Some removal is essential in primary sedimentation tanks because of the grease and other floating matter which is present in wastewater.Sludge is removed by scraping it into collecting hoppers at the inlet end of the tank.Inlets should be baffled to dissipate the momentum of the incoming flow and to assist in establishing uniform forward flow.The maximum weir loading rate, to limit the influence of draw-down currents, is preferably about 300 m 3/d-m, this figure is sometime increased where the design flow is great then 3 ADWF.The maximum forward velocity to avoid the risk of scouring settled sludge is 10 to 15 mm/s (06 to 09m/min or 2 to 3 ft/ min), indicating that the ratio of length to width l/w should referrals be about.Length ranges 15 to 100m an width from 3 to 24m (length/ width ratio 3:1 to 5:1).They can be economically built side-by-side with common walls. ![]() These are most commonly used for primary sedimentation, since they The removal rate is 50-70% of suspended solids and 25-40% of BOD whereas, generally more than two rectangular or circular tanks are used. Primary Sedimentation takes place in the sedimentation tanks with the objective to remove readily settleable solids and floating materials and thus reduce the suspended solids content.
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