The City of Mebane Wastewater Treatment Plant is dedicated to the prevention of water pollution and the protection of our environment.
The City of Mebane Wastewater Treatment Plant is designed to handle 2.5 million gallons per day (MGD) of wastewater at the following concentrations:
- Biochemical Oxygen Demand (BOD) - 250 milligrams per liter (mg/l)
- Total Suspended Solids (TSS) - 250 milligrams per liter (mg/l)
- Ammonia-Nitrogen (NH3-N) - 25 milligrams per liter (mg/l)
- Phosphorus (P) - 7.0 milligrams per liter (mg/l)
The treatment process consists of the following structures:
Influent Bar Screen - This structure removes the larger objects that may enter the collection system such as sticks, rags, and other such debris to prevent damage to pumps and other equipment
Grit Chamber - This structure removes the smaller inorganic (nondecomposable) debris such as sand, gravel and cinders. This prevents unnecessary wear on the pumps, valves, etc. in the plant.
Aeration Basin - This structure supplies large amounts of air to a mixture of wastewater, bacteria, and other microorganisms. Oxygen in the air speeds the growth of helpful microorganisms, which consume harmful organic matter in the wastewater.
Final Clarifiers - These structures separate the settleable solids (Activated Sludge) formed in the Aeration Basins from the treated water. The treated water is discharged to the Sand Filters and the activated sludge is either returned to the Aeration Basins (Return Activated Sludge - RAS) to treat more wastes or sent to a Rotary Drum Thickener if it is no longer needed (Waste Activated Sludge - WAS).
Sand Filters - These structures help remove any remaining suspended solids in the water. The filters are regularly backwashed to remove the trapped solids which are returned to the head of the plant for treatment.
Chlorine Contact Basin - This structure is where Chlorine is mixed with the wastewater to act as a disinfectant.
Sulfur Dioxide Basin - This structure is where sulfur dioxide is mixed with the wastewater to reduce the chlorine levels.
Reaeration Basin - This structure adds air (Dissolved Oxygen - D.O.) to the treated water (Effluent) before it is discharged into Moadams creek. The City is required to have a minimum of 6.0 mg/l of D.O. in it's effluent at all times.
Rotary Drum Thickener - This structure takes the Waste Activated Sludge (WAS) and with the addition of polymer removes more water than is possible through normal settling. The water that is removed is returned to the start of the plant to be treated again. Thickening reduces the space required for final digestion. The thickened sludge is discharged to the Aerobic Digesters for further treatment.
Aerobic Digesters - These structures further treat the sludge and organic solids removed from the water during the treatment process. The digestion consists of continuously aerating the sludge without the addition of new food, other than the sludge itself, so the sludge is always in the endogenous (a reduced level of respiration in which organisms break down compounds within their own cells to produce the oxygen they need) region. The City has two digesters that operate in series.
The City land applies it's treated sludges (Biosolids) to farmland for use as a soil conditioner. Biosolids recycling is regulated under 40 CFR (Code of Federal Regulations) Part 503, Standards for the Use or Disposal of Sewage Sludge. These standards, commonly known as the "503" regulations, are promulgated by the US Environmental Protection Agency (US EPA).
Individual or groups can take plant tours. The timing of these tours may be limited by weather or staffing requirements. When scheduling, please discuss your specific needs and objectives for the plant visit. Plan on 45 minutes for a tour of the plant. To schedule a tour, Linda Holt or Darrin Allred at 919-563-6141.
Where does wastewater come from?
Wastewater comes from homes, industry, schools, and businesses.
Where is the wastewater treatment plant?
The plant is located at 635 Corrigidor Road off Third Street.
Why is it necessary to treat wastewater?
The Federal Clean Water Act requires municipalities to treat wastewater. The treated water is then discharged to Moadams Creek. Treatment helps protect the water aquatic life as well as protect water quality.
Are discharge requirements hard to meet?
At times meeting requirements can present a significant challenge. Since our wastewater treatment plant is biological in nature, it is influenced by weather, wastewater flow changes, waste-strength fluctuations, etc. Meeting our stringent discharge standards requires our facility to always operate at its optimum level.
Lately I've heard several references to biosolids. What are biosolids?
Biosolids are the treated solids removed from the waste stream during treatment. The City's biosolids are aerobically digested to reduce and stabilize organic materials. If there are any measurable levels of harmful materials such as metals and other toxics, those levels meet all of the stringent Federal and State environmental standards.
What is "Pretreatment"?
The term "Pretreatment" refers to the treatment an industrial discharger often must provide to its wastewater before it reaches the municipal wastewater treatment plant.
The pretreatment program is designed to prevent industrial wastewater discharges from adversely affecting the local municipal wastewater treatment plant's operations and/or its workers. The City of Mebane has both legal and moral obligations to assure that its wastewater is properly treated and that the resulting biosolids and effluent are safe for disposal or reuse. The health and economic welfare of the community are of the utmost importance to us. For this reason, the City of Mebane's Industrial Pretreatment Program is committed to protecting your water resources.
State: North Carolina Administrative Code 2H.0900
Federal: The "General Pretreatment Regulations" define the National Pretreatment Program. These regulations are published in volume 40, Part 403 of the "Code of Federal Regulations" (40 CFR 403).
Why does Mebane need a pretreatment program?
The City of Mebane has both legal and moral obligations to assure that its wastewater is properly treated and that the resulting biosolids and effluent are safe for disposal or reuse. The City's Wastewater Treatment Facility is not designed to treat toxic and hazardous wastes.
The City's treatment plant uses both physical and biological removal treatment processes. Certain caustic and/or acidic substances can cause extensive and costly damages to piping, pumps, and motors. However, the most common damage is that caused by toxic wastes, which destroy the delicately balanced biological treatment systems. Such damage can lead to virtually untreated wastes being discharged into Moadams Creek. Under these conditions, the North Carolina Department of Environment and Natural Resources and/or EPA is authorized to fine the City of Mebane up to $25,000 per day per violation.
Who must be in the pretreatment program?
A sewer user is qualified as a Significant Industrial User under the following: conditions:
- Any user of the sanitary sewer that contributes 25,000 gallons or more per day of PROCESS wastewater into the sanitary sewer.
- Any industrial user that is categorically regulated by Federal regulations.
- Any user that contributes 5% (percent) or more of any design parameter of the wastewater treatment plant.
- Any user whose discharge is considered by the Director to cause or have the potential to cause pass-through or interference with the wastewater treatment process, or which restricts the City's options in disposing of its biosolids residuals.
- The City through the Sewer Use Ordinance regulates a non-significant industrial user, a document intended to control wastewater discharges from users not required to possess an Industrial Discharge Permit.
- Administrative fees:
- Application Fee - No fee
- Permit Renewal Fee - No fee.
- Permit Maintenance Fee - No Fee
- Sampling Charges - Normal monitoring of industries is performed through a self-monitoring program; however, the City is required to semi-annually monitor each industry. The following charges apply to semi-annual required monitoring as well as additional monitoring due to real or suspected noncompliance:
- Composite Sampling fee per visit $64
- Testing through outside lab: At cost to City
- Parameter Base Conc. (mg/l) Cost per Pound
- BOD5 250 $0.25
- COD 750 $0.09
- TSS 250 $0.34
- NH3 as N 15 $0.85
- Oil & Grease 100 $0.25
- Phosphorus 7 $0.66
- Groundwater Remediation Program:
- Permit Application Fee: No fee
- Permit Renewal Fee: No fee
- Sampling Charges - Normal monitoring of remediations is performed through a self-monitoring program; however, the City semi-annually monitors each remediation. The following charges apply to semi-annual required monitoring as well as additional monitoring due to real or suspected noncompliance:
- Testing through outside lab: At cost to City
- Rates: Each discharger will be required to pay a standard rate for wastewater discharge. Each permittee will be required to furnish a water meter or method for measuring the quantity of wastewater discharged. Approval of alternative wastewater measurement methods shall be at the discretion of the Director.
State: North Carolina Administrative Code 2H.0800
Federal: These regulations are published in volume 40, Part 136 of the "Code of Federal Regulations" (40 CFR 136).
The wastewater laboratory conducts tests for process control, operating efficiency, and regulatory requirements. The facility is required in the NPDES permit to analyze the following parameters:
- 5-day biochemical oxygen demand (BOD5)
- Total suspended solids (TSS).
- Fecal Coliforms
- Dissolved Oxygen
Acute whole effluent toxicity analyses must be performed quarterly.
A well-maintained laboratory control and analysis program is essential to treatment plant process control. The data must be accurate, so the operator can interpret and correct any operational problems. The laboratory maintains strict quality control standards. Duplicates, spikes, blanks, and quality control standards are analyzed to assure test validity.