Clarifiers 101: Clearing the Way For a Sustainable Future

Clarifiers are perhaps the most overlooked piece of the wastewater treatment process, yet they are critical to any wastewater plant’s performance. They’re so vital to wastewater operations that some facilities use them twice for solids removal. Clarifiers increase the effectiveness of downstream treatment stages, such as disinfection, solids handling, and biological nutrient removal.

To give these workhorses their due, BW Water went in-depth into why the wastewater treatment process uses clarifiers, where they fit into the water purification process, and how they operate.

The Basics

Clarifiers rely on the relentless force of gravity to separate suspended solids from wastewater, floating fats, oils, and grease to the top while sinking heavy solids to the bottom. When designing clarifiers, engineers consider wastewater characteristics, hydraulic flow, and available space to determine arrangement, shape, and depth.?

Primary clarifiers are usually found downstream of the headworks, where solids and other inorganic matter are screened to protect treatment equipment. Secondary clarifiers are typically located after the aeration tank to settle carryover sludge mainly composed of weaker, dead bacteria. There are two typical clarifier shapes:

Circular Clarifiers: More common for municipal wastewater plants, circular clarifiers feed wastewater either from the center well or the sides of the clarifier and are designed to slowly float wastewater towards its outlet.

Rectangular Clarifiers: More common for industrial facilities with heavy organics, metals, and fats loading, rectangular clarifiers feed wastewater from the bottom or sides of the tank. Scraping mechanisms slough off the top and bottom solids, allowing the solids to pass onto further treatment stages.

Clarification Aids

While gravity is cost-effective, wastewater plants often need chemical and mechanical settling aids to remove organic matter from wastewater effectively within the plant’s design parameters.

Lamella Plates: These slanted plates add surface area within clarifiers to increase the rate of settling and clarifier capacity. These plates are typically added to clarifiers when space or resources for additional clarifiers are not available.

Chemicals: Chemicals such as aluminum sulfate and iron chloride incite the coagulation of suspended solids. Adding these chemicals causes individual solid particles to attach to one another, preparing them for effective flocculation. Flocculation is the phenomenon of smaller solid particles clustering together to form larger clumps called “floc.”

Clarifiers and their supplemental technologies work to remove solids from wastewater. However, how they’re operated defines their performance.

Operations

Efficient clarifier operations require a coordinated effort among operations and maintenance staff, integrating various treatment stages to ensure a smooth transition from wastewater to clean water. From hydraulic retention time to regular maintenance, onsite operators can adjust different parameters to get the most from their clarifiers.

Hydraulic Retention Time (HRT): HRT refers to the time wastewater spends within a clarifier and directly impacts the settling process. Maintaining an optimal HRT allows sufficient time for solids to settle and promotes effective purification while avoiding overloads or underutilization of a clarifier's capacity.

Sludge Removal Mechanisms: Sludge scrapers, pumps, and airlifts transport settled solids to troughs where they are either returned as activated sludge to the biological treatment process or to solids handling stations for digestion, dewatering, and disposal. Clarifier operations can dictate how efficiently these solids handling processes run.

Monitoring Systems: Monitoring technologies track turbidity, sludge blanket health, and flow rates, providing valuable insights into the effectiveness of the clarification process. Real-time data empowers operators to make informed decisions, optimizing treatment performance.

Maintenance: Regular inspection and cleaning of clarifier weirs, baffles, and mechanical arms mitigate the risk of malfunction or structural degradation. Clarifier manufacturers often offer periodic equipment maintenance services and technical guidance to operators to keep them maintained correctly.

By orchestrating these different parameters of clarifier operations, operators remove pollutants and maintain other stages of treatment. The benefits of operating primary and secondary clarifiers are why they are used by communities and industries spanning the globe.

Relevant Industries

The facilities that produce fuel, food products, and high technologies all require vast volumes of water. To protect the earth’s most precious resource, these industries must treat the resulting wastewater after using it. These include:

Oil & Gas: Clarifiers are instrumental in treating wastewater generated during the extraction, refining, and production of the oil and gas products that move our world. This crucial yet, at times, toxic process relies on clarifiers to minimize harm to the environment while delivering these services.

Food & Beverage: Food and beverage processing facilities use clarifiers to separate heavy organic loading, food particles, and food processing cleaning agents from wastewater. This permits them to feed the world while remaining good environmental stewards.

Metals and Mining: The metals and mining industry provides the raw materials that make the consumer products we use daily. Separating heavy metals from the wastewater that results from these processes is crucial to protecting local water bodies and ecosystems.

Dairies: Dairy processing facilities utilize clarifiers to treat wastewater containing milk solids, fats, and cleaning agents. Forward-thinking dairies anaerobically digest these separated solids to produce renewable energy.

All Clear

We can’t overstate the importance of clarification. It’s a fundamental aspect of our commitment to environmental stewardship, quietly but effectively removing impurities to safeguard water resources.

As industries and communities worldwide move toward sustainable water management, clarifier technology must evolve to treat pollutants while minimizing the consumption of chemicals and energy. Applying the principles listed in this article, BW Water has designed and deployed its own high-rate clarifier, the Hydro-PAQ(TM), across many industries, such as oil & gas, food & beverage, metals and mining, and semiconductor manufacturing. The Hydro-PAQ (TM)’s multistage clarification design intensifies the process of delivering clarified water while outperforming traditional clarifiers on water quality and cost of operations.

Together, let’s champion the cause of clarification to ensure our environmental legacy for generations.