Public Utilities - Wastewater Environmental Technologies (WET)

Frequently Asked Questions

Grease Questions

• Why is grease a problem?
• What is a grease trap and how does it work?
• What is a grease trap interceptor?
• How often should a grease trap be cleaned?
• Does my facility need a grease trap?

Industrial Pretreatment Questions

• Under what Statutory Authority is the Pretreatment Program Administered?
• Are there any prescribed National Standards for Pretreatment?
• What are Categorical Pretreatment Standards?
• What are Prohibited Discharge Standards?
• What is the National Pretreatment Program?

Grease Questions

Q. Why is grease a problem?

A: Grease is singled out for special attention because of its poor solubility in water and its tendency to separates from the liquid solution.

Oil and grease in the wastewater cause trouble in the collection system pipes. It decreases pipe capacity and, therefore requires that piping systems be cleaned more often and/or some piping to be replaced sooner that otherwise expected. Oil and grease also hamper effective treatment at the wastewater treatment plant.

Problems caused by wastes from restaurants and other grease-producing establishments have served as the basis for ordinances and regulations governing the discharge of grease materials to the sanitary sewer system. This type of waste has forced the requirement of the installation of preliminary treatment facilities, commonly known as grease traps or interceptors.

Q. What is a grease trap and how does it work?

A: A trap is a small reservoir built into the wastewater piping a short distance from the grease producing area. Baffles in the reservoir retain the wastewater long enough for the grease to coagulate and rise to the surface. The grease can then be removed and disposed properly.

Q. What is a grease trap interceptor?

A: An interceptor is a vault with a minimum capacity of 750 gallons that is located on the exterior of the building. The vault includes a minimum of two compartments, and flow between each compartment is through a 90° fitting designed for grease retention. The capacity of the interceptor provides adequate residence time so that the wastewater has time to cool, allowing any remaining grease not collected by the traps time to coagulates and rise to the surface where it accumulates until the interceptor is cleaned.

Q. How often should a grease trap be cleaned?

A: Undersink grease waste interceptors shall be monitored by the food service facility at least once per week. Removal of grease waste and sediments is required when operational capacity is reduced to 80% or less.

In ground grease waste interceptors shall be pumped at a frequency that maintains a grease and oil layer of less than 6 inches on the top of the grease waste interceptor and a solids layer of less than 8 inches on bottom of the grease waste interceptor. The measurement point for determination of the grease and solids layer shall be adjacent to the outlet pipe.

Q. Does my facility need a grease trap?

A: Grease trap interceptors shall be required at all food service facilities in Clearwater if grease waste is produced in quantities that could otherwise cause line stoppage or hinder grease waste disposal as determined by the administrator. All fixtures within such food service facility which may introduce fats, oil or grease into the wastewater collection system must be connected through the grease waste interceptor, including sinks, dishwashers, automatic food wash units, floor drains in food preparation and storage areas, and any other fixture which is determined by the administrator to be a source of fats, oil or grease. In no case shall grease waste be introduced into the wastewater collection system.

Industrial Pretreatment Questions

Q. Under what Statutory Authority is the Pretreatment Program Administered?

A: The National Pretreatment Program's authority comes from section 307 of the Federal Water Pollution Control Act (more commonly referred to as the Clean Water Act). The federal government's role in pretreatment began with the passage of the Clean Water Act in 1972. The Act called for EPA to develop national pretreatment standards to control industrial discharges into sewerage systems.

Q. Are there any prescribed National Standards for Pretreatment?

A: There are two sets of standards: "categorical Pretreatment Standards" and "Prohibited Discharge Standards." These are uniform national requirements that restrict the level of pollutants that may be discharged by nondomestic sources to sanitary sewer systems. All POTWs that are required to implement a Pretreatment Program must enforce the federal standards.

Q. What are Categorical Pretreatment Standards?

A: These are technology-based limitations on pollutant discharges to POTWs promulgated by EPA in accordance with Section 307 of the Clean Water Act that apply to specified process wastewaters of particular industrial categories [see 40 CFR 403.6 and 40 CFR Parts 405- 471]. Go to http://www.epa.gov/ost/guide/ and NPDES Regulations for more information.

Q. What are Prohibited Discharge Standards?

A: These are standards that prohibit the discharge of wastes that pass through or interfere with POTW operations (including sludge management). These are the general prohibitions. There are also specific prohibitions that prohibit the discharge from all nondomestic sources certain types of wastes that

1. create a fire or explosion hazard in the collection system or treatment plant,
2. are corrosive, including any discharge with a pH less than 5.5, unless the POTW is specifically designed to handle such wastes,
3. are solid or viscous pollutants in amounts that will obstruct the flow in the collection system and treatment plant, resulting in interference with operations,
4. any pollutant discharged in quantities sufficient to interfere with POTW operations, and
5. discharges with temperatures above 113 F (45 C) when they reach the treatment plant, or hot enough to interfere with biological processes.

Q. What is the National Pretreatment Program?

A: The National Pretreatment Program is a cooperative effort of federal, state, and local regulatory environmental agencies established to protect water quality. The program is designed to reduce the level of pollutants discharged by industry and other non-domestic wastewater sources into municipal sewer systems, and thereby, reduce the amount of pollutants released into the environment through wastewater. The objectives of the program are to protect the Publicly Owned Treatment Works (POTW) from pollutants that may interfere with plant operation, to prevent pollutants that may pass through untreated from being introduced into the POTW, and to improve opportunities for the POTW to reuse wastewater and sludges that are generated.

The term ""pretreatment"" refers to the requirement that nondomestic sources discharging wastewater to POTWs control their discharges, and meet limits established by EPA, the state or local authority on the amount of pollutants allowed to be discharged. The control of the pollutants may necessitate treatment prior to discharge to the POTW (therefore the term ""pretreatment""). Limits may be met by the nondomestic source through pollution prevention techniques (product substitution recycle and reuse of materials) or treatment of the wastewater.

Program objectives are:

• To prevent industrial facilities' pollutant discharges from passing through municipal wastewater treatment plants untreated;
• To protect treatment plants from the threat posed by untreated industrial wastewater, including explosion, fire, and interference with the treatment process
• To improve the quality of effluents and sludges so that they can be used for beneficial purposes.

There are more than 1500 publicly owned treatment works that are required to implement local Pretreatment programs. By reducing the level of pollutants discharged by industry into municipal sewage systems, the program ensures the protection of America's multi-billion dollar public investment in treatment infrastructure.