That distinctive rotten egg smell wafting through South Portland isn’t a mystery to us in the wastewater industry. It’s sulfur, plain and simple. Most people recognize it as the same odor added to natural gas, which is actually odorless on its own. What’s happening at that 50-year-old Pearl Street pump station is something we see all the time, just on a much larger scale.
The basic issue is pretty straightforward. You’re dealing with the decomposition of organic matter in sewage, and that process has what we call a biochemical oxygen demand. Bacteria in wastewater live and breathe like we do. When a system “goes septic,” it means it’s dead. There wasn’t enough air. The system didn’t incorporate the oxygen demand properly.
Municipal vs Residential Odors
The smell issues in South Portland’s municipal system aren’t that different from what homeowners might experience with their septic tanks. Sure, you could have some trace chemicals and other things in a city system because you’re collecting from a multitude of residents and commercial properties. But the fundamental problem is actually very similar, just on a smaller scale for home systems.
In a residential septic tank, it’s the wastewater decomposing that creates odors. That’s the purpose of the tank, to put everything together. Some things are clean water. Some things are bacteria and waste. Some things are paper and soap. They all decompose and eat all the living organic material.
Why Pump Stations Go Bad
Typical pump stations are deep in the ground. You’re in a section of town where the gravity flow is deep, and then it has to be pumped back up towards the treatment plant. Whether it’s pumped all the way there or not depends on the layout of that city system.
If they had properly oxygenated the wastewater and exposed it to air, they wouldn’t have this problem. There are formulas for this. A pump station gets a lot of volume, so the more waste going through it, the more air that’s needed to meet that biochemical oxygen demand.
Typically, you want to be able to give enough air for about five days so the waste can decompose as much as possible. That’s why when you drive around cities in the winter, sometimes you see steam coming out of little holes in sewer manholes. They’re vented to let the gases out and let oxygen in.
The Age Factor
Newer designs are better because engineers have learned from the mistakes of the past. In a city like Portland, the population 50 years ago might not have been overly different, probably less, but the amount of people hooked up to the sewer system now is likely much greater. Most big cities have had to add on to their treatment plants to keep up with capacity.
The way they did things has changed dramatically. Go back more than 50 years, even a hundred years ago, they trapped an entire house. Today, you have a trap in every plumbing fixture under your sink. The water goes down before it comes back up, which stops airflow and prevents the gas from coming out in the house. In the old days, they did things differently. They had one trap outside the house. Pump stations and similar infrastructure have benefited from quite a bit of learning over the years.
Modern Solutions for Odor Control
The issue with wastewater systems is that they need to breathe, but that breathing process creates odor. That’s why the vents on buildings are all on the roof. The idea is that you’re getting the smell to go up before anybody senses it. On low-pressure days, this doesn’t always work as planned.
Modern pump stations now often have a little building where they can send air through filters before it goes out. They’ll put carbon filters to scrub the air, which takes a lot of the scent away.
For South Portland’s $50 million upgrade, they’ll focus on proper venting and oxygenation. They can make sure that the waste is getting oxygen prior to entering the pump station. The flow coming from upstream can be addressed to add oxygen so it’s not as bad when it gets to the pump station. The upgrade will almost certainly include additional air handling, venting, and filter systems.
What Homeowners Should Know
When a homeowner calls us about septic odors, the first thing we check is the traps. It’s real simple. If a trap dries out, like in a sink you don’t use regularly, it’ll be letting gases in. There’s no exact science to finding the source because you’re looking for air. The best way to do it is with a smoke test. We introduce smoke into your plumbing pipe and then look for any place smoke comes out.
Venting is also important. Squirrels that build nests in a vent pipe can cause you problems. Home additions often become an issue because vents aren’t added properly during construction.
One of the biggest misconceptions homeowners have is that an odor means something is broken. When anybody gets an odor in their house, they immediately flip out. But it’s hard to explain that it just means there’s an opening in what should be a closed system. Your plumbing system should be closed to the interior of your home. If it’s open, you’re going to get a whiff.
I bought a house personally where the venting was poor. A toilet in the center of the house was sucking water out of a sink trap to get its air when it flushed, rather than drawing from the vent on the roof. So the people would get a smell, and it was hard to figure out. Once we elongated the trap so it held more water, the toilet couldn’t suck it out anymore, and they never got the smell inside their house again.
So an odor doesn’t mean your system is working improperly. Actually, just the opposite. It means that your waste is decomposing and your septic system is working properly. It’s just that there’s an opening in your plumbing system that lets you smell it.
The Importance of Movement in Wastewater
Most people reading this aren’t worried about running a South Portland Municipal Pump Station, but they own a septic system. Any time flow is stagnant, you’ll have problems. If there was a change in the city, and this big pump station suddenly only gets one-hundredth of its normal volume, it won’t turn on very often.
Ideally, you really want sewage to be on the move, other than in settling tanks at the treatment plant or in a septic tank. And it is on the move in a septic tank, though homeowners might not think of it that way. The point is that when wastewater isn’t moving, there’s no flow. Water gets oxygenated with movement and flow. You can add air to it, which certainly helps.
In a septic tank, the system is designed for solids to settle out, and then the liquid water flows out of the outlet. If the outlet gets clogged and the wastewater sits too long, it does get stagnant. It loses its oxygen, it stops deteriorating, and the cleaning process is essentially over until you re-oxygenate it.
With our 65+ years of experience in Connecticut’s wastewater industry, we’ve seen how proper system design and maintenance can prevent most odor issues before they start. The South Portland situation is a reminder that even large municipal systems face the same basic challenges as the residential septic systems we service every day.