Designing the disinfection system for your water treatment plant

1. You are in charge of designing the disinfection system for your water treatment plant. You have decided to use ozone for you design, and will inject 2 mg/L ozone into the contractor. Your design needs to have Ct of 20 mg*min/L to properly disinfect the water. The decay rate constant for ozone has been found to be 4.25×10-3 L/mg/min. Assume that the hydraulic efficiency of all chambers (t10/to) = 0.65. Suggest a design that incorporates multiple cells and achieves the desired disinfection goals. You should report the number of cells and the volume of each cell. (Hint: Don’t forget to consider the decay rate of ozone!)

2.Your water treatment plant has been treating its water with 1 mg/L ozone to oxidize arsenite compounds to As(V) for subsequent removal.

a.If the water concentration changes to have the following concentrations, will this process still work?

As(III) = 80 mg/L

Fe(II) = 3.0 mg/L

H2S = 0.5 mg/L


1.Reaction of ozone with iron should be of the form (a-f are stoichiometric coefficents):

a H2O + b Fe2+ + c O3  d Fe(OH3) + e O2 + f H+

2.For all oxidation reactions, mass and charge must be conserved

Molecular weights (g/mol)

Fe – 55.845

As – 74.9216

Mn – 54.938

O3 – 48

b. A vendor proposes that you can oxidize more of the metal ions if you switch to permanganate. Do you believe her? Justify your answer.

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