Question

6. (1) A water treatment plant applies chlorine for disinfection so that 10 mg/L chlorine is achieved immediately after mixing. The volume of water treated each day is 25,000,000 gal. What is the mass of chlorine needed by this plant every day? (2) The disinfection takes place in a contact tank which is a CSTR at steady state. Chlorine concentration in the contact tank is constant at 3 mg/L. Effluent of this contact tank will enter drinking water distribution systems directly. What is the chlorine residual and chlorine demand, respectively, for water in this plant? (3) It takes 15 minutes to get 0.5-log Giardia inactivation under current operation condition (chlorine concentration, pH, temperature, etc.). How long does it take to get 3-log Giardia inactivation under the same condition?

Answer #1

A new water treatment plant will treat a maximum flowrate of
95,000 m3 /d. You have been asked to design the chlorine contact
basin. The plant must achieve 0.5 log inactivation of Giardia
lamblia cysts with chlorine. The CT value for 0.5 log removal at
the design conditions is 36 mg-min/L. The chlorine residual leaving
the basin will be 1.5 mg/L.
a. Calculate the required volume of the chlorine contact basin
if the basin is baffled so that the t10/τ...

A new disinfection system is being designed for a treatment
plant with a flow of 400 m3/min. The desired chlorine concentration
in the treated water is 7 mg/L. (a) It is proposed to inject a
concentrated chlorine feed solution into the main flow. If the
chlorine concentration in the feed solution is 150 mg/L, what
flowrate is required? (b) If the applicable Ct factor is 180
mg-min/L, what volume of chlorine contact chamber is needed? (c)
State whether the chlorine...

The water coming out of the sand filtration system at a plant
with Q = 1 MGD contains 100 bacteria/L when it enters the
disinfection system. What must the minimum removal rate be in the
pseudo-PFR 1000 gal tank to have an effluent concentration of <1
bacteria/L?

A coagulation treatment plant with a flow of 0.5 m3/s
is dosing alum at 20 mg/l.
Concentration of suspended solid is 25 mg/l. The effluent suspended
solid
concentration is 12 mg/l. The sludge content is 1 % and specific
gravity of sludge
is 3 %. What volume of sludge must be disposed of each day?

The amount of 38*10 6 gallons/day of raw water enters a water
treatment plant to produce potable drinking water. The water source
has high turbidity and hardness. The plant’s engineers have decided
to use alum to address the turbidity problem and use other
appropriate techniques to reduce the hardness. They performed jar
tests and an optimum dose for alum was determined as 14.7
mg/L.
a) Calculate the amount of alkalinity consumed (mg/L as
CaCO3)
b) Calculate the amount of required...

Problem #3: Biochemical Oxygen Demand (BOD) and Stream
Quality
A wastewater
treatment plant designed for a community of 45,000 people has a
flow of 100 gal/person/day and a BOD5 loading of 0.2
lb/person/day. The upstream characteristics of the receiving waters
are:
stream flow rate =
20 cfs and BOD5 = 2 mg/L
The water quality
standards require the in-stream BOD5 to be less than 7
mg/L in this stretch of the river.
The minimum BOD
removal efficiency that the treatment...

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