatment Works

7 Common Sources of Fats, Oils, and Grease in Wastewater Systems

Publicly Owned Treatment Works (POTWs) often face challenges controlling fats, oils, and grease (FOG) entering municipal wastewater collection systems.

Excessive FOG can accumulate inside sewer lines, restrict wastewater flow, contribute to blockages, and increase collection system maintenance. High FOG loading can also disrupt biological treatment processes after the wastewater reaches the treatment plant.

An effective FOG pretreatment and management program begins with understanding where grease is coming from.

The following seven sources commonly contribute FOG to municipal wastewater systems.

1. Residential and Household Sources

Households can contribute significant amounts of FOG when residents pour cooking grease, oil, or food waste down kitchen sinks and other drains.

For many people, pouring grease down the drain is simply a long-standing habit. Residents may not realize how quickly fats and oils can cool, solidify, and accumulate within sewer lines.

Common household FOG sources include:

  • Cooking oils

  • Bacon and meat grease

  • Butter and shortening

  • Sauces and gravies

  • Dairy products

  • Food scraps

Public education is one of the most important strategies for reducing household grease loading.

Residents should be encouraged to collect cooking grease for proper disposal rather than pouring it into sinks or toilets.

2. Restaurants and Food-Service Establishments

Restaurants are among the most important commercial sources of FOG in wastewater collection systems.

Grease can enter the sewer when grease traps or interceptors are poorly maintained or when kitchen employees use improper disposal practices.

FOG may enter wastewater through:

  • Kitchen sinks

  • Floor drains

  • Mop sinks

  • Floor sinks

  • Trench drains

  • Dishwashing areas

  • Food-preparation equipment

Food-service establishments can generate wastewater with much higher grease concentrations than normal domestic sewage.

Proper grease interceptor maintenance, employee training, and pretreatment compliance are therefore important for reducing FOG discharges.

Educating Restaurant Employees

Restaurant staff should understand how everyday kitchen practices affect the wastewater system.

Important practices include:

  • Scraping food waste into trash containers before washing dishes

  • Collecting used cooking oil separately

  • Keeping grease out of floor drains

  • Maintaining grease traps and interceptors

  • Following local sewer-use requirements

Consistent education can reduce grease-related blockages and help protect both collection systems and wastewater treatment plants.

3. Car and Truck Washes

Car and truck washes may also contribute oils, grease, petroleum residues, and suspended solids to municipal wastewater systems.

Wash water can contain:

  • Motor oil

  • Lubricants

  • Fuel residues

  • Road grime

  • Detergents

  • Suspended solids

Although these discharges are different from food-service grease, they may still contribute significant oil and grease loading.

Municipal pretreatment programs should therefore consider car washes and truck washes when identifying potential commercial FOG and hydrocarbon sources.

Depending on the wastewater characteristics and local requirements, additional pretreatment may be necessary before discharge.

4. Hot Water and Dishwashing Practices

Commercial kitchens use hot water to clean dishes, equipment, floors, and food-preparation areas.

Warm water can temporarily liquefy fats and grease, allowing them to travel farther through plumbing and sewer lines.

As the wastewater cools, however, FOG can separate from the water and accumulate on pipe walls.

Over time, this buildup can contribute to:

  • Sewer restrictions

  • Blockages

  • Pump maintenance

  • Increased cleaning requirements

  • Sanitary sewer overflows

This is one reason proper grease interceptors and kitchen-management practices remain important even when hot-water cleaning is required.

5. Inadequate Wastewater Pretreatment Programs

An effective FOG pretreatment program depends on reliable wastewater data and a clear understanding of the treatment plant's capacity.

Municipalities should evaluate:

  • Current FOG loading

  • Industrial and commercial dischargers

  • Collection system problem areas

  • Grease interceptor performance

  • Treatment plant capacity

  • Local discharge limits

Poor sampling or incomplete data can make it difficult to identify major grease sources or establish appropriate local limits.

Wastewater utilities may also evaluate Maximum Allowable Headworks Loading (MAHL) when developing technically based local limits for pollutants entering the treatment plant.

A successful program should clearly communicate requirements to local businesses and provide them with sufficient information to understand how to comply.

6. Inconsistent Enforcement of Local FOG Regulations

Having a grease ordinance is only useful if the requirements are consistently implemented and enforced.

Wastewater utilities may use:

  • Routine inspections

  • Grease interceptor records

  • Sampling

  • Warning notices

  • Corrective-action requirements

  • Penalties when appropriate

Consistent enforcement helps create a fair system for all businesses.

Restaurants and other commercial dischargers are more likely to follow FOG requirements when expectations are clear and applied equally throughout the community.

Education should also remain part of the enforcement process.

Helping businesses understand why FOG regulations exist can improve long-term compliance.

7. Food Manufacturing and Processing Facilities

Food-processing industries can generate extremely high-strength wastewater containing substantial concentrations of organic material and FOG.

Potential sources include:

  • Dairy processors

  • Meat-processing facilities

  • Slaughterhouses

  • Vegetable processors

  • Commercial bakeries

  • Prepared-food manufacturers

  • Cooking oil processors

These facilities may discharge significantly more FOG, BOD, COD, and suspended solids than typical residential or commercial users.

Without appropriate pretreatment, high-strength food-processing wastewater can overwhelm collection infrastructure and biological treatment processes.

This concern can be especially important for small and rural POTWs, which may have limited treatment capacity.

Building an Effective FOG Management Program

FOG enters wastewater systems from many different sources, and no single control strategy will solve every problem.

An effective municipal program may combine:

  • Residential education

  • Restaurant inspections

  • Grease interceptor requirements

  • Industrial pretreatment

  • Wastewater sampling

  • Local FOG limits

  • Consistent enforcement

  • Commercial outreach

Restaurants, food processors, car washes, and other businesses can often be addressed through local pretreatment and sewer-use programs.

Household FOG requires a different approach focused largely on public education and proper disposal practices.

Reducing FOG in Municipal Wastewater Systems

POTWs that understand where fats, oils, and grease enter their collection systems are better prepared to prevent grease-related problems.

Reducing FOG can help municipalities:

  • Prevent sewer blockages

  • Reduce collection system maintenance

  • Lower the risk of sanitary sewer overflows

  • Protect pumps and treatment equipment

  • Improve biological wastewater treatment

  • Reduce operating costs

  • Support permit compliance

A successful FOG management and pretreatment program depends on cooperation among wastewater operators, local businesses, government officials, and residents.

Education, monitoring, proper pretreatment, and consistent enforcement can significantly reduce the amount of grease entering municipal wastewater systems.