CE40340
Wastewater Design
Spring 2009
Wastewater Characterization Lab
OBJECTIVE
Determine basic wastewater characteristics for primary and secondary effluent from a local
treatment plant. We will use freshly collected samples from the Mishawaka Wastewater
Treatment Plant.
BACKGROUND and METHODS
Wastewater characterization is important for determining loadings to treatment facilities and
assessing process performance. This lab will measure suspended solids (SS), chemical oxygen
demand (COD), pH, nitrogen species, and phosphorus. Background information and basic
methods pertaining to each of these parameters follow; more detailed method descriptions can be
found in the attached handout.
Four groups will be formed, and four samples will be analyzed (one sample per group):
1.
2.
3.
4.
Unfiltered primary effluent (PE)
Filtered primary effluent (PEf)
Unfiltered secondary effluent (SE)
Filtered secondary effluent (SEf)
The results for all four samples will be compiled by the TA and made available to all of the
groups for report writing.
Solids Analysis
Total suspended solids (TSS) and volatile suspended solids (VSS) will be calculated as described
in Standard Methods for Water and Wastewater (attached handout). A specified amount of
sample is filtered; filters are dried for one hour at 103°C to determine total suspended solids
(TSS). Volatile suspended solids (VSS) are those suspended solids that burn off at 550°C.
Nitrogen
Excessive nitrogen in wastewater effluent can lead to eutrophication of receiving waters, and
nitrates in drinking water can cause methemoglobinemia. Within wastewater treatment systems,
nitrogen exists in a variety of forms; following nitrogen species through the wastewater
treatment system can help to identify biological transformations. Different types of biological
transformations occur under aerobic and anoxic conditions:
Aerobic conditions:
Hydrolysis: Conversion of organic nitrogen into soluble ammonium
Nitrification: Conversion of ammonium to nitrite and nitrate
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Wastewater Design
Spring 2009
Nitrogen assimilation: Incorporation of nitrogen into biomass - cells are composed of
approximately 12.4% nitrogen
Anoxic conditions:
The main transformation is denitrification, where nitrite and nitrate are reduced to nitrogen gas,
which evolves to the atmosphere.
Denitrification and nitrogen assimilation are the only ways to remove nitrogen from the system.
All other processes are only transforming nitrogen from one dissolved species to another.
Traditional wastewater treatment processes utilize a two stage system for TN removal (Figure 1).
NOTE THAT THE MISHAWAKA PLANT DOES NOT DENITRIFY, i.e. it only has aerobic
tanks.
Aerobic BOD Oxidation
and Nitrification
Organic N -> NH4+-N
NH4+-N -> NO2--N -> NO3- -N
NH4+-N -> N assimilation
PE
Aerobic
Denitrification
NO2--N -> N2
NO3- -N -> N2
NH4+-N -> N assimilation
Anoxic
SE
Figure 1 Two stage activated sludge treatment process
In the lab, Hach kits will be used to analyze the following nitrogen species:
Total Nitrogen
An alkaline persulfate digestion converts all forms of nitrogen to nitrate. Sodium metabisulfite is
added after the digestion to eliminate halogen oxide interferences. Nitrate then reacts with
chromotropic acid under strongly acidic conditions to form a yellow complex with an absorbance
maximum at 410 nm.
Ammonia
Ammonia compounds combine with chlorine to form monochloramine, which then reacts with
salicylate to form 5-aminosalicylate. The 5-aminosalicylate is oxidized in the presence of a
sodium nitroprusside catalyst to form a blue-colored compound. The blue color is masked by the
yellow color from the excess reagent present to give a final green-colored solution. Test results
are measured at 655 nm.
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Wastewater Design
Spring 2009
Nitrate
Nitrate in the sample reacts with chromotropic acid under strongly acidic conditions to yield a
yellow product with a maximum absorbance at 410 nm.
Nitrite
Nitrite in the sample reacts with sulfanilic acid to form an intermediate diazonium salt. This couples with
chromotropic acid to produce a pink colored complex directly proportional to the amount of nitrite
present. Note: our previous analyses suggest that nitrite concentrations are negligible in the
Mishawaka wastewater. In the interest of time, we will not analyze for nitrite in this lab.
Phosphorus
Phosphorus is a key nutrient for living organisms, and a key component of cell macromolecules
such as RNA, phospholipids (cell membranes), and ATP. In aqueous solution, phosphorus is
typically found as orthophosphate, polyphosphate, and organic phosphate. Orthophosphates
(H3PO4) are readily available as nutrients. Polyphosphates, which are chains of phosphorusbased molecules, must be converted to orthophosphates via hydrolysis prior to utilization as a
nutrient. Organic phosphates also must be converted to orthophosphate to be available as a
nutrient. Cells are composed of approximately 2.5% phosphorus.
In the lab, orthophosphate can be determined by colorimetric methods, using a Hach kit. Other
phosphorus species must first be converted to orthophosphate, via acid digestion, prior to
analysis. Note: in this lab we will only determine orthophosphates.
Chemical Oxygen Demand
COD is a measure of the matter that can be chemically oxidized, excluding reduced nitrogen
species (i.e., NH4+). COD is expressed in terms of oxygen equivalents, i.e., the amount of
oxygen that can be reduced by electrons released during the oxididation. COD is different from
biochemical oxygen demand (BOD), which is the biological capacity for oxygen consumption.
COD is always greater than or equal to the BOD. COD can be separated into soluble COD
(sCOD) and total COD (tCOD).
In the lab, COD will be measured using a Hach kit. In this procedure, the sample is heated for
two hours with potassium dichromate, a strong oxidizing agent. Oxidizable organic compounds
reduce the dichromate ion (Cr2O72–) to green chromic ion (Cr3+). Test results for the 3 to 150
mg/L range are measured at 420 nm. The mg/L COD results are defined as the mg of O2
consumed per liter of sample under conditions of this procedure.
pH
pH probes are one of the most standard laboratory probes. When one metal is brought in contact
with another, a voltage difference develops due to their differences in electron mobility. When a
metal is brought in contact with a solution of salts or acids, a similar electric potential is caused,
which has led to the invention of batteries. Similarly, an electric potential develops when one
liquid is brought in contact with another one, but a membrane is needed to keep such liquids
apart.
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Wastewater Design
Spring 2009
A pH meter measures the electrochemical potential between a known liquid inside the glass
electrode (membrane) and an unknown liquid outside. Because the thin glass bulb allows mainly
the small hydrogen ions (H+) to interact with the glass, the glass electrode measures the
electrochemical potential of hydrogen ions or the potential of hydrogen. To complete the
electrical circuit, a reference electrode is needed. Note that the instrument measures voltage, not
current. A pH meter must not be used in moving liquids of low conductivity (thus measuring
inside small containers is preferable).
The pH meter measures the electrical potential (follow the drawing clockwise from the meter)
between the mercuric chloride of the reference electrode and its potassium chloride liquid, the
unknown liquid, the solution inside the glass electrode, and the potential between that solution
and the silver electrode. Only the potential between the unknown liquid and the solution inside
the glass electrode changes from sample to sample, so all other potentials are calibrated from that
equation.
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Wastewater Design
Spring 2009
LAB PROCEDURES
In order to use the allotted time effectively, lab analyses should be carried out in the following
order (NOTE: The filtered PE and filtered SE will be filtered prior to the start of class). Record
all data in the data sheet on page 9 of this handout.
1) Each group obtains their respective sample
2) COD test – Hach kit
Prepare samples for analysis (requires 2 hours to digest)
3) Suspended Solids analysis (requires 1 hour in the oven) – weigh clean filter + filtration
This step only applies to the groups analyzing unfiltered PE and unfiltered SE.
4) Total Nitrogen – Hach kit
This analysis is lengthy and involves a number of steps. Each group should choose one
person to be dedicated specifically to this analysis.
5) The following tests may be carried out in any order by the remaining group member(s):
Ammonia – Hach kit
Nitrate – Hach kit
Phosphate – Hach kit
pH – Probe measurement
6) Suspended Solids analysis – Reweigh filter after drying at 103°C, prepare for 550°C oven
This step only applies to the groups analyzing unfiltered PE and unfiltered SE.
7) Suspended Solids analysis – Reweigh filter after drying at 550°C
This step only applies to the groups analyzing unfiltered PE and unfiltered SE.
8) COD test – read sample
9) Record all data on your data sheet before leaving the lab. Note any comments or
observations on the sheet (e.g., “we calibrated the pH meter with a pH 7 standard prior to
analysis”, “only 20 mL were filtered for SS analysis”).
Please turn in data sheet to TA before leaving lab so she can compile the data and
return to all groups.
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Wastewater Design
Spring 2009
DELIVERABLES
1) Calculate total suspended solids (TSS) and volatile suspended solids (VSS) for the PE
and SE
2) Compare the soluble COD (sCOD) and total COD (tCOD) of the PE and SE samples
a. The sCOD is the COD of a filtered sample, which is typically the readily
degradable portion of the COD in wastewater, and is the fraction removed during
aerobic treatment processes.
b. The tCOD includes the oxygen demand of the VSS, which can be chemically
oxidized.
3) See if the relationship of 1.42 mgCOD/mgVSS holds true for the PE and SE
4) Estimate the amount of TN and TP in the suspended solids
a. Assume 0.124 gN/gVSS
b. Assume 0.025 gP/gVSS
5) Nitrogen calculations/completed nitrogen balance through the treatment system
a. Organic nitrogen in PE and SE
i. Organic NPE = TNPE – (NO2--N + NO3- -N + NH3-N + NH4+-N)PE
ii. Organic NSE = TNSE – (NO2--N + NO3- -N + NH3-N + NH4+-N)SE
iii. TN, NO3- -N, NH3-N, and NH4+-N are known from Hach kit
measurements
iv. Assume all nitrite (NO2- -N) = 0
b.
Total Kjeldahl Nitrogen (TKN) in PE and SE
i. TKN is a measure of organic nitrogen, ammonia (NH3-N), and ammonium
(NH4+-N). Since organic nitrogen is mostly converted to NH4+ during
wastewater treatment, influent TKN is used as a measure of the total NH4+
load to the plant. TKN analysis is complex and requires a special
digestion analysis. However, it can be calculated based upon other
parameters measured in the lab.
ii. TKNPE = Organic NPE + (NH3-N + NH4+-N)PE
iii. TKNSE = Organic NSE + (NH3-N + NH4+-N)SE
c. Total Nitrogen (TN) in PE and SE
i. TN can be measured directly in the lab using such techniques as the Hach
kit analysis. TN can also be calculated knowing Total Kjeldahl Nitrogen
(TKN), nitrate (NO3- -N), and nitrite (NO2--N). Calculate TN for the PE
and SE and compare to the measured laboratory results from the Hach kit
analysis.
ii. TNPE(calculated) = TKNPE + NO3- -NPE + NO2--NPE
iii. TNSE(calculated) = TKNSE + NO3- -NSE + NO2--NSE
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Wastewater Design
Spring 2009
iv. Assume all nitrite (NO2- -N) = 0
d. Total nitrogen removed
i. TNremoved = TNPE - TNSE
e. Organic nitrogen hydrolyzed to ammonium
i. Organic Nhydrolized = Organic NPE - Organic NSE
f. Ammonium oxidized to nitrate
i. NO3--NSE = NH3-NPE - NH3-NSE + Organic Nhydrolized - NO2—NSE +
Nassimilation
ii. Assume nitrite (NO2- -NSE) = 0
iii. Assume nitrogen assimilation (Nassimilation) = 0
While this is clearly not a valid assumption – we know that nitrogen is
being incorporated into biomass - measuring nitrogen assimilation is a
beyond the scope of this laboratory exercise.
REPORT ORGANIZATION
One report should be prepared for each student. Reports are due at the beginning of class on
Friday, February 20. Reports should contain the following sections:





Introduction – discuss wastewater characterization and its importance. Briefly describe
the Mishawaka wastewater treatment plant and the expected transformations between PE
and SE.
Materials and methods – summarize the procedures of the lab
Results – experimental results (laboratory measurements)
Discussion – discuss the results, any discrepancies, and address the points in the
“Deliverables” section (NOTE: In order to receive full credit, equations and sample
calculations must be included for each of the points listed in “Deliverables.”)
Conclusions
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CE40340
Wastewater Design
Spring 2009
DATA SHEET
Date:__________________
Group members: ____________________________________________
Primary Effluent
Wastewater Characteristic
Unfiltered PE
Filtered PE
Secondary Effluent
Unfiltered SE
Filtered SE
Solids Analysis
Sample Volume (mL)
Mass of Clean Filter (g)
Mass of Filter after 103°C
Mass of Filter after 550°C
Nitrogen Species
TN (mgN/L)
Ammonia (mgN/L)
Nitrate (mgN/L)
Phosphorus Species
Orthophosphate (mgP/L)
Chemical Oxygen Demand
COD (mgO2/L)
Probe Measurements
pH
Comments:
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CE40340
Wastewater Design
Spring 2009
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