{"id":20152,"date":"2026-06-20T11:46:13","date_gmt":"2026-06-20T03:46:13","guid":{"rendered":"https:\/\/www.energycle.com\/"},"modified":"2026-06-20T11:46:13","modified_gmt":"2026-06-20T03:46:13","slug":"guide-sur-le-traitement-des-eaux-usees-par-decantation","status":"publish","type":"post","link":"https:\/\/www.energycle.com\/fr\/guide-sur-le-traitement-des-eaux-usees-par-decantation\/","title":{"rendered":"Les d\u00e9canteurs dans le traitement des eaux us\u00e9es : types, fonctionnement et crit\u00e8res de choix"},"content":{"rendered":"\n

A clarifier is the quiet workhorse of almost every wastewater treatment plant \u2014 the tank where suspended solids separate from water so the clean fraction can move on. Get the clarifier right and the whole plant runs stable; undersize it or pick the wrong type and solids carry over into every stage downstream. This guide explains what a clarifier is, how it works, the difference between primary and secondary clarifiers, and how to choose the right design for your wastewater.<\/p>\n\n\n\n

It is written for plant engineers and operators specifying clarification equipment. Where a compact, high-rate option fits, we point to the relevant machine so you can match the technology to your site.<\/p>\n\n\n\n

What Is a Clarifier?<\/h2>\n\n\n\n

A clarifier is a settling tank that separates suspended solids from water by gravity, producing clear effluent on top and concentrated sludge at the bottom. Water enters slowly so that heavier particles sink, while a scraper mechanism collects the settled sludge for removal. A wastewater clarifier is used across municipal and industrial plants to cut suspended solids and turbidity before or after biological treatment.<\/p>\n\n\n\n

The principle is gravity. Slow the water down enough, give particles enough time and area, and they settle out. Everything in clarifier design \u2014 tank size, flow distribution, retention time \u2014 exists to give solids the calm conditions they need to drop.<\/p>\n\n\n\n

In short:<\/strong> a clarifier slows water down so suspended solids settle out by gravity, leaving clear water on top and sludge below.<\/p><\/blockquote>\n\n\n\n

How a Clarifier Works<\/h2>\n\n\n\n

A clarifier works by reducing flow velocity so suspended particles settle to the bottom, where a slow-moving scraper pushes them to a sludge hopper for discharge. Clarified water overflows a weir at the surface and continues to the next stage. The four steps below describe a typical cycle.<\/p>\n\n\n\n

    \n
  1. Inlet and flow distribution.<\/strong> Water enters through a center well or distribution baffle that spreads flow evenly and drops the velocity so settling can begin.<\/li>\n
  2. Settling.<\/strong> In the calm settling zone, particles heavier than water sink toward the floor. Chemical coagulation upstream makes fine particles settle faster.<\/li>\n
  3. Sludge collection.<\/strong> A rotating or traveling scraper moves settled sludge to a central or end hopper for pumping out.<\/li>\n
  4. Effluent overflow.<\/strong> Clarified water rises and spills over a peripheral weir, leaving the tank with most of its suspended solids removed.<\/li>\n<\/ol>\n\n\n\n

    Primary vs Secondary Clarifiers<\/h2>\n\n\n\n

    Primary and secondary clarifiers do the same physical job at different points in the plant. A primary clarifier removes settleable solids from raw wastewater before biological treatment. A secondary clarifier separates the biological sludge from treated water after the aeration stage. The table below shows how they differ.<\/p>\n\n\n\n

    \n\n\n\n
    Factor<\/th>Primary Clarifier<\/th>Secondary Clarifier<\/th><\/tr>\n<\/thead>\n
    Position<\/td>Before biological treatment<\/td>After aeration \/ biological stage<\/td><\/tr>\n
    Removes<\/td>Raw settleable solids, grit, some organics<\/td>Biological floc (activated sludge)<\/td><\/tr>\n
    Sludge type<\/td>Primary sludge<\/td>Secondary \/ return activated sludge<\/td><\/tr>\n
    Main goal<\/td>Cut load on downstream biology<\/td>Produce clear final effluent<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n\n\n

    Types of Clarifiers<\/h2>\n\n\n\n

    Clarifiers come in a few designs, and the right one depends on footprint, flow, and how fast your solids settle. The three below cover most industrial and municipal needs.<\/p>\n\n\n\n

    Conventional Circular and Rectangular Clarifiers<\/h3>\n\n\n\n

    The classic design: a large circular or rectangular tank with a rotating or traveling scraper. It is simple, reliable, and handles high flows, but it needs a large footprint because all the settling area sits on a single plane.<\/p>\n\n\n\n

    Lamella (Inclined Plate) Clarifiers<\/h3>\n\n\n\n

    A lamella clarifier<\/a> stacks inclined plates inside the tank, multiplying the effective settling area in a fraction of the floor space. Particles settle onto the plates and slide down to the sludge hopper. For the same flow, a lamella unit can be a fraction of the size of a conventional clarifier, which makes it the practical choice where space is tight.<\/p>\n\n\n\n

    Flotation as an Alternative<\/h3>\n\n\n\n

    When the solids are lighter than water \u2014 oil, grease, fibers, or chemically coagulated light flocs \u2014 settling struggles. There, a dissolved air flotation (DAF) system<\/a> floats the contaminants up instead of settling them down. It is the standard answer for oily or buoyant loads that a gravity clarifier cannot catch.<\/p>\n\n\n\n

    How to Choose a Clarifier<\/h2>\n\n\n\n

    Choosing a wastewater clarifier comes down to your solids, your flow, and your floor space. Work through these factors before you specify a tank.<\/p>\n\n\n\n