Math for Water Technology MTH 082 (pg. 468) C.T Calculation “Required by Law” Math for Water Technology MTH 082 (pg. 468)

C.T calculation “C” is the concentration of chlorine, “T” is the amount of time the water has been in contact with chlorine before the first user. Calculated daily and compared against the EPA CT “Required” Table EPA rules states - “Measurements must be taken on the same day of the week, every week, for one year (52 measurements), during peak hourly flow for that day. Data can be measured manually or with on-line instrumentation.”

C.T calculation Surface Water Treatment Rule: all surface water and GWUDI systems require 99.9% (3-log removal) and/or inactivation of Giardia and 99.99% (4-log) removal of viruses through disinfection and treatment Ground Water Treatment Rule: If a system is fecal positive may be required to achieve inactivation of 99.99% (4-log) removal of viruses through disinfection and treatment

C.T Calculation Problems To calculate the contact time T, the results of a recent tracer study must be used!! The peak flow must be measured from the effluent side of the clearwell or contact chamber, NOT the flow through the plant. The chlorine residual, pH, and temperature values used to calculate CT must be measured at the effluent side of the clearwell or contact chamber, or before the first user.

CT Calculation Problems When using the EPA CT tables, make sure you round down for temperature, and round up for pH. log-reduction must equal 3.0 for Giardia

For surface water systems without filtration, the Surface Water Treatment Rule requires public water systems to? Provide coagulation and filtration Maintain a C X T value above the minimum value Continuously sample for total coliforms Maintain public notification

In the application of chlorine for disinfection, which of the following is not normally an operational consideration? Mixing Contact time Dissolved oxygen pH None of these answers are correct

The chlorine residual, pH, and temperature values used to calculate CT must be measured at? effluent side of the clearwell effluent side of the contact chamber before the first user Any of the above would be ok

The C.T calculation must be calculated Once a year Once a month Once a week Once a day

The peak flow must be measured as total flow through the plant? True False

The final C.T calculation has what units? Mg/L Lbs/day mg-min/L time

What is the acceptable log reduction for Giardia? 1 2 3 4

What is the acceptable log reduction for viruses? 1 2 3 4

Four log removal is? 90.00 % 99.00 % 99.90 % 99.99 %

If your temperature is 8 degrees with a pH of 7 If your temperature is 8 degrees with a pH of 7.2, you should use the ____ degree page and the _____ pH table (please look at your tables). 5, 19 10, 8.5 5, 7.5 10, 7

Disinfection CTs have been established for? Free chlorine Chloramine Chlorine dioxide Ozone All of the above

Disinfection C.T are impacted by which of the following? Chlorine residual concentrations (mg/L) Contact Time (min) Water Temperature Water pH All of the above

T =contact time= Detention Time C.T Calculation T =contact time= Detention Time “the length of time water is retained in a vessel or basin ”

The units of T in the final CT calculation are ? Seconds Minutes Hours Days

Want T value to be in minutes Determining T in CT? Detention time (DT) = volume of tank = MG (1440min) flow rate MGD (1day) Want T value to be in minutes T = volume X Baffle Factor (table) flow rate

Baffle Factor? Poor circulation Baffling efficiency = 5-10% out Poor circulation Baffling efficiency = 5-10% in out No circulation Baffling efficiency = 0% in out

Baffle Factor? No circulation Baffling efficiency = 0% Good circulation Baffling efficiency = 30-50% in out in out Superior circulation Baffling efficiency = 70%

Baffle Factor? Perfect circulation Baffling efficiency = 100% out Poor circulation/hydropneumatic tank Baffling efficiency = 10% in out No circulation/Bladder type pressure tank Baffling efficiency = 0%

Baffle Factor? Unbaffled Tank 0.1 Poor Baffling 0.3 Average Baffling 0.5 Superior baffling 0.7 Pipe Flow 1.0 “How well the chlorine is in contact with the water”

What is the average detention time in a basin that is 1240 ft3 when the flow rate is 4.1 MGD? 3.3 min .03 min 303 min 435,512 min

What is the average detention time in a basin given the following: diameter = 80' depth = 12.2' flow = 5 MGD 132 min 101 min 144 min 105 min

Determine T at the effluent side of a superior baffled contact chamber basin that has the following: diameter = 30' depth = 15' flow = 700 gpm 65.8 min. 79.1 min 75 min. 86.1 min.

96.17 min 67.32 min 12.85 min 9 min DRAW: Given: Formula: Solve: Determine T at the effluent side of a superior baffled contact chamber basin that has the following: Length of = 30ft, width of 20 ft, depth = 15' flow = 700 gpm? DRAW: Given: Formula: Solve: tank= L X W X D , Flow rate 700 gpm, BF=0.7 T= DT X BF T= volume of tank/flow rate X BF Vt= L X W X D Vt=30 ft X 20 ft X 15 ft= 9000 ft3 9000 ft3 (7.48 gal/1ft3)= 67320 gal DT=VT/FR X BF Time = 67,320 gal/700gpm X 0.7 Time= 96.17 min X 0.7 Time= 67.32 min in 700 gpm out 30 ft 20 ft 15 ft 96.17 min 67.32 min 12.85 min 9 min

Disinfection C•T Requirements Chlorine residual concentrations (mg/L) Contact Time (min) Water Temperature Water pH Disinfection power= [residual chlorine] • time of its contact

Disinfection C•T Calculation C•T= [disinfection concentration mg/L] • contact time (min) C•T units= mg/L• min or mg •min/L Required C•T CTrequired is # established by EPA to provide log inactivation. Based on Giardia cysts. Look up in charts Actual C•T CTactual is # established by multiplying actual chlorine residual by hydraulic detention time and baffle factor.

Disinfection C•T Calculation C•T actual =[Residual chlorine]•hydraulic detention time•baffle factor (table) Hydraulic detention time = volume/flow rate C•Tact/ CTreq= ratio must be > or = to 1. C•Tact/ CTreq > 1.0 “You want to make sure that you are actually meeting the necessary requirements”

Disinfection C•T Rules Chlorine residuals used for C•T calculations are measured after contact, but before first customer. 2. Contact times are determined by calculating the hydraulic detention time (HDT) as water flows through pipes and tanks. Based on highest flow of day.

Disinfection C•T Rules 3. Water flowing through pipes provides contact times that are equal to the calculated HDT. Circular or rectangular tanks used for contact time are given only partial credit due to short circuiting.

Removal Credits Requirements Viruses Table 7.2: Typical Removal Credits and Inactivation Requirements for Various Treatment Technologies Process Typical Log Removal Credits Resulting Disinfection Log Inactivation Requirements Giardia Viruses Conventional Treatment 2.5 2.0 0.5 Direct Filtration 1.0 3.0 Slow Sand Diatomaceous Earth Filtration Unfiltered 4.0 * Systems must demonstrate to the State by pilot study or other means that the alternative filtration technology provides the required log removal and inactivation shown in Table 7-1.