What Is Tertiary Water Treatment?

What Is Tertiary Water Treatment?

Tertiary water treatment is the final stage of wastewater treatment that removes contaminants primary and secondary treatment couldn’t eliminate. It improves water quality to meet environmental discharge standards or make water safe for reuse.

In this article, as a professional water treatment supplier, I will share everything about tertiary water treatment.

tertiary water treatment

How Tertiary Water Treatment Works

Tertiary treatment kicks in after primary and secondary processing. While extremely useful for sanitation, the first two phases still leave some pollutants behind.

Tertiary treatment tackles stubborn contaminants using advanced technologies so facilities can safely discharge water or make it potable. Sometimes called “effluent polishing,” it’s the last line of defense against dangerous pathogens, chemicals, and particulates.

Methods vary, but often entail high-tech combinations of:

  • Sedimentation
  • Filtration
  • Membrane systems
  • Adsorption
  • Ion exchange
  • Disinfection

So tertiary treatment not only deals with what slips through primary and secondary processing, but also whatthose phases leave behind. With multi-stage defense, facilities ensure no stone goes unturned in water purification.

The result is H20 safe enough for drinking, recreation, agriculture, and wildlife. Tertiary treatment allows facilities in environmentally-sensitive areas to take extra precautions as well. That prevents damage to the surrounding ecosystem.

Why Tertiary Water Treatment Matters

Tertiary processing seems redundant considering earlier phases remove most impurities already. However, removing that final 1% makes all the difference for:

Meeting Regulatory Standards

Primary and secondary treatment get rid of roughly 85% of contaminants. Tertiary tackles the remainder to meet local, state, and federal requirements. Without it, facilities wouldn’t satisfy environmental regulations for effluent discharge or reuse.

Water Reuse

Using recycled H20 curtails withdrawals from natural water bodies. But wastewater only becomes reusable after tertiary treatment eliminates hazards like bacteria, nutrients, and toxic chemicals. Agricultural and industrial reuse need the highest quality effluent.

Sensitive Ecosystems

Facilities near fragile aquatic habitats need to take extra precautions with wastewater discharge. Tertiary treatment reduces threats from residual toxicants to species and ecosystems in the receiving body of water.

Drinking Water Augmentation

Some cutting-edge facilities can treat sewage to drinking water quality standards. After rigorous tertiary and advanced treatment, H20 once deemed unusable becomes a viable source for potable water.

As you can see, tertiary processing goes the extra mile to protect human and environmental health wherever facilities discharge wastewater or reuse effluent.

Common Tertiary Water Treatment Methods

Tertiary configurations vary based on treatment goals and local needs. But most rely on at least one or a combination of the following methods:

Filtration

Filtration uses physical barriers to trap particulates present after initial clarification. Common tertiary filters include sand, multimedia, cloth, and microscreens:

  • Sand filters contain layers of sand and gravel that grab particles as water flows through.
  • Multimedia filters hold a mix of anthracite, sand, and garnet to capture diverse particle sizes.
  • Disc filters use rows of polyester mesh discs to filter water to extremely fine levels.
  • Microscreens employ stainless steel or synthetic mesh screens with microscopic pores to catch particles.

Backwashing cleans filters when they become saturated. The process reverses the flow of water to flush out accumulated solids.

Membrane Systems

Membrane systems separate contaminants using thin, porous films. As source water passes through the membrane barrier, particulates and impurities become concentrated in the reject stream while the permeate contains the clarified product water.

Reverse osmosis and nanofiltration are common membrane methods for tertiary treatment:

Reverse osmosis (RO) uses extreme pressure to push water through semipermeable membranes that reject dissolve salts, organics, bacteria, and more. RO removes up to 99% of impurities, producing near-distilled quality effluent.
Nanofiltration works similarly but uses membrane pores sizes between RO and ultrafiltration. These membranes filter out divalent ions, large organics, and bacteria.

Since they operate without chemicals, both RO and nanofiltration create minimal byproduct waste. However, membrane fouling that reduces effectiveness over time remains an operational challenge.

Adsorption

Adsorption extracts compounds and particulates by adhering them to a solid substrate. Granular activated carbon is the most common medium. As water flows through carbon beds, pollutants attach to the porous carbon surface through intermolecular forces. This effectively removes traces of organic compounds along with residual tastes and odors.

Operators regenerate saturated carbon through thermal reactivation or microbial degradation. Otherwise, spent carbon becomes solid waste needing appropriate disposal.

Ion Exchange

Ion exchange alters water chemistry to remove heavy metals, radionuclides, nitrates, and other ions. The process exchanges target ions for more innocuous ones using an exchange resin bed. Cation exchange swaps positively charged ions while anion exchange replaces negatively charged ions.

For example, a cation exchange bed removes hardness ions like calcium (Ca2+) by trading them for non-scaling sodium (Na+) ions. The calcium and sodium simply switch places, softening the water.

After the exchange capacity depletes, regeneration returns the bed to usable condition. Most systems use acid, caustic sodium hydroxide, or brine to reactivate the resin.

Disinfection

Since tertiary treatment deals with trace pollutants, most configurations add a final disinfectant to eradicate pathogens. Common chemical disinfectants include:

Chlorine immediately kills microbes through cell membrane destruction. Facilities worldwide use it as a primary and final disinfectant.
Chlorine dioxide works similarly but without producing harmful byproducts like trihalomethanes (THMs) and haloacetic acids (HAAs).
Ozone destroys microorganisms by oxidizing cellular components.

Aside from chemicals, advanced facilities often use ultraviolet radiation. When water passes UV lamps, the rays modify microbes’ DNA so they cannot replicate. This physical process provides effective disinfection without using toxic biocides.

Real-World Tertiary Water Treatment Applications

Tertiary methods adapt to unique treatment challenges across industries like wastewater, food and beverage, oil and gas, mining, and more.

For example, the Orange County Water District advanced water purification facility in California treats wastewater for indirect potable reuse. Their process combines microfiltration, reverse osmosis, and UV disinfection with advanced oxidation before sending water to underground injection wells. After further soil aquifer treatment, H20 eventually reaches drinking water wells scores of miles away.

Singapore’s NEWater plants treat municipal wastewater to ultra-clean levels for direct non-potable reuse. After microfiltration, RO, and UV, the water undergoes post-treatment with minerals and corrision inhibitors to become suitable for industrial facilities expecting extreme purity.

These are just two instances of innovative tertiary treatment allowing sustainable, reliable water reuse. As freshwater resources come under pressure globally, such cutting-edge purification will become essential.

Looking Ahead With Tertiary Treatment

Continual advances allow tertiary methods to push contaminant removal to previously unachievable levels. One day technologies like forward osmosis, advanced oxidation, even nanomaterial membranes and sorbents could make tertiary treatment even more effective.

But even without major breakthroughs, tertiary processing already unlocks invaluable water reuse potential using battle-tested techniques. When leveraging sound science and engineering, facilities implement customized tertiary treatment achieving almost any conceivable water quality goal.

What is tertiary water treatment? In essence, it’s the vital phase making effluent reuse and ecological sustainability possible for modern communities.

After learning about its role and function, one sees that tertiary processing is anything but redundant or excessive. It’s an indispensable catalyst allowing smart water utilization in a resource-constrained world.

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