ENGR10004 Engineering Technology and Society
Engineering Technology and Society
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ENGR10004 Engineering Technology and Society
Water Treatment 2
• Develop MATLAB code around the water disinfection
subsystem of the design project
ETS: Water Treatment 2
MATLAB: log-inactivation credit calculator
• Write a MATLAB script that will calculate the log-inactivation credits for
giardia and viruses using the following inputs:
o Temperature [°C]
o Ozone half-life [min]
o Initial concentration of ozone [mg/L]
o Exposure time [min]
log!" " = #$!,"$! 1 − &'"!($! = ln 2 ⁄! *
# = .+ = 1.0380× 1.0741 ,- = 2.1744× 1.0726 ,
Chick-Watson Law
Ozone decay rate
constant
Pathogen inactivation
rate constant
2
ETS: Water Treatment 2
Contactor section
• Use Chick-Watson to decide on the appropriate contactor length, L
o Depending on the flow rate, this affects the exposure time, t
3
ETS: Water Treatment 2
Contactor section
Suggested Sequence of Steps in Design of the Contactor
Section
Create a MATLAB script to calculate the following:
1. Set a water volumetric flow rate.
a. Use the total amount of water required in a day for the community
b. Choose a process time length (from 3-5 hours)
c. Calculate the water volumetric flow rate
2. Calculate the time it takes for water to pass through the contactor section
a. Set the length, L, of the contactor section
b. Choose a pipe material and schedule
c. Calculate the ID for the DN100 of that pipe
d. Use the ID to and flow rate to calculate the velocity of the water in the pipe
e. Calculate the contact time using the velocity and length, L
3. Calculate the log inactivation credits for giardia and viruses using the Chick
Watson Law.
a. Assume a temperature, 25oC
b. Calculate kP and kO3
c. Use the contact time from above and the exit concentration of ozone from the membrane
d. Calculate the log inactivation credit for both giardia and viruses
4
ETS: Water Treatment 2
Contactor section
Decision point: Do the calculated log inactivation credits for both giardia
and viruses at least meet the required values of 3 for giardia and 4 for
viruses?
YES - Progress to Step 4
NO – Go back to Step 1, change either the process time or length of
the contactor, L, and repeat Steps 1-3
4. Calculate the time the water travels from the reducer in contactor section to
the water tower.
a. Add up the remaining length of pipe after the reducer: 100 m - L to the length of vertical
pipe going to the water tower
b. Choose a pipe diameter using a DN size smaller than DN100 using the same pipe
material and schedule as the contactor section
c. Calculate the ID and velocity in the length of pipe
d. Calculate the total time the water spends in the length of pipe.
e. Ensure this time is at least 10 minutes and no more than 20.
If less than 10 minutes, go back to step b and choose a new size pipe.
5
ETS: Water Treatment 2
MATLAB: contactor design example
1. Set a water volumetric flow rate
a) Use the total amount of water
required in a day for the
community: 70 m3
b) Choose a process time length
(from 7-9 hours): 9 hrs
c) Calculate the water volumetric
flow rate
2. Calculate the time it takes for
water to pass through the
contactor section
o Set the length, L, of the contactor
section, L (20-25)
§ L = 25 m
o Choose a pipe material and
schedule – use PVC
o Calculate the ID for the DN150 of
that pipe
o Use the ID to and flow rate to
calculate the velocity of the water
in the pipe v = Q/A
o Calculate the contact time, t, using
contact time = L/v in minutes
This is an example – do NOT use these specifications in your design!