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the chart the bacteria settled well in the first 10 minutes, a 70% reduction in volume, <br /> however only reduced in volume by 6% in the remaining 20 minutes. This break in the <br /> curve is called the "knee of the curve". The knee is the point at which the bacteria has <br /> settled sufficiently and should be returned to the head of the aeration tank by the RAS <br /> pump. Biomass that settles slowly and cannot compact is considered "slow settling" and <br /> can be easily "carried" up and over the clarifier wier. <br /> o Testing should occur at location A/B 3 in the middle of the aeration process <br /> o Testing should ideally occur every weekday <br /> o Good settability is between 400 and 500 ml at 30 minutes <br /> ■ If settleometer is > 500 then operator should increase wasting <br /> ■ If settleometer is < 300 then operator should stop wasting <br /> ir <br /> i <br /> ^Fr I <br /> 1 <br /> 1I <br /> s� 1 <br /> 1 <br /> i <br /> Sludge with Excess Filamentous Bacteria Slow Settling Young Sludge <br /> Photographs curtesy of Class A training Manual Ohio EPA <br /> • Mixed Liquor Suspended Solids Testing <br /> Mixed Liquor Suspended Solids (MLSS)testing shows the concentration of the biomass in <br /> the aeration basin. <br /> o Testing should occur at location A/B 3 in the middle of the aeration process <br /> o Testing should ideally occur every weekday <br /> o A good MLSS for this plant is in the range of 2800 mg/I to 4000 mg/I with a good <br /> summer range of around 3200 mg/I,and a higher range of 4000 mg/I in the winter, <br /> due to cooler temperatures and higher BOD loading. <br />