WATER PLANT OPERATOR TRAINING PROGRAM
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It is most necessary for a plant operator to know how to calculate the dosages of the various chemicals used in water and wastewater treatment. It is important to be accurate when calculating dosages as too little or too much chemical may be ineffective and too much chemical is a waste of money or even dangerous. In process control the exact dose of chemical must be determined through calculation for the purposes of efficient operation and economy. Example 1 The chlorine dosage of an effluent is 15mg/L. How many kilograms of chlorine will be required to dose a flow of 8 500m3/d? In this question, it will be necessary to utilize your knowledge of the metric system. For every 1 000 m3 of water of flow, we will need to use 15kg of chlorine. 15 kg Cl2/1000 m3 x 8500 m3/d = 127.5 kg Cl2 /d Above we expressed 15mg/L as 15kg Cl2/1000 m3 and multiplied it by the flow to obtain the answer expressed as 127.5 kg Cl2 /d. Example 2 A chlorinator is set to feed a 94.8 kg/d of chlorine. If the average daily flow through the plant is 7 900 m3/d, what is the DAILY AVERAGE CHLORINE DOSAGE IN mg/L We are told that we use 94.8 kg chlorine for every 7900 m3 water. Above we divide the mass of chlorine used per day by the flow expressed in 1000 m3 per day and found we used 12 kg Cl2 for every 1000 m3 of flow or 12 mg/L. Dosage calculations Example 3 An effluent is treated with 15 mg/L of chlorine. How many kilograms of chlorine are required each day for a flow of 8,500 m3/day? (15 mg/L) (8,500 m3/day) (1,000 L/m3) (1 kg/106)=127.5 kg/day In this example, we multiplied the concentration of Cl2 by the flow and converted the units. Example 3 A chlorinator feeds 94.8 kg/day of chlorine. If the flow is 7,900 m3/day, what is the chlorine dosage in mg/L? (94.8 kg/day) (1 day/7,900 m3) (106 mg/kg) (1 m3/103 L) = 12 mg/L In this example, we divided the mass of Cl2 used per day by the flow and converted the units. |