Effluent treatment primary sedimentation

Clarifiers are used to remove large suspended solids, colloids, organics, and color from surface water supplies. Coagulation and flocculation using chemical treatments, and sedimentation or "settling" are the three primary steps used to achieve reduction of contaminants. However, the typical effluent quality from a clarifier is not low enough... 

Secondary treatment removes 90-plus percent of the organic matter in wastewater by making use of the bacteria it contains. The two principal processes for secondary treatment are trickling filters and the activated-sludge process. The effluent from the sedimentation tank in the primary treatment stage flows or... 

This treatment process employs the use of physical operations such as screening and sedimentation to partially remove suspended solids and organic matter from the wastewater. This process provides the secondary treatment with wastewater that is partially free of solids, in order to facilitate further treatment. The effluent from the primary treatment contains primarily organic matter and is characterized by a relatively high biochemical oxygen demand (BOD).2... 

The primary distinguishing feature of the improved activated sludge treatment system is that high-rate DAF is the secondary clarifier for separation of suspended solids from the activated sludge aeration basin effluent, as opposed to secondary sedimentation alone in a conventional activated sludge system. 

In the Strait of Georgia, Canada, a study was performed on the fate of AgPEO in marine sediments [28]. Box core sediment samples were taken in a region heavily impacted by two municipal wastewater effluents. The sewage only receives primary treatment, which is clearly reflected in the results of this study. 

Thickening and clarification are sedimentation processes, and the equipment used for the two techniques are similar. The primary purpose of thickening is to increase the concentration of a relatively large quantity of suspended solids, whereas that of clarifying, as the name implies, is to remove a small quantity of fine solids to produce a clear liquid effluent. Thickening and clarification are relatively cheap processes when used for the treatment of large volumes of liquid. 

Cleaning-up processes of tannery effluents usually include (i) a primary or chemical-physical treatment (coarse screen, equalization and chemical-physical precipitation with sedimentation and sludge separation) (ii) a secondary or biological treatment with partial or total recycle of sludge and their separation and (iii) a tertiary treatment (filtration, stripping, redox processes) (Cassano et al., 2001). 

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