CE 3040 ENVIRONMENTAL ENGINEERING

Assignment-III

1. The sewage flows from a primary settling tank to a standard rate trickling filter at a rate of 5

million liters per day having a 5-day BOD of 150 mg/L. Determine the depth and volume of the

filter, adopting a surface loading rate of 2500 L/m2/day and an organic loading of 165 g/m3/day.

Also, determine the efficiency of the filter unit, using NRC formula.

2. Design a septic tank with a dispersion trench for a hostel with 125 students. Assume that the soil

has a percolation rate of 20 minutes per cm.

3. Determine the size of a high rate trickling filter for the following data:

i. Sewage flow = 5 MLD

ii. Recirculation ratio = 1.5

iii. BOD of raw sewage = 230 mg/L

iv. BOD removal in primary clarifier = 30%

v. Final effluent BOD desired = 25mg/L

4. A municipal wastewater with a flow of 17550m3/day and a BOD5 of 150mg/L is to be treated in a

bio-tower with plastic modular medium. Pilot-plant analysis has established a treatability constant

of 0.05/min for the system at 200C. The maximum temperature expected is 230C and the

minimum is 130C. For a 2:1 recycle ratio and a 7.0m depth, determine the area of the tower

required to produce a 20mg/L BOD5 effluent.

5. An average operating data for conventional activated sludge treatment plant is as follows:

i. Wastewater flow = 50000m3/day

ii. Volume of aeration tank = 15500m3

iii. Influent BOD = 200mg/L

iv. Effluent BOD = 25mg/L

v. Mixed liquor suspended solids (MLSS) = 3000mg/L

vi. Effluent suspended solids = 40 mg/L

vii. Waste sludge suspended solids = 12000mg/L

viii. Quantity of waste sludge = 250 m3/day

Based on the given information, determine:

a. Aeration period (hour)

b. Food to micro-organism ratio (F/M) (kg BOD/day/kg MLSS)

c. Sludge age (day)

6. Design a continuous flow completely mixed activated sludge process to yield an effluent BOD5 of

20mg/L and suspended solids of 23mg/L. The influent BOD5 following primary clarification is

200mg/L. The waste flow is 0.2m3/sec. Take Y=0.65, kd=0.05, θc=10day, MLVSS=3000mg/L,

return-sludge concentration=15000mg/L of suspended solids (SS), and MLVSS ratio=0.8.

7. Design a conventional activated sludge plant to treat settled domestic sewage with diffused air

aeration system, for the following data:

i. Population = 120000

ii. Per capita sewage contribution = 160 lpcd

iii. Settled sewage BOD5 = 200mg/L

iv. Effluent BOD5 required = 15mg/L

8. Design an oxidation pond for the following data:

i. Location = 240 Latitude

ii. Elevation = 900m above MSL

iii. Mean monthly temperature = 300 max and 100 min

iv. Population to be served = 8000

v. Sewage flow = 160 lpcd

vi. Desired effluent BODs = 30mg/L

vii. Pond removal constant at 200C = 0.1/day

9. A wastewater flow 5000m3/day is treated in a facultative oxidation pond that is 2.0m deep with a

surface area of 20ha. The wastewater has a soluble BOD5 of 150mg/L and a reaction rate

coefficient of 0.3/day. Determine the soluble BOD of the effluent. [Assume a completely mixed

reactor without solids recycle].

10. A wastewater flow of 3550 m3/day is to be treated in facultative pond system. The reaction rate

coefficient at the average operating temperature is 0.35/day. The pond is expected to operate at a

dispersion factor of 0.5. Determine the surface area required for 85% removal of soluble BOD for

a pond depth of 2.0m with (a) a single-cell pond and (b) a four-cell system

11. Determine the sludge volume index of the ASP at two different times of operation based on

experimental data. The volume of sludge after 30 minutes of settling at the two time periods were

176 and and 300ml. What is your inference about the settleability and suggestion for the recycle

ratios?

12. Design a secondary settling tank for a sludge with an initial concentration of 3200mg/l so that the

final underflow sludge concentration is 22,000mg/l. Experiments with the ASP effluent in a

400mm cylindrical jar indicated that the time taken to achieve this is 34.5 minutes and the

settling velocity of the interface in hindered zone is 20 mm/min. Determine the solids and

hydraulic loading rate