Merced’s wastewater treatment plant plays a crucial role in protecting the environment

Merced’s Wastewater Treatment Plant plays a vital role in protecting the environment as well as humans as treated water and biosolids eventually make their way back into the environment.

Multiple steps area involved in treating the wastewater that enters the plant. Merced Wastewater Treatment Plant Manager Bill Osmer, said there are about five or six processes the water goes through after coming into the plant, before it the treated product is eventually released back into the environment. These processes involve the removal of pollutants, solids, fats, greases ammonia and bacteria.

The plant’s role goes beyond just the treatment of wastewater and is critical to the area’s water management and environmental sustainability efforts.

“So after the citizens use it, we’re really protecting the environment, because we’re a point source discharge here to the slough which is that’s where we would be impacting,” said Osmer. “There’s many benefits to that because people are able to irrigate with it, fish, whatever, however far it made it to the different wildlife areas.”

Osmer said fats, oils, grease and any trash are the first things the plant removes from the water. The processes then go on to remove the solids and ammonia. If solids are allowed to pass through into the receiving water it would cause an oxygen depletion and result in odors, flies, mosquitoes and could ultimately result in the spread of disease.

Removing the ammonia from the water is important to prevent algae growth which could kill microbes that are eventually consumed by animals such as crawfish or fish, eventually killing them. Osmer said if the nitrogen isn’t completely removed it could make its way into the environment going from nitrate to nitrite. If that were to get into the blood of fish or other aquatic life, it could bind to the fish’s blood and suffocate them.

Once water enters the plant, it flows through a series of primary clarifiers which slow the water down, allowing settable solids to sink while the rest of the water flows into aeration basins for microbe removal. The process takes about 12 to 18 hours per gallon of water, depending on peak flows, Osmer said.

“Everybody thinks that there’s a lot of solids in the water, but there’s not. It’s like 99.9% water. And the point one or less are the solids,” said Osmer. “So we kind of concentrate, we filter the water through some screens and then it goes to the activated sledge basin, where microbes do most of the work. They’re getting rid of the total suspended solids and the nitrogen. We’re fixating the nitrogen, more importantly, so it doesn’t harm the environment.”

Osmer said it is microbes which include nitrosomonas and nitrobacter bacteria, that are responsible for the breaking down of the solids and ammonia in the wastewater. When the water enters the aeration basins, these microbes consume the suspended solids and ammonia stripping hydrogen off the ammonia converting it to nitrites and then nitrates.

“So they’ll strip off the hydrogen and convert it to nitrite, and then the second, the nitrobacters, will convert it to nitrates,” Osmer said.

The microbes working to break down the solids and ammonia in the water entering the facility include nitrobacters such as tardigrades or water bears, rotifers and stalked ciliates.

The result is the microbes essentially farming the wastewater by consuming the organic matter and nutrients. This process prevents issues such as algae growth and oxygen depletion that could in turn harm the environment. Employees at the plant carefully monitor and control the microbe population as too many older microbes could result in settling and turbidity issues, according to Osmer.

“People think that we put chemicals in the water, but we’re just brooding bacteria is what we’re doing. We’re keeping them happy out there,” said Osmer.

Taking care of the ammonia in the water is an important step in order to prevent algae growth and the same bacteria under aeration will nitrify it. In order to get ride of the nitrates and nitrites in the water, the plant cycles the air on and off sending them into an anoxic zone.

“They don’t have any dissolved oxygen but now they have molecular oxygen so to survive, they’ll go after the oxygen on the molecule and all that’s left is the N (nitrogen) and it pops up into the atmosphere.

About 65% to 70% of the water is recycled by the plant and meets Title 22 drinking water standards. The treated product then eventually makes its way into areas such as the Hartley Slough which could result in water making it into the San Joaquin River and the delta, the plant’s land application were it can be used to grow crops and to get rid of bio solids as well as the wildlife management areas where it helps to replenish the water basin.

The plant has a unique approach when it comes to handling the biosolids or sludge, that is produced during the treatment process. An active solar drying system on about 1.7 acres of land, allows the bioslilds to dry more efficiently. The dried biosolids contain nutrients such as nitrogen and phosphorus that can be spread across farmland and biosolids and recycled water from the treatment plant can be used to grown crops.

“This replaced about 50 acres of land where we would dry the biosolids before,” said Osmer.

In that process, the biosolids could be exposed to rainfall which would lengthen the time of the drying process. It also resulted in nitrogen going into the groundwater and dirt would be mixed in with the biosolids during the extraction process.

“This is 77,000 square-feet, about 1.7 acres, said Osmer. We can dry the biosolids in about 10-14 days in the summertime and when we go to remove it, all we’re pulling out are the biosolids.”

Osmer said there are about 45 employees at the plant that working in different capacities. Regular samples are collected and examined under a microscope to determine the microbe population and how well the treatment is working.

Merced’s wastewater treatment plant is pretty unique, according to Osmer, in that the biosolids produced from the treatment process are recycled and reused in relatively local areas even right on site, which has eliminated the need to have the biosolids collected and trucked out ultimately reducing the plant’s carbon footprint.

The plant also uses ultra violet light as a means of disinfecting the treated water. The water flows through channels containing submerged UV lamps. The UV light disrupts the DNA of pathogens, microbes and other organisms present in the water effectively rendering them harmless, according to Osmer. The use of the UV lights is a critical part of the plant’s treatment process and provides a chemical free way of eliminating pathogens before the treated water is released back into the environment.

The plant used to use chlorine gas for disinfection, explained Osmer. The plant has moved away from that due to the risks and environmental impact. The use of chlorine gas, although inexpensive and effective, was too dangerous to handle and required many safety protocols. It also created issues such as the harmful byproduct trihalomethane when reacting with organic matter present in the wastewater.

In an effort to address these problems, the plant transitioned to using sodium hypochlorite or bleach, instead of the chlorine gas. Osmer explained that this transition eliminated the need for an extensive risk management plan and safety training, but the plant still experienced issues with introducing salts to the environment.

Ultimately the plant has transitioned to the ultra violet disinfection system which costs more to operate but is much more environmentally friendly.

Future plans for the plant include making it more energy efficient such as updated and more efficient aerator basins as well as using the methane gas created by the digesters, to run a micro turbine on a blower effectively putting air into the aeration basin.

“The micro turbine will run the air compressor which will feed the aeration basin,” said Osmer.

A lot of people consider the turbines and blowers that put the dissolved oxygen into the aeration basins the heart of the plant, according to Osmer.

“If we have any problems with the dissolved oxygen the microbes will die in the aeration basin which is the true heart right there. So without oxygen, everything dies,” Osmer said.

Although the direct benefits to Merced residents may not be obvious, the wastewater treatment plant plays a critical role in maintaining both healthy environment and water supply as well as supporting local agriculture.

This story was originally published February 6, 2025 at 10:38 AM.