Straining and microstraining

Straining is the simplest separation procedure for suspended substances, these being trapped by rakes or screens with smaller mesh dimensions than those of the separated material. This process is usually used for removal of the large-size floating impurities. 

Floating impurities trapped by rakes or screens are generally strained mechanically. They are disposed of by composting, dumping, incineration, pressing, etc. Mechanically wipped-off rakes are shown in Fig. 3.47. 

Microstraining is a type of mechanical separation in the course of which suspended matter is trappped on the surface and inside a thin netting with smaller meshes than the trapped particles (10-20 /xm). 

The system operates as a rotary drum screen with continuous washing to prevent clogging of the meshes (Fig. 3.48). Such systems are part of a technological line as a substitute for sedimentation in the case of waste-water purification they can replace flotation equipment. The efficiency of separation carried out in this way is about 60%. 

Sedimentation is one of the most wide-spread separation procedure in both water treatment technology and the wastewater treatment. Separation of suspended particles is based on gravity. 

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