CE 40340 – Wastewater Design
Homework No. 1
Due January 28, 2009
Wastewater Constituents
Problem 1
The following test results were obtained for a 100-mL wastewater treatment sample, with
weights expressed in grams:
Tare mass of evaporating dish
Mass of evaporating dish plus residue after evaporation at 105 oC
Mass of evaporating dish plus residue after ignition at 550 oC
22.6445
22.6832
22.6795
Determine concentrations of the following (in mg/L):
a. Total solids
b. Total volatile solids
Problem 2
The following test results were obtained for a 50-mL sample taken at the headworks of a
wastewater treatment plant, with weights expressed in grams:
Tare mass of evaporating dish
Mass of evaporating dish plus residue after evaporation at 105 oC
Mass of evaporating dish plus residue after ignition at 550 oC
Tare mass of Whatman GF/C (glass fiber) filter
Tare mass of Whatman GF/C (glass fiber) filter plus
residue after evaporation at 105 oC
Tare mass of Whatman GF/C (glass fiber) filter plus
residue after ignition at 550 oC
53.5434
53.5693
53.5652
1.5435
1.5705
1.5575
Determine concentrations of the following (in mg/L):
a. Total solids
b. Total volatile solids
c. Total suspended solids
d. Volatile suspended solids
e. Dissolved solids
Please note any negative values. What could have caused negative results?
Problem 3
Estimate the alkalinity, expressed in mg/L as CaCO3, for a wastewater sample with the
constituents listed below. Use only the appropriate constituents! The pH of the sample is
7.8.
Constituent
Ca2+
Mg2+
Fe2+
HCO3SO42ClNO3- (as N)
CO32H2CO3
Concentration (mg/L)
127
27
2.5
48
231
115
17
4
0.01
Problem 4
Assuming volatile suspended solids are mostly bacteria, and that bacteria are 12.4% N by
weight (i.e., 0.124 gN/gVSS) and 2.5 % P by weight (i.e., 0.025 gP/gVSS),
a) Determine the concentration of particulate (suspended) nitrogen and phosphorus
in the sample of Problem 2.
b) If the dissolved phase has a TKN = 12, NH4+ = 3 mgN/L, NO3- = 5 mgN/L, and
NO2- = 0.5 mgN/L, what is the total nitrogen (TN) of the sample? And the total
inorganic nitrogen (TIN)?
Note that the sample pH is 7.2, so NH3 can be neglected.
Problem 5
For the wastewater samples listed below, determine dissolved ultimate BOD (BODL),
particulate BODL, particulate COD, total COD, dissolved total nitrogen (TN) and total
phosphorus (TP), and particulate TN and TP for primary effluent, secondary effluent
(prior to settling), and final effluent (following settling). Assume the dissolved COD is
completely biodegradable. Assume fd = 0.8
Primary Effluent
Filtered COD
(mgCOD/L)
Xa (mgVSS/L)
Xi (mgVSS/L)
TKN (mgN/L)
Filtered NH4+
(mgN/L)
NO3- (mgN/L)
NO2- (mgN/L)
Filtered P (mgP/L)
Final Effluent
120
Aeration Tank
Effluent
5
5
50
28
19
851
730
NA
15
7
6
NA
5
0
0
6
2
1
4
2
1
4
5
Problem 6
Using Table 7-7 (pg. 572) of the M&E textbook, write the half reactions, overall
reactions, and Gibb’s free energy for the following metabolic processes:
a) Electron donor: domestic wastewater; Electron acceptor: Oxygen
b) Electron donor: domestic wastewater; Electron acceptor: nitrate (NO3-) to
nitrogen gas (N2)
c) Electron donor: ammonium to nitrite (NO2-); Electron acceptor: oxygen
d) Electron donor: methanol; Electron acceptor: sulfate (SO42-) to sulfide (HS-)
e) Electron donor: hydrogen (H2); Electron acceptor: CO2 to methane (CH4)
Based on the free energy alone, rate these reactions in terms of biomass yield (i.e., the
amount of biomass produced per electron donor used).
Problem 7 – COD and TOC
a) Calculate the theoretical OD for waters containing:
i) 179 mg/L glucose (C6H12O6, MW = 180 mg/mMol))
ii) 89 mg/L carbohydrate (CH2O, MW = 30 mg/mMol)
iii) 1.6 mg/L hydrogen (H2, MW = 2 mg/mMol)
iv) 50 mg/L NH4+ (MW = 18 mg/mMol)
In which cases would you expect the Theoretical OD to differ from the COD?
b) What is the TOC of (i) and (ii)?
Problem 8 – BOD
Assuming the compounds in Problem 7 are completely biodegradable (i.e., the COD is
equal to the ultimate BOD), calculate the ultimate BOD. For 7(i), calculate the BOD5 for
a k=0.28 1/days (base e).