State Water Resources Control BoardDivision of Drinking WaterFebruary 2018Example Calculations of Chlorine DosageNote: Percent sodium hypochlorite (%NaOCl) is based on weight per volume (w/v) in theequations below. Specific gravity is incorporated as part of the solution strength (% w/v).Equation 1A: Average Dose - Chlorine dosage (mg/L) measured as Cl 2 :Eq. 1A:wmg 9,525 (gallons of NaOCl solution injected) (% NaOCl v )Cl2 Dosage, (gallons of water produced)LDosage Example 1: Over a seven day period, a system produced 40,000 gallons of water. Inthat time period, the system used 41.64 liters of 0.5% NaOCl solution (w/v). What is the averagechlorine dosage in mg/L?Step 1: Convert liters of NaOCl solution injected to gallons:Unit conversion: 1 gallon 3.785 L;1 gal# gallons 41.64 L 3.785 L 11 gal (Use this value to input into Eq. 1A)Solution, using Eq. 1A:wmg 9,525 (11 gal of NaOCl injected) (0.5% NaOCl v )mg 1.31as Cl2Cl2 Dosage,L40,000 gallons of water producedLEquation 2A: Chlorine dosage (mg/L) measured as Cl 2 :Eq. 2A:mLwmg 2.52 (min of NaOCl solution injected) (% NaOCl v )Cl2 Dosage, (flow, gpm)LDosage Example 2: The chemical feed rate is 40 mL/min of 0.25% NaOCl solution (w/v) andflow is 35 gpm. What is the chlorine dosage in mg/L as Cl 2 ?Solution, using Eq. 2A:mLwmg 2.52 (40 min of NaOCl injected) (0.25% NaOCl v )mgCl2 Dosage, 0.72as Cl2(35 gpm)LL
Example Calculations of NaOCl Solution Strength (% w/v)Note: The equations for sodium hypochlorite solution strength preparation are based on mixing12.5% NaOCl (w/w) to 10 gallons of water.Equations 1B & 2B: Volume (ounces) of 12.5% NaOCl added to 10 gallons of water for targetsolution strength (valid between 0.047 to 3.5% NaOCl, w/v):Eq. 1B (Valid between 0.047% to 1% NaOCl solution strength, w/v):2Oz. of 12.5% NaOCl added / 10 gal of water 6.2715 (% NaOCl) 85.108 (% NaOCl)Eq. 2B (Valid between 1% to 3.5% NaOCl solution strength, w/v):2Oz. of 12.5% NaOCl added / 10 gal of water 9.2551 (% NaOCl) 77.091 (% NaOCl) 5.6136% Solution Strength Preparation Example 1: How many ounces of 12.5% NaOCl added to10 gallons of water are required to make a 0.5% NaOCl solution (w/v)?Solution, using Eq. 1B:2Oz. of 12.5% NaOCl 6.2715 (0.5% NaOCl) 85.108 (0.5% NaOCl) 44 oz.(This is the volume amount of 12.5% NaOCl added to 10 gal of water)Table 1 on the following page lists the NaOCl solution strengths from 0.047 to 3.5% (w/v) basedon the volume of 12.5% NaOCl added to 10 gallons of water.For example, if 20 oz. (2.5 cups) of 12.5% NaOCl (w/w) with a specific gravity (SG) of 1.2 isadded to 10 gallons of water, the percent strength (w/v) is 0.2307% (table).To determine the amount of liquid chlorine (12.5%) added to 25 gallons of water, multiply theresults for a 10 gallon solution by 2.5 (2.5 20 oz. 50 oz.).
Table 1: % NaOCl (w/v) based on volume of 12.5% NaOCl (w/w) added to 10 gallons of 30.860.890.920.950.981.001.051.08% 582.632.672.722.772.812.862.912.953.00% 1683.2023.2543.2893.3303.3753.4203.462
Example Calculations of NaOCl Feed Rate (mL/min)Equation 1C: Chemical feed rate calculation:Eq. 1C:mgmL (Cl2 dosage, L ) (Flow, gpm) 0.3785Feed Pump, wmi% NaOCl solution vFeed Pump Rate Example 1: Water flow is 35 gpm and chlorine solution strength is 0.7%NaOCl (w/v). What is the chemical feed rate (mL/min) needed to achieve a chlorine residual of1.3 mg/L as Cl 2 ?Solution, using Equation 1C:mgmL (1.3 L ) (35 gpm) 0.3785mLFeed Pump, 25wmimin0.7% NaOCl solution vFeed Pump Rate Example 2: Water flow is 40 gpm and chlorine solution strength is 0.2307%NaOCl (w/v). Using the table below, what is the chemical feed rate (mL/min) needed to achievea chlorine residual of 1.5 mg/L as Cl 2 ?Solution, using Table 2:From Table 2, go to the column that has 0.2307% NaOCl. Move down the column until youintercept the far left row that has 40 gpm.The feed rate is 68.9 mL/min at 40 gpm for a target dosage of 1 mg/L as Cl 2 . Since we want totarget a chlorine residual of 1.5 mg/L, multiply the feed rate by 1.5 (68.9 mL/min 1.5) and therequired feed rate is 103 mL/min.Note: If flow exceeds the table value (i.e., 80 gpm), then lookup the chemical feed rate for 40gpm and double the results.Unit conversions:Using the results (103 mL/min) from Example 2, convert the units to L/hr, L/day, gal/hr andgal/day.##πΏπΏ103 ππππ 60 min1Lπ³π³ ππ. 1 βππ1,000 πππππππππΏπΏ6.18 πΏπΏ 24 βπππ³π³ ππ1 ππππππ6.18 πΏπΏ1 galππππππ ππ. ππππβππβππ3.785 8 πΏπΏ1 galππππππ πππ3.785 πΏπΏπ π π π π π
Table 2: Chemical Feed Rate (mL/min) for a Target Dose of 1 mg/L as Cl 2Based on % NaOCl Solution Strength (w/v)Strength0.04705%4 oz0.09309%8 oz0.13928%12 oz0.1854%16 oz0.2307%20 oz0.2761%24 oz0.3213%28 oz0.3658%32 oz0.4100%36 oz0.45471%40 oz0.4985%44 oz0.54177%48 oz0.6498%58 oz0.7777%70 oz0.9027%82 oz1.024%94 oz1.147%106 oz1.261%118 oz1.384%130 oz1.499%142 oz1.613%154 oz1.719%166 oz1.833%178 oz1.939%190 oz2.064%204 oz2.215%222 oz2.363%240 oz2.533%260 oz2.704%282 oz2.899%306 oz3.071%330 oz3.254%354 oz3.462%384 oz10gpm84.515202530354045505560gpm gpm gpm gpm gpm gpm gpm gpm gpm gpm126.7 168.9 211.2 253.4 295.6 337.9 380.1 422.3 464.6 506.842.764.085.4106.7 128.1 149.4 170.7 192.1 213.4 234.8 256.128.542.857.171.385.699.9114.1 128.4 142.7 156.9 171.221.432.242.953.664.375.085.896.5107.2 117.9 93.44.04.65.126.96.36.199Note: The ounces (oz) below the % strength in each column is the number of ounces of 12.5% NaOCl(w/w) mixed with 10 gallons of water to produce the solution strength (% w/v).