Waste Water Engineering Final Exam and Study Guide, Exams
of Nursing - 103 Questions
This exam assesses advanced knowledge of wastewater characteristics and sampling methods, covering physical,
chemical, and biological parameters, sampling strategies, preservation techniques, and quality assurance.
Emphasis is on application of concepts to complex real-world scenarios and critical analysis of data. It contains
103 multiple-choice questions, each with four distractors and a fully worked rationale that explains why the keyed
answer is correct. Content is organized into 10 focused sections: Wastewater Characteristics and Sampling,
Primary Treatment: Screening, Grit Removal, Sedimentation, Secondary Treatment: Activated Sludge Process,
Secondary Treatment: Trickling Filters and Rotating Biological Contactors, Tertiary Treatment: Nutrient
Removal and Advanced Treatment, Sludge Treatment and Disposal, Disinfection and Chlorination, Wastewater
Treatment Plant Design and Hydraulics, Regulations and Standards (e.g., EPA, BOD/COD limits), Industrial
Wastewater Pretreatment. Targeted learning outcomes include: Analyze and interpret wastewater characteristic
data to assess treatability and regulatory compliance.; Design and justify appropriate sampling plans based on
objectives, variability, and constituent properties.; Evaluate and apply sample preservation, handling, and
QA/QC protocols to ensure data integrity.. Every item has been reviewed for clinical accuracy, current guidelines,
and clarity so that students can study with confidence and self-correct as they work through the bank. Use it as a
high-yield review immediately before the exam, or as a structured practice tool during the unit - the rationales
Section 1: Wastewater Characteristics and Sampling (Questions 1-9)
1 For an industrial wastewater with a COD:BOD5 ratio of 5:1, which of the
following best explains the relatively low BOD5 compared to COD?
A) The wastewater contains a high concentration of readily biodegradable
organics that are rapidly oxidized.
B) The wastewater contains a significant fraction of recalcitrant or toxic
compounds that inhibit microbial activity during the 5-day test.
C) The wastewater has a high concentration of inorganic reducing agents that
contribute to COD but not BOD.
D) The wastewater has an abnormally high pH that suppresses BOD5
measurements.
Answer: B
Rationale: A high COD:BOD5 ratio (e.g., >3) indicates a large fraction of
non-biodegradable or inhibitory organics. Option B correctly identifies that
recalcitrant or toxic compounds suppress microbial activity in the BOD test,
leading to a low BOD relative to COD. Option A is opposite. Option C
(inorganics) could contribute but is less common for industrial effluents, and
pH effects are usually corrected by neutralization.
,2 A sampling plan for a river requires detection of trace levels of volatile
organic compounds (VOCs) in wastewater effluent. Which sampling method
and preservation technique are most appropriate?
A) Grab sample collected in a glass bottle with zero headspace, preserved
with HCl to pH <2, and stored at 4°C prior to analysis.
B) Composite sample collected over 24 hours using a peristaltic pump with
Teflon tubing, stored in a polyethylene container at ambient temperature.
C) Grab sample collected in a plastic bottle with headspace, preserved with
Na2S2O3 to neutralize residual chlorine, and stored at -20°C.
D) Composite sample collected using a refrigerated automatic sampler with
glass containers, preserved by adding ascorbic acid, and shipped overnight
without cooling.
Answer: A
Rationale: Volatile organics require minimal headspace to avoid volatilization,
glass containers to prevent adsorption, pH <2 to inhibit microbial activity, and
cooling to reduce volatilization. Option A meets all criteria. Option B uses
plastic (adsorption) and ambient temp (loss). Option C has headspace (loss)
and freezing may cause breakage. Option D lacks cooling during shipping
(loss) and ascorbic acid is for chlorine not preservation of VOCs.
3 The temperature coefficient for the BOD rate constant (k) is typically
around 1.047 at 20°C. If the reaction rate triples when temperature increases
from 20°C to 30°C, what is the approximate value of based on this
observation?
A) 1.047
B) 1.072
C) 1.116
D) 1.231
Answer: C
Rationale: Using the Arrhenius relationship: k2/k1 = ¸^(T2-T1). Here, k2/k1 =
3, T = 10°C. So = 3^(1/10) 1.116. Option C is correct. Option A (1.047)
would give k2/k1 = 1.047^10 1.58, not 3. Option B (1.072) gives ~2.0, Option
D (1.231) gives ~8.5.
,4 During a wastewater characterization study, a lab reports: total solids (TS) =
850 mg/L, total volatile solids (TVS) = 420 mg/L, total suspended solids
(TSS) = 310 mg/L, and volatile suspended solids (VSS) = 280 mg/L. Which
of the following best describes the dissolved solids fraction?
A) 430 mg/L
B) 540 mg/L
C) 140 mg/L
D) 570 mg/L
Answer: B
Rationale: Dissolved solids (TDS) = TS - TSS = 850 - 310 = 540 mg/L. Option
B is correct. Option A (430) is TS - TVS (fixed solids). Option C (140) is TSS
- VSS (fixed suspended). Option D (570) is incorrect calculation.
5 A technician is collecting a sample for heavy metals analysis from an
industrial discharge. Which preservation method is correct and why?
A) Add concentrated HCl to pH <2 to precipitate metals as chlorides for
easier filtration.
B) Add concentrated HNO3 to pH <2 to prevent metal adsorption onto
container walls and maintain solubility.
C) Add NaOH to pH >10 to stabilize metals as hydroxides and prevent
volatilization.
D) No preservation is needed; heavy metals are stable in solution for up to 48
hours at room temperature.
Answer: B
Rationale: Nitric acid (HNO3) at pH <2 is standard for heavy metals: it
dissolves precipitates, prevents adsorption, and inhibits microbial activity. HCl
can cause chloride interference in some analyses (e.g., ICP-MS). Option A
incorrectly suggests precipitation. Option C (base) precipitates metals as
hydroxides. Option D is false.
6 A wastewater sample has a total Kjeldahl nitrogen (TKN) of 45 mg/L,
ammonia-N of 25 mg/L, and nitrate-N of 2 mg/L. What is the concentration
of organic nitrogen?
A) 20 mg/L
B) 18 mg/L
C) 23 mg/L
, D) 22 mg/L
Answer: A
Rationale: TKN = organic N + ammonia N. So organic N = TKN - NH3-N = 45
- 25 = 20 mg/L. Option A is correct. Nitrate is not part of TKN. Option B (18)
subtracts nitrate incorrectly. Option C (23) adds nitrate. Option D (22) uses
wrong intermediate.
7 A wastewater treatment plant experiences large diurnal flow variations
(peak-to-average ratio of 3:1). The permit requires accurate mass loading
data for BOD and TSS. Which sampling approach is most appropriate?
A) Grab samples collected every hour and analyzed separately.
B) Time-composite sampling with equal volumes collected every 15 minutes.
C) Flow-weighted composite sampling with sample volume proportional to
flow rate.
D) Passive sampling using diffusion bags deployed for 24 hours.
Answer: C
Rationale: Flow-weighted composite sampling ensures that each sample aliquot
represents the same proportion of total flow, giving a representative average
concentration for mass loading. Option A yields many grab data but not a
composite. Option B (time-composite) gives a sample weighted by time, not
flow, which is biased when flow varies. Option D (passive) is for
time-weighted average concentrations, not suitable for mass loading.
8 A quality assurance protocol requires duplicate samples for a series of BOD5
measurements. The relative percent difference (RPD) between duplicates
should be less than a certain threshold. Which statement about RPD
acceptance criteria is correct?
A) RPD must be < 10% for all BOD5 values above the method detection
limit.
B) RPD is calculated as (|difference|/average) × 100 and should be < 20% for
typical wastewater samples.
C) RPD is not applicable to BOD because it is a bioassay; instead, use
absolute difference < 5 mg/L.
D) RPD should be < 5% for samples with BOD > 100 mg/L and < 10% for
samples with BOD < 100 mg/L.
Answer: B
of Nursing - 103 Questions
This exam assesses advanced knowledge of wastewater characteristics and sampling methods, covering physical,
chemical, and biological parameters, sampling strategies, preservation techniques, and quality assurance.
Emphasis is on application of concepts to complex real-world scenarios and critical analysis of data. It contains
103 multiple-choice questions, each with four distractors and a fully worked rationale that explains why the keyed
answer is correct. Content is organized into 10 focused sections: Wastewater Characteristics and Sampling,
Primary Treatment: Screening, Grit Removal, Sedimentation, Secondary Treatment: Activated Sludge Process,
Secondary Treatment: Trickling Filters and Rotating Biological Contactors, Tertiary Treatment: Nutrient
Removal and Advanced Treatment, Sludge Treatment and Disposal, Disinfection and Chlorination, Wastewater
Treatment Plant Design and Hydraulics, Regulations and Standards (e.g., EPA, BOD/COD limits), Industrial
Wastewater Pretreatment. Targeted learning outcomes include: Analyze and interpret wastewater characteristic
data to assess treatability and regulatory compliance.; Design and justify appropriate sampling plans based on
objectives, variability, and constituent properties.; Evaluate and apply sample preservation, handling, and
QA/QC protocols to ensure data integrity.. Every item has been reviewed for clinical accuracy, current guidelines,
and clarity so that students can study with confidence and self-correct as they work through the bank. Use it as a
high-yield review immediately before the exam, or as a structured practice tool during the unit - the rationales
Section 1: Wastewater Characteristics and Sampling (Questions 1-9)
1 For an industrial wastewater with a COD:BOD5 ratio of 5:1, which of the
following best explains the relatively low BOD5 compared to COD?
A) The wastewater contains a high concentration of readily biodegradable
organics that are rapidly oxidized.
B) The wastewater contains a significant fraction of recalcitrant or toxic
compounds that inhibit microbial activity during the 5-day test.
C) The wastewater has a high concentration of inorganic reducing agents that
contribute to COD but not BOD.
D) The wastewater has an abnormally high pH that suppresses BOD5
measurements.
Answer: B
Rationale: A high COD:BOD5 ratio (e.g., >3) indicates a large fraction of
non-biodegradable or inhibitory organics. Option B correctly identifies that
recalcitrant or toxic compounds suppress microbial activity in the BOD test,
leading to a low BOD relative to COD. Option A is opposite. Option C
(inorganics) could contribute but is less common for industrial effluents, and
pH effects are usually corrected by neutralization.
,2 A sampling plan for a river requires detection of trace levels of volatile
organic compounds (VOCs) in wastewater effluent. Which sampling method
and preservation technique are most appropriate?
A) Grab sample collected in a glass bottle with zero headspace, preserved
with HCl to pH <2, and stored at 4°C prior to analysis.
B) Composite sample collected over 24 hours using a peristaltic pump with
Teflon tubing, stored in a polyethylene container at ambient temperature.
C) Grab sample collected in a plastic bottle with headspace, preserved with
Na2S2O3 to neutralize residual chlorine, and stored at -20°C.
D) Composite sample collected using a refrigerated automatic sampler with
glass containers, preserved by adding ascorbic acid, and shipped overnight
without cooling.
Answer: A
Rationale: Volatile organics require minimal headspace to avoid volatilization,
glass containers to prevent adsorption, pH <2 to inhibit microbial activity, and
cooling to reduce volatilization. Option A meets all criteria. Option B uses
plastic (adsorption) and ambient temp (loss). Option C has headspace (loss)
and freezing may cause breakage. Option D lacks cooling during shipping
(loss) and ascorbic acid is for chlorine not preservation of VOCs.
3 The temperature coefficient for the BOD rate constant (k) is typically
around 1.047 at 20°C. If the reaction rate triples when temperature increases
from 20°C to 30°C, what is the approximate value of based on this
observation?
A) 1.047
B) 1.072
C) 1.116
D) 1.231
Answer: C
Rationale: Using the Arrhenius relationship: k2/k1 = ¸^(T2-T1). Here, k2/k1 =
3, T = 10°C. So = 3^(1/10) 1.116. Option C is correct. Option A (1.047)
would give k2/k1 = 1.047^10 1.58, not 3. Option B (1.072) gives ~2.0, Option
D (1.231) gives ~8.5.
,4 During a wastewater characterization study, a lab reports: total solids (TS) =
850 mg/L, total volatile solids (TVS) = 420 mg/L, total suspended solids
(TSS) = 310 mg/L, and volatile suspended solids (VSS) = 280 mg/L. Which
of the following best describes the dissolved solids fraction?
A) 430 mg/L
B) 540 mg/L
C) 140 mg/L
D) 570 mg/L
Answer: B
Rationale: Dissolved solids (TDS) = TS - TSS = 850 - 310 = 540 mg/L. Option
B is correct. Option A (430) is TS - TVS (fixed solids). Option C (140) is TSS
- VSS (fixed suspended). Option D (570) is incorrect calculation.
5 A technician is collecting a sample for heavy metals analysis from an
industrial discharge. Which preservation method is correct and why?
A) Add concentrated HCl to pH <2 to precipitate metals as chlorides for
easier filtration.
B) Add concentrated HNO3 to pH <2 to prevent metal adsorption onto
container walls and maintain solubility.
C) Add NaOH to pH >10 to stabilize metals as hydroxides and prevent
volatilization.
D) No preservation is needed; heavy metals are stable in solution for up to 48
hours at room temperature.
Answer: B
Rationale: Nitric acid (HNO3) at pH <2 is standard for heavy metals: it
dissolves precipitates, prevents adsorption, and inhibits microbial activity. HCl
can cause chloride interference in some analyses (e.g., ICP-MS). Option A
incorrectly suggests precipitation. Option C (base) precipitates metals as
hydroxides. Option D is false.
6 A wastewater sample has a total Kjeldahl nitrogen (TKN) of 45 mg/L,
ammonia-N of 25 mg/L, and nitrate-N of 2 mg/L. What is the concentration
of organic nitrogen?
A) 20 mg/L
B) 18 mg/L
C) 23 mg/L
, D) 22 mg/L
Answer: A
Rationale: TKN = organic N + ammonia N. So organic N = TKN - NH3-N = 45
- 25 = 20 mg/L. Option A is correct. Nitrate is not part of TKN. Option B (18)
subtracts nitrate incorrectly. Option C (23) adds nitrate. Option D (22) uses
wrong intermediate.
7 A wastewater treatment plant experiences large diurnal flow variations
(peak-to-average ratio of 3:1). The permit requires accurate mass loading
data for BOD and TSS. Which sampling approach is most appropriate?
A) Grab samples collected every hour and analyzed separately.
B) Time-composite sampling with equal volumes collected every 15 minutes.
C) Flow-weighted composite sampling with sample volume proportional to
flow rate.
D) Passive sampling using diffusion bags deployed for 24 hours.
Answer: C
Rationale: Flow-weighted composite sampling ensures that each sample aliquot
represents the same proportion of total flow, giving a representative average
concentration for mass loading. Option A yields many grab data but not a
composite. Option B (time-composite) gives a sample weighted by time, not
flow, which is biased when flow varies. Option D (passive) is for
time-weighted average concentrations, not suitable for mass loading.
8 A quality assurance protocol requires duplicate samples for a series of BOD5
measurements. The relative percent difference (RPD) between duplicates
should be less than a certain threshold. Which statement about RPD
acceptance criteria is correct?
A) RPD must be < 10% for all BOD5 values above the method detection
limit.
B) RPD is calculated as (|difference|/average) × 100 and should be < 20% for
typical wastewater samples.
C) RPD is not applicable to BOD because it is a bioassay; instead, use
absolute difference < 5 mg/L.
D) RPD should be < 5% for samples with BOD > 100 mg/L and < 10% for
samples with BOD < 100 mg/L.
Answer: B
