title: Increased performance of secondary clarifiers using dynamic distribution of minimum return sludge rates.
abstract: Most wastewater treatment plants have several secondary clarifiers or even more sets of clarifiers including several secondary clarifiers, and in practice it is a well known problem that equal distribution of the load to the single clarifier (or set of clarifiers) is very difficult-not to say impossible-to obtain. If the problem is neglected, quite a big percentage of the total clarifier capacity-measured as the max. allowed hydraulic load-can be lost. Further, return sludge rates are seldom controlled by any other means than as a (typically too high) percentage of the inlet to the wastewater treatment plant-giving a varying and too low suspended solids concentration in the return sludge, which again can lead to an unnecessary use of polymer in the pre-dewatering of the surplus sludge taken from the return sludge. A control of the return sludge rate divided into two parts - control of the total return sludge flow and control of how the total flow shall be distributed between the secondary clarifiers - is able to solve the mentioned problems. Finally, as shall be demonstrated on full scale wastewater treatment plants, a considerable increase of the hydraulic capacity of the treatment plants can be obtained.
authors.affiliation: DHI, Gustav Wieds Vej 10, DK, 8000, Aarhus C, Denmark. alj@dhigroup.com
authors.forename: A
authors.initials: A
authors.lastname: Lynggaard-Jensen
authors.forename: P
authors.initials: P
authors.lastname: Andreasen
authors.forename: F
authors.initials: F
authors.lastname: Husum
authors.forename: M
authors.initials: M
authors.lastname: Nygaard
authors.forename: J
authors.initials: J
authors.lastname: Kaltoft
authors.forename: L
authors.initials: L
authors.lastname: Landgren
authors.forename: F
authors.initials: F
authors.lastname: Møller
authors.forename: E
authors.initials: E
authors.lastname: Brodersen
mesh_terms: D012722:Sewage; D013997:Time Factors; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014877:Water Pollution, Chemical / Q000517:prevention & control; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods*
chemical_list: D012722:Sewage; D014874:Water Pollutants, Chemical