Due to construction, we will not be conducting a rain barrel sales event in 2024. Please check back in 2025. 


Odor Management

Odor Monitoring Report


The Portland Water District manages wastewater systems including four area wastewater treatment plants.  We recognize odors can eminate from processes at the plants, pump stations, manholes, etc.  That is why we have spent considerable investments in odor control equipment.  We encourage the public to assist us identify odor sources and frequency so that we can continue efforts to manage unpleasant odors. Every odor complaint is logged and investigated and corrective actions are put in place if possible.  There are times, for example during construction, that operational situations make odor management more challenging.  Still, our staff prioritizes odor reducing operations.


Recent Odor Management Projects


Northeast Pump Station – an activated carbon odor control system was installed to capture odorous air from the pump station where nearly ¾ of Portland’s 15 million gallons of raw sewage from residential, commercial, and industrial sources.  The carbon system adsorbs the odors so they are not released from the pump station.

Aeration system – The aeration system at the East End Wastewater Treatment Facility was upgraded over several years beginning in 2015.  This upgrade provided improved technology designed to deliver up to 4 times the air needed by the treatment process.  By ensuring sufficient air is delivered to the aeration treatment process, the generation of offensive odors from the process can be avoided.  Since this system was placed into operation, odors have been greatly reduced.

Additionally, this system helps to manage the biological treatment process at the plant.  Through this process, floating material that once collected on downstream process tanks and occasionally generated odors, has been nearly eliminated.  If material does collected downstream, the District installed a spray system to direct any collected material from the surface of tanks before odors are generated.

Chlorine contact tanks allow effluent wastewater to be disinfected by holding it for an hour or so after chlorine is added. Before the effluent flows to Casco Bay, chlorine is removed.  Material can settle in these tanks and the tanks need to be manually drained and flushed.  This is done weekly to minimize the amount of settled material so that significant odors are not generated during the process.

The headworks, grit removal, primary clarifiers, aeration basin influent channel, and the gravity thickeners are covered so that odors can be vented through our scrubber system to remove odors. These areas were identified through an evaluation of the facility and generally are considered some of the most odorous areas of a wastewater treatment plant.  The system has the capacity to treat 65,000 cu ft per minute through a two-stage wet scrubber system where odors are removed from the air stream and removed.  The system has been operating for 15 years. 

The dewatering system prepares the solid materials generated during the pollution treatment process for final use through landfilling, composting, or digestion. This process treats organic material that can produce significant odors.  A dedicated odor control system, similar to the main odor control system, removes odors from the air vented from this process.  HVAC improvements further enhance the effectiveness of this system by ensuring the process areas are well ventilated and odor sources are directed to the odor control system.

The Peaks Island Wastewater Treatment Facility is located adjacent to the ferry terminal off of Welch Drive, right in the heart of the island’s busiest streets, restaurants, shops and parking area. Since its construction in the early 1990’s, the District has made being a good neighbor one of its very top priorities.  As the ventilation systems began to age, the District proactively addressed systems nearing the end of its service life. One such example is the ventilation system installed in 2018 to serve the headworks area. The headworks receives raw wastewater from the collection system and screens out debris from the flow in advance of further treatment and processing in the treatment reactors. The headworks also includes equipment that reduces the volume of the residuals created in the treatment process that must be removed periodically to keep the system running. The system installed in 2018 brings 450 cubic feet per minute of fresh air through the space periodically to reduce humidity and avoid the buildup of any odor. The air is cleaned as it is drawn through a bed of specialty carbon based material designed to absorb any odorous compounds. The system is regularly monitored by our Operations staff using sensitive testing apparatus to confirm system performance. Throughout the first three years of operation the system has been performing extremely well based on the testing results.


Other odor control measures include adual vessel activated carbon system installed at the India Street Pumping Station in 2013 and a bioxide system at Mallison Pump Station in Gorham.