DAVIS

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

50 MJ · day−1

15%

Question 2

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 2

20,000 kg manure per hectare

Question 3

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. What is the expected concentration of DDT in the fish living in the pond?

Answer 3

270 mg · kg−1

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 × 10^11 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 ug · L−1

Question 6

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 6

12,615 humanoids

Question 7

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 7

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

Question 8

Population 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 8

0.029 year−1

Question 9

Population of spotted wolves lives on the mountain Hesperides. There were 26 wolves in the year 2054 and 54 wolves counted in 2079. 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 9

91 wolves

Question 10

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 10

4.053 × 10^12

Question 11

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 11

1.19 × 10−5 s−1 or 376 year−1

Question 12

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 12

3247

Question 13

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 13

715

Question 14

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 14

12.3 ug L

Question 15

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 15

3.92 /day

Question 16

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 16

1.74 × 10−4 mg / kg day

Question 17

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 17

3.3 × 10−2 mg /kg day

Question 18

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 18

HI = 1.95

Question 19

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 19

0.81 m −

Question 20

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 20

4000 m2

Question 21

(Example 4-12) The Rhett Butler Peach, Co. dips the peaches in boiling water (100◦ C) to remove the skin (a process called blanching) before canning them. The wastewater from this process is high in organic matter and it must be treated before disposal. The treatment process is a biological process that operates at 20◦ C. Thus, the wastewater must be cooled to 20◦ C before disposal. Forty cubic meters (40 m3) of wastewater is discharged to a concrete tank at a temperature of 20◦C to allow it to cool. Assuming no losses to the surroundings, that the concrete tank has a mass of 42,000 kg and a specific heat capacity of 0.93 kJ · kg−1 · K−1, what is the equilibrium temperature of the concrete tank and the wastewater?

Answer 21

T = 358 K or 85◦C

Question 22

As mentioned in Example 4–12, heat losses due to convection and radiation were not considered. Using the following assumptions, estimate how long it will take for the wastewater and concrete tank to come to the desired temperature (20◦C) if radiative cooling and convective cooling are considered. Assume that the average temperature of the water and concrete tank while cooling between 85◦C (their combined temperature from Example 4–12) and 20◦C is 52.5◦C. Also assume that the mean radiant temperature of the surroundings is 20◦ C, that both the cooling tank and the surrounding environment radiate uniformly in all directions, that their emissivity are the same (0.90), that the surface area of the concrete tank including the open water surface is 56 m2, and that the convective heat transfer coefficient is 13 J · s−1 · m−2 · K−1.

Answer 22

193,452 s, or 2.24 days

Question 23

The Rappahannock River near Warrenton, VA, has a flow rate of 3.00 m3 · s−1. Tin Pot Run (a pristine stream) discharges into the Rappahannock at a flow rate of 0.05 m3 · s−1. To study mixing of the stream and river, a conservative tracer is to be added to Tin Pot Run. If the instruments that measure the tracer can detect a concentration of 1.0 mg · L−1, what minimum concentration must be achieved in Tin Pot Run so that 1.0 mg · L−1 of tracer can be measured after the river and stream mix? Assume that the 1.0 mg · L−1 of tracer is to be measured after complete mixing of the stream and Rappahannock has been achieved and that
no tracer is in Tin Pot Run or the Rappahannock above the point where the two streams mix. What mass rate (in kilograms per day) of tracer must be added to Tin Pot Run?

Answer 23

263.52, or 264 kg · day−1

Question 24

A municipal landfill has available space of 16.2 ha at an average depth of 10 m. Seven hundred sixty-five (765) m3 of solid waste is dumped at the site 5 days a week. This waste is compacted to twice its delivered density. Draw a mass-balance diagram and estimate the expected life of the landfill in years.

Answer 24

16.25, or 16 years

Question 25

If biodegradable organic matter, oxygen, and microorganisms are placed in a closed bottle, the microorganisms will use the oxygen in the process of oxidizing the organic matter. The bottle may be treated as a batch reactor, and the decay of oxygen may be treated as a first-order reaction. Write the general mass-balance equation for the bottle. Using a computer spreadsheet program you have written, calculate and then plot the concentration of oxygen each day for a period of 5 days starting with a concentration of 8 mg · L−1. Use a rate constant of 0.35 d−1
.

Answer 25

Day 1 = 5.64, or 5.6 mg · L−1; Day 2 = 3.97, or 4.0 mg · L−1

Question 26

Liquid hazardous wastes are blended in a CMFR to maintain a minimum energy content before burning them in a hazardous waste incinerator. The energy content of the waste currently being fed is 8.0 MJ · kg−1 (megajoules per kilogram). A new waste is injected in the flow line into the CMFR. It has an energy content of 10.0 MJ · kg−1. If the flow rate into and out of the 0.20 m3 CMFR is 4.0 L · s−1, how long will it take the effluent from the CMFR to reach an energy content of 9 MJ · kg−1 ?

Answer 26

t = 34.5, or 35 s

Question 27

What is the pH of a water that contains 120.00 mg · L−1 of bicarbonate ion and 15.00 mg · L−1 of carbonate ion?

Answer 27

9.43

Question 28

A water contains 100.0 mg · L−1 CO2−3 and 75.0 mg · L−1 HCO−3 at a pH of 10 (T = 25◦C).Calculate the exact alkalinity. Approximate the alkalinity by ignoring the appropriate chemical
species.

Answer 28

233 mg · L−1 as CaCO3

Question 29

A 1-m3 sample of air was found to contain 80 g · m−3 of SO2. The temperature and pressure were 25.0◦C and 103.193 kPa when the air sample was taken. What was the SO2 concentration in parts per million?

Answer 29

= 0.030 ppm of SO2

Question 30

A soil sample is collected and the soil water is analyzed for the chemical compound
1,2-dichloroethane (DCA). The concentration in the water is found to be 12.5 g · L−1. The organic matter content of the soil is 1.0%. Determine the concentration of DCA that would be sorbed to the soil and that associated with the organic matter. DCA has a Kd of 0.724 (g · kg−1)(g · L−1)−1 .

Answer 30

905 g · kg−1

Question 31

The pH of a water is measured to be 7.5. What are the concentrations of carbonate, bicarbonate, carbonic acid, and CT? Assume this system is open to the atmosphere. The temperature is 25◦C.The Henry’s constant for carbon dioxide is 10−1.47 M · atm−1 at this temperature. The partial pressure of carbon dioxide is 10−3.53 atm.

Answer 31

1.70 × 10−4 M ≈ 1.7 × 10−4 M

Question 32

The pH of a water is measured to be 7.5. The concentration of bicarbonate was measured to be 1.3 × 10−3 M. What are the concentrations of carbonate, carbonic acid, and CT? Assume this system is closed to the atmosphere.

Answer 32

1.384 × 10−3 M ≈ 1.4 × 10−3 M

Question 33

Find the mass of sodium bicarbonate (NaHCO3) that must be added a 1.00 L volumetric flask containing distilled water to make a 1.0 M solution. Find the normality of the solution.

Answer 33

84 g · L−1

Question 34

A ferric phosphate solution is prepared by adding 2.4 g of ferric phosphate to a volumetric flask and bringing the final volume to 1.00 L by adding water having a phosphate concentration of 1.0 mg · L−1 .What is the concentration of soluble iron in this solution? (Assume that the temperature of the solution is 25◦C.

Answer 34

1.20 × 10−17 M

Question 35

A magnesium hydroxide solution is prepared by adding 10.00 g of magnesium hydroxide to a volumetric flask and bringing the final volume to 1.00 L by adding water buffered at a pH of 7.0. What is the concentration of magnesium in this solution? (Assume that the temperature is 25◦
C and the ionic strength is negligible).

Answer 35

0.17 M

Question 36

A solution of acetic acid is prepared in water by adding 11.1 g of sodium acetate to a volumetric flask and bringing the volume to 1.0 L with water. The final pH is measured to be 5.25. What are the concentrations of acetate and acetic acid
in solution? (Assume that the temperature of the solution is 25◦C.)

Answer 36

[HA] = 0.033 M [A−] = 0.102 M

Question 37

Hypochlorous acid decays in the presence of ultraviolet radiation. Assume that degradation occurs according to first-order kinetics and the rate of degradation was measured to be 0.12 day−1 (at a particular sunlight intensity and temperature). Given this, how long does it take for the concentration of hypochlorous acid to reach nondetectable levels (0.05 mg · L−1 ) if the initial concentration were 3.65 mg · L−1 ?

Answer 37

35.8 days

Question 38

A water initially contains 40 mg · L−1 of Mg2+. The pH of the water is increased until the concentration of hydroxide ion (OH−) is 0.001000 M. What is the concentration of magnesium ion in this water at this pH? Give your answer in milligrams per liter. Assume that the temperature of the solution is 25◦ C.

Answer 38

0.4423 mg · L−1

Question 39

The concentration of a chemical degrades in water according to first-order kinetics. The degradation constant is 0.2 day−1
. If the initial concentration is 100.0 mg · L−1, how many days are required for the concentration to reach 0.14 mg · L−1?

Answer 39

32.9 days

Question 40

What is the “exact” alkalinity of a water that contains 0.6580 mg · L−1 of bicarbonate, as the ion, at a pH
of 5.66?

Answer 40

0.4302 mg · L−1 as CaCO3

Question 41

What is the pH of a water that, at 25◦
C, contains 0.5000 mg · L−1 of hypochlorous acid? Assume equilibrium has been achieved. Ignore the dissociation of water. Although it may not be justified based on the data available to you, report the answer to two decimal places.

Answer 41

: pH 6.28

Question 42

You made up a saturated solution of calcium sulfate (CaSO4). The temperature is 25°C. You then add 5.00 × 10−3 M sodium sulfate (Na2SO4 ). What are the concentrations of calcium and sulfate after equilibrium is reached? The pKs of CaSO4 is 4.58.

Answer 42

Ca2+ = 0.0032 M,
SO2−4 = 0.0082 M

Question 43

A bankrupt chemical firm has been taken over by new management. On the property they found a 20,000-m3 brine pond containing 25,000 mg · L−1 of salt. The new owners propose to flush the pond into their discharge pipe leading to the Atlantic Ocean, which has a salt concentration above 30,000 mg · L−1. What flow rate of fresh water (in m3 · s−1 ) must they use to reduce the salt concentration in the pond to 500 mg · L−1
within one year?

Answer 43

Q = 0.0025 m3 · s−1

Question 44

A railroad tank car derails and ruptures. It discharges 380 m3 of pesticide into the Mud Lake drain. As shown in Figure P-4–24, the drain flows into Mud Lake, which has a liquid volume of 40,000 m3. The water in the creek has a velocity of 0.10 m · s−1, and the distance from the spill site to the pond is 20 km. Assume that the spill is short enough to treat the injection of the pesticide as a pulse, that the pond behaves as a flow-balanced CMFR, and that the pesticide is nonreactive. Estimate the time for the pulse to reach the pond and the time it will take to flush 99% of the pesticide from the pond.

Answer 44

Time to reach the pond = 2.3 days Time to flush = 21.3, or 21 days

Question 45

A sewage lagoon that has a surface area of 10 ha and a depth of 1 m is receiving 8640 m3 · d−1 of sewage containing 100 mg · L−1 of biodegradable contaminant. At steady state, the effluent from the lagoon must not exceed 20 mg · L−1 of biodegradable contaminant. Assuming the lagoon is well mixed and that there are no losses or gains of water in the lagoon other than the sewage input, what biodegradation reaction rate coefficient (d−1) must be achieved for a first-order reaction?

Answer 45

k = 0.3478, or 0.35 day−1

Question 46

For the following conditions determine whether a CMFR or a PFR is more efficient in removing a reactive compound from the waste stream under steady-state conditions with a first-order reaction: reactor volume = 280 m3, flow rate = 14 m3 · day−1, and reaction rate coefficient = 0.05 day−1
.

Answer 46

CMFR = 50%; PFR = 63%

Question 47

The discharge pipe from a sump pump in the dry well of a sewage lift station did not drain properly and thewater at the discharge end of the pipe froze. A hole has been drilled into the ice and a 200-W electric heater has been inserted in the hole. If the discharge pipe contains 2 kg of ice, how long will it take to melt the ice? Assume all the heat goes into melting the ice.

Answer 47

55.5 or 56 min

Question 48

The water in a biological wastewater treatment system must be heated from 15◦ C to 40◦C for the microorganisms to function. If the flow rate of the wastewater into the process is 30 m3 · day−1, at what rate must heat be added to the wastewater flowing into the treatment system? Assume the treatment system is completely mixed and that there are no heat losses once the wastewater is heated.

Answer 48

3.14 GJ · d−1

Question 49

The radiative heat load on two surfaces of a horizontal leaf is about 1.7 kW · m−2 (Gates, 1962). The leaf in turn radiates away a portion of this heat load. If the leaf temperature is near that of the ambient temperature, say 30◦C, what fraction of the heat loss is by radiation? Assume the emissivity of the leaf is 0.95.

Answer 49

Fraction = 0.2676 or 0.27 or 27%

Question 50

A cooling water pond is to be constructed for a power plant that discharges 17.2 m3 · s−1 of cooling water. Estimate the required surface area of the pond if the water temperature is to be lowered from 45.0°C at its inlet to 35.5°C at its outlet. Assume an overall heat transfer coefficient of 0.0412 kJ · s−1 m−2 K−1
(Edinger, Brady, and Graves, 1968). Note: the cooling water will be mixed with river water after it is cooled. The mixture of the 35°C water and the river water will meet thermal discharge standards.

Answer 50

174.76 or 175 ha

Question 51

A 1-m3 volume tank contains a gas mixture of 18.32 mol of oxygen, 16.40 mol of nitrogen, and 6.15 mol of carbon dioxide. What is the partial pressure of each component in the gas mixture at 25.0◦C?

Answer 51

O2: 45.4 kPa, N2: 40.6 kPa, CO2: 15.2 kPa

Question 52

The partial pressures of the gases in a 22,414-L volume of air at STP are: oxygen, 21.224 kPa; nitrogen,79.119 kPa; argon, 0.946 kPa; and carbon dioxide, 0.036 kPa. Determine the gram-molecular weight of air.

Answer 52

28.966

Question 53

A chemical, Spartan Green, has a partition coefficient of 12,500 (mg · kg−1 )(mg · L−1 )
−1. If the concentration of this chemical in water is found to be 105 g · L−1, at equilibrium, what is the concentration on
the soil?

Answer 53

1312.5 mg · kg−1

Question 54

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 54

0.36

Question 55

A 28-L volume of gas at 300.0 K contains 11 g of methane, 1.5 g of nitrogen, and 16 g of carbon dioxide. Determine the partial pressure exerted by each gas

Answer 55

CH4: 61.2 kPa, N2: 4.77 kPa, CO2: 32.4 kPa

Question 56

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 56

77.1 mm, or 7.7 cm

Question 57

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 57

7.6 cm

Question 58

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 58

1.57 W

Question 59

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 59

0.005 m · m−1

Question 60

Assume that the population of the greater roadrunner in the Guadelope Desert was 200 per hectare at the beginning of 1999. If the carrying capacity, K, is 600 and r = 0.25 · year−1, what is the number of roadrunners one, five and ten years later? What happens when the number of roadrunners equals K?

Answer 60

N(5) = 381 roadrunners
N(10) = 515 roadrunners

Question 61

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 61

20 ug · L−1

Question 62

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 62

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

Question 63

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 63

715

Question 64

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 64

12.3 ug L

Question 65

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 65

4.6 × 10−4 m/ s

Question 66

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 · s1. If the flow is steady and the discharge is 0.014 m3 · s1, determine the drawdown at a site 100.0 m from the well.

Answer 66

9.90 m

Question 67

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 non pumping 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 67

1.50 × 10−4 m · s
−1

Question 68

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 68

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

Question 69

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 69

1.61 × 106 m3

Question 70

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 70

4.7 mm/ day

Question 71

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 71

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

Question 72

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 72

S = 1.9 × 10−5

Question 73

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 73

S2 = 51.08 m

Question 74

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 74

61.6 or about 62%

Question 75

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

Answer 75

0.60

Question 76

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 76

44.7 or 45 years

Question 77

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 77

2.4 × 105 m3 · year−1

Question 78

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 78

23.23, or 23◦C.

Question 79

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 79

2080 MW

Question 80

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 80

4.336, or 4.3 g

Question 81

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

Answer 81

200,000 kg

Question 82

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 82

40.08 or 40 years

Question 83

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 83

5.98 or 6 Mg / ha

Question 84

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 84

176 EJ / year

Question 85

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 85

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

Question 86

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 86

135 GJ

Question 87

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 87

160 Tg /year

Question 88

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 88

3330 Tg or 3.33 Pg

Question 89

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

Answer 89

98%

Question 90

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 90

Ts = 46.42 or 46 years

Question 91

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

C6H12O6 + 6O2 −→ 6CO2 + 6H2O

Answer 91

116 mg / L O2

Question 92

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 92

116 mg / L1

Question 93

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 93

0.12

Question 94

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 94

Dilution factor =0.0233 1.2 mg

Question 95

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 95

11.86, or 12 mg / L

Question 96

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 96

0.632 mg / L · day

Question 97

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 97

0.408 mg /L day

Question 98

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 98

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

Question 99

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 99

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

Question 100

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 100

[OH−]= 1.32 × 10^−10 M

Question 101

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 101

354 days

Question 102

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 102

212 mg /L

Question 103

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 103

16.906 mg / L

Question 104

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 104

k = 0.233 /day

Question 105

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 105

363 mg /L

Question 106

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 106

BOD5 = 200 mg /L

Question 107

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 107

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

Question 108

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 108

625 mg / L

Question 109

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 109

9.27 mg /L

Question 110

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 110

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

Question 111

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 111

DO = 7.4 mg · L−1

Question 112

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 112

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

Question 113

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 113

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

Question 114

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 114

Mass flux = 6.2 × 103 kg · day−1

Question 115

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 115

1.00e-07 m · s−1

Question 116

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 116

11.2 kg · day−1

Question 117

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 117

61.2 kg · day−1

Question 118

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 118

9690 kg · day−1 of CaCO3

Question 119

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 119

13.4 min

Question 120

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 120

470.6, or 471 L · day−1

Question 121

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 121

Va= 211.4 m · day−1

Question 122

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 122

21.7, or 22 m

Question 123

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 123

Depth = 1.684 m, or 1.7 m

Question 124

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 124

Cc = 99,650 mg · L−1

Question 125

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 125

VT= 19.5 m3 · day−1

Question 126

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 126

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.

Question 127

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 of4.2 × 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 127

A= 3987 m2 ≡ 4000 m2

Question 128

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 128

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

Question 129

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 129

2.3 m3 · s−1

Question 130

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 130

64.2 m · s−1

Question 131

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 131

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?

Question 132

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 132

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

Question 133

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 133

0.26 m−1

Question 134

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 134

25,500 m2

Question 135

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 135

V = 972 m3, or 970 m3

Question 136

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 136

123409 kg · day−1

Question 137

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 137

t= 54 s

Question 138

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 138

10.5 m

Question 139

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 139

38,774.9, or 38,000 m3 · day−1

Question 140

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 140

20.95, or 21.0 mg · L−1

Question 141

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 141

42.29, or 42.3 m3 · day−1

Question 142

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 142

V2 = 50.0 m3

Question 143

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 143

Volume = 1.29 × 104 m3

Question 144

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 144

Volume = 1.29 × 104 m3

Question 145

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 145

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

Question 146

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 146

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

Question 147

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 147

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

Question 148

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 148

SSO2 = 1.80 × 106 kg · year−1

Question 149

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 149

−1.00◦C · 100 m−1

Question 150

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 150

−1.00◦C · 100 m−1

Question 151

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 151

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

Question 152

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 152

625.39, or 630 Ug · m−3

Question 153

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

Answer 153

14.5

Question 154

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 154

5.8 km

Question 155

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 155

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

Question 156

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 156

784,020 m2 , or 78.4 ha

Question 157

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 157

6.75 × 10−5 m3 · s−1

Question 158

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 158

7.5 homes

Question 159

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 compacted 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 159

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 160

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 160

4.6 m3 · year−1

Question 161

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 161

2.76 years

Question 162

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 162

1.04 m

Question 163

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 163

2.8 m3 · day−1

Question 164

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 164

8.399, or 8.4

Question 165

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 165

ZT A = 29.69 m3

Question 166

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 166

t = 3.71 × 108 s, or about 12 years

Question 167

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 167

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

Question 168

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 168

Mevap. = 362.18 or 360 kg · week−1

Question 169

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 169

237.25 g · min−1

Question 170

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

Answer 170

Lp= 68.7, or 69 dBA

Straight arithmetic averaging would yield 58.7, or 59 dB.

Question 171

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 171

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

Question 172

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 172

Lp= 68.77 or 69 dB at 1000 Hz

Question 173

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 173

One wavelength

Question 174

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

Answer 174

85.5 or 86 dB

Question 175

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 175

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

Question 176

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 176

SPL at 408.0 m = 50.50 or 50 dB at 4000 Hz

Question 177

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 177

8.7 x10^-3 Gy

Question 178

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 178

t = 548.23 or 550 days.

Question 179

What are the elements 40X18 and 14X7?

Answer 179

argon and nitrogen

Question 180

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

Answer 180

beta

Question 181

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

Answer 181

4.04 x10^10 g

Question 182

A residential development of 280 houses is being planned. Assume that the American Water Works Associ- ation average daily household consumption applies, and that each house has three residents. Estimate the additional average daily water production in L /d that will have to be supplied by the city.

Answer 182

3.70 x 10^5 L/d

Question 183

A solution is initially supersaturated with CO2− and Ca2+ such that the concentrations are both 3
50.0 mg · L−1. When equilibrium is ultimately reached what will be the final concentration of Ca2+?

Answer 183

16.7 mg/L

Question 184

If 100 mg of H2SO4 (MW = 98) is added to water, bringing the final volume to 1.0 L, what is the final pH?

Answer 184

2.69

Question 185

A solution of HOCl is prepared in water by adding 15 mg HOCl to a volumetric flask, and adding water to the 1.0 L mark. The final pH is measured to be 7.0. What are the concentrations of HOCl and OCl? What percent of the HOCl is dissociated? Assume the temperature is 25◦ C.

Answer 185

22.4%

Question 186

As a result of the Aykhal Crystal detonation in 1974 (in the former Soviet Union), cesium-137 was measured (in 1993) in the soil at a concentration of 2 × 104 Bq · kg−1 soil.* If the background con- centration of 137Cs is 0.5 Bq · kg−1 soil, how many years will it take before the concentration of 137Cs reaches background levels? The decay of radionuclides occurs by a first-order reaction.

Answer 186

t = 459 years

Question 187

A falling raindrop initially has no dissolved oxygen. The saturation concentration for oxygen in the drop of water is 9.20 mg · L−1. If, after falling for 2 s, the droplet has an oxygen concentra- tion of 3.20 mg · L−1, how long must the droplet fall (from the start of the fall) to achieve a con- centration of 8.20 mg · L−1? Assume that the rate of oxygen exchange is first-order.

Answer 187

t = 10.4 s

Question 188

The pH of a water is measured to be 7.5. What are the concentrations of carbonate, bicarbonate, carbonic acid, and CT? Assume this system is open to the atmosphere. The temperature is 25◦C. The Henry’s constant for carbon dioxide is 10−1.47 M · atm−1 at this temperature. The partial pressure of carbon dioxide is 10−3.53 atm.

Answer 188

1.7 x 10^-4 M

Question 189

A soil sample is collected and the soil water is analyzed for the chemical compound 1,2-dichloroethane (DCA). The concentration in the water is found to be 12.5 ug · L−1 . The organic matter content of the soil is 1.0%. Determine the concentration of DCA that would be sorbed to the soil and that associated with the organic matter. DCA has a Kd of 0.724 (ug · kg−1)(ug · L−1)−1 .

Answer 189

109 ug/kg

Question 190

A 1-m3 sample of air was found to contain 80 ug · m−3 of SO2. The temperature and pressure were 25.0◦C and 103.193 kPa when the air sample was taken. What was the SO2 concentration in parts per million?

Answer 190

0.030 ppm of SO2

Question 191

A wastewater treatment plant must disinfect its effluent before discharging the wastewater to a near-by stream. The wastewater contains 4.5 × 105 fecal coliform colony-forming units (CFU) per liter. The maximum permissible fecal coliform concentration that may be discharged is 2000 fecal coliform CFU · L−1. It is proposed that a pipe carrying the wastewater be used for dis- infection process. Determine the length of pipe required if the linear velocity of the wastewater in the pipe is 0.75 m · s−1. Assume that the pipe behaves as a steady-state plug-flow system and that the reaction rate constant for destruction of the fecal coliforms is 0.23 min−1.

Answer 191

1060 m

Question 192

A chemical degrades in a flow-balanced, steady-state CMFR according to first-order reaction kinetics. The upstream concentration of the chemical is 10 mg · L−1 and the downstream con- centration is 2 mg · L−1. Water is being treated at a rate of 29 m3 · min−1. The volume of the tank is 580 m3. What is the rate of decay? What is the rate constant?

Answer 192

0.4mg·L−1 ·min−1

0.20/min

Question 193

Assume that the population of the greater roadrunner in the Guadelope Desert was 200 per hectare at the beginning of 1999. If the carrying capacity, K, is 600 and r = 0.25 · year−1, what is the number of roadrunners one, five and ten years later? What happens when the number of roadrunners equals K?

Answer 193

N(1) = 234 roadrunners
Doing the same for the five- and ten-year solutions, we get
N (5) = 381 roadrunners
N (10) = 515 roadrunners
When the number of roadrunners is 600, that is, K, no additional roadrunners can be sustained on this land and the population will remain at 600.

Question 194

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 194

HI = 1.95

Question 195

A wastewater treatment plant must disinfect its effluent before discharging the wastewater to a near-by stream. The wastewater contains 4.5 × 105 fecal coliform colony-forming units (CFU) per liter. The maximum permissible fecal coliform concentration that may be discharged is 2000 fecal coliform CFU · L−1. It is proposed that a pipe carrying the wastewater be used for dis-infection process. Determine the length of pipe required if the linear velocity of the wastewater in the pipe is 0.75 m · s−1. Assume that the pipe behaves as a steady-state plug-flow system and that the reaction rate constant for destruction of the fecal coliforms is 0.23 min−1
.

Answer 195

L = 1060 m

Question 196

A contaminated soil is to be excavated and treated in a completely mixed aerated lagoon at a Superfund site. To determine the time it will take to treat the contaminated soil, a laboratory completely mixed batch reactor is used to gather the following data. Assuming a first-order reaction, estimate the rate constant, k, and determine the time to achieve 99% reduction in the original concentration.

Time (d) Waste Concentration (mg · L−1)
1 280
16 132

Answer 196

t = 92 days