__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). q_{c} = 3 days, q = 2 hours.
Calculate the effluent nitrate concentration and methanol requirement in
Kg/d. (Y_{T})_{DN} =
0.8; (K_{s})_{DN} = 0.1 mg/L; (K_{d})_{DN}
= 0.04 /d; (q_{m})_{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
(q_{c}) = 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