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ENGINEERING REPORT

California State University Fresno CE 142L Environmental Quality Laboratory

Laboratory Manual

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PRELUDE: WHAT IS ENVIRONMENTAL CHEMISTRY

INTRODUCTION:

What is environmental chemistry? This question is a little difficult to answer because environmental chemistry encompasses many different topics. Some define it as follows:

“Environmental chemistry is the study of the sources, reactions, transport, effects, and fates of chemical species in water, soil, and air environments." (Stanley E. Manahan. 1991. Environmental Chemistry, 5th ed.). "(The) central position of aquatic chemistry in the natural sciences gives it an increasing popularity in science and engineering curricula; it also makes it a difficult topic to teach for it requires exploring some aspects of almost all sciences." (Francois M. M. Morel. 1983. Preface to Principles of Aquatic Chemistry).

Basically, Environmental Chemistry is the use of chemistry to understand the interactions of environmental systems. Water chemistry is an important aspect of Environmental Chemistry.

A fundamental tool in analyzing water chemistry is total dissolved solids (TDS). The TDS in water consists of dissolved inorganic salts and organic materials. In natural waters, salts are chemical compounds comprised of anions (-) such as carbonates, chlorides, sulfates, and nitrates (primarily in ground water), and cations (+) such as potassium (K), magnesium (Mg), calcium (Ca), and sodium (Na) (EPA, 1986). In ambient conditions, these compounds are present in proportions that create a charge- balanced solution. If there are additional inputs of dissolved solids to the system, the balance is altered and the solution will adjust to achieve charge balance.

This lab manual includes exercises in water chemistry calculations in order to better understand chemical reactions within the aquatic environment. A fundamental understanding of water chemistry is necessary for the remaining laboratory experiments and, later on, for professional practice in civil engineering.

PREPARATION BEFORE ARRIVING AT LAB: 1. The knowledge provided in high school chemistry courses and in CHEM 1A and 3A, while

important, is not adequate for this course or for CE 142 lecture. In view of this, all students in both courses are expected to devote a considerable amount of time outside of class expanding their knowledge of the chemical concepts contained in the lab manual for this course and in the textbook adopted for CE 142.

2. Students are expected to arrive to lab with a complete understanding of the topic assigned for the week. Therefore, students are to (a) study in advance of the lab all relevant material in the lab manual pertaining to the topics and (b) conduct additional reading on the topics from the recommended textbook and other sources (books, Web, etc..). An excellent source of knowledge can be found in YouTube videos.

3. Students are expected to print and bring to class hard copies of each lab exercise, or to have ready access to the material on their laptop.

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Contents LAB 1: WATER CHEMISTRY CALCULATIONS ....................................................... 4 LAB 2: GAS TRANSFER .............................................................................................. 5 LAB 3: BIOCHEMICAL OXYGEN DEMAND .......................................................... 12 LAB 4: ADSORPTION................................................................................................ 21 LAB 5: SOLIDS IN WATER ....................................................................................... 24 LAB 6: CHEMICAL COAGULATION JAR TESTING .............................................. 30 LAB 7: CHEMICAL EQUILIBRIUM, BUFFERING, AND ALKALINITY ............... 36 LAB 8: HARDNESS .................................................................................................... 44 LAB 9: CADILLAC DESERT: WATER & TRANSFORMATION OF NATURE ...... 48

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LAB 1: WATER CHEMISTRY CALCULATIONS Instructions: Do your calculations on engineering paper and then transfer the answers to the spaces indicated near the problem statement. Attach your calculations to the lab sheets when you are finished. Your calculations should be presented in a professional manner -- legible, organized, and complete so that someone else can understand them. Recommended reading from your course textbook (Sawyer, C.N., P.L. McCarty, and G.F. Perkin, Chemistry for Environmental Engineering, 4th ed., McGraw Hill, New York, 1994.): Chapter 2 1. (15 pts.) Molecular weights -- Calculate molecular weights of the compounds:

a. Sodium bicarbonate (baking soda) -- NaHCO3 Answer: b. Ferric Chloride -- FeCl3 Answer: c. Ammonium sulfate -- (NH4)2SO4 Answer:

2. Molar and mass concentrations a. (10 pts.) If the molar concentration of sodium bicarbonate (NaHCO3) is 2.00 mM (millimolar),

what is the mass concentration of NaHCO3 (in mg/L)? For the same molar concentration, what is the mass concentration of Na+? Answer: Answer:

b. (15 pts.) What are the molar concentrations of iron (Fe3+) and chloride (Cl-) in a solution with a mass concentration of 40.7 mg/L FeCl3? Answer:

3. Mass loading and concentration calculations a. (10 pts.) What mass of ammonium sulfate (NH4)2SO4 must you add to water to make a 1.50 L

solution that is 0.045 M? Answer:

b. (10 pts.) Suppose 1.50 L of a solution with a mass concentration of 45 mg/L of some salt is left uncovered in a warm dry room. If, after a week, the volume has dropped to 0.45 L due to evaporation, what is the final concentration? Answer:

c. (10 pts.) A treatment plant discharges a wastewater flow to a lake. If the flow is 3.550 million gallons per day and the concentration is 25.00 mg/L of Nitrate (NO3), what is the annual mass loading of total Nitrogen (N) (in lb/yr). Answer:

4. Ideal Gas Law (15 pts): How many pounds of Argon are there in a 3.880 cubic foot tank if the pressure is 18.00 atm, the temperature is 20.00 �C, and the Argon purity is 99.0%?

Answer: 5. Adsorption (15 pts): In an adsorption batch test, substance Y is dissolved in the solution with an initial

concentration of 370 mg/L. 0.450 gram of granulate activated carbon (GAC) was added to 100 mL of such solution and had sufficient contact time with the solution. The substance Y solution now has a concentration of 12.0 mg/L. What is the mass of substance Y that is adsorbed to the GAC? What is mass to mass ratio of the adsorbed substance Y to GAC in mg/kg at this equilibrium concentration?

Answer:

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LAB 2: GAS TRANSFER

INTRODUCTION Gas transfer is defined as the process of allowing any gas to dissolve into a fluid, or, the process of promoting the release of a dissolved gas from a fluid. For our purposes the gas of interest is oxygen. Gas transfer of oxygen to water plays an important role in water and wastewater treatment through a process known as aeration. In wastewater treatment, aeration has several functions, which are as follows:

· Prevents the formation of hydrogen sulfide, an odor causing substance. · Stripping of volatile organics and inorganics from the water. · Oxygen supply for aerobic biological treatment of activated sludge. This is also needed for a

process known as nitrification in which bacteria convert ammonia nitrogen into Nitrate NO3-

(Vesilind 1997). · Raising the dissolved oxygen (D.O.) levels in treated effluent to waterways to protect aquatic life. · Increasing oxygen concentration in receiving waterways for emergency situations, to restore

aquatic life in waterways that have been contaminated. In water treatment, Aeration also aids in the following:

· Remove taste and odor causing hydrogen sulfide. · Removal of excess carbon dioxide in groundwater. · Oxidizing ions such as iron and manganese (Schroeder 1987).

Diffusers and mixers, large scale versions of those used in this lab, are often utilized in the Aeration process.

The objective of this lab is to observe and measure gas transfer rates in three different types of systems with the aid of a Dissolved Oxygen meter. The three systems observed are a control system, where the water is not disturbed, a system involving mixing, and a final system utilizing a fine bubble diffuser.

BACKGROUND:

Dissolved oxygen (DO) is the measure of the concentration of free (i.e. not chemically bonded) molecular oxygen, usually measured in mg/L or percent saturation. Considered the most important and commonly employed measure of water quality, DO is primarily used to assess a body of water’s ability to support aquatic life. Adequate concentrations of DO are necessary for aerobic respiration as well as the prevention of offensive odors.

The presence of DO is a result of a continuous circulation of oxygen within the environment, commonly called the oxygen cycle. This process has two primary phases, one where oxygen is produced and one where it is consumed. Oxygen is produced during photosynthesis, a process that converts carbon dioxide (CO2) to oxygen and sugar using energy from the sun. Respiration and decomposition consume oxygen in highly complex processes that covert organic matter into usable energy.

This cycle of production and consumption, for the most part, maintains DO levels throughout the environment at a constant level. On a daily basis, however, noticeable differences can occur. Because photosynthesis is dependent upon sunlight, levels of oxygen production decline during the night. While

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production declines, consumption, from respiration and decomposition, continue at a steady pace. The net result is a decline in DO levels, usually most noticeable during early twilight.

The amount of dissolved oxygen within water is controlled primarily by the concentrations of DO both within the water and within the surrounding air. Oxygen concentrations within air are usually around 21% while those in water are about 10 ppm. This differential in concentrations causes oxygen molecules at the waters surface to dissolve into the water, a result of partial pressures between the two substances. Because this process is directly proportional to the area of air in contact with the water, movement of the water greatly affects the amount of DO present. Movement of the water creates waves on the waters surface. These waves produce a net increase in the available surface area that, in turn, allows for more diffusion of oxygen into the water. The more turbulent the flow, the more surface area and the greater the concentration of DO within the water.

The amount of DO within the water may be described using Henry’s Law.

))(( CCak dt dC

SL -=

where:

C = the concentration of dissolved gas (mg/L or mole/L) CS = the concentration of gas under saturated conditions kL = gas transfer coefficient (cm/s or m/s) a = ratio of gas/liquid interfacial area to liquid volume (cm-1 or m-1) t = time

CS describes the saturation concentration which is the concentration predicted by Henry’s Law. By integrating this equation and applying the necessary boundary conditions (at t = 0 and C = C0) we are left with the exponential decay function;

)( 0 )(

atk SS

LeCCCC --=-

(CS –C), often called the “deficit” shows how the relationship between the initial concentration and the saturated concentration effects the decay function. Notice that when C is farthest away from CS, the slope of the decay curve is greatest. This implies that as the concentration increases towards saturation, the amount of dissolving decreases. Also note how the decay function is related to “a,” the ratio of surface area to volume. This relationship shows how the creation of waves affects the amount of dissolving.

Another physical attribute of water that greatly affects DO concentrations is that of temperature. Saturation, the point at which a substance has the maximum amount of another substance within in it, is greatly affected by temperature. Colder water, for instance, is capable of holding more oxygen than warmer water (i.e. warmer water becomes saturated more easily than cold water). If a body of water, say

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a lake, is warm it will be capable of holding less oxygen than if it were cold. Even if the water is 100% saturated, it will still have less DO than an equivalent lake at a lower temperature.

This affect of temperature on the levels of DO can lead to stratification of the body of water. Thermal stratification can lead to layers within the water body that are completely devoid of DO while other layers may have too much. This can be of great concern to aquatic life that may be dependent upon specific levels of DO. Too much or too little DO may result in death.

CONCLUSION Gas transfer is defined as the process of allowing any gas to dissolve into a fluid, or, the process of promoting the release of a dissolved gas from a fluid. Gas transfer of oxygen to water plays an important role in water and wastewater treatment through a process known as aeration. Therefore, the objective of this lab is to observe and measure the gas transfer rates in three different types of systems with the aid of a Dissolved Oxygen meter. The three systems observed are a control system, where the water is not disturbed, a system involving mixing, and a final system utilizing a fine bubble diffuser.

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LAB 2: PROCEDURES (Gas Transfer)

Objective: To observe and measure gas transfer rates in several systems.

Equipment and Materials: · Dissolved oxygen meter · Deoxygenated water (provided by instructor) · 1,000 mL beaker (1) · Watch with second hand

Procedures

Your instructor will brief you on the use of the dissolved oxygen (DO) meter. Before lab, your instructor de-oxygenated several beakers of tap water by storing them under a vacuum and/or reacting them with sodium sulfite (Na2SO3) and/or bubbling nitrogen gas in the water. 1. Gently pour approximately 400 mL of deoxygenated water in the beaker with the beaker at a 45

degree slope and the pour spout of the carboy resting on the inner wall of the beaker. Try not to disturb the water excessively while doing so. (Do you know why?)

2. Set up the beaker either on the counter (control), on a mixer, or on a bubbler as directed by your instructor. Assign at least two people to each beaker -- one to measure the DO and one to keep track of the time. Either person (or a third) can record the data.

3. Before starting any testing set the meter measurement mode to “Continuous.” Then measure the initial DO and the temperature using the DO meter. Wait for the reading to stabilize. Once the reading has stabilized and you have an initial DO measurement, you can start the experiment and the timer.

4. The control beaker should be started first because it takes the most time. You can run the mixed beaker test in parallel with the control, except, start it 30 minutes later. When the mixed beaker measurements are complete you can start the bubbler beaker test. When moving the probe from the mixed beaker or bubbled beaker back to the control it will take time for the probe to adjust to the lower DO condition, so you must wait for the reading to stabilize before taking/ recording the first reading.

5. At the beginning, take time and concentration readings every 1 to 5 minutes in the systems with slower transfer (i.e., the control) and every 1 to 10 seconds in the systems that you expect will have a lot of gas transfer (mixed, bubbled). After you see how fast the concentration is changing, you can adjust the time interval. The goals are to make a minimum of 15 to 20 measurements spread out over the test period for each beaker and to have each test period be long enough for the DO to approach saturation (you will not achieve this for the control, so measure that one for only 1.5 to 2 hours).

Data Analysis 1. Using the temperature read in the lab, find and record the saturation concentration from an

environmental textbook or from the Internet. 2. Record the data for all of the water samples. Continued

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3. Use a spreadsheet program and create a table with time in the first column and corresponding values of raw DO concentration in the second column. Create a plot of DO concentration against time.

4. Add a column to the spreadsheet containing deficit values (D = CS - C). · Note that the saturation concentration value (CS) is obtained from a reference book and the

value will depend only on the water temperature. · For the control beaker, omit deficit data collected in the early time period when DO values

were constant (before they began increasing). 5. Add another column containing the quantity -ln(D/D0). The initial deficit (D0) is the first value of

deficit in the table. Plot -ln(D/D0) against time (in minutes). Show your plot on a separate worksheet. Determine the transfer coefficient for each test using the slopes of your plots (See the gas transfer notes.) You can use the linear trend line function to get the best-fit regression line. Be sure to force the regression through zero. Format your graph so that the lab data are displayed as points only (no connecting line) and the linear trend line.

6. To check the reasonableness of your calculated transfer coefficient, prepare a plot with your original data points (plotted as points only) and a line (only) generated from the integrated gas transfer equation* using your calculated transfer coefficient.

7. Exchange results with the other groups. Why are the transfer rates different? Are the differences what you would expect? Explain.

* C = CS - (CS - C0)e -(KLa)t

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LAB 2: NOTES ON GAS TRANSFER KINETICS Henry's Law describes an equilibrium situation -- the rate of gas dissolving into the liquid from the atmosphere (rd) equals the rate at which the gas volatilizes from the liquid (rv). Under equilibrium, rd = rv. But what if we are not in equilibrium? Suppose, for instance, a jar of water with little or no oxygen in it is opened to the atmosphere and left on a countertop. If we were to monitor the concentration of oxygen in the water over time, the results might look like:

Figure 1. Variation of DO Level v.s. the Saturated DO Concentration

As can be seen, the concentration approaches some maximum concentration (CS) asymptotically. Experiments of this kind have shown that the rate of change of dissolved gas concentration can be expressed mathematically by:

where C = the concentration of dissolved gas (mg/L or mole/L) CS = the concentration of gas under saturated conditions (called Cequil in your text, p 267) kL = gas transfer coefficient (cm/s or m/s) (kL*a) = overall gas transfer coefficient (1/s) a = ratio of gas/liquid interfacial area to liquid volume (cm-1 or m-1) t = time

CS is called the saturation concentration. It is the concentration when the system is at equilibrium. In other words, it is the concentration predicted by Henry's Law. Let's see if this equation makes sense. If C < CS, then dC/dt > 0, and the concentration rises, indicating that the net movement is from the air into the water (rd>rv). If C > CS, then dC/dt < 0, and the concentration drops, indicating that the net movement is from the water into the air (rd

)( 0 )(

atk ss

LeCCCC --=- C0: Dissolved Oxygen Concentration at t = 0 sec In the environment, C is usually less than CS, so the term (CS-C) is often called the "deficit", D. Rewriting the integrated equation in terms of the deficit yields:

D = D0e-(kLa)t D0: Deficit of Dissolved Oxygen at t = 0 sec

0 1 2 3 4 5 6 7 8 9

10

0 5 10 15 Time (min)

C on

ce nt

ra tio

n of

di ss

ol ve

d O

2

(m g/

L)

Cs = 9 mg/L

))(( CCak dt dC

SL -=

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Notice that this is an exponential decay function. Can you see it in the graph of experimental results shown above? It is helpful to think of the deficit (or CS-C) as a "driving force" for net gas transfer. Looking at the differential equation dC/dt = kLa(CS-C), the slope of the C curve is steepest when C is farthest from CS (i.e., when the deficit is largest). As C approaches CS, the slope gets smaller and smaller. In other words, the driving force for net gas transfer diminishes as the system approaches equilibrium. This is another example of Le Chatelier's Principle. When the system's equilibrium is disturbed, it attempts to re-establish that equilibrium. The larger the disturbance, the "harder" the system works to re-establish the equilibrium. Besides the deficit, what other factors do you think might affect the rate of gas transfer? Recall our hypothetical experiment. We left the jar sitting quietly on a countertop and watched the oxygen climb to the saturation value. What if we mixed the jar? What if we bubbled air through the jar? Would the degree of mixing or the size and number of the bubbles affect the results? Yes they would. Physical factors like mixing and bubbles change the gas transfer rate by their effects on the overall gas transfer coefficient, kLa. Identifying and measuring the many factors that affect kLa is usually so difficult that it is easier to measure k directly by experiment. We can do this by linearizing the integrated deficit equation as shown below:

D = D0e-(kLat) D/D0 = e-(kLa)t ln(D/D0) = -(kL a) t (or, y = mx) If we run the hypothetical experiment and graph the results according to the linearized equation, we should get a plot that looks like: The slope of a regression line forced through the origin will be kLa. Measuring the kLa values for several gas transfer systems is the goal of our lab exercise this week.

Figure 2. Linear Regression of the –Ln (D/D0) Time Sequence Data

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LAB 3: BIOCHEMICAL OXYGEN DEMAND OBJECTIVES The objectives of this lab are to measure the seven-day Biochemical Oxygen Demand (BOD7) of a dairy wastewater sample, to learn how BOD is related to the amount of organic substances present the wastewater, and to learn the importance of dilution.

INTRODUCTION1

Biochemical Oxygen Demand (BOD) is the amount of oxygen used in the metabolism of biodegradable organics. Typically, BOD tests are conducted over a five day period. However, for convenience, this experiment will be conducted over a seven day period. To understand how BOD is related to organic substances in water, it is necessary to know about the degradation of these substances. Bacteria and other forms of microbes feed on organic waste. These microbes, like most life forms, consume oxygen while metabolizing food, causing a demand for oxygen, or BOD. In water, there is only a limited amount of oxygen, dissolved oxygen (D.O.), present for consumption. If all the available oxygen is consumed by microbes, it can be catastrophic to the aquatic life in the water that also depend on the D.O. for survival. In wastewater treatment, these same microbes are used to aid in the removal of organic substances from the water. This is done through aeration, by transfer of oxygen to the water through diffusers or mixers, to keep the D.O. constant until the microbes consume all the organic matter present. For these reasons it is important for engineers to be able to determine the BOD of waters as an indirect measure of the organic substances in the water.

BACKGROUND

Biochemical Oxygen Demand BOD measures the amount of oxygen required by aerobic bacteria and other microorganisms which decompose organic matter. Microorganisms use oxygen directly proportional to the amount of organic matter oxidized in biochemical oxidations. BOD determination is used in studies to measure the purification capacity of streams. It also serves regulatory authorities as a means of checking the quality of effluents discharged into such waters. The BOD test is the only test that can measure the amount of biologically oxidizable organic matter present. It determines the rates at which oxidation will occur or BOD exertion in the receiving bodies of water. This is the reason why BOD is a major criterion used in stream pollution control where organic loading must be restricted to maintain desired dissolved-oxygen levels. BODt is the amount of BOD exerted during the duration of a test, while the BODu is proportional to the total biodegradable organic content of the water. The BODu is the ultimate or limiting BOD, meaning the DO reaches a point where it stops dropping and remains constant. The total DO drop at this point represents the ultimate BOD. This means that the bacteria consumed all of the organic material or that there was not a sufficient supply of oxygen for decomposition.

Dissolved Oxygen (DO) DO is a major determinant of water quality in streams, lakes, and other water courses such as groundwater. The saturation of oxygen in water is a function of temperature and pressure. Also, the concentration of dissolved solids in the water affects the saturation levels of oxygen in water. For

1 Adapted from the Technical Information Series—Booklet No. 7 by Clifford C. Hach, Robert L. Klein, Jr., Charles R. Gibbs

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example, the solubility is less in saline waters. Also, solubility of oxygen varies greatly with the temperature. DO will be measured using an oxygen probe and meter for this experiment. For a successful experiment, two factors must be taken into consideration. Since the rate of oxygen consumption is temperature dependent, temperature must remain constant, ± 2 �C for an accurate analysis of BOD. Also the reaction needs to take place in the dark. This is very important because the presence of algae will produce an error in the BOD measurements. Algae photosynthesizes in the light, producing oxygen in the testing bottles, creating an error in the end results.

Dilution The size of the sample volume plays an important factor in the success of a BOD measurement. If the sample volume is too large, oxygen supply will be diminished before the five day mark yielding an inaccurate BOD analysis. Bacteria will be overwhelmed by the massive amount of organic material available and will quickly deplete the oxygen supply since decomposition of organic material is proportional to oxygen consumption. In the other case, if the sample volume is too small, the change in DO will be too small to give reliable results. The change in DO will be minimal. Therefore, the dilution is crucial to ascertain reliable results. The following table shows the standard DO thresholds, which will be used to discredit sample volumes falling into the two DO concentrations conditions:

Threshold Test Problem Final DO < 1 mg/L Sample volume too large DOo – DOt < 2 mg/L Sample volume too small

Any test that falls in either of the conditions listed above is considered invalid. The effect of sample volume on the D.O. in the bottle during a BOD test is shown in the Figure 1.

Figure 1. Effect of Sample Volume on Dissolved Oxygen During a BOD Test

For any chosen dilution, you can calculate the range of BOD values that give valid tests. The upper BOD value can be calculated from assuming the starting D.O. to be a typical saturation value at room temperature (say, 8 mg/L) and setting the final D.O. equal to 1 mg/L. The lower BOD value can be calculated by setting the �D.O. value to be 2 mg/L. A table of BOD ranges for different dilution factors is shown below in Table 1. (Can you duplicate these calculations?)

0

2

4

6

8

10

0 1 2 3 4 5 6 7 8

time (day)

D O

(m g/

L)

Too much organic mat'l

Not enough organic mat'l

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Table 1 BOD Measurable with Different Sample Dilutions (Adapted from Sawyer, et. al.) Volume of Sample in a 300-mL Bottle

(mL) Range of BOD Measurable

(mg/L) 0.02 30,000 - 105,000 0.05 12,000 - 42,000 0.1 6,000 - 21,000 0.2 3,000 - 10,500 0.5 1,200 - 4,200 0.7 857 - 3,000 0.8 750 - 2,625 1 600 - 2,100

1.25 480 - 1,680 1.5 400 - 1,400 1.75 343 - 1,200

2 300 - 1,050 5 120 - 420 10 60 - 210 50 12 - 42

100 6 - 21 300 2 - 7

Based on past experience, we've chosen sample volumes for the wastewater to be tested. To cover possible fluctuations from past experience, we will choose several dilutions to cover a wide range of possible BOD5 values. Some bottles will exceed the threshold values discussed above, but if we've chosen wisely, at least one bottle will result in a valid test. Length of Test The standard BOD test is read after 5 days. For the sake of convenience, we'll read ours after 7 days during the normal lab period.

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BOD Equations Expressing the word definition of BOD in the form of an equation yields:

VolumeSample VolumeBottleSampleConc.)DOFinal-Conc.DO(Initial

SampleofVolume usedDOofMass

BOD ´

==

The shorted version is:

P DO-DO

BOD t0t =

where: BODt = Biochemical oxygen demand at time t, mg/L DO0 = Initial dissolved oxygen concentration in the BOD bottle, mg/L DOt = Final dissolved oxygen concentration in the BOD bottle, mg/L P = Ratio of the sample volume to the bottle volume (Vsample/Vbottle) Vbottle = 300 mL for standard bottle

CONCLUSION Biochemical Oxygen Demand (BOD) is the amount of oxygen used in the metabolism of biodegradable organics. The design of treatment facilities relies on the information concerning the BOD of wastes. It factors into the choice of treatment methods and is used to determine the size of treatment units, particularly trickling filters and activated-sludge units. The BOD test is used to evaluate the efficiency of various processes during operation at treatment plants. Typically, BOD tests are conducted over a five day period. However, for convenience, this experiment will be conducted over a seven day period. The objectives of this lab is to measure the seven-day Biochemical Oxygen Demand (BOD7) of a dairy wastewater sample and to learn the importance of dilution.

Second Week of BOD Pre-Lab, Final Report & Presentation The material below applies to (1) the pre-lab for the second week of the BOD lab, (2) the final report and (3) the presentation. Define and discuss the terms and topics listed below in your own words (paraphrase the works of others). CITE YOUR SOURCES (provide references).

1. A. Ultimate BOD (BODU) B. Carbonaceous BOD (CBOD) C. Nitrogenous BOD (NBOD) D. Addition of nutrients E. Addition of seed microorganisms. F. Modeling BOD Remaining (BODR(t)) and BOD Exerted (BOD(t))*.

2. Theoretical Oxygen Demand (ThOD) 3. Chemical Oxygen Demand (COD)

* See additional notes (located after the procedures below).

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LAB 3: PROCEDURES Objective: The objectives of this lab are to measure the seven-day Biochemical Oxygen Demand (BOD7)

of a dairy wastewater sample, to learn how BOD is related to the amount of organic substances present the wastewater, and to learn the importance of dilution.

Bottle Set-up and Incubation 1. Each group will be given a water sample to test. The instructor will brief you on the source of the

sample to be tested. 2. We don't know in advance the BOD values of the different waters. Consequently, we will need to

make several dilutions so that the change in dissolved oxygen (DO) is neither too great nor too small. Each group will set up several BOD bottles, but because some tests are likely to fail, we'll combine everyone's data at the end.

3. Your instructor will direct you on how many bottles to set up, and what volumes of sample to test. Use a pipet for volumes less than 50 mL, and a graduated cylinder for larger volumes.

4. Without excessive agitation fill the remaining volume of each BOD bottle with dilution water provided by your instructor.

5. Measure the dissolved oxygen concentration using a DO meter and probe. Be very careful that there are no air bubbles in the bottle when you do this measurement. a. Remove the probe shield (remove it carefully to avoid damaging the plastic probe cap). b. When the probe shield is off, be careful to protect the probe tip from being scraped. c. Record the bottle numbers, their contents, and the DO concentrations (after dilution).

6. Seal each bottle with a glass plug. Be very careful that there are no air bubbles in the bottle. After sealing, make sure that there is water in the "wet well" at the top of the bottle. If not, remove the glass stopper, add more dilution water, and reseal. Finally, place a plastic cap over the "wet well" to prevent the seal from evaporating.

7. Place all of the bottles in the constant temperature room as directed by your instructor. Dissolved Oxygen Measurement 8. After seven days (i.e., the next lab period), take your samples from the constant temperature room.

Before opening each bottle, note (and record) if the water seal in the wet well is not intact and if any bubbles are visible in the bottle. (Bubbles may be CO2, but they may also indicate a malfunctioning seal.)

9. Measure the DO concentrations and record your data. 10. Rinse the DO probe with DI water; carefully replace the probe shield (CAUTION – do not tighten

shield while it is resting on the plastic probe cap; move it back before tightening.) 11. Wash the glassware, caps, etc…. and set them to dry on the glassware rack. Data Analysis 1. Check your data against the threshold values (i.e., the minimum allowable DO after seven days and

the minimum allowable change in DO). Throw out any invalid test results. 2. Calculate the BOD7 values associated with your valid test data and record those values. (Don't forget

to provide sample calculations.) 3. Collect and record the valid BOD7 values from the other groups. 4. Summarize all of the valid test results (BOD values from the entire class) the data statistically by

reporting the range, mean and standard deviation values.

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LAB 3: ADDITIONAL NOTES ON BOD

Let's think about how one might measure organic material. If the material was a single substance, such as sucrose (table sugar), it would be possible to employ one of several chemical techniques to isolate and measure the amount of sucrose. But suppose you wanted to measure a mixture of organics. It might be possible to isolate each and measure it through chemical means, but this wouldn't be practical or useful. In wastewater or even natural waters like rivers and lakes, there may be hundreds of organic substances. Analyzing for all of these compounds would be a huge task, and wouldn't tell us what we really want to know anyway. We could use a "lumped" parameter like Total Organic Carbon (TOC), but this doesn't tell us anything about the biodegradability of the organic substances or the rates of conversion. Biodegradability is a key issue.

All natural environments teem with microbial life (e.g., a typical agricultural soil can contain as many as a million bacteria per gram!). For these microorganisms, organic waste is a source of food. Like virtually all higher forms of life (i.e., you and me), many of these microbes use oxygen to metabolize their food. As microbes degrade organic substances, they pull oxygen from the local environment in direct proportion to the amount of organic material metabolized. There's lots of oxygen in the air, but the amount dissolved in water is limited (recall the gas transfer lab). If enough organics are present, microbes will use up all of the available oxygen and fish will die. This is the reason engineers are interested in measuring organic materials.

The Biochemical Oxygen Demand (BOD) test was developed in Britain in the early part of this century. It is a simplified physical model of what would happen if an organic waste is added to a stream. In the test, a liquid containing organic wastes (either full strength or diluted) is placed in a bottle. The DO is measured and the bottle is sealed. After some incubation time (usually 5 days), the DO of the sample is measured again. Because the bottle is sealed, the difference in the DO values represents the oxygen used by microbes in degrading the waste. The change in DO is an indirect measure of the organic substances in the bottle. Through this process we see that biodegradable organic materials have associated with them a potential demand for oxygen when they are degraded (hence the name biochemical oxygen "demand").

The calculation of the BOD uses the following equation:

Where

DO0, DOt = dissolved oxygen concentrations at t=0 and t=t P = dilution factor = Volume of sample � Volume of the BOD bottle (300 mL)

If the waste is strong, the oxygen in the bottle will run out before the end of the incubation period. This is why we dilute the waste. If we over-dilute it, the change of DO will be too small to be statistically reliable.

P DODO

BOD t -

= 0

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A typical graph of DO in the BOD bottle as a function of time might look like Figure 1 below:

Figure 1. Decay of the DO in the BOD Bottle

As shown in the graph, if we wait a long time, the bacteria consume all of the organic material, and the DO stops dropping. The total DO drop at this point represents the "ultimate BOD" (also called BODu or sometimes BODL for "limiting BOD"). Twenty to thirty days is a long time to wait, so usually the bottles are opened and measured after 5 days, and the test results are reported as the "5-day BOD" or BOD5. Originally, 5 days was chosen as the incubation time because that is the longest travel time of any river in Britain. We continue to use this value today, although the choice of incubation time is really arbitrary. To convert between BOD5 and BODu, we need to know something about the kinetics of the BOD test. Suppose we set up 7 BOD bottles on day 0. Periodically over the next month, we open a bottle and measure the DO. If we use these DO values in the BOD equation shown above, we would see an increasing BOD result. In other words, BOD1 > BOD2 > BOD3 … because DO1 < DO2 < DO3 …. If we plot the BOD values against time, we get a curve like that shown in Figure 2.

Figure 2 Increase of BOD values with time

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Notice that the measured values of BOD start at 0 and end up at the ultimate value. When you compare Figure 2 with Figure 1, you see that Figure 2 is actually Figure 1 flipped over. While it is not always true, very often we can fit a first order exponential model to these data. The equation of the model is: BODt = BODu (1 - e-kt)

If you plug "5" in for "t", you can convert between BOD5 and BODu using this equation.

It is important that you understand the difference between BODu and BODt. BODu is proportional to the total biodegradable organic content of the water. If you add more biodegradable organic material to water, BODu will increase. BOD5 is the amount of BOD exerted in the 5-day test and is proportional to the amount of organic material degraded in 5 days. It is normally assumed that BOD5 is proportional to the BODu but this may not always be true. In Figure 3 for instance, three samples all exerted about the same BOD5, yet they all had different BODu's. How might this happen? Different organic substances degrade at different rates. Most waters contain a mixture of organic substances. In two samples, if the amounts of organic substances degradable in 5 days are equal, then the BOD5 values will be equal. The two samples could have different amounts of organics that degrade more slowly, so the BOD u values will be different.

Figure 3. Measured BOD variation over time for different organic substances

Please note that the first order model does not always fit BOD data. Don't be surprised if in real life, you get data that doesn't plot out in such neat curves. Like any mathematical model, use the first order equation with care.

Finally, there is one more kinetic issue to consider. Suppose we put a water sample with biodegradable organics into a batch reactor and supply it with oxygen in the form of air bubbles. Now suppose we take a sample out each day and test the sample in a BOD5 test. We would see that the BOD5 of the original water decline over time as shown below:

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Figure 4 BOD decay over time

What we see here is that the BOD5 of the water declines over time. If the k value is constant, then the relationship between BOD5 and BODu will be constant. So if the measured BOD5 declines over time, the BODu, representing the organic material in the water, also declines over time. In other words, the organic material remaining in the water is being converted to something else -- CO2 and other nondegradable substances -- by the bacteria. Often, a first order decay reaction can be fit to these data. If the organic material in the water (expressed in BOD units) is called "L" (as it is in your book), then

L = L0 e-kt

Usually L is measured as BODu. We will see this relationship often in solving mass balance problems for the degradation of organic materials in streams, lakes, or treatment plants. Be warned, however, that not all organics decay according to a first order model. Don't be surprised by real-life data following a different pattern.

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LAB 4: ADSORPTION Objectives The purpose of this exercise is to demonstrate the phenomenon of adsorption and compare the adsorptive behaviors of different materials. Batch adsorption tests will be conducted using methylene blue (MB), a cationic organic dye, and several different adsorbents (activated carbon, clay, and sand). Background Adsorption of solutes originating from the bulk of one phase on to the surface of an adjacent phase occurs throughout nature. This mass transfer process is used to remove contaminants in water treatment operations. The Freundlich and Langmuir isotherms are two mathematical models commonly used to describe adsorption phenomenon. The isotherm is an empirical relation between the concentration of a solute on the surface of an adsorbent (mass/mass) to the concentration of the solute in the liquid with which it is in contact (mass/volume or mass/mass). Another model is the B.E.T. The Freundlich isotherm equation is as follows:

q = x/m = KCe 1/n

where: K and n are empirical coefficients; K represents adsorption capacity at unit concentration 1/n represents strength of adsorption.

x = mass of MB adsorbed (mg) = (mass of MB in the liquid at the start) - (mass of MB in the liquid at the end) = (Ci*VMB)start - (Ce*VMB)end = (Ci - Ce)VMB Ci = initial concentration of MB in the solution (mg/L) Ce = final concentration of MB in the solution when at equilibrium (mg/L) VMB = volume of MB solution (L) m = mass of adsorbent (the material that adsorbs MB) (mg)

Procedures Calculating the methylene blue concentration Methylene blue can be measured using a spectrophotometer. The intensity of a ray of monochromatic light decreases exponentially as the concentration of light-absorbing material in the medium (water in our case) increases (Beer's Law). A spectrophotometer can sense the absorbance of light at specified wavelengths.

Absorbance = log(I0/I) = proportional to concentration where I0 and I are the intensities of the light entering and leaving the test sample, respectively. Light absorbance at a wavelength of 655 nm has been found to work well for detecting methylene blue. The absorbance can be related to the concentration of the light-absorbing substance through use of a linear calibration curve. 1. Your instructor will provide a series of dilutions of a stock methylene blue solution. Use a pipet to

remove about 10 mL of the solution and place it into a small test cell designed for the spectrophotometer (we will use the square 10 mL sample cells).

2. Zero the spectrophotometer unit using deionized water, then measure absorbance values of the standards your instructor gives you and report those values to the class to be recorded in your lab notebook.

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3. Plot concentration of standard (y-axis) against absorbance (x-axis) and use the trendline function on the computer (in Excel) or on your calculator to fit a linear curve through the data. Be sure to include the equation for the curve on your plot. What we want is a calibration curve equation that yields concentration values when experimentally-found values of absorbance are plugged in to it.