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 we add chlorine.  Before the effluent flows to Casco Bay, we remove the chlorine.    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.  The District is in the process of having HVAC improvements designed to 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.


India St. – carbon


Peaks – headworks odor control


Malison – odor control system, bioxide system