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Operations High Effluent Suspended Solids? Elevated concentrations of activated sludge effluent suspended solids can be a red flag for plant operators. Testing for flocculated and dispersed suspended solids helps pinpoint the causes. wastewater treatment planes A good thickening function means turbulence in the aeration basin or in the effluent solids level is a barom- solids are moved quickly to the bottom mixed liquor transport system between eter of performance efficiency of the clarifier and exit in the return the-aeration basin and the clarifier. as well as a report card for regulators activated sludge flow.A good clarifying who enforce discharge permits.When function means only solids-free effluent Simple tests the solids level shows a rising trend,no leaves the clarifier.Both thickening Testing for dispersed suspended solids one is happy. and clarifying depend on proper floccula- (DSS) and flocculated suspended solids The solids in activated sludge tion and hydraulic functioning for (FSS)—see center box—can give plant secondary effluents occur as a operators the information result of high sludge blankets they need to distinguish caused by prolonged thickening between flocculation and overloads or when denitrification rI A G NrS I N G T H E PR 0B L E Mflow short-circuiting causes them to float.They can problems that cause high also be caused by hydraulic Simple diagnostic tests can help treatment plant effluent suspended solids. short-circuiting or flocculation operators determine whether elevated suspended In the DSS test,the problems from poor floc forma- mixed liquor entering the [ion or floc breakup in the mixed solids are caused by inadequate flocculation or by clarifier(or from any other liquor transfer channel before it hydraulic short-circuiting. The dispersed suspended point between the aeration enters the secondary clarifier. basin and the clarifier)is The corrective actions for solids, or DSS, test quantifies a mixed liquor sample's sampled and allowed to each of these problems differ, state of flocculation and the flocculated suspended settle.Sampling and settling however,so it is important toSolidsare done in the same con- identify which problem is caus- , OY F$$, test quantifies the extent of activated tainer.This maintains ing the elevated effluent sus- sludge flocculation. Both tests are easy to perform the integrity of the flocs, pended solids at a particular and require no sophisticated equipment. which might break up if plant.A close look will tell you the sample was transferred if the problem is caused by For a copy of the DSS and FSS test procedures and results, to another container.After prolonged thickening(sludge please contact Andrea Atkins at(510) 210-2464 or write to Brown the sample settles,the blanket too high) or denitrifica- and Caldwell,Attention Marketing Dept,BO.Box 8045, supernatant is drawn off tion(bubbles attached to floc Walnut Creek,CA 94596-1220. and analyzed for suspended particles),but detecting mixed solids concentration. liquor flocculation or secondary clarifier effective solids removal. In the FSS test,a mixed liquor short-circuiting problems is less obvious. Some biological solids,even relative- sample is drawn from the same location Brown and Caldwell has developed ly large,well-flocculated solids,can be as the DSS test sample. The sample is two tests to help plant operators distin- swept up by high velocity currents and flocculated in a square flocculation jar guish between mixed liquor flocculation carried into the effluent.This is flow for 30 minutes at 50 rotations per minute and clarifier short-circuiting problems. short-circuiting,a hydraulic problem. and then allowed to settle for another 30 Other biological solids are carried minutes.After settling,the supernatant Proper clarifier function out of activated sludge secondary clari- is analyzed for suspended solids.Finally, Secondary clarifiers perform two func- fiers because they are too light.These the results of an effluent suspended tions:They thicken sludge and clarify, solids lack sufficient weight to overcome solids test are needed to complete the or remove solids from,the effluent. the upward velocities created by flow data.Analyzing the results of the tests The overall performance of the activated exiting the tank. These dispersed can reveal the source of the high effluent sludge process rests essentially on the biosolids either have not been incorpo- suspended solids problem. efficiency of the clarifier to accomplish rated into a floc particle or have been High concentrations of DSS and low these two tasks. sheared from a floc particle by excessive concentrations of FSS suggest the mixed 6