WASTEWATER TREATMENT-V

SOLUTION

1.      Describe the differences in the nature of recycling between activated sludge process and trickling filter.                                                                                       (3)

Solution:

 Activated Sludge Process   ·        The sludge or biomass is recycled in the activated sludge process ·        Purpose of recycling is to maintain a high biomass concentration in the aeration tank Trickling Filter   ·        Treated wastewater is recycled in the trickling filter ·        Purpose of recycling is to maintain adequate hydraulic loading rate, without changing organic loading rate, so that all portions of the filter may be wetted adequately all the time.

2.      A tricking filter with the following dimensions is available.  Depth: 2 m, Surface area: 150 m2.  The media consists of stones of 7-10 cm diameter.  This filter will be used to treat 0.6 MLD wastewater with BOD5 = 300 mg/L.  The trickling filter will be operated in the high-rate mode, i.e., OLR: 0.48 – 0.96 Kg/m3/d, HLR: 10 – 40 m3/m2/d, re-circulation ratio: 1-2.  Based on this information, calculate the expected BOD5 removal efficiency.

Hint:

, ,

Where,             So =     BOD5 in Raw Wastewater, mg/L

Se =      Total BOD5 of settled effluent from the filter, mg/L

Sa =      Total BOD5 of wastewater applied to the filter, mg/L

k =       Treatability constant, 2.36

D =      Depth of the Trickling Filter, m

Q =      Total Flow rate applied to the filter without recirculation, m3/d

A =      Surface Area of the Trickling Filter, m2

n =       0.5

V =      Volume of the Trickling Filter, m3                                              (7)

Solution:

Volume of trickling filter = D.A = (2).150 = 300 m3

(The above value is inadequate and hence must be increased).  So, let R = 2

Hence, HLR = .  This value is adequate.

Now, to calculate BOD5 removal efficiency.

It is known that,            , Where,

Also,

or,                 or,

or,        ;

Therefore, BOD5 removal efficiency:     or, 96.64%