Annapolis WRF Frequently Asked Questions

The initial phase of monitoring measured the presence of hydrogen sulfide. Hydrogen sulfide is the most common cause of odor in the wastewater treatment process and it smells similar to rotten eggs. 

Monitors were placed near the most active components of the treatment process in an attempt to identify which processes are causing the most odor.

An overflow storage pond is the only component located on the east side of the facility. Since this pond is seldomly used and it is surrounded by trees, it was not considered a high potential for producing odors. For these reasons, monitors were not located in this area during the initial phase of monitoring.

We are analyzing many components of the facility and will continue to monitor the odors until we identify the cause for increased odor.

Ammonia enters the facility in liquid form within the wastewater. The pH of the wastewater would need to exceed the permitted levels in order for the ammonia to convert to a gaseous state. In order for this conversion to occur, the wastewater would need a pH between 10.8 - 11.5 and our NPDES permit limit for pH is between 6.5 - 8.5.

We treat ammonia through the biological oxidation process, known as nitrification. According to our Discharge Monitoring Reports, in May 2024, the wastewater influent at Annapolis WRF contained around 31 mg/l of ammonia and our treated effluent contains around 0.2 mg/l. The County has been in 100% compliance with this discharge permit since 2016.

Yes, four additional higher sensitivity parts per billion (ppb) monitors are being procured and will be deployed in the surrounding communities.

The second phase of monitoring is being developed based on data gathered during the initial monitoring phase, as well as the valuable feedback received during the public meeting on June 10, 2024. The phase 2 monitoring plan will be shared on DPW’s website once it is finalized.

Hydrogen sulfide is a colorless, flammable, hazardous gas with a “rotten egg” smell. It is produced by bacterial breakdown of organic materials, including human and animal wastes (e.g., sewage). The level of exposure is measured by average dose (e.g., parts per million) over a particular duration (e.g., minutes).

The Occupational Safety and Health Administration (OSHA) set an acceptable ceiling limit of 20 parts per million (ppm) for hydrogen sulfide. The ceiling limit is based on a 10-minute time-weighted average. The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure limit of 10 ppm based on a 10-minute time-weighted average. The World Health Organization (WHO) advises a limit of five parts per billion (equivalent to 0.005 ppm) to avoid an odor nuisance, which is below the threshold of a health advisory.

More information on the health impacts of hydrogen sulfide can be found at the following resources:
https://www.osha.gov/hydrogen-sulfide/hazards

https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=388&toxid=67

https://wwwn.cdc.gov/TSP/ToxProfiles/ToxProfiles.aspx?id=389&tid=67

Hydrogen sulfide can not be entirely eliminated during the wastewater treatment process because it is part of the natural biological process to breakdown organic matter within wastewater. Odor control devices, intended to reduce the emission of hydrogen sulfide, have been in operation at the facility for decades.  The initial odor monitoring indicates some of these devices are not performing well.  We are evaluating the areas that need odor control upgrades to minimize the amount of hydrogen sulfide emitted.

Hydrogen sulfide is the main gaseous byproduct of the wastewater treatment process. The typical treatment of wastewater may also produce indiscernible amounts of other sulfur compounds, nitrogen compounds, and ammonia. Considering that the odors at Annapolis WRF are not typical, the next phase of monitoring will test for gasses that are typically indiscernible, such as volatile sulfur compounds, volatile organic compounds, ammonia, and amines.

Hydrogen sulfide is a colorless, flammable, hazardous gas with a “rotten egg” smell. It is produced by bacterial breakdown of organic materials, including human and animal wastes (e.g., sewage). The level of exposure is measured by average dose (e.g., parts per million) over a particular duration (e.g., minutes).

The Occupational Safety and Health Administration (OSHA) set an acceptable ceiling limit of 20 parts per million (ppm) for hydrogen sulfide. The ceiling limit is based on a 10-minute time-weighted average. The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure limit of 10 ppm based on a 10-minute time-weighted average. The World Health Organization (WHO) advises a limit of five parts per billion (equivalent to 0.005 ppm) to avoid an odor nuisance, which is below the threshold of a health advisory.

More information on the health impacts of hydrogen sulfide can be found at the following resources:
 https://www.osha.gov/hydrogen-sulfide/hazards

https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsDetails.aspx?faqid=388&toxid=67

https://wwwn.cdc.gov/TSP/ToxProfiles/ToxProfiles.aspx?id=389&tid=67

Hydrogen sulfide can not be entirely eliminated during the wastewater treatment process because it is part of the natural biological process to breakdown organic matter within wastewater. Odor control devices, intended to reduce the emission of hydrogen sulfide, have been in operation at the facility for decades.  The initial odor monitoring indicates some of these devices are not performing well.  We are evaluating the areas that need odor control upgrades to minimize the amount of hydrogen sulfide emitted.

Hydrogen sulfide is the main gaseous byproduct of the wastewater treatment process. The typical treatment of wastewater may also produce indiscernible amounts of other sulfur compounds, nitrogen compounds, and ammonia. Considering that the odors at Annapolis WRF are not typical, the next phase of monitoring will test for gasses that are typically indiscernible, such as volatile sulfur compounds, volatile organic compounds, ammonia, and amines.

The grit and screen process is part of the preliminary treatment portion of the plant that removes large debris and heavier material from the wastewater stream.  Currently, the grit and screen odor control unit is not operating at full efficiency. We are actively working with the manufacturer to troubleshoot solutions and explore other actions to make the unit work more effectively.

The denitrification process is an anaerobic process that converts nitrate to nitrogen gas, returning the biologically available nitrogen to the atmosphere and reducing nitrogen in the effluent water discharge.  While the process itself does not generate significant odors, the denitrification process includes a filter backwash station and this area was also identified as creating high levels of odor. The facility manager recently started to manually flush the troughs each day to reduce stagnation in the backwash residue and limit additional odors.
 

No. While the WRF is undergoing upgrades and there is continual maintenance, there have not been significant changes in the operations or processes at this facility in the past several years.

Facility operators hired a contractor to replace the door. It isn’t likely that the broken door resulted in increased odor since the odor control device pulls the air in from outside through the door.

We have already initiated a capital improvement project to design and construct new odor control devices. Information derived from the current odor monitoring study will be used to set the parameters of this project to ensure we properly size the new odor control unit(s). Additionally, new denitration filter covers are currently in design, and capital funds were secured in the FY25 budget for this work.

On June 14, 2024, the County Council approved more than $3.5 million in capital funding for these efforts. This funding will be used to support the initial design and additional funding will be requested once we have a more established project scope and cost estimate.

Please visit the Annapolis WRF webpage for the projected schedule.

Yes. In addition to participating in multiple regional and national municipal wastewater associations, the County operates a total of seven water reclamation facilities. We garner knowledge and expertise from industry partners and from previous experience operating the WRFs.

 We originally suspected the grit filters were the primary problem. Results from the initial odor monitoring indicate the denitrification filter backwash area is generating significant odors. After receiving the early testing data indicating the high odors in this area, the operators immediately started manually flushing the troughs each day. However, it still remains a source of odor. We suspect there are multiple factors leading to increased odor and want to capture enough data on all the processes to ensure we properly address all of the odor emissions across the whole facility.

No. The rate of wastewater influent has remained consistent over recent years

New development will not be approved unless there is available capacity at the treatment plant and in the collection system. The Annapolis WRF has a rated capacity of 13 million gallons per day (MGD). The plant is currently operating at an average of 8.5 MGD.

The Mayo WRF was redirected to Annapolis WRF on October 17, 2017. The Mayo redirect is approximately 0.01% of the daily effluent of the Annapolis WRF, or 548,000 gallons of the total 8.5 MGD. While it is not likely that this additional flow is contributing to the recent increase in odor, we will investigate the collection systems and sanitary pump stations leading to the Annapolis WRF.

The shift to work-from-home practices did not create a significant increase of effluent to the Annapolis WRF. The Annapolis WRF received 8.5 MGD in 2019 and it continues to receive 8.5 MGD in 2023. It is not likely that work-from-home practices are contributing to the increased odor.
 

We have an obligation to accept septage from septic tanks owned by County residents and businesses. The County only accepts septage at the Cox Creek and Annapolis WRFs, where we have the infrastructure to weigh the amount of septage we are accepting. The amount of septage accepted from septage haulers is less than 1% of the overall sewage received at the Annapolis WRF. We must continue to accept this waste at Annapolis WRF.

There were a couple of instances in which these ponds were used in March, during which time the waste remained in the pond for approximately one week. The ponds were not used in April or May of 2024.

These storage ponds are mostly used during heavy rain events, in which stormwater infiltrates the public sewer system and exceeds the capacity of the plant. The storage ponds may also be used when there are mechanical problems and the flow must be diverted while repairs are made. They are not used on a daily basis as part of the treatment process.
 

The NPDES permit is a wastewater discharge permit and the County has made significant investments to treat Annapolis WRF influent at an enhanced nutrient removal before it is discharged to the Severn River. For eight consecutive years, the Annapolis WRF has been recognized by the National Association of Clean Water Agencies (NACWA) with the Peak Performance Award for perfect permit compliance since 2016.  

The County applied to renew this NPDES permit in 2023, as part of our typical renewal process with MDE. In response to public feedback and without substantiated findings, MDE revised the Annapolis WRF NPDES permit to include language about odor mitigation. MDE did not provide quantifiable goals in which it can measure or regulate the County’s performance toward odor mitigation. DPW does not find these permit revisions to be objective, nor are they relevant to the discharge of wastewater effluent.
 

Stormwater runoff from the facility, not to be confused with the discharge of wastewater effluent, is no more harmful than stormwater draining from any other impervious surface. As for the storage and discharge of wastewater, the Annapolis WRF has two emergency storage ponds should the rate of wastewater influent exceed the plant’s capacity or should the facility experience a mechanical failure. The wastewater is then treated to advanced levels of treatment prior to being discharged to the Severn River.