Question

What are the full chemical reactions that ensue for each of the following disinfectants: (5 points) C2 (g) at pH 4.0 (5 points) C2 (g) at pH 7.8 (5 points) Clh (g) at pH 8.0 with excessive ammonia (NH3) in the water (5 points) Os (g) (5 points) Name the exact mechanism by which UV light damages cells. (5 points) Draw the "water treatment-water resources-wastewater treatment" loop with all of its connections.

Answer 1

i) At lower pH due to high concentration of H⁺(aq) formation of HOCl is favored, forming more and more HOCl and increases disinfectant power. Hence the chemical reaction is  

Cl2(g) + H2O ---- > HOCl + HCl

H⁺(aq) + OCl^-(aq) ----- > HOCl

ii) At higher pH, due to the low concentration of H⁺(aq) formation of OCl^-(aq) is favored decreasing the disinfectant power. Hence the chemical reaction is

Cl2(g) + H2O ---- > HOCl + HCl

HOCl -------- > H⁺(aq) + OCl^-(aq)

or Cl2(g) + OH^-(aq) ----- > OCl^-(aq) + HCl

iii)

NH3 + Cl2 ------ > NH2Cl + HCl

NH2Cl + Cl2 ------- > NHCl2 + HCl

NHCl2 + Cl2 -------- > NCl3 + HCl

iv) O3 (g) forms oxygen free radical which acts as a disinfectant (strong disinfectant)

O3 (g) -------> O2 + O-

(oxygen free radiacl)