Tertiary Treatment of Wastewater

The science behind sustainable water

We flush it, we forget it. But what happens to our wastewater after it disappears down the drain? Increasingly, the answer is: it gets a second life, thanks to the power of tertiary treatment. Tertiary wastewater treatment, the unsung hero of water sustainability, is transforming wastewater from a waste product into a valuable resource. It’s not just about cleaning water; it’s about protecting our environment, ensuring our future, and even creating new possibilities.

Wastewater treatment is a three-step process. Think of it like cleaning your house. Primary treatment is like picking up the big stuff – removing solids. Secondary treatment is like a deeper clean – getting rid of most organic matter. But tertiary treatment? That’s the final polish, the deep clean that makes the water truly sparkle. It removes remaining pollutants, disinfects, and prepares the water for reuse or safe return to the environment.

Various technologies can be used in tertiary treatment, either individually or in combination, depending on the specific contaminants being targeted and the required water purity.

Advanced Filtration

Imagine filtering coffee, then filtering it again, and again, with progressively finer filters. That’s the idea behind advanced filtration. We use everything from sand filters to high-tech membranes to remove even the tiniest impurities. Membrane processes include:

• Microfiltration, with pore sizes ranging from 0.1 to 10 microns. This can remove bacteria and suspended particles and is commonly used as a pretreatment stage before other membrane treatment processes.
• Ultrafiltration, with smaller pore sizes ranging from 0.005 to 0.1 microns. This offers finer filtration capable of removing bacteria, viruses, suspended solids, and macromolecules, making it suitable for stand-alone treatment or as part of a multi-barrier advanced wastewater treatment system.
• Nanofiltration: With pore sizes typically ranging from 0.001 to 0.01 microns, nanofiltration removes a wider range of contaminants than ultrafiltration, including dissolved organic matter, some salts, and specific micropollutants. It’s often used for softening water or treating wastewater for reuse applications.
• Reverse osmosis. The membranes used in RO have pore sizes ranging from 0.0001 to 0.001 microns, making them highly effective at removing tiny microscopic molecules to produce extremely high-quality water suitable for reuse.

Nutrient Removal

Nitrogen and phosphorus are essential for plant growth, but too much in our waterways can cause algal blooms that suffocate aquatic life. Biological nutrient removal (BNR), which uses specific microorganisms to break down nitrogen and phosphorus, is often incorporated into advanced wastewater treatment systems as a tertiary treatment to remove these nutrients. Chemical coagulants such as aluminum sulfate or ferric chloride can also be added to remove phosphorus through precipitation.

Disinfection

To eliminate any remaining pathogens and microorganisms, a final disinfection step is essential. Common methods include:

• Ultraviolet (UV) light, which disrupts the DNA of bacteria and viruses, rendering them harmless
• Ozonation, which uses ozone gas to oxidize and destroy microorganisms
• Chlorination, a method commonly used in municipal wastewater treatment, where chlorine or chlorine compounds are added to kill pathogens.

Micropollutant Removal

Emerging contaminants such as pharmaceuticals, hormones, and personal care products in discharged wastewater can enter drinking water sources, where they can pose a health risk even at relatively low levels. Specialized treatment can help remove micropollutants and protect source waters from contamination. These include technologies such as activated carbon, which removes organic pollutants through adsorption, and membrane technologies such as reverse osmosis and nanofiltration.

Cost-Effective Wastewater Treatment Solutions

Tertiary treatment can be complex and expensive, but it doesn’t have to be. At Seven Seas Water Group, we’re making advanced treatment accessible through flexible leasing options and innovative Water-as-a-Service® partnerships. These approaches eliminate the need for large upfront investment and, in the case of Water-as-a-Service®, place the ongoing responsibility for plant operation and maintenance in the hands of experienced water professionals.

By embracing these technologies, communities can secure a sustainable water future while protecting natural resources. Contact Seven Seas to learn more about our advanced wastewater treatment technologies and flexible financing solutions.

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