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5.35 A city has a population of 50,000 people, an average household generated wastewater flow
of 430 L/day-person, and the average BOD5 of the untreated wastewater in population
equivalents is 0.1 kg BOD5/day-person. If the BOD reaction rate coefficient for the wastestream
is 0.4/day, determine the ultimate (L0) BOD of the wastewater.
Solution:
5.36 A 10-mL sample is added to a 300-mL BOD bottle. Dilution water is added to the sample
bottle and the initial dissolved oxygen concentration is measured as 8.5 mg/L. After the sample
is sealed, the laboratory incorrectly takes a measurement of dissolved oxygen reading on day 6
of 3 mg/L. If the BOD reaction rate coefficient for the sample is 0.30/day, (a) estimate what the
5-day BOD should have been. (b) estimate what the dissolved oxygen reading should have been
on day 5. (c) determine the ultimate BOD of this sample.
Solution:
5.37 You are provided the following BOD data collected over a 10 day period. Day 1: BOD =
28 mg/L, Day 2: BOD = 45 mg/L; Day 5: BOD = 89 mg/L; Day 6: BOD = 100 mg/L; Day 9:
BOD = 120 mg/L. Calculate the BOD rate constant and the ultimate BOD of the sample.
Solution:
According to the plot, the slope is 0.0109 and the intercept is 0.326. kL can now be calculated.
𝑘𝐿= 6.01 0.0109
0.326 =𝟎.𝟐𝟎/𝒅𝒂𝒚
Use equation 5.34 to solve for the ultimate BOD:
0
(1 )
L
t
kt
y
Le
−
=
−
= 120 𝑚𝑔 𝑂2/𝐿
1−𝑒−(0.20/𝑑𝑎𝑦)(9𝑑𝑎𝑦)=𝟏𝟒𝟒 𝒎𝒈 𝑶𝟐/𝑳
y = 0.0109x + 0.3257
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 2 4 6 8 10
(t/y)1/3
Time (days)
5.38 Suppose the estimated BOD of an influent sample is expected to be 150 mg/L and the
dissolved oxygen of oxygen saturated dilution water used in the BOD test is 8.5 mg/L. If you are
using a 300-mL BOD bottle, estimate the maximum and minimum amount of sample you would
add to the BOD bottle to ensure satisfactory test results.
Solution:
5.39 If the BOD rate constant at 20oC is 0.12/day, what is the BOD rate constant at 10oC?
What fraction of ultimate BOD would remain in a sample that has been incubated for 3 days (a)
at 20oC and (b) at 10oC? (c) Solve for the fraction of ultimate BOD remaining at 20 and 10oC,
but after 6 days of incubation.
Solution:
5.40 As written in the textbook, end of chapter problem 5.40 duplicates problem 5.38. The
answer to problem 5.38 is provided.
If an instructor is looking for a similar problem with different values, here is a new problem they
can use.
New Problem (not in end of chapter)
The estimated BOD of an influent sample is expected to be 280 mg/L and the dissolved oxygen
of oxygen saturated dilution water used in the BOD test is 9 mg/L. If you are using a 250-mL
BOD bottle, estimate the maximum and minimum amount of sample you would add to the BOD
bottle to ensure satisfactory test results.
Solution:
5.41 Excess nitrogen inputs to estuaries have been scientifically linked to poor water quality
and degradation of ecosystem habitat. The nitrogen loading to Narragansett Bay was estimated
to be 8,444,631 kg N/year and to Chesapeake Bay is 147,839,494 kg N/year. The watershed area
for Narragansett Bay is 310,464 ha and for Chesapeake Bay is 10,951,074 ha. The nitrogen
loading rates are estimated for Galveston Bay to be 16.5 kg N per ha per year, 26.9 kg N per ha
per year for Tampa Bay, 49.0 kg N per ha per year for Massachusetts Bay, and 20.2 kg N per ha
per year for Delaware Bay. (a) Rank the loading rates from lowest to highest for these six
estuaries.
Solution:
5.42 Excess nitrogen inputs to estuaries have been scientifically linked to poor water quality and
degradation of ecosystem habitat. Perform a library search for the paper title “Nitrogen inputs to
seventy-four southern New England estuaries: Application of a watershed nitrogen model (J.S.
Latimer and M.A. Charpentier, Estuarine, Coastal and Shelf Science, 89:125-136, 2010).
Based on this article, what is the percent contribution of the following four sources of nitrogen to
the watershed of the New England estuaries? i) Direct atmospheric deposition to the estuaries,
ii) wastewater, iii) indirect atmospheric deposition to the watershed of the estuary, iv) fertilizer
runoff from lawns, golf courses, and agriculture.
Solution:
5.43 Humans produce 0.8 to 1.6 L of urine per day. The annual mass of phosphorus in this urine
on a per capita basis ranges from 0.2 to 0.4 kg P. a) what is the maximum concentration of
phosphorus in human urine in mg P/L? b) what is the concentration in moles P/L? c) most of
this phosphorus is present as HPO42-. What is the concentration of phosphorus in mg HPO42-/L?
Solution:
5.44 Assume 66% of phosphorus in human excrement in found in urine (the remaining 34% is
found in feces). Assume humans produce 1 L of urine per day and the annual mass of
phosphorus in this urine is 0.3 kg P. If indoor water usage is 80 gallons per capita per day in a
single individual apartment, what is the concentration (in mg P/L) in the wastewater that is
discharged from the apartment unit? Account for phosphorus in urine and feces.
0.66 × 𝑥 = 0.3 𝑘𝑔
𝑥= 0.3 𝑘𝑔
0.66 = 0.45 𝑘𝑔 P
This value is the total P in urine and feces.
(80)𝑔𝑎𝑙𝑙𝑜𝑛𝑠
3.78 𝐿×1000 𝑔
1 𝑘𝑔 × 1000 𝑚𝑔
1 𝑔 = 𝟒.𝟏𝒎𝒈 𝐏
𝑳
5.45 Fish that reside in the Potomac River Estuary have bioaccumulation factors (BAFs) reported
as 26,200,000 (units of L/kg) for largemouth bass and 10,500,000 for white perch. If the
concentration of PCB116 dissolved in the water column is 0.064 ng/L, what is the estimated
concentration of PCB116 in the fish (ng/kg).
Solution:
5.46 Concentrations of one particular PCB dissolved in the waters of Lake Washington near
Seattle were reported to be 42 pg/L. Estimate the fish-specific BAF (in units of L/kg) for (a)
cutthroat with a measured fish concentration of 375 ppb, (b) yellow perch with a measured fish
concentration of 191 ppb, and (c) pikeminnows which have a measured fish concentration of
1,000 ppb.
Solution:
5.47 Go to the IPCC Web site (www.ipcc.ch). Choose a specific ecosystem to study, and use
information from the Web site to research the impact of climate change on that ecosystem. Write
a one-page essay (properly referenced) summarizing your findings.
Solution:
Students’ responses will vary.
5.48 Biofuels are being suggested as a method to close the carbon loop. Do a library and Internet
search on a particular type of biofuel. Write a one-page essay that addresses the link between
biofuels and the global carbon cycle. Also address the impact that your particular biofuel may
have on water quality, food supply, biodiversity, and air quality.
Solution:
Students’ responses will vary.
5.49 According to the U.S. Environmental Protection Agency, mountain top coal mining
consists of removal of mountaintops to expose coal seams and subsequent disposal of the
associated mining overburden in adjacent valleys (see http://www.epa.gov/region3/mtntop/). In
your own words, discuss the environmental impacts associated with mountain top mining. How
does this relate to EPA’s Healthy Waters Priority Program and does this method of providing
energy fit into a sustainable future that considers social, environmental, and economic balance?
Solution:
Students’ responses will vary.
5.50 The U.S. Environmental Protection Agency defines a TMDL as the calculation of the
maximum amount of a pollutant that a waterbody can receive and still meet water quality
standards. The TMDL approach is a way to apply carrying capacity to a particular waterbody.
Under section 303(d) of the Clean Water Act, states, territories, and authorized tribes are
required to develop lists of impaired waters. Go the following web site
(http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/index.cfm) that lists the states which EPA
is under court order or agreed in a consent decree to establish TMDLs for. Produce a clear and
easy to read map of all 50 states that shows the locations of these states.
Solution:
Guam
47
State Name
Number of Waters on 303(d) List
North Dakota
201
Ohio
267
Oklahoma
723
Oregon
1,397
