Stop and think about what wastewater treatment processes do. It’s not surprising that plants release noxious odors. The goal is to remove fecal matter, urine, and other waste products from the wastewater to make sure it’s clean before it’s released to lakes, ponds, rivers, or storage tanks where it’s reused by homes and businesses. The very nature of wastewater makes it a smelly venture.
While wastewater treatment plants do smell, it’s important to reduce those smells for several reasons. First, you don’t want people who live nearby to constantly complain to the town or city about the odors. Second, those odors are linked to harmful gases being released during the treatment process. Odor management helps protect the environment.
To best understand how to take care of problems with unpleasant odors, you have to look at each step of a wastewater treatment process. Figure out the best ways to reduce odors along the way.
The Steps to Wastewater Treatment
The exact steps to wastewater treatment depend on a plant’s design. Most follow these steps.
#1 – Screening: Wastewater that comes in from the sewer or is dropped off at a septage station is screened to remove things like plastic wrappers, tampon applicators, grease, rags, and other objects that could clog equipment.
#2 – Pumping: Once the wastewater is screened, it’s pumped to the next station for grit removal.
#3 – Grit Removal: Grit removal systems separate grit like sand where it sinks to the bottom of the vessel and is removed and trucked to landfills or compost piles.
#4 – Primary Settling: After grit is removed, the wastewater is moved to clarifiers where it sits so that sludge can settle at the bottom and grease floats to the top. Grease is skimmed away and joins the sludge in digesters. Some plants use chemicals to start removing phosphorus from the wastewater. The remaining water leaves the tank.
#5 – Aeration: The wastewater that remains is aerated so that microorganisms can start feeding on the pollutants.
#6 – Secondary Settling: As microorganisms finish their job, the wastewater goes to a secondary settling tank or lagoon and any remaining sludge goes to the bottom where it’s pumped out and goes back to aeration tanks.
#7 – Filtration: Wastewater is almost fully treated at this point. Any contaminants that remain are captured in the filtration materials. Filters are regularly rinsed out and that liquid goes back to the start of the wastewater treatment plant.
#8 – Disinfection: The final step in wastewater treatment involves the use of disinfection to kill remaining bacteria to 98% or higher. Ultraviolet disinfection is common and brings the now clean water to the levels needed to release it back to the environment or public water storage tanks. Before water goes back into rivers, ponds, and lakes, it may be aerated one more time to boost oxygen levels.
What Causes the Odor and How Do You Stop It?
Sewer and septic water smells anyway. As anaerobic digestion of the waste takes place, the organisms that break down the waste release certain gases like hydrogen sulfide and methane. These gases do not smell pleasant. Some liken it to the smell of a really rotten egg.
To understand what causes the foul odor, you need to understand what happens to the sludge removed during wastewater treatment. Here’s what happens to the sludge that’s removed from wastewater.
#1 – Sludge is separated and goes through anaerobic digestion. It’s heated to a certain temperature and uses anaerobic bacteria to break it down. In this process, hydrogen sulfide, carbon dioxide, and methane are produced and add to the smells found in a wastewater treatment plant.
#2 – Once the anaerobic digestion process ends, sludge is pumped from the digester onto a belt that allows water to drain. The water (filtrate) goes into tanks that will sit for several months before going to a site to be spread onto land. Remaining solids go to a facility where it’s composted and sometimes used to fertilize the soil.
If an anaerobic digester is sealed off with a cover or similar enclosure, the smell can’t go far. If the digestion tanks are open, that smell will permeate the air. The smell can travel, so people who live nearby may complain. It’s not too different from the way a farm that spreads liquid manure on fields ends up making an entire neighborhood smell of the manure. It’s important, but people do not like it. You may also know the foul odors that come from a manhole when you walk past on a hot summer’s day.
The odors can seem worse on some days over others. On a windy day, neighbors may notice the smell more. On a hot, humid day, the smell will likely seem worse.
Your first goal is to find where the odors are worse and address those issues. Consult with a wastewater treatment expert if you’re having problems narrowing it down. Sometimes, equipment upgrades and the installation of biofilters or carbon filters within ductwork systems can help reduce odors. Deodorizing systems can also help.
Be aware that masking the odor won’t stop it. You’re still going to find the odor leads to complaints from time to time. It’s most likely that you’ll hear the bulk of the complaints in the spring and summer when people want to open their windows and let fresh air into the home.
Benefits to Covering Your Wastewater Lagoons and Tanks and Other Equipment
Start with the screw pumps you use to move wastewater from plant lift stations or to return sludge from clarifiers back to aeration tanks. Open screw pumps will allow odors to escape. You should consider if enclosed screw pumps are better for your odor reduction goals.
If you put a cover over the open tanks and lagoons at your wastewater treatment plant, there’s a second benefit to consider. You could trap the gas that’s released and use it for biogas. That biogas can lower your plant’s heating costs by using it to fuel your heating system. You gain twice the benefits as you slash your heating bills and eliminate odors that may have locals complaining.
When you cover your open tanks and lagoons, there’s a second benefit. Less water is lost to evaporation. This reduces the quantity of chemicals your plant needs to use in the wastewater treatment process. You’ll save money on the cost of chemicals, too.
Covers are a smart investment, but they’re not a one-size-fits-all solution. Covers may be made of metals like aluminum or steel or fiberglass. Some float on the surface, some are retractable, and some are flexible and made from geomembranes. They have to be airtight and designed to stand up to your area’s weather. You need to be able to remove them in a timely manner for testing, repairs, and emergencies. To know which best fits your needs, you need to talk to an expert in wastewater treatment plant design and installation.
Is it time to upgrade your wastewater treatment plant? Are you looking at making changes that help lower energy costs and make the people in your district happier with your dedication to quality and costs at the same? Contact our experts for advice. Lakeside Equipment has been in the wastewater treatment industry for close to 100 years. We’ll assure you achieve your goals.