Responding to Water Quality Changes
In the event of deteriorating river water quality, we can activate additional treatment measures to ensure the safety of our water supply:
• Powdered Activated Carbon (PAC): This is added to adsorb potential contaminants, such as cyanotoxins, allowing them to settle out of the water column.
• Acetic Acid: Introduced as a food source to enhance the effectiveness of the biological layer in our filters, helping to consume contaminants.
• Increased Ozonation: This step further removes any cyanotoxins that may have passed through the filtration process.
• Enhanced Chlorine Dosage: We may increase chlorine levels to ensure effective disinfection throughout the distribution system.
Through these comprehensive treatment processes, the City of Salem is dedicated to providing safe, high-quality drinking water to our community.
How Slow Sand Filtration Protects Salem’s Water.
At the heart of our treatment process lies one of the nation's largest slow sand filter systems, a testament to our commitment to excellence in water treatment. For more than 80 years, these filters have effectively purified Salem's drinking water through a natural, gravity driven process that consistently delivers high quality drinking water for the City.
Here's how it works: River water enters Geren Island through an intake and flows through a constructed channel to one of seven slow sand filter ponds. Here, a naturally occurring biological layer called the Schmutzdecke forms along the filter beds, consuming algae and other impurities as the water is filtered through the sand.
By the time the water reaches a depth of 8 inches in the sand filter, 99.5% of E. coli bacteria is filtered out, and by 14 inches, 98% of viruses and other bacteria are removed.
Once filtered, the water is transferred to the Frank Mauldin Ozone Treatment Facility via a perforated pipe.
The Frank Mauldin Ozone Treatment Facility
To ensure the longevity and resilience of our drinking water supply, Salem has invested over $50 million in the design and construction of the Frank Mauldin Ozone Treatment Facility at Geren Island.
Ozone treatment offers numerous benefits:
• Destruction of cyanotoxins and other pathogens
• Enhanced assurance of safe drinking water
• Compatibility with existing treatment processes
• Improvement of water taste and clarity year-round
• Reduction in chlorine usage • Complete elimination of residual ozone in the treated water
What is Ozone?
Ozone (O3) is a highly potent disinfectant, even more effective than chlorine. It not only eliminates pathogens but also enhances water clarity, taste, and odor. Our multi-step approach to cyanotoxin removal ensures that any remaining toxins are effectively neutralized by ozone treatment, guaranteeing the highest standard of water quality for our community.
How Ozone Works
Step 1: Oxygen Supply
Ozone (O3) is made from oxygen (O2). We are using super-cooled liquid oxygen. The liquid oxygen is first warmed and converted to oxygen gas. The oxygen gas is then sent to an "ozone generator."
Step 2: Ozone Generation
The ozone generator uses an electric charge to turn oxygen gas (O2) into ozone gas (O3). Once formed, ozone gas moves to a "contactor" chamber where it dissolves into and begins to clean our drinking water.
Step 3: Ozone Injection and Contactor
In the contactor chamber, ozone gas (O3) dissolves into the water. Here, it destroys cyanotoxins (if they are there) and breaks down any remaining materials that may affect the taste or smell of the water.
Step 4: Dissolved Ozone
Under normal operating conditions, all of the dissolved ozone is used in the treatment process. If all the dissolved ozone (O3) isn't used, it will go through a process to turn it back into oxygen gas (O2) before it is discharged back into the atmosphere.
Clean and healthy drinking water
At the end of the ozone process, hydrogen peroxide is added to quench ozone. Hydrogen peroxide, H2O2, combines with ozone, O3, to make water and oxygen, H2O and O2. The water is piped to the west side of the facility where Fluoride, Soda Ash, and Chlorine are added to the treated water in accordance with Federal Safe Drinking Water Act rules.
In general, processing water at Salem’s drinking water facility uses minimal chemical or energy inputs. Instead it uses gravity and natural processes to be treated and transported to the residents of Salem.
