## Wastewater Denitrification

SOLUTION

1.                  10 MLD of wastewater is to be denitrified, and methanol is to be added for this purpose to the denitrification tank.  Nitrate concentration influent to the denitrification tank is 40 mg/L (as N).  qc = 3 days, q = 2 hours.  Calculate the effluent nitrate concentration and methanol requirement in Kg/d.  (YT)DN = 0.8; (Ks)DN = 0.1 mg/L; (Kd)DN = 0.04 /d; (qm)DN = 0.5/d.  All bio-kinetic constants are in terms of  Neglect nitrogen incorporation into bio-mass.

Hint:

·        Methanol consumption is due to both energy requirement for denitrifying microorganisms and bio-mass growth

·        Bio-mass Formula:

·        Nitrate Reduction Equation:

(10)

SOLUTION:

BSRT (qc) = 3 days;

Therefore,

Also,    ;

or,        ;                          Also,

Also,

Therefore,        X = 992 mg/L

V = q.Q =

Sludge produced per day =

Bio-mass Formula is ;          Formula Weight = 113

i.e.,                   113 g bio-mass has 5 moles of carbon

Therefore,        275 g of bio-mass has  moles of carbon

275 Kg of bio-mass has 12194 moles of carbon

Influent nitrate loading =

Effluent Nitrate =

Nitrate conversion = 400 – 14 = 386 Kg/d

Equation for nitrate conversion:

i.e.,       84 Kg of nitrate-N requires 5000 moles of carbon

386 Kg of nitrate-N requires  of carbon

i.e., total carbon requirement per day = 12194 + 22976 = 35171 moles

1 mole of carbon = 32 g methanol

35171 moles of carbon =

Methanol requirement is 1125 Kg/d