Circular or Rectangular: Which Clarifier Is Better?

Clarifier basins typically use both circular and rectangular configurations. For decades, the industry has been discussing the comparative qualities of these two options. Traditionally, the industry based their choice on experiences and the preference of the design company or engineer. In the United States, they balanced the designs of the primary wastewater treatment plants between both configurations when they designed scraper or collector systems from steel.

The dawn of biological treatment led to the popularity of wastewater clarifiers, particularly because corrosion became the main concern. Over a couple of decades ago, experts introduced the use of rectangular clarifiers for flight sludge and non-metallic chain collection systems. Through this, they were able to beat the corrosion issues that led to the rebirth of rectangular clarifiers, especially for massive wastewater treatment plants.

Ashton Tucker Water Treatment provides a comparison of benefits to give you more idea regarding each configuration:


As long as each of these clarifiers is designed well, their shape alone doesn’t display visible differences in their performance. The Sanitation District of Los Angeles County led a clarifier investigation that is widely documented. Their study revealed that narrow rectangular clarifiers of about 3m deep with simultaneous sludge removal function effectively at a surface flow rate of up to 2,000 gpd/ft2. They compared this data from a sequence of former circular clarifier researches. They found that the 3m rectangular clarifier in their study is as effective as 5.5m circular qualifiers.

This means they can build rectangular clarifiers narrower to achieve similar effluent quality and increased cost savings.


The rectangular clarifier offers a longer way for the wastewater to flow and for the deferred solids to travel. Moreover, subsequent longer detention time allows for a reduced amount of possible short circuit. It even allows more sludge settling in comparison to peripheral or center-feed circular clarifiers.

Flight and non-metallic systems have lightweight features, don’t require lubrication, and are non-corrosive, allowing for easy maintenance and installation. Its advantages in performance and hydraulics, along with its cost, have made more companies choose it instead of its counterpart.