Wastewater Characterization Lab 020409 Final

7/30/2019 Wastewater Characterization Lab 020409 Final

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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 WastewaterTreatment Plant.

BACKGROUND and METHODS

Wastewater characterization is important for determining loadings to treatment facilities andassessing 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. Unfiltered primary effluent (PE)

2. Filtered primary effluent (PEf)

3. Unfiltered secondary effluent (SE)4. Filtered secondary effluent (SEf)

The results for all four samples will be compiled by the TA and made available to all of thegroups 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 103C to determine total suspended solids(TSS). Volatile suspended solids (VSS) are those suspended solids that burn off at 550C.

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 wastewatertreatment 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.

In the lab, Hach kits will be used to analyze the following nitrogen species:

Total NitrogenAn 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 absorbancemaximum at 410 nm.

Ammonia

Ammonia compounds combine with chlorine to form monochloramine, which then reacts withsalicylate 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 resultsare measured at 655 nm.

2

Aerobic BOD Oxidation

and NitrificationDenitrification

AnoxicAerobic

Organic N -> NH4

+-N

NH4

+-N -> NO2

--N -> NO3

- -N

NH4

+-N -> N assimilation

NO2

--N -> N2

NO3

- -N -> N2

NH4

+-N -> N assimilation

PE SE

Figure 1 Two stage activated sludge treatment process


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CE40340

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 withchromotropic 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 macromoleculessuch 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 phosphorus-based 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 frombiochemical oxygen demand (BOD), which is the biologicalcapacity 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 contactwith 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 liquidsapart.

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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 mainlythe small hydrogen ions (H+) to interact with the glass, the glass electrode measures the

electrochemical potential of hydrogen ions or thepotential of hydrogen. To complete the

electrical circuit, a reference electrode is needed. Note that the instrument measures voltage, notcurrent. 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 insidethe glass electrode changes from sample to sample, so all other potentials are calibrated from that

equation.

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CE40340

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Spring 2009

LAB PROCEDURES

In order to use the allotted time effectively, lab analyses should be carried out in the followingorder (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 kitPrepare 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 kitpH Probe measurement

6) Suspended Solids analysis Reweigh filter after drying at 103C, prepare for 550C oven


7) Suspended Solids analysis Reweigh filter after drying at 550C


8) COD test read sample

9) Record alldata 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

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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 duringaerobic 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/gVSSb. Assume 0.025 gP/gVSS

5) Nitrogen calculations/completed nitrogen balance through the treatment system

a. Organic nitrogen in PE and SEi. Organic NPE = TNPE (NO2

--N + NO3- -N + NH3-N + NH4

+-N)PEii. Organic NSE = TNSE (NO2

--N + NO3- -N + NH3-N + NH4

+-N)SEiii. 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 specialdigestion 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 Hachkit 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 kitanalysis.

ii. TNPE(calculated) = TKNPE + NO3- -NPE + NO2

--NPEiii. TNSE(calculated) = TKNSE + NO3

- -NSE + NO2--NSE

iv. Assume all nitrite (NO2- -N) = 0

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CE40340

Wastewater Design

Spring 2009

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 + Nassimilationii. 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 abeyond 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 theDeliverables 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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Wastewater Design

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DATA SHEET

Date:__________________

Group members:____________________________________________

Unfiltered PE Filtered PE Unfiltered SE Filtered SE

Sample Volume (mL)

Mass of Clean Filter (g)

Mass of Filter after 103C

Mass of Filter after 550C

TN (mgN/L)

Ammonia (mgN/L)

Nitrate (mgN/L)

Orthophosphate (mgP/L)

COD (mgO2/L)

Probe Measurements

pH

Nitrogen Species

Phosphorus Species

Chemical Oxygen Demand

Wastewater Characteristic

Primary Effluent Secondary Effluent

Solids Analysis

Comments:

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CE40340

Wastewater Design

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Wastewater Characterization Lab 020409 Final