Environmental Engineering 2

Question 1

A deer eats 25 kg of herbaceous material per day. The herbaceous matter is approximately 20%
dry matter (DM) and has an energy content of 10 MJ · (kg DM)−1
. Of the total energy ingested
per day, 25% is excreted as undigested material. Of the 75% that is digested, 80% is lost to metabolic waste products and heat. The remaining 20% is converted to body tissue.
How many megajoules are converted to body tissue on a daily basis? Calculate the percentage of energy consumed that is converted to body tissue

Answer 1

15%

Question 2

The concentration of the pesticide DDT was found to be 5 g · L−1 in the water of a pond. The
bioconcentration factor for DDT is 54,000 L · kg−1 (U.S. EPA, 1986). What is the expected concentration of DDT in the fish living in the pond?

Answer 2

270 mg · kg−1

Question 3

A farmer has a 7-year rotation of corn, soybeans, and wheat and 4 years of alfalfa. Manure will
be applied before corn and wheat and before seeding to alfalfa. The initial soil test results indicate total phosphorus level of 48 kg P · hectare−1. Manure is to be surface-applied in mid-March
and disk-incorporated within 2 days of application. One-third of the organic nitrogen and 50% of
the nitrogen from NH4 is available to the corn crop. To obtain the desired yield of corn, the local
extension agent has told the farmer to apply 100 kg of nitrogen per hectare.

Answer 3

20,000 kg manure per hectare

Question 4

If the initial density of bacteria is 104 cells per liter at the end of the accelerated growth phase,
what is the number of bacteria after 25 generations?

Answer 4

3.4 × 1011 cells · L−1

Question 5

Greenlawn Lake has a surface area 2.6 × 106 m2
. The average depth is 12 m. The lake is fed by a
stream having a flow rate of 1.2 m3 · s−1 and a phosphorus concentration of 0.045 mg · L−1. Runoff from the homes along the lake adds phosphorus at an average annual rate of 2.6 g · s−1. The settling rate of the lake is 0.36 day−1
. A river flows from the lake at a flowrate of 1.2 m3 · s−1. What is the steady-state concentration of phosphorus in the lake? What is the trophic state of the lake?

Answer 5

20 g · L−1

Question 5

A population of humanoids on the island of Huronth on the Planet Szacak has a net birth rate (b) of
1.0 individuals/(individual × year) and a net death rate (d) of 0.9 individuals/(individual × year).
Assume that the net immigration rate is equal to the net emigration rate. How many years are
required for the population to double? If in year zero, the population on the island is 85, what is
the population 50 years later?

Answer 5

12,615 humanoids

Question 5

opulation of spotted wolves lives on the mountain Hesperides. There were 26 wolves in the year 2054
and 54 wolves counted in 2079. Assuming exponential growth, what is the net growth rate constant?

Answer 5

0.029 year−1

Question 5

A population of purple rabbits lives on the island of Zulatop. The rabbits have a net growth rate of 0.09 year−1
.
At the present time there are 176 rabbits on the island. What is the predicted number of rabbits 5, 10, and
20 years from now? Use the simple exponential growth equation to calculate the number of rabbits.

Answer 5

P(5) = 276 rabbits P(10) = 433 P(20) = 1,065

Question 6

Using the data presented in Problem 5–3, a net growth rate of 0.04 year−1 and a carrying capacity of 159,
what will be the predicted population of wolves in the year 2102?

Answer 6

91 wolves

Question 7

The initial density of bacteria is 15,100 cells per liter at the end of the accelerated growth period. What is
the density of bacteria (cells per liter) after 28 generations?

Answer 7

4.053 × 10^12

Question 8

Suppose there is a grove of 1334 Asphodel plants on Prometheus Island located in Andarta Lake. The trees are growing with an r of 0.21 individuals/(individual × year). The carrying capacity on the island is 3250. What is the population in 35 years, assuming a logistic growth model applies?

Answer 8

3247

Question 9

You have been conducting a water quality study of Lake Arjun, which has a surface area of 8.9 × 105 m2. The average depth of the lake is 9 m. The lake is fed by a stream having a flow rate of 1.02 m3 · s−1 and a phosphorus concentration of 0.023 mg · L−1 . Runoff from the homes along the lake adds phosphorus at an average annual rate of 1.25 g · s−1 . The river flows from the lake at a flow rate of 1.02 m3 · s−1. The average phosphorus concentration in the lake is 13.2 g · L−1 . Assume evaporation and precipitation negate each other. What is the calculated average settling rate of phosphorus?

Answer 9

1.19 × 10−5 s−1 or 376 year−1

Question 10

The concentration of the pentachlorophenol has been measured to be 42.8 g · L−1 in Adonis Pond. A study
of the Matsu fish revealed an average lipid concentration of 30,600 g · kg−1 . What is the bioconcentration
factor for this fish?

Answer 10

715

Question 11

One of the congeners of toxaphene, a persistent pesticide that was used on cotton, is 1,2,3,4,7,7-
heptachloro-2-norbornene. The bioconcentration factor for this chemical in fish was determined to be
11,200 L · kg−1. If the concentration is 1.1 ng · L−1 in Lake Greenway, determine the estimated concentration in fish in g · kg−1.

Answer 11

12.3 ug L

Question 12

Farmer Tapio is raising deer. She has 110 female deer age 3–15 months. The deer require 22 MJ of
metabolizable energy per day during the spring months. The deer are being fed a mixture of 50% wheat and 50% silage. The wheat contains 85% dry matter (DM) and has 12.5 MJ metabolizable energy per kilogram of DM. The silage has 30% dry matter and 10.5 MJ metabolizable energy per kilogram of DM. calculate the energy (in megajoules) converted to body tissue on a daily basis. Assume that
19% of the feed consumed is excreted as undigested material. Of the remaining 81% that is digested, 78% is
used in generating metabolic waste products and heat. The remaining 22% is incorporated into tissue.

Answer 12

3.92 /day

Question 13

Estimate the lifetime average chronic daily intake of benzene from exposure to a city water
supply that contains a benzene concentration equal to the drinking water standard. The allowable drinking water concentration (maximum contaminant level, MCL) is 0.005 mg · L−1
.
Assume the exposed individual is an adult male who consumes water at the adult rate for
63 years*, that he is an avid swimmer and swims in a local pool (supplied with city water) 3 days
a week for 30 minutes from the age of 30 until he is 75 years old. As an adult, he takes a long
(30 minutes) shower every day. Assume that the average air concentration of benzene
during the shower is 5 µg · m−3 (McKone, 1987). From the literature, it is estimated that the
dermal uptake from water is 0.0020 m3 · m−2 · h−1. (This is PC in Table 6–6. PC also has units
of m · h−1 or cm · h−1.) Direct dermal absorption during showering is no more than 1% of the
available benzene because most of the water does not stay in contact with skin long enough
(Byard, 1989).

Answer 13

1.74 × 10−4 mg / kg day

Question 14

Estimate the chronic daily intake of toluene from exposure to a city water supply that contains a toluene concentration equal to the drinking water standard of 1 mg · L−1. Assume the exposed individual is an adult
female who consumes water at the adult rate for 70 years, that she abhors swimming, and that she takes a long (20 minute) bath every day. Assume that the average air concentration of toluene during the bath is 1 µg · m−3 . Assume the dermal uptake from water (PC) is 9.0 × 10−6 m · h−1 and that direct dermal
absorption during bathing is no more than 80% of the available toluene because she is not completely submerged. Use the EPA lifetime exposure of 75 years.

Answer 14

3.3 × 10−2 mg /kg day

Question 15

Characterize the hazard index for a chronic daily exposure by the water pathway (oral) of 0.03 mg / kg d of toluene, 0.06 mg / kg · d of barium, and 0.3 mg · kg · d of xylenes.

Answer 15

HI = 1.95

Question 16

Sulis Lake has a surface area of 708,000 m2
. Based on collected data, Okemos Brook flows into the lake at an average rate of 1.5 m3 · s−1 and the Tamesis River flows out of Sulis Lake at an average rate of 1.25 m3 · s−1 during the month of June. The evaporation rate was measured as 19.4 cm · month−1
. Evapotranspiration can be ignored because there are few water plants on the
shore of the lake. A total of 9.1 cm of precipitation fell this month. Seepage is negligible. Due to the dense forest and the gentle slope of the land surrounding the lake, runoff is also negligible. The average depth in the lake on June 1 was 19 m. What was the average depth on June 30th?

Answer 16

0.81 m − month

Question 17

In 1997, the Upper Grand watershed near Lansing, Michigan, with an area of 4530 km2 received 77.7 cm of precipitation. The average rate of flow measured in the Grand River, which drained the watershed, was 39.6 m3 · s−1
. Infiltration was estimated to occur at an average rate of 9.2 × 10−7 m · s−1. Evapotranspiration was estimated to be 45 cm · year−1
. What is the change in storage in the watershed?

Answer 17

0.36

Question 18

Anjuman’s Lake has a surface area of 70.8 ha. For the month of April the inflow was 1.5 m3 · s−1
.The dam regulated the outflow (discharge) from Anjuman’s Lake to be 1.25 m3 · s−1. If the precipitation recorded for the month was 7.62 cm and the storage volume increased by an estimated 650,000 m3, what is the estimated evaporation in cubic meters and centimeters? Assume that no water infiltrates into or out of the bottom of Anjuman’s Lake.

Answer 18

7.6 cm

Question 19

During April, the wind speed over Anjuman’s Lake was estimated to be 4.0 m · s−1. The air temperature averaged 20◦C, and the relative humidity was 30%. The water temperature averaged 10◦C. Estimate the evaporation rate using the Dalton’s equation.

Answer 19

77.1 mm, or 7.7 cm

Question 20

You are working for a construction company and are building a school. In digging the foundation
you find water at 7 m bgs. One hundred meters away, you find water at 7.5 m bgs. Choose the
datum as the confining layer that is 25 m bgs. What is the piezometric surface at each point, the
direction of groundwater flow, and the hydraulic gradient? Note: This assumes that the confining
layer is parallel to the surface, which may or may not be true; however, assuming this allows us
to simplify a complicated problem.

Answer 20

0.005 m · m−1

Question 21

Let’s assume that in the previous example, the aquifer is coarse sand and that the cross-sectional area of the aquifer through which water flows is 925 m2. What is the Darcy velocity of groundwater in this aquifer? What is the specific discharge?

Answer 21

275.65 m3 / day

Question 22

The geological material in the column shown in Figure 7–26 is coarse sand. The piezometric surfaces, h1 = 10 cm and h2 = 8.0 cm. The distance between the two points where h1 and h2 were measured is 10.0 cm. The cross-sectional area is 10 cm2. What is the linear velocity of the water flowing through the column?

Answer 22

4.6 × 10−4 m/ s

Question 23

An artesian aquifer 10.0 m thick with a piezometric surface 40.0 m above the bottom confining layer is being pumped by a fully penetrating well. Steady state drawdowns of 5.00 m and 1.00 m, were observed at two nonpumping wells located 20.0 m and 200.0 m, respectively, from the pumped well. The pumped well is being pumped at a rate of 0.016 m3 · s−1
. Determine the hydraulic conductivity of the aquifer.

Answer 23

1.50 × 10−4 m / s

Question 24

A 0.50-m diameter well fully penetrates an unconfined aquifer, which is 30.0 m thick. The drawdown at the pumped well is 10.0 m and the hydraulic conductivity of the gravel aquifer is
6.4 × 10−3 m / s. If the flow is steady and the discharge is 0.014 m3 /s. Determine the drawdown at a site 100.0 m from the well.

Answer 24

9.90 m

Question 25

Lake Kickapoo, TX, is approximately 12 km in length by 2.5 km in width. The inflow for the month of April is 3.26 m3 · s−1 and the outflow is 2.93 m3/ s. The total monthly precipitation is 15.2 cm and the evaporation is 10.2 cm. The seepage is estimated to be 2.5 cm. Estimate the change in storage during the month of April.

Answer 25

1.61 × 106 m3

Question 26

Using the values of fo, fc, and k for a Dothan loamy sand, find the infiltration rate at times of 12, 30, 60, and 120 min. Compute the total volume of infiltration over 120 min in an area 1 m2. Assume that the rate of precipitation exceeds the rate of infiltration throughout the storm event.

Answer 26

Rates are 83, 77, 72, and 68 mm · h−1 for times of 12, 30, 60, and 120 min

Question 27

Using the empirical equation developed for Lake Hefner (Equation 7–8), estimate the evaporation from a lake on a day that the air temperature is 30◦C, the water temperature is 15◦
C, the wind speed is 9 m /s, and the relative humidity is 30%.

Answer 27

4.7 mm/ day

Question 28

Four monitoring wells have been placed around a leaking underground storage tank. The wells are located at the corners of a 1-ha square. The total piezometric head in each of the wells is as follows: NE corner, 30.0 m; SE corner, 30.0 m; SW corner, 30.6 m: NW corner 30.6 m. Determine the magnitude and direction of the hydraulic gradient.

Answer 28

Hydraulic gradient = 6 × 10−3 m · m−1
; direction is from west to east.

Question 29

A gravelly sand has hydraulic conductivity of 6.1 × 10−4 m · s−1, a hydraulic gradient of 0.00141 m · m−1, and a porosity of 20%. Determine the Darcy velocity and the average linear velocity.

Answer 29

Darcy velocity = 8.6 × 10−7 m · s−1
; average linear velocity = 4.3 × 10−6 m · s−1
.

Question 30

A fully penetrating well in a 28.0-in thick artesian aquifer pumps at a rate of 0.00380 m3 · s−1 for 1,941 days (assume to be sufficient to obtain steady state conditions) and causes a drawdown of 64.05 m at an observation well 48.00 m from the pumping well. How much drawdown will occur at an observation well 68.00 m away? The original piezometric surface was 94.05 m above the bottom confining layer. The aquifer material is sandstone. Report your answer to two decimal places.

Answer 30

S2 = 51.08 m

Question 31

Awell with a 0.25-m diameter fully penetrates an unconfined aquifer that is 20 m thick. The well has a discharge of 0.015 m ·s−1 and a drawdown of 8 m. If the flow is steady and the hydraulic conductivity is 1.5 × 10−4m ·s−1, what is the height of the piezometric surface above the confining layer at a site 80 in from the well?

Answer 31

S = 1.9 × 10−5

Question 32

Estimate the percent growth of the global population from 2010 to 2050 using the following
assumptions: crude birth rate ∼20 per 1000 people, crude death rate ∼8 per 1000 people,
population ∼6,892,000,000 or 6.892 × 109 (PRB, 2010).

Answer 32

61.6 or about 62%

Question 33

Estimate the risk of a 100-year return period event occurring by the year 2100 if the current year is 2010.

Answer 33

0.60

Question 34

In 2004, the international consumption of coal for energy was 120.8 EJ (EIA, 2006). Assuming
the 2004 demand remains constant, how long will world reserves last? The average world
consumption of coal-based energy increased 5.15% per year from 2000 to 2004. If that rate of
increase remains constant, how long will world reserves last?

Answer 34

44.7 or 45 years

Question 35

A coal-fired power plant converts about 33% of the coal’s energy into electrical energy. For a
large 800-MW electrical output, estimate the volume of ash that is produced in a year if the
anthracite coal has a NHV of 31.5 MJ · kg−1, an ash content of 6.9%, and the bulk density of the
ash is about 700 kg · m−3. Assume that 99.5% of the ash is captured by a combination of the air
pollution control equipment and settling in the combustion chamber.

Answer 35

2.4 × 105 m3 · year−1

Question 35

A coal-fired power plant converts about 33% of the coal’s energy into electrical energy. For a
large 800-MW electrical output, estimate the volume of ash that is produced in a year if the
anthracite coal has a NHV of 31.5 MJ · kg−1, an ash content of 6.9%, and the bulk density of the
ash is about 700 kg · m−3. assuming that 15% of the waste heat goes up the stack and that 85% must be removed by cooling water, estimate the flow rate of cooling water required if the change in temperature of the cooling water is limited to 10◦ C. If the stream has a flow rate of 63 m3 · s−1 and a temperature of 18◦C above the intake to the power plant, what is the temperature after the cooling water and the stream water have mixed?

Answer 35

23.23, or 23◦C.

Question 35

The Hoover Dam on the Colorado River at the Arizona–Nevada border is the highest dam in the
United States. It has a maximum height of 223 m and a storage capacity of about 3.7 × 1010 m3.
What is the potential energy of the Hoover Dam and reservoir? If the maximum discharge is
950 m3 · s−1, what is the electrical capacity of the generating plant?

Answer 35

2080 MW

Question 35

A typical residential construction from the 1950s consisted of the layers shown in the drawing.
Estimate the heat loss with the existing insulation scheme and with an additional 20 cm of
organic bonded-glass fiber insulation, if the indoor temperature is to be maintained at 20◦
C and the outdoor temperature is 0◦C.

Answer 35

1.57 W

Question 35

In 2002, the international production of iron was 1080 Tg. Assuming the 2002 demand remains
constant, how long will world reserves last? World production increased 2.85% from 2001 to
2002. If that rate of increase remains constant, how long will world reserves last?

Answer 35

40.08 or 40 years

Question 36

Estimate the amount of waste rock generated in producing 100 kg of copper from an ore containing 0.5% copper

Answer 36

200,000 kg

Question 37

Assume that you could track a single aluminum beverage can (with a mass of 16 g) through several cycles of reclamation and that a 10% “loss” occurred in each recovery cycle. How much new aluminum must be supplied to replace the loss at the end of the third reclamation?

Answer 37

4.336, or 4.3 g

Question 38

Assume that you could track a single aluminum beverage can (with a mass of 16 g) through several cycles of reclamation and that a 10% “loss” occurred in each recovery cycle. What is the equivalent mass of aluminum saved if the beverage can recycled an infinite number of times?

Answer 38

160 g

Question 39

Using the USLE estimate, determine the annual soil loss for a farm in central Indiana that has a
Marshall silt loam with a slope of 2% and an average slope length of 91.5 m. The land is in
continuous corn cultivation, and the farmer uses conventional tillage up and down the slope and
leaves the residue.

Answer 39

5.98 or 6 Mg / ha

Question 40

It has been estimated that at 2004 consumption rates, the world’s petroleum reserve will last 37.5 years. Estimate the world consumption rate in 2004

Answer 40

176 EJ / year

Question 41

A house built in the 1950s has 14.86 m2 of single-glazed windows. Estimate the heat loss with the existing single-glazed window and the loss if the windows are replaced with (a) double-glazed, and (b) triple-glazed windows. Assume the indoor temperature is 20°C and the outdoor temperature is 0°C

Answer 41

Single-glaze = 1.86 × 103 W; double-glaze = 9.29 × 102 W

Question 42

A university computer lab has 32 machines. Each machine draws 400 W of power, most of which is given
off as heat. Assuming that 100% of the electrical demand is given off as heat, estimate the amount of energy
that is wasted each year if the computers are left running during the 8 hours at night that the lab is closed.
(Note that the computers draw virtually as much power when they are in the “sleep mode” as they do when
they are active.)

Answer 42

135 GJ

Question 43

One author has estimated that the time until exhaustion for aluminum is 156 years if the world production remains constant. What is the annual demand based on this estimate?

Answer 43

160 Tg /year

Question 44

In 2004, the United States produced 54.9 Tg of iron from ore with an iron content of 63.0%. Estimate the amount of waste rock generated in mining this ore if the production remains constant until the U.S. reserve is depleted.

Answer 44

3330 Tg or 3.33 Pg

Question 45

If the decay constant for recovery of a metal is 0.0202 cycle−1, what is the percent recovery for each cycle?

Answer 45

98%

Question 46

In 2004, the U.S. Geological Survey estimated that 29% of the demand for copper in the United States was supplied by recycled copper. If the demand for copper remains constant at the 2002 rate of 2.6 Tg per year, how many years will be added to the time until exhaustion of the U.S. reserve?

Answer 46

Ts = 46.42 or 46 years

Question 47

Compute the ThOD of 108.75 mg · L−1 of glucose (C6H12O6).

C6H12O6 + 6O2 −→ 6CO2 + 6H2O

Answer 47

116 mg / L O2

Question 48

If the 3-day BOD (BOD3) of a waste is 75 mg / L1 and the BOD decay constant, k, is 0.345 /day
,what is the ultimate BOD?

Answer 48

116 mg / L1

Question 49

A waste is being discharged into a river that has a temperature of 10◦C. What fraction of the maximum oxygen consumption has occurred in 4 days if the BOD rate constant, k, determined in the laboratory under standard conditions is 0.115 day−1
?

Answer 49

0.12

Question 50

The BOD of a wastewater sample is estimated to be 180 mg · L−1. What volume of undiluted
sample should be added to a 300-mL bottle? Also, what are the sample size and dilution factor
using this volume? Assume that 4 mg · L−1 BOD can be consumed in the BOD bottle.

Answer 50

Dilution factor =0.0233 1.2 mg

Question 51

(a) Compute the theoretical NBOD of a wastewater containing 30 mg · L−1 of ammonia as nitrogen.
(b) If the wastewater analysis was reported as 30 mg · L−1 of ammonia (NH3), what would the
theoretical NBOD be?

Answer 51

113 mg O2 / L

Question 52

The town of Aveta discharges 17,360 m3 · day−1 of treated wastewater into the Tefnet Creek. The
treated wastewater has a BOD5 of 12 mg /L1 and a BOD decay constant, k, of 0.12 /day at 20◦C. Tefnet Creek has a flow rate of 0.43 m3 / s and an ultimate BOD, Lo, of 5.0 mg /L. The DO of the river is 6.5 mg /L and the DO of the wastewater is 1.0 mg / L. Compute the DO and initial ultimate BOD, Lo, after mixing.

Answer 52

11.86, or 12 mg / L

Question 53

A stream containing no biochemical oxygen demand (this is a hypothetical situation and rarely occurs) has a DO of 5.00 mg /L and a flow rate, Q, of 8.70 m3 /s. The temperature of the stream is 18◦C. The average velocity in the stream is 0.174 m / s. The average depth, H, of the stream is 5 m. Determine the reaeration coefficient, kr, and the rate of reaeration.

Answer 53

0.632 mg / L · day

Question 54

Determine the deoxygenation rate constant for the reach of Tefnet Creek (Examples 9–7 and 9–8)
below the wastewater outfall (discharge pipe). The average speed, u, of the stream flow in the
creek is 0.03 m · s−1. The depth, h, is 5.0 m and the bed-activity coefficient, , is 0.35. What is
the rate of deoxygenation, in units of mg / L · day?

Answer 54

0.408 mg /L day

Question 55

A city of 200,000 people disposes of 1.05 m3 · s−1 of treated sewage that still has a BODu of
28.0 mg / L and 1.8 mg / L of DO into a river. Upstream from the outfall, the river has a
flowrate of 7.08 m3 / s and a velocity of 0.37 m · s. At this point, the BODu and DO in the
river are 3.6 and 7.6 mg · L, respectively. The saturation value of DO (at the temperature of the
river) is 8.5 mg /L. The deoxygenation coefficient, kd, is 0.61 day, and the reaeration coefficient, kr, is 0.76 day. Assume complete mixing and that the velocity in the river is the same upstream and downstream of the outfall

Answer 55

Initial deficit = 1.6 mg / L
DO = 5.9 mg / L

Question 56

Acidic rainfall infiltrates into a geological formation that is predominantly dolomite, a commonly occurring rock-forming mineral. In 1940, the average pH of the groundwater was 6.6. By 1995, the average yearly groundwater pH was 5.6. Assuming that as the groundwater percolates through the dolomite it is at equilibrium, calculate the calcium and magnesium at the two pHs. Assume that the temperature is 25◦C and that the concentration of calcium, magnesium, and carbonate in the rainwater is negligible.

Answer 56

pH 5.6, s = 0.0207 M = [Ca2+] = [Mg2+]

Question 56

A chemical analysis has revealed the following composition for the rain falling on the city of
Thule.
1.38 mg · L−1 HNO3
3.21 mg · L−1 H2SO4
0.354 mg · L−1 HCl
0.361 mg · L−1 NH3
What is the pH of the rainwater?

Answer 56

[OH−]= 1.32 × 10^−10 M

Question 57

Two houses are located adjacent to each other. House A has a septic system located 60 m upgradient from the drinking water well for house B. The owner of house A disposed of a pesticide down the drain, causing the septic field to become contaminated with this pesticide. The linear velocity of the water in the unconfined aquifer used for drinking water is 4.7 × 10−6 m /s. Assuming that the pesticide does not degrade in the soil and that it has a retardation coefficient of 2.4, how many days will it take for the pesticide to reach the well of house B?

Answer 57

354 days

Question 58

Glutamic acid (C5H9O4N) is used as one of the reagents for a standard to check the BOD test. Determine the theoretical oxygen demand of 150 mg · L−1 of glutamic acid. Assume the following reactions apply.
C5H9O4N + 4.5O2 −→ 5CO2 + 3H2O + NH3
NH3 + 2O2 −→ NO−3 + H+ + H2O

Answer 58

212 mg /L

Question 59

The company you work for plans to release a waste stream containing 7.0 mg · L−1 of benzaldehyde. Assuming that benzaldehyde degrades according the reaction:
C7H6O + 8O2 −→ 7CO2 + 3H2O
calculate the theoretical carbonaceous oxygen demand of this waste stream (in mg · L−1).

Answer 59

16.906 mg / L

Question 60

If the BOD5 of a waste is 220.0 mg · L−1 and the ultimate BOD is 320.0 mg · L−1, what is the rate constant?

Answer 60

k = 0.233 /day

Question 61

The BOD rate constant is 0.233 day−1 for a municipal wastewater. The BOD5 was measured to be 250 mg · L−1. What is the ultimate BOD?

Answer 61

363 mg /L

Question 62

A sample of municipal sewage is diluted to 1% by volume prior to running a BOD5 analysis. After 5 days the oxygen consumption is determined to be 2.00 mg · L−1. What is the BOD5 of the sewage?

Answer 62

BOD5 = 200 mg /L

Question 63

If the ultimate BOD values of two wastes having k values of 0.3800 day−1 and 0.220 day−1 are
280.0 mg · L−1, what would be the 5-day BOD for each?

Answer 63

k = 0.38 /day
, BOD5 = 238 mg / L ; for k = 0.22 /day
, BOD5 = 187 mg / L

Question 64

The following data are provided to you:
Seeded wastewater:
Initial DO = 8.6 mg · L−1
Final DO (after 5 days) = 2.1 mg · L−1
Volume of wastewater = 2.5 mL
Total volume in BOD bottle = 300.0 mL

Seeded dilution water:
Initial DO = 8.6 mg · L−1
Final DO (after 5 days) = 7.3 mg · L−1
Volume of seeded dilution water = 300.0 mL
T = 20◦C. Calculate the BOD of the sample (in units of mg · L−1 ).

Answer 64

625 mg / L

Question 65

The Waramurungundi tannery with a wastewater flow of 0.011 m3 / s and a BOD5 of 590 mg/ L discharges into the Djanggawul Creek. The creek has a 10-year, 7-day low flow of 1.7 m3 / s. Upstream of the Waramurungundi tannery, the BOD5 of the creek is 0.6 mg / L. The BOD rate constants (k) are 0.115 /day for the Waramurungundi tannery and 3.7 / day for the creek. Calculate the initial ultimate BOD
after mixing.

Answer 65

9.27 mg /L

Question 66

The initial ultimate BOD after mixing of the Bergelmir River is 12.0 mg · L−1. The DO in the Bergelmir River after the wastewater and river have mixed is at saturation. The river temperature C. At 10◦C, the deoxygenation rate constant (kd) is 0.30 day−1, and the reaeration rate constant (kr) is 0.40 day−1. Determine
the critical point (tc) and the critical DO.

Answer 66

tc = 2.88 days. Critical DO = 7.53 mg · L−1

Question 67

The discharge from the Renenutet sugar beet plant causes the DO at the critical point to fall to 4.0 mg · L−1. The Meskhenet Stream has a negligible BOD and the initial deficit after the river and wastewater have mixed is zero. What DO will result if the concentration of the waste (Lw) is reduced by 50%? Assume that the flows remain the same and that the saturation value of DO is 10.83 mg · L−1 in both cases

Answer 67

DO = 7.4 mg · L−1

Question 68

What combination of BOD reduction and wastewater DO increase is required so the Audhumla wastewater in Problem 9–28 does not reduce the DO below 5.00 mg · L−1 anywhere along the Einherjar River? Assume that the cost of BOD reduction is three to five times that of increasing the effluent DO. Because the cost of
adding extra DO is high, limit the excess above the minimum amount such that the critical DO falls between 5.00 and 5.25 mg · L−1.

Answer 68

Raising the wastewater DO to 2.7 mg · L−1 is the most cost-effective remedy

Question 69

Assuming that the mixed oxygen deficit (Da) is zero and that the ultimate BOD (Lr) of the Manco Capac River above the wastewater outfall from Urcaguary is zero, calculate the amount of ultimate BOD (in kg · day−1) that can be discharged if the DO must be kept at 4.00 mg · L−1 at a point 8.05 km downstream. The stream deoxygenation rate (kd) is 1.80 day−1 at 12◦C, and the reaeration rate (kr) is 2.20 day−1
at 12◦ C. The river temperature is 12◦C. The river flow is 5.95 m3 · s−1 with a speed of 0.300 m · s−1. The Urcaguary wastewater flow is 0.0130 m3 · s−1.

Answer 69

Mass flux = 1.14 × 104 kg · day−1 of ultimate BOD

Question 70

Assume that the Urcaguary wastewater also contains 3.0 mg · L−1 of ammonia nitrogen with a stream deoxygenation rate of 0.900 day−1 at 12◦C. What is the amount of ultimate carbonaceous BOD (in kg · day−1 ), that Urcaguary can discharge and still meet the DO level of 4.00 mg · L−1 at a point 8.05 km downstream? Assume also that the theoretical amount of oxygen will ultimately be consumed in
the nitrification process

Answer 70

Mass flux = 6.2 × 103 kg · day−1

Question 71

A chemical contaminates an aquifer. The average linear velocity of water in the aquifer is 2.650 ×
10−7 m · s−1. The aquifer has a porosity of 48.0%. The chemical has a retardation coefficient of 2.65. Calculate the average linear velocity of the pollutant (in m · s−1).

Answer 71

1.00e-07 m · s−1

Question 72

A small lake is surrounded by agricultural land. The lake is 150 m long and 120 m wide. The average depth is 30 m. The lake is fed by a small pollution-free stream having an average flow rate of 1.5 m3 · s−1. A herbicide, Greatcrop, is detected at a concentration of 45.2 g · L−1 in the lake. Greatcrop degrades biologically with a rate constant of 0.22 day−1 . Assuming that the lake is at steady-state conditions and completely mixed at the time of sampling, what would have been the mass input of herbicide? Assume that the stream is the only source of water to the lake and that evaporation, precipitation, and seepage can be neglected.

Answer 72

11.2 kg · day−1

Question 72

A water treatment plant with an average flow of Q = 0.044 m3 · s−1 treats its water with alum
(Al2(SO4)3 · 14H2O) at a dose of 25 mg · L−1. Alum coagulation is used to remove particulate
matter, reduce the concentration of organic matter, and reduce the alkalinity of the water according to Equation 10–1. If the organic matter concentration is reduced from 8 mg · L−1 to
3 mg · L−1, determine the total mass of alkalinity consumed and the total mass of dry solids
removed per day

Answer 72

61.2 kg · day−1

Question 73

The groundwater mentioned in Example 10–5 contains 2.3 × 10−5 M CO2. It also contains
300 mg · L−1 as CaCO3 of carbonate hardness due to calcium and 50 mg · L−1 as CaCO3 of carbonate hardness due to magnesium. It is treated at the same rates mentioned in Example 10–5. You are to remove all of the carbonate hardness due to calcium but do not need to remove the magnesium ions. Assume that you remove all but 20 mg · L−1 (as CaCO3) of the calcium ions. What mass of calcium carbonate sludge is produced on a daily basis?

Answer 73

9690 kg · day−1 of CaCO3

Question 73

The abandoned Catequil Street Water Treatment Plant is to be turned into a research facility treating 0.044 m3 · s−1. A low-turbidity iron coagulation plant has been proposed with the following design parameters:

Answer 73

13.4 min

Question 74

A home water softener has 0.1 m3 of ion-exchange resin with an exchange capacity of
62 kg · m−3. The four home residents each use water at a rate of 400 L · day−1. The well water
they are using contains 340.0 mg · L−1 of hardness as CaCO3. It is desirable to soften it to
achieve a total hardness of 100 mg · L−1 as CaCO3. What should the bypass flow rate be?

Answer 74

470.6, or 471 L · day−1

Question 74

As part of a proposed new research treatment plant, Dr. Novella is planning to use rapid sand filtration after sedimentation. Dr. Novella plans to use two banks of sand filters. Each filter bed has a surface area of 3 m × 2 m. The design flow rate to each bank of filters is 0.044 m3 · s−1
. The design loading rate to each bank of filters is 150 m3 · day−1 m−2.
Determine the number of filter beds in each bank of filters. Determine the loading rate when
one filter is out of service.

Answer 74

Va= 211.4 m · day−1

Question 75

A research-scale water treatment plant uses low-turbidity raw water and is designing its overflow
weir at a loading rate of 175 m3 · day−1 m−1. If its plant flow rate is 0.044 m3 · s−1, how many
linear meters of weir is required?

Answer 75

21.7, or 22 m

Question 76

The design flow and overflow rates for a settling tank are 0.044 m3 · s−1 and 20 m · day−1,
respectively. Determine the surface area of this tank. Determine the length of the tank, using
conventional wisdom for length-to-width ratios. Determine the tank depth, assuming a detention
time of 2 hours.

Answer 76

Depth = 1.684 m, or 1.7 m

Question 77

A desalination plant treats sea water with a salt concentration of 30,000 mg · L−1 at a flow rate of
1.5 m3 · s−1
. The recovery is 70%. The salt rejection is 99.5%. Determine the concentration of
salt in the concentrate stream.

Answer 77

Cc = 99,650 mg · L−1

Question 78

A coagulation treatment plant with a flow of 0.044 m3 · s−1 is dosing alum at 33.0 mg · L−1. No other chemicals are being added. The raw water/suspended solids concentration is 47.0 mg · L−1. The effluent/suspended solids concentration is measured at 10.0 mg · L−1. The sludge solids content is 1.05%, and the specific gravity of the sludge solids is 2.61. What volume of sludge must be disposed of each day?

Answer 78

VT= 19.5 m3 · day−1

Question 79

A water treatment plant is to treat 0.1 m3
/s of water. Chlorine is to be used as a disinfectant. At the temperature and pH of the source water, a CT of 200 mg · min · L−1 is required. The t10 for the contact chamber is 100 min. The ratio of t10 to to is 0.7. What is the required volume of the reactor? Determine the necessary average chlorine concentration.

Answer 79

C= 2.0 mg/L

Question 80

You are to design a membrane system for the community of Red Bull. The design flow rate is
0.100 m3 · s−1. The temperature of the water ranges from 5◦C in winter to 22◦C in summer.
The membrane you have chosen has maximum TMP of 200 kPa and a resistance coefficient of
4.2 × 1012 m−1. Based on pilot testing, the operating TMP should be no greater than 80% of the maximum TMP. Determine the required membrane area.

Answer 80

A= 3987 m2 ≡ 4000 m2

Question 81

Determine the lime and soda ash dose, in mg/L as CaCO3, to soften the following water to a final hardness
of 80.0 mg/L as CaCO3. The ion concentrations reported below are all mg/L as CaCO3.
Ca2+ = 120.0
Mg2+ = 30.0
HCO−
3 = 70.0
CO2 = 10.0

Answer 81

Total lime addition = 100 mg/L as CaCO3
Total soda ash addition = 40 mg/L as CaCO3

Question 81

A water softener is used to treat well water that has a total hardness of 420 mg · L−1
. The design flow rate is 3.0 m3 · s with a total hardness of 100 mg · L−1. According to the manufacturer, the ion exchange resin used in
the water softener has a leakage of 1% (which means that the effluent concentration from the softener is 1% of the influent concentration). What is the required flow rate through the softener to achieve the desired hardness?

Answer 81

2.3 m3 · s−1

Question 82

Determine the terminal settling velocity of particle having a density of 2540 kg · m−3 and a diameter of 10 mm in water having a temperature of 10◦C.

Answer 82

64.2 m · s−1

Question 83

If a 1.0 m3 · s−1 flow water treatment plant uses ten sedimentation basins with an overflow rate of 15 m3 · day−1 · m−2 , what should be the surface area (m2) of each tank?

Answer 83

576.0 m2

Question 84

If a dual-media filter with a loading rate of 300 m3 · day−1 · m−2 were built instead of the standard filter in Problem 10–24, how many filter boxes would be required?

Answer 84

Four filters (rounding to next largest even number)

Question 85

A water treatment plant is to treat 0.1 m3
/s of water. Chloramines are to be used as the primary disinfectant.
At the temperature and pH of the source water, a CT of 1,250 mg · min · L−1 is required to achieve 2.5 log inactivation of Giardia cysts. The t10 for the contact chamber is 20 min. The ratio of t10 to to is 0.7. What is the required volume of the reactor? Determine the necessary average chloramine concentration.

Answer 85

Volume = 180 m3
Concentration = 62.5 mg · L−1

Question 85

Using Chick’s law determine the rate constant for the disinfection of E. coli. Initially, the number of organisms is 200 per 100 mL. After 10.0 min, the number is 15 per 100 mL. Assume that the concentration of the disinfectant is constant.

Answer 85

0.26 m−1

Question 86

You are to design a microfiltration membrane system for the community of Lastnight. The design flow rate is 0.960 m3 ·s−1. The temperature of the water is constant throughout the year at 10. The membrane you have chosen has maximum TMP of 230 kPa and a resistance coefficient of 3.5 × 1012 m−1. Based on pilot testing, the operating TMP should be no greater than 75% of the maximum TMP. Determine the required membrane area.

Answer 86

25,500 m2

Question 87

The town of Gatesville has been directed to upgrade its primary WWTP to a secondary plant that can meet an effluent standard of 30.0 mg · L−1 BOD5 and 30.0 mg · L−1 suspended solids. They have selected a completely mixed activated sludge system. Assuming that the BOD5 of the suspended solids may be estimated as equal to 63% of the suspended solids concentration, estimate the required volume of the aeration tank. The following data are available from the existing primary plant.
Existing plant effluent characteristics
Flow = 0.150 m3 · s−1
BOD5 = 84.0 mg · L−1
Assume the following values for the growth constants: Ks = 100 mg · L−1 BOD5; m = 2.5 day−1 kd = 0.050 day−1
; Y = 0.50 mg VSS · mg−1 BOD5 removed.

Answer 87

V = 972 m3, or 970 m3

Question 88

A water contains 50.40 mg · L−1 as CaCO3 of carbon dioxide, 190.00 mg · L−1 as CaCO3 of Ca2+ and 55.00 mg · L−1 as CaCO3 of Mg2+. All of the hardness is carbonate hardness. Using the stoichiometry of the lime soda ash softening equations, what is the daily sludge production (in dry weight, kg · day−1) if the plant treats water at a rate of 2.935 m3 · s−1 ? Assume that the effluent water contains no carbon dioxide, 30.0 mg · L−1 as CaCO3 of Ca2+ and 10.0 mg · L−1 as CaCO3 of Mg2+. Be sure to calculate the mass
of CaCO3 and Mg(OH)2 sludge produced each day.

Answer 88

123409 kg · day−1

Question 88

Will a grit particle with a radius of 0.04 mm and a specific gravity of 2.65 be collected in a
horizontal grit chamber that is 13.5 m in length if the average grit-chamber flow is 0.15 m3 · s−1
, the width of the chamber is 0.56 m, and the horizontal velocity is 0.25 m · s−1
? The wastewater temperature is 22◦C.

Answer 88

t= 54 s

Question 89

A water treatment plant is designed at a flow rate of 42.5 L · s−1. The water is to flow into two primary settling tanks operating in parallel. A detention time of 2.5 hours has been determined to be effective. Using a length to width ratio of 2:1 and an effective depth of 3.5 m, calculate the length of the tank in meters.

Answer 89

10.5 m

Question 90

Estimate the volume of air to be supplied (m3 · day−1) for the new activated sludge plant at
Gatesville (Examples 11–4 and 11–8). Assume that BOD5 is 68% of the ultimate BOD and that
the oxygen transfer efficiency is 8%.

Answer 90

38,774.9, or 38,000 m3 · day−1

Question 91

If a wastewater has a soluble orthophosphate concentration of 4.00 mg · L−1 as P, what theoretical amount of ferric chloride will be required to remove it completely?

Answer 91

20.95, or 21.0 mg · L−1

Question 92

Using the following primary settling tank data, determine the daily sludge production.
Operating Data
Flow = 0.150 m3 · s−1
Influent suspended solids = 280.0 mg · L−1 = 280.0 g · m−3
Removal efficiency = 59.0%
Sludge concentration = 5.00%
Volatile solids = 60.0%
Specific gravity of volatile solids = 0.990
Fixed solids = 40.0%
Specific gravity of fixed solids = 2.65

Answer 92

42.29, or 42.3 m3 · day−1

Question 93

One hundred cubic meters (100.0 m3
) of mixed sludge at 4.0% solids is to be thickened to 8.0% solids. Assuming that the specific gravity is not appreciably different from that of water and that it does not change during thickening, what is the approximate volume of the sludge after
thickening?

Answer 93

V2 = 50.0 m3

Question 94

If a particle having a 0.0170-cm radius and density of 1.95 g · cm−3 is allowed to fall into quiescent water having a temperature of 4◦
C, what will be the terminal settling velocity? Assume the density of water =1000 kg · m−3. Assume Stokes’ law applies.

Answer 94

3.82 × 10−2 m · s−1

Question 95

If the F/M of a 0.4380 m3 · s−1 activated sludge plant is 0.200 day−1, the influent BOD5 after primary settling is 150 mg · L−1, and the MLVSS is 2200 mg · L−1, what is the volume of the aeration tank?

Answer 95

Volume = 1.29 × 104 m3

Question 95

Using an overflow rate of 26.0 m · day−1 and a detention time of 2.0 h, size a primary sedimentation tank for the average flow at Cynusoidal City (Problem 11–3). What would the overflow rate be for the unequalized maximum flow? Assume 15 sedimentation tanks with length to width ratio of 4.7.

Answer 95

Tank dimensions = 15 tanks @ 2.17 m deep × 4.34 m × 20.4 m
Maximum overflow rate 39.3 m · day−1

Question 96

Determine the surface area of a primary settling tank sized to handle a maximum hourly flow of
0.570 m3 · s−1 at an overflow rate of 60.0 m · day−1. If the effective tank depth is 3.0 m, what is the effective theoretical detention time?

Answer 96

Surface area = 820.80, or 821 m2
; to= 1.2 h

Question 97

Two activated sludge aeration tanks at Turkey Run, Indiana, are operated in series. Each tank has the following dimensions: 7.0 m wide × 30.0 m long × 4.3 m effective liquid depth. The plant operating parameters are as follows:
Flow = 0.0796 m3 · s−1 MLVSS = 1500 mg · L−1
Soluble BOD5 after primary settling = 130 mg · L−1 MLSS = 1.40 (MLVSS)
Determine the following: aeration period, F/M ratio.

Answer 97

Aeration period = 6.3 h; F/M = 0.33 mg · mg−1 · d−1

Question 98

An Illinois coal is burned at a rate of 1.00 kg · s−1. If the analysis of the coal reveals a sulfur
content of 3.00%, what is the annual rate of emission of SO2?

Answer 98

SSO2 = 1.80 × 106 kg · year−1

Question 99

Given the following temperature and elevation data, determine the stability of the atmosphere.
Elevation Temperature
(m) (◦C)
2.00 14.35
324.00 11.13

Answer 99

−1.00◦C · 100 m−1

Question 99

Determine whether or not a pulverized coal, dry bottom, wall-fired boilers using bituminous coal
at a power plant rate at 61 MW meets the NSPS for SO2, particulate matter, and NOx. The power
plant burns bituminous coal with a sulfur content of 1.8% and ash content of 6.2%. The coal has
a heating value of 14,000 Btu/lb. The boiler efficiency is 35%. Use the EPA emission factors to
estimate the emissions. Assume the efficiency of SO2 control is 85% and the efficiency of particulate control equipment is 99%.

Answer 99

0.60 lbm/106 Btu.

Question 100

It has been estimated that the emission of SO2 from a coal-fired power plant is 1656.2 g · s−1.
At 3 km downwind on an overcast summer afternoon, what is the centerline concentration
of SO2 if the wind speed at the top of the stack (120.0 m) is 4.50 m · s−1? (Note: “centerline”
implies y = 0.)

Answer 100

= 1.45 × 10−3 g · m−3
, or 1.5 × 10−3 g · m−3 of SO2

Question 101

An unvented kerosene heater is operated for 1 h in an apartment having a volume of 200 m3
. The heater emits SO2 at a rate of 50 g · s−1
. The ambient air concentration (Ca) and the initial indoor air concentration (Co) of SO2 are 100 g · m−3 . If the rate of ventilation is 50 L · s−1
, and the apartment is assumed to be well mixed, what is the indoor air concentration of SO2 at the end of 1 h?

Answer 101

625.39, or 630 Ug · m−3

Question 102

Determine the stoichiometric air-to-fuel ratio for C7H13. Ignore constituents other than oxygen
and nitrogen in air and ignore the oxidation of nitrogen to nitrogen oxides

Answer 102

= 14.5

Question 103

A power plant in a college town is burning coal on a cold, clear winter morning at 8:00 A.M. with a wind speed of 2.6 m · s−1 measured at 30 m elevation and an inversion layer with its base at a height of 697 m. The effective stack height is 30 m. Calculate the distance downwind XL at which the plume released will reach the inversion layer and begin to mix downward.

Answer 103

5.8 km

Question 104

1 A town of 20,000 in Germany generates 0.95 kg · (capita)−1 · day−1 of MSW. A town of the same
size in the United States generates 1.9 kg ·(capita)−1 · day−1 of MSW.
1. How much MSW is generated in each town?
2. How many trucks would be needed to collect the waste twice weekly? The trucks each
have a capacity of 4.5 t (metric tonnes) and operate 5 days per week. Assume that the
trucks average two loads per day at 75% capacity.
3. If each of the towns recycles waste in percentages given in Figure 13–4, determine the
mass of MSW that enters the landfill. If the density of the waste is 280 kg · m−3
, what is the volume of MSW?

Answer 104

1. 38,000 kg · day−1
2. 7.88, or 8 trucks
3. 104.5 m3 · day−1

Question 105

Determine the area required for a new landfill site with a projected life of 30 years for a population of 250,000 generating 2.02 kg · (capita)−1 · day−1. The density of the compacted waste is 470 kg · m−3. The height of the landfill cannot exceed 15 m.

Answer 105

784,020 m2 , or 78.4 ha

Question 106

Calculate the volumetric flow rate of leachate through a compacted clay liner if the area of the
landfill is 15 ha and the liner thickness is 1 m. The hydraulic conductivity is 7.5 × 10−10 m · s−1
. Assume that the head of water is 0.6 m.

Answer 106

= 6.75 × 10−5 m3 · s−1

Question 106

A landfill with a gas collection system is in operation and serves a population of 200,000. MSW is generated at a rate of 1.95 kg · (capita)−1 · day−1. Gas is produced at an annual rate of
6.2 L · kg−1 of MSW delivered to the landfill. The gas contains 55% methane. Gas recovery is
15% of that generated. The heat content of the landfill gas is approximately 17,000 kJ · m−3
(a value lower than the theoretical value because of dilution of the methane with air during
recovery). The landfill company and a developer have proposed to build a subdivision in the
684 Chapter 13 Solid Waste Engineering
vicinity of the landfill and pipe the methane generated to the homes to be used for heating. The homes are estimated to use an average of 110 × 106 kJ of heat energy each year. Peak usage during winter is 1.5 times the average usage. How many homes can be built in the subdivision?

Answer 106

7.5 homes

Question 107

How much landfill space does Apocatequil County require for 20 years of operation? You may
assume that 142,000 persons are being served by this landfill and that each person generates
2.0 kg · day−1 of waste. The density of the uncompacted waste is 106 kg · m−3 and a compaction
ratio of 4.2 can be used. The ratio of cover to compacted fill is 1.9.

Answer 107

8,900,000 m3

Had we not considered the volume of cover material we would have determined the volume to be 4.66 × 106 m3.

Question 108

The Bailey Stone Works employs six people.Assuming that the density of uncompacted waste is 480 kg · m−3,
determine the annual volume of solid waste produced by the stone works assuming a waste generation rate of
1 kg · capita−1 · day.

Answer 108

4.6 m3 · year−1

Question 109

The Nairyosangha landfill located in Peshdadians serves a population of 562,400 people generating MSW at a rate of 1.89 kg · capita−1 · day. The volume of the landfill is 11,240,000 m3
. At the present time, 63% of the landfill is used. The ratio of cover to compacted fill is 1.9. Determine projected life remaining for the landfill. Assume the density of the compacted waste to be 490 kg · m−3
.

Answer 109

2.76 years

Question 110

A landfill that is 12 ha in area has a liner of thickness 0.9 m. Each year 1700 m3 of leachate is collected. The hydraulic conductivity of the liner is 3.9 × 10−10 m · s−1. What is the head of water above the liner?

Answer 110

1.04 m

Question 110

Calculate the volumetric flow rate of leachate through a compacted clay liner if the area of the landfill is 21 ha and the liner thickness is 1.3 m. The hydraulic conductivity is 2.5 × 10−10 m · s−1
. Assume that the head of water is 0.8 m.

Answer 110

2.8 m3 · day−1

Question 110

A metal plating firm is installing a precipitation system to remove zinc. They plan to use a pH meter to control the feed of hydroxide solution to the mixing tank. What pH should the controller be set at to achieve a zinc effluent concentration of 0.80 mg · L−1? The Ksp of Zn(OH)2 is 7.68 × 10−17.

Answer 110

8.399, or 8.4

Question 111

Well 12A at the City of Tacoma is contaminated with 350 g · L−1 of 1,l,2,2-tetrachloroethane.
The water must be cleaned to the detection limit of 1.0 g · L−1. Design a packed tower stripping
column to meet this requirement using the following design parameters.
Henry’s law constant = 5.0 × 10−4 atm · m3 · mol−1
Temperature = 25◦C
KLa = 10 × 10−3 s−1
Column diameter may not exceed 4.0 m
Air flow rate = 13.7 m3 · s−1
Liquid flow rate = 0.044 m3 · s−1
Column height may not exceed 6.0 m

Answer 111

ZT A = 29.69 m3

Question 112

How long will it take for leachate to migrate through a 0.9-m clay liner with a hydraulic conductivity of 1 × 10−7 cm · s−1 if the depth of leachate above the clay layer is 30 cm and the porosity of the clay is 55%?

Answer 112

t = 3.71 × 108 s, or about 12 years

Question 113

A dry cleaner accumulates 10 kg · month−1 of a hazardous waste solvent. To save shipping cost he would like to accumulate 6 months’ worth before he ships it to a TSD facility. Can he do this? Explain. (Note: This is a “trick” question that requires searching the applicable regulations in the CFR.)

Answer 113

Yes

Question 113

Determine whether the following is a RCRA hazardous waste: Municipal wastewater containing 2.0 mg · L−1
of selenium.

Answer 113

Not a hazardous waste

Question 114

A metal plating sludge as removed from a clarifier has a solids concentration of 4%. If the volume of sludge is 1.0 m3 · day−1
, what volume will result if the sludge is processed in a filter press to a solids concentration of 30%? If the pressed sludge is dried to 80% solids, what volume will result?

Answer 114

Press V−2 = 0.133 m3 · day−1; dryer V−2 = 0.05 m3 · day−1

Question 115

A vapor degreaser uses 590 kg · week−1 of trichloroethylene (TCE). It is never dumped. The incoming parts have no TCE on them and the exiting parts drag out 3.8 L · h−1 of TCE. The sludge removed from the bottom of the degreaser each week has 1.0% of the incoming TCE in it. The plant operates 8 h · d−1 for
5 d · week−1. Draw the mass balance diagram for the degreaser and estimate the loss due to evaporation (in kg · week−1). The density of TCE is 1.460 kg · L−1

Answer 115

Mevap. = 362.18 or 360 kg · week−1

Question 116

A hazardous waste incinerator is being fed methylene chloride at a concentration of 5858 mg · L−1 in a aqueous stream at a rate of 40.5 L · min−1. Calculate the mass flow rate of the feed in units of grams per
minute.

Answer 116

237.25 g · min−1

Question 117

Compute the mean sound level from the following four readings (all in decibels): 38, 51, 68, and 78.

Answer 117

Lp= 68.7, or 69 dBA

Straight arithmetic averaging would yield 58.7, or 59 dB.

Question 118

Consider the case where a noise level of 90 dBA exists for 10 min and is followed by a reduced
noise level of 70 dBA for 30 min. What is the equivalent continuous equal energy level for the
40-min period? Assume a 5-min sampling interval.

Answer 118

Leq = 10 log(2.58 × 108) = 84.11, or 84 dBA

Question 119

The sound power level (re: 10−12 W) of a compressor is 124.5 dB at 1000 Hz. Determine the SPL 200 m downwind on a clear summer
afternoon if the wind speed is 5 m · s−1
, the temperature is 20°C, the relative humidity is 50%, and the barometric pressure is 101.325 kPa. At these conditions, the attenuation by air absorption (Ae1) is 0.94 dB. The total ground attenuation (Ae2) is−2.21 dB, that is reflection increases the noise level.

Answer 119

Lp= 68.77 or 69 dB at 1000 Hz

Question 120

A building located near a road is 6.92 m high. How high is the building in terms of wavelengths of a 50.0-Hz sound? Assume that the speed of sound is 346.12 m · s−1
.

Answer 120

One wavelength

Question 121

Determine the sum of the following sound levels (all in dB): 68, 82, 76, 68, 74, and 81.

Answer 121

85.5 or 86 dB

Question 122

A law enforcement officer has taken the following readings with her sound level meter. Is the noise source
a predominantly low- or middle-frequency emitter? Readings: 80 dBA, 84 dBB, and 90 dBC.

Answer 122

Predominantly low frequency

Question 123

Compute the average sound pressure level of the following readings by simple arithmetic averaging and by logarithmic averaging (Equation 15–13) (all readings in dB): 42, 50, 65, 71, and 47. Does arithmetic averaging underestimate or overestimate the sound pressure level?

Answer 123

x = 55.00 or 55 dB; Lp= 61.57 or 62 dB

Question 124

Two oil-fired boilers for a 600 megawatt (MW) power plant produce a sound power level of 139 dB (re: 10−12W) at 4000 Hz, from the induced draft fans. Determine the sound pressure level 408.0 m downwind on a clear winter night when the wind speed is 4.50 m · s−1, the temperature is 0.0°C, the relative humidity is 30.0%, and the barometric pressure is 101.3 kPa. The air attenuation at these conditions is 28.15 dB.
The height of the boiler is 12 m. The ground attenuation is 2.86 dB.

Answer 124

SPL at 408.0 m 50.50 or 50 dB at 4000 Hz

Question 125

A dose of 1.0 R of gamma radiation was measured in air. From empirical studies, it is known that, on the average, 34 eV of energy is transferred (or absorbed) in the process of forming each ion pair in air. What is the equivalent absorbed dose in 1.0 cubic centimeter of air?

Answer 125

8.7 x10^-3 Gy

Question 125

Kal Karbonate must dispose of a vial containing 2.0 uCi / L of 45Ca. How long must the
radioisotope be held to meet an allowable sewer discharge standard of 2.0 x10-4 uCi /mL?

Answer 125

t = 548.23 or 550 days.

Question 126

What are the elements 40X18 and 14X7?

Answer 126

argon and nitrogen

Question 126

What particle is emitted in the decay chain represented by
14C6 −→14N7?

Answer 126

beta

Question 127

What is the mass of a 50 µCi sample of pure 131i ?

Answer 127

4.04 x1010 g