Homework Set VI - CE 310 Spring 2014 Due April 25 B.A. DeVantier

Homework Set VI - CE 310
Spring 2014
Due April 25
B.A. DeVantier
Problem 1
Class text End of Chapter Problem 11-9. Using an overflow rate of 26 m/day
3
2
(m /m -day) and a detention time of 2.0 hours, size a primary sedimentation tank for an average
flow at Cynusoidal City (Problem 11-3 of 0.4 m3/s). What would the overflow rate be for the
unequalized maximum flow (Problem 11-3 of 0.604 m3/s at 6 pm). Assume 15 tanks with a length
to width ratio of 4.7.
Problem 2
Class text End of Chapter Problem 11-12. The influent BOD5 to a primary settling
tank is 345 mg/L. The average flow rate to the tank is 0.05 m3/s. If the BOD5 removal efficiency is
30%, how many kilograms of BOD5 are removed in the primary settling tank each day?
Problem 3
Class text End of Chapter Problem 11-20. The 500-bed Lotta Hart Hospital has a
small activated sludge plant to treat its wastewater. The average daily discharge is 1200 L/day per
bed, and the average soluble BOD5 after primary settling is is 500 mg/L. The aeration tank has
effective liquid dimensions of 10.0 m wide x 10.0 m long x 4.3 m effective depth. The plant
operating parameters are as follows:
MLVSS = 2000 mg/L
MLSS = 1.2 (MLVSS)
Return sludge concentration = 12,000 mg/L
Determine the following: Aeration period (hydraulic retention time) and F/M ratio.
Problem 4
Class text End of Chapter Discussion Question 11-2.What is the purpose of
recirculation and how does it differ from return sludge? Note: recirculation refers to trickling filter
return flow.
The purpose of recirculation as noted in this class text is to pass feed waste flow by material
multiple times resulting in increased efficiency, equalizing flow by damping the inflow
variations in time, increasing aeration through the multiple passes, reduction of the likelihood
of biological film drying out, and to improve the distribution of flow down through the media.
Another point related to the last text point stated (cited in class) is more uniform sloughing of
biological solids due to higher hydraulic loading. The most significant difference between
recirculation and return sludge recycling is the level of suspended solids, which are very much
higher in return sludge. The return sludge purpose is to increase the time biological solids
spends in biotreatment, whereas recirculation has minimal effect on solids retention time.
Another major difference between the two flows is the point from which they are taken in the
secondary clarifier. Recirculation is taken from clarifier overflow, while sludge return is
taken from clarifier underflow.
Problem 5
Use ppmv conversion factors to find the temperature at which μg/m3 standard for
maximum hourly ozone in Class Text Table 12-1 is taken? Hint: you will need to use the
conversion method covered in the chemistry review of Chapter 2.
Problem 6
Class text End of Chapter Problem 12-6. Given the following observations, use the
Key to Stability Categories (Table 12-9) to determine the stability.
(a) Clear winter morning at 9:00 am; wind speed of 5.5 m/s
(b) Overcast summer afternoon at 1:30 pm; wind speed of 2.8 m/s,
(c) Clear winter night at 2:00 am; wind speed of 2.8 m/s,
(d) Summer morning at 11:30 am; wind speed of 4.1 m/s
Problem 7
Class text End of Chapter Problem 12-12 plus addition at problem end. Calculate
the downwind concentration at 30 km (y = 0) in g/m3 resulting from an emission of 1976 g/s of SO2
into a 2.5 m/s wind at 1:00am on a clear winter night. Assume an effective stack height of 85 m and
an inversion layer at 185 m. Identify the stability class and show all work.
Problem 8
A plume from a smokestack has a pollutant emission rate of 1 kg/sec, at an exit
velocity of 10 m/sec and a temperature of 50 C. The stack height is 20 m, its radius is 1.5 m,
and the plume is known to rise under moderately stable conditions (the measured lapse rate is
–7.5 C/km). The measured wind speed at the effective stack height is 4 m/sec and the air
temperature is 27 C. Find the effective stack height to use for the Gaussian plume model using
the Briggs model. Do not apply the actual plume model.