_O & M MANUAL - WEST LANE MOBILE HOME PARK

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7. Calculate how long the bacteria have been in the aeration tank which is the Cell Residence Time (CRT). If too old increase wasting and if to young decrease wasting. The formulas used to determine the solids wasting rate are as follows: Organic Loading—Biochemical Oxygen Demand-BOD Organic loading is the number of pounds per day of BOD (food) entering the plant. The Pounds formula is used to make the calculation. Multiple the influent flow rate in mgd by the weight of a gallon of water (8.34 lbs/gallon) and then multiple by the BOD mg/I.The BOD in mg/I is determined by an outside lab. It may be helpful to calculate the organic loading on a 5-day moving average to average out the day to day fluctuations. Organic Loading Formula - BOD (influent flow mgd) x (weight of water lbs/gallon) x (BOD mg/1) = lbs/day of BOD Example: Given a BOD of 120 mg/I Given Influent flow of 54,000 gpd or .0540 mgd ❖ (.0540 mgd) x (8.34 lbs/gal) x (120 rng/i) = 54 lbs/day of BOD Mixed Liquor Suspended Solids-MLSS The MLSS in the aeration tank is a combination of microorganisms and inorganic material. The microorganism portion of the MLSS is the part that is used for treatment and is what is actually eating the incoming food/pollutants/BOD.This portion is called Mixed Liquor Volatile Suspended Solids (MLVSS). MLSS is calculated by the operator by filtering a known volume of mixed liquor from the aeration tank, drying the residue left on the filter, and then weighing it. The dried mass in mg is then multiplied by 100 (assuming a starting sample volume of 10 ml) to determine the MLSS in mg/I. Mixed Liquor Suspended Solids Calculation- MLSS (weight of dried sample mg) x (factor used to bring sample volume up to 1 liter) = MLSS mg/I Example: Given dried sample weight of 36.0 mg Given initial sample volume of 10 ml (10 ml x 100 = 1 liter) ❖ (36.0 mg) x (100) = 3,600 mg/I MLSS