ABC Wastewater Treatment Operator Class I Practice Test
Bacteriological analyses Container Preparation & Sterile Bottles:
Preservatives
Dechlorination (Sodium Thiosulfate): If you are sampling chlorinated effluent
Do Not Rinse:
Bacteriological analyses Proper Aseptic Sampling Bacteriological samples are always Grab Samples.
Technique
Do not fill the bottle completely to the brim. Leave approximately 1 inch (2.5 cm)
of air space at the top.
Positioning for Bacteriological analyses Hold the bottle near the base. Plunge it into the flow with the mouth facing
upstream (into the current) to avoid getting bacteria from your hand into the
bottle.
Sample Locations for Bacteriological analyses Effluent: Usually collected at the very end of the chlorine contact chamber or
after dechlorination.
Bacteriological analyses Representativeness: Choose a point where the wastewater is well-mixed. Avoid areas with excessive
floating scum or stagnant "dead zones" in a tank.
Preservation and Holding Times for Bacteriological Samples must be cooled immediately to 4 C or 39F but must not be allowed to
analyses freeze.
Maximum Holding Time for Bacteriological analyses Wastewater Compliance (NPDES): The sample must be analyzed within 6 hours.
Documentation for Bacteriological analyses Every bacteriological sample must be accompanied by a Chain of Custody
(COC) form. You must document:
Chain of Custody (COC) form Sample site location.
Date and exact time of collection (critical for the 6-hour window).
Type of analysis required (e.g., Fecal Coliform).
Name of the sampler.
Chlorine residual at the time of sampling (to prove the $Na_{2}S_{2}O_{3}$ had
a job to do).
1. Interferences for Bacteriological analyses (What ruins Residual Chlorine
the test?)
Highly Turbid Samples:
Sunlight:
Laboratory Methods for Bacteriological analyses Membrane Filtration
Multiple-Tube Fermentation
Membrane Filtration The sample is filtered, and the filter is placed on a petri dish. Results are
reported in CFU/100 mL (Colony Forming Units).
Multiple-Tube Fermentation Uses a series of tubes to estimate the population. Results are reported in
MPN/100 mL (Most Probable Number).
primary way we measure the "strength" of wastewater BOD (Biochemical Oxygen Demand) and CBOD (Carbonaceous BOD)
and the efficiency of the plant.
, ABC Wastewater Treatment Operator Class I Practice Test
Sample Type for Biological analyses Composite Sampling
Composite Sampling consists of several individual portions (increments) collected at specific time
intervals and mixed together.
Flow-Proportional Composite "Gold Standard" for BOD. The automatic sampler is programmed to take a larger
volume of sample when the plant flow is high and a smaller volume when the
flow is low.
why composite for BOD BOD measures the organic "load." Since flow and organic concentration change
throughout the day, a single grab sample would not represent the true average
load reaching the plant.
BOD: Measures the oxygen used by all microorganisms, including those that break
down carbon and those that break down nitrogen (nitrifiers).
CBOD: A chemical "inhibitor" (like TCMP) is added to the sample to stop the nitrogen-
eating bacteria from working. This measures only the oxygen used to break down
carbon-based organic matter.
Sample Preservation for Biological analyses Samples must be cooled immediately to 4C or 39F
Store the sample in a dark cooler or refrigerator.
Never add chemical preservatives
Maximum Holding Time for Biological analyses 48 hours.
Once in the lab, the samples are kept at 20C
Sampling Locations for Biological analyses Influent BOD:
Effluent BOD:
Percent Removal for BOD % Removal = (In-Out)/in X 100
COD (Chemical Oxygen Demand) COD measures nearly all organic matter using a strong chemical oxidant.
Sample Type for COD Usually a 24-hour composite for compliance, though grab samples are used for
process control.
COD Preservation Add Sulfuric Acid H2SO4 to lower the pH to < 2.
cool temp to less than or equal to 6C
COD Holding Time: Can be held for up to 28 days once preserved.
nutrients are highly "labile" (change quickly), so preservation is mandatory.
preservation of Nitrogen (Ammonia, TKN, Nitrate) and Add Sulfuric Acid H2SO4 to pH< 2
phosphourus
keep at temp less than or equal to 6C
, ABC Wastewater Treatment Operator Class I Practice Test
Holding Time: Nitrogen (Ammonia, TKN, Nitrate): Up to 28 days (except for Nitrate-only, which is often 48 hours).
metals sampling Composite or Grab.
Container: Plastic (polyethylene) is preferred.
metals Preservation : Add Nitric Acid HNO3 to pH < 2.
Holding Time: Most metals can be held for up to 6 months once preserved.
all chemical sampling types composite besides metal which is composite or grab
composite sample mixtures of multiple grab samples collected over time or flow, providing an
averaged representation of conditions over a period
Grab sample single, instantaneous collections taken at a specific time and location, acting as a
"snapshot
. In-Situ and Immediate Testing for Physical analyses "In-situ" means testing performed directly in the water (like a probe lowered into
(e.g., pH, temperature, DO, settleable solids an aeration basin).
holding time for Testing for Physical analyses (e.g., pH, For pH, Temperature, and Dissolved Oxygen (DO), the holding time is 15
temperature, DO, settleable solids minutes. In practice, these should be measured immediately at the source.
Sample Type: for Physical analyses (e.g., pH, These are always Grab Samples. You cannot use a 24-hour composite for these
temperature, DO, settleable solids because the values will drift significantly over time.
PH Method: Electrometric (using a pH meter) is the standard.
Calibration: The meter must be calibrated daily using at least two buffer solutions
(typically pH 4, 7, or 10) that bracket the expected range of your wastewater.
Interference: High temperatures can affect pH readings; most modern meters
have Automatic Temperature Compensation (ATC).
Temperature Method: Must be measured using a calibrated thermometer or a digital probe.
Procedure: The measurement must be taken in the stream or immediately after
collection. Do not let the sample sit in the sun or a cold room before measuring.
Unit: Usually recorded in Degrees Celsius (°C) for regulatory reporting.
Dissolved Oxygen (DO) Method: Typically measured with a membrane electrode (probe)
Key Fact: DO is critical for the Activated Sludge process.
Most Class I plants aim to maintain a DO of 1.0 to 3.0 mg/L in the aeration tank.
Settleable Solids Method: The Imhoff Cone test.
Reporting: Results are reported in milliliters per liter (mL/L).
Holding Time: The test should ideally begin within 48 hours, but for process
control, it is usually done immediately.
Bacteriological analyses Container Preparation & Sterile Bottles:
Preservatives
Dechlorination (Sodium Thiosulfate): If you are sampling chlorinated effluent
Do Not Rinse:
Bacteriological analyses Proper Aseptic Sampling Bacteriological samples are always Grab Samples.
Technique
Do not fill the bottle completely to the brim. Leave approximately 1 inch (2.5 cm)
of air space at the top.
Positioning for Bacteriological analyses Hold the bottle near the base. Plunge it into the flow with the mouth facing
upstream (into the current) to avoid getting bacteria from your hand into the
bottle.
Sample Locations for Bacteriological analyses Effluent: Usually collected at the very end of the chlorine contact chamber or
after dechlorination.
Bacteriological analyses Representativeness: Choose a point where the wastewater is well-mixed. Avoid areas with excessive
floating scum or stagnant "dead zones" in a tank.
Preservation and Holding Times for Bacteriological Samples must be cooled immediately to 4 C or 39F but must not be allowed to
analyses freeze.
Maximum Holding Time for Bacteriological analyses Wastewater Compliance (NPDES): The sample must be analyzed within 6 hours.
Documentation for Bacteriological analyses Every bacteriological sample must be accompanied by a Chain of Custody
(COC) form. You must document:
Chain of Custody (COC) form Sample site location.
Date and exact time of collection (critical for the 6-hour window).
Type of analysis required (e.g., Fecal Coliform).
Name of the sampler.
Chlorine residual at the time of sampling (to prove the $Na_{2}S_{2}O_{3}$ had
a job to do).
1. Interferences for Bacteriological analyses (What ruins Residual Chlorine
the test?)
Highly Turbid Samples:
Sunlight:
Laboratory Methods for Bacteriological analyses Membrane Filtration
Multiple-Tube Fermentation
Membrane Filtration The sample is filtered, and the filter is placed on a petri dish. Results are
reported in CFU/100 mL (Colony Forming Units).
Multiple-Tube Fermentation Uses a series of tubes to estimate the population. Results are reported in
MPN/100 mL (Most Probable Number).
primary way we measure the "strength" of wastewater BOD (Biochemical Oxygen Demand) and CBOD (Carbonaceous BOD)
and the efficiency of the plant.
, ABC Wastewater Treatment Operator Class I Practice Test
Sample Type for Biological analyses Composite Sampling
Composite Sampling consists of several individual portions (increments) collected at specific time
intervals and mixed together.
Flow-Proportional Composite "Gold Standard" for BOD. The automatic sampler is programmed to take a larger
volume of sample when the plant flow is high and a smaller volume when the
flow is low.
why composite for BOD BOD measures the organic "load." Since flow and organic concentration change
throughout the day, a single grab sample would not represent the true average
load reaching the plant.
BOD: Measures the oxygen used by all microorganisms, including those that break
down carbon and those that break down nitrogen (nitrifiers).
CBOD: A chemical "inhibitor" (like TCMP) is added to the sample to stop the nitrogen-
eating bacteria from working. This measures only the oxygen used to break down
carbon-based organic matter.
Sample Preservation for Biological analyses Samples must be cooled immediately to 4C or 39F
Store the sample in a dark cooler or refrigerator.
Never add chemical preservatives
Maximum Holding Time for Biological analyses 48 hours.
Once in the lab, the samples are kept at 20C
Sampling Locations for Biological analyses Influent BOD:
Effluent BOD:
Percent Removal for BOD % Removal = (In-Out)/in X 100
COD (Chemical Oxygen Demand) COD measures nearly all organic matter using a strong chemical oxidant.
Sample Type for COD Usually a 24-hour composite for compliance, though grab samples are used for
process control.
COD Preservation Add Sulfuric Acid H2SO4 to lower the pH to < 2.
cool temp to less than or equal to 6C
COD Holding Time: Can be held for up to 28 days once preserved.
nutrients are highly "labile" (change quickly), so preservation is mandatory.
preservation of Nitrogen (Ammonia, TKN, Nitrate) and Add Sulfuric Acid H2SO4 to pH< 2
phosphourus
keep at temp less than or equal to 6C
, ABC Wastewater Treatment Operator Class I Practice Test
Holding Time: Nitrogen (Ammonia, TKN, Nitrate): Up to 28 days (except for Nitrate-only, which is often 48 hours).
metals sampling Composite or Grab.
Container: Plastic (polyethylene) is preferred.
metals Preservation : Add Nitric Acid HNO3 to pH < 2.
Holding Time: Most metals can be held for up to 6 months once preserved.
all chemical sampling types composite besides metal which is composite or grab
composite sample mixtures of multiple grab samples collected over time or flow, providing an
averaged representation of conditions over a period
Grab sample single, instantaneous collections taken at a specific time and location, acting as a
"snapshot
. In-Situ and Immediate Testing for Physical analyses "In-situ" means testing performed directly in the water (like a probe lowered into
(e.g., pH, temperature, DO, settleable solids an aeration basin).
holding time for Testing for Physical analyses (e.g., pH, For pH, Temperature, and Dissolved Oxygen (DO), the holding time is 15
temperature, DO, settleable solids minutes. In practice, these should be measured immediately at the source.
Sample Type: for Physical analyses (e.g., pH, These are always Grab Samples. You cannot use a 24-hour composite for these
temperature, DO, settleable solids because the values will drift significantly over time.
PH Method: Electrometric (using a pH meter) is the standard.
Calibration: The meter must be calibrated daily using at least two buffer solutions
(typically pH 4, 7, or 10) that bracket the expected range of your wastewater.
Interference: High temperatures can affect pH readings; most modern meters
have Automatic Temperature Compensation (ATC).
Temperature Method: Must be measured using a calibrated thermometer or a digital probe.
Procedure: The measurement must be taken in the stream or immediately after
collection. Do not let the sample sit in the sun or a cold room before measuring.
Unit: Usually recorded in Degrees Celsius (°C) for regulatory reporting.
Dissolved Oxygen (DO) Method: Typically measured with a membrane electrode (probe)
Key Fact: DO is critical for the Activated Sludge process.
Most Class I plants aim to maintain a DO of 1.0 to 3.0 mg/L in the aeration tank.
Settleable Solids Method: The Imhoff Cone test.
Reporting: Results are reported in milliliters per liter (mL/L).
Holding Time: The test should ideally begin within 48 hours, but for process
control, it is usually done immediately.
