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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)

Co nc

en tr

at io

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 usedDOofMassBOD ´==

The shorted version is:

P DO-DOBOD 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 DODOBOD 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 BODu 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 = KCe1/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.

4. Use this equation to calculate methylene blue concentrations from absorbance values in the rest of the lab.

Adsorption Test 1. Place 50 ml of methylene blue solution into four100-ml beakers. 2. Weigh out the adsorbent material assigned to your group and prepare to add it to the beakers with the

dye in the next step. It's OK if you don't hit the specified amount exactly; just record the mass you use.

Mass of Adsorbent: 0.01, 0.05, 0.10, & 0.50 grams 3. When your instructor gives the signal, add all of your adsorbent masses to the flasks containing MB

and swirl or stir the beakers for 15 minutes. 4. Transfer approximately 15 mL of solution from the top of your beaker (avoid the solids) into

centrifuge tubes and give it to your instructor for centrifugation. 5. After centrifugation, remove your tube. Use a pipet to remove about 10 mL of the supernatant, and

place it into a small test cell. Do this step very carefully. Suspended solid material will cause you to get an inaccurate absorbance reading.

6. Put the test tube into the spectrophotometer and read the absorbance.

Data Analysis 1. Calculate the mass of MB adsorbed per mass of adsorbent, q = x/m 2. Using your data, plot either:

a. log(x/m) as a function of log(Ce) on arithmetic scales. A linear trend line is used to obtain the Freundlich coefficients as follows: K = 10y-Intercept and 1/n = the slope.

b. x/m as a function of Ce on log-log scales (as shown in Figure 1 below). A power function trend line yields the Freundlich equation directly.

3. Exchange data with your classmates; Compare the results; In the final report explain why the adsorption capacities of the materials are different.

4. For the best adsorbent use the Freundlich isotherm equation to generate a smooth plot and plot values of x/m as a function of Ce on arithmetic scales.

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Figure 1. Example of Freundlich Isotherm-generated data plotted on log-log scales. When plotted in this manner a power function trend line yields the Freundlich equation directly. [Note: When plotting Log(q) vs Log(Ce) on arithmetic scales a linear trend line is used to obtain the Freundlich coefficients as follows: K = 10y-Intercept and 1/n = the slope.]

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LAB 5: SOLIDS IN WATER

BACKGROUND

Tests will be performed to measure solid materials present in wastewater. These tests are of great use in assessing the reuse potential of a wastewater and in determining which types of treatment processes are best for the wastewater. Four types of tests will be performed to determine total solids (TS), total suspended solids (TSS), volatile suspended solids (VSS), and turbidity. The measure of solid materials within water supplies is of particular importance to engineering practice. While the effects of such measures are of primary concern to environmental and biological engineers, they are not independent of other engineering applications. Water’s abundance and its significant role in life processes has made it into one of the many commonalties shared by all engineering disciplines. As such, the effects that solid materials have on water’s chemical and physical properties are of considerable importance to the practicing engineer. With this in mind, this lab was developed to familiarize one with four different measures of solid materials in water and to provide a means to obtain such measures.

TOTAL SOLIDS

The first measure, total solids (TS) deals with both undissolved and dissolved solids. Undissolved solids are usually referred to as suspended solids (discussed further below). Total solids, as the name implies, is a measure of all residue left after evaporation of the water phase, usually at around 103 C. This test consists of placing a known volume of a sample in a pre-weighed evaporating dish, allowing all water to evaporate, and then determining the mass of dried solids as the difference between the dish plus dried solids and the dish alone. Total solids is calculated as mass of dried solids divided by the sample volume as follows:

Note: A & B are defined differently here than in the eqn.’s that follow.

where: TS = Total Solids (mg/L) A = Final mass of container with sample after dry (mg) B = Initial mass of empty container (mg) V = Sample volume (mL)

There are many reasons for determining the total amount of solids present in water. One reason is for determining if water is suitable for domestic use, such as for drinking water. Water that contains more than 500 mg/L of solids often has a laxative effect on humans, especially those who are not accustomed to it (Schroeder 1987). It is also extremely valuable in analyzing raw and digested sludges, which is important when designing and operating sludge-digesters, vacuum-filters, and incinerators for wastewater treatment facilities. Another use of the total solids test is in detecting changes in the water density of waterways to determine if there is possible contamination from wastewater.

TOTAL SUSPENDED SOLIDS

The second measure concerns total suspended solids (TSS). Suspended solids are the undissolved solids present in water. Analysis of suspended solids is useful when the turbidity measurements do not provide adequate information and is very valuable in analyzing polluted waters. Measurement of suspended solids aids in evaluating the strength of wastewaters and helps when evaluating the efficiency of treatment facilities. While total solids measured all solid material, total suspended solids is a measure of only those solids that are larger than approximately 1.2 µm in size and typically held in suspension within the sample. In other words, total suspended solids are those that are “undissolved”. The measurement of TSS is accomplished by means of a filter that removes all suspended solids within a given sample. Total suspended solids can be classified into two main categories, those that are volatile and those that are not.

V 1000 xB)-(ATS=

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Note: A & B are defined differently here than in the other equations.

where: TSS = Total Suspended Solids (mg/L) A = Final mass of container with filter and sample after dry (mg) B = Initial mass of container with filter (mg) V = Sample volume (mL)

VOLATILE SUSPENDED SOLIDS

Volatile suspended solids (VSS), also called organic solids, are solids that are combustible at 550 C. The volatile solids test is often used in estimating the organic characteristics of solids present in a wastewater and thus is an indirect measurement of the organic matter present. VSS is measured by igniting the total suspended solids and measuring whatever is left. The mass that is left behind after combustion is a measure of the non-volatile solids while the mass lost during incineration comprises the amount of volatile solids.

V 1000 xB)-(AVSS= Note: A & B are defined differently here than in the other equations.

where: VSS = Volatile Suspended Solids (mg/L) A = Mass of container with filter and sample after drying and before ignition (mg) B = Mass of container with filter and sample after ignition (mg) V = Sample volume (mL)

TURBIDITY

The final measure of solid material within water is called turbidity. The turbidity test is useful in water treatment for determining the quality of drinking water. When colloidal (clay-size) particles are present in the water (mud puddle water for our purposes), they cause incoming light to become scattered, thus causing the water to appear cloudy or turbid. The portion of light that scatters at an angle of 90 degrees from the direction of the source light is measured using photo-sensitive cells. A turbidimeter is an instrument capable of measuring turbidity. Turbidity is often measured using a special the unit NTU.

CONCLUSION

The measure of solid materials within water supplies is of particular importance to engineering practice. While the effects of such measures are of primary concern to environmental and biological engineers, they are not independent of other engineering applications. Water’s abundance and its significant role in life processes has made it into one of the many commonalties shared by all engineering disciplines. As such, the effects that solid materials have on water’s chemical and physical properties are of considerable importance to the practicing engineer. In this Lab, tests will be performed to measure solid materials present in wastewater. Four types of tests will be performed to determine total solids (TS), total suspended solids (TSS), volatile suspended solids (VSS), and turbidity.

V 1000 xB)-(ATSS =

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LAB 5: PROCEDURES (Measuring solids in water)

Purpose of Lab The purpose of this lab exercise is for the student to become familiar with four different measures of solid materials in water: (1) total solids (TS), (2) total suspended solids (TSS), (3) volatile suspended solids (VSS), and (4) turbidity. Procedures Total Solids 1. Weigh two (2)* clean evaporating dishes on the precision balance (the one with a glass enclosure

with sliding sides). Record those values. 2. Add a known volume of representative sample (about 10 ml) to the dish and place it in the drying

oven (at 105 C) until the water is completely evaporated away. 3. Weigh the evaporating dish plus sample. Record that value. 4. Remove the dish from the oven and cool in a dessicator. 5. Reweigh the dish (with solids) and record the mass. * Normally three or more samples would be analyzed. Do you know why? We are using less due to the

limited time available during the lab period. Total and Volatile Suspended Solids (TSS and VSS) 1. Obtain two (2) filters and aluminum boats from your instructor. These filters will have been

previously washed and dried. Because you are weighing things on an analytical balance, which can read 1/10,000 gram, you want to be careful to avoid contaminating the sample with dust or dirt from the bench top, oils from your fingers, etc. So, handle the filters and boats with tongs or tweezers at all times, and rest them only on clean surfaces. One suggestion is keep the boats on a designated clean piece of paper.

2. Identify the boat with a physical mark (indentation). This is your identification mark, so take care that each filter stays with the same boat.

3. Weigh the aluminum boats with the filters in them on the analytical balance. Record those masses. 4. Using tweezers, place a filter on the suction apparatus as directed by the instructor. Be sure the filter

flask is clean. 5. Filter 25 to 50 mL of representative sample (or another volume as directed by the instructor). You

want to put as much sample through the filter as you can without causing it to clog. Stop adding sample when the flow rate through the filter slows noticeably. Approximately 15 ml of filtrate will be needed for turbidity measurement.** Record the amount of sample filtered, and take care that your sample is well-mixed at all times. ** Dilution, while not desirable, may be necessary for water containing significant amounts of particulate

matter in order to obtain 15 ml of filtrate. If done, the resulting TSS and VSS values must be multiplied by the appropriate dilution factor and diluted sample must be used for the initial turbidity reading.

6. Turn off the vacuum, and without disassembling the filter holder and funnel, remove them from the filter flask. Pour the filtrate into a labeled beaker for later turbidity analysis. Replace the filter holder and funnel and restart the vacuum.

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7. Wash the filter with three successive washings of deionized water (about 10 mL each) while continuing suction. Wait 3 minutes between washings. If some solids have been caught in your glassware (graduated cylinder, funnel), rinse them out with these washings.

8. Turn off the suction and, using tweezers, place the filter in its boat. 9. Repeat steps 4-8 for each sample as directed by your instructor.

10. Place the all the aluminum boats and filters in the drying oven (at 105 C) for at least one hour. 11. Remove the aluminum boats and filters from the oven and place in the desiccator for at least 15

minutes or until they are at room temperature. 12. Weigh the aluminum boats and filters. Record those values.

13. Place the filters and boats into the muffle furnace (at 550 C) for 20 to 30 minutes. The muffle furnace is hot, so be careful!

14. Remove the filters from the muffle furnace and place them into the desiccator for at least 15 minutes or until they are at room temperature.

15. Weigh the filters and record the masses again. Look again at the filters. How do their appearances

compare with their appearances before combustion at 550 C? Turbidity 1. Turbidity is measured on an instrument. Your instructor will describe how to use the instrument. 2. Measure and record the turbidities of the available water samples as directed by your instructor. 3. Measure and record the turbidities of the filtrates for those samples you used in the TSS test. Data Analysis Calculate the TS values for the samples you analyzed. TS is the mass of dry solids on the dish (after drying at 105 C) divided by the volume of sample passed through the filter. Express your results in mg/L (milligrams of dry particles per liter of suspension). Show all your work in your lab notebook. Calculate the TSS values for the samples you filtered. TSS is the mass of dry solids on the filter (after drying at 105 C) divided by the volume of sample passed through the filter. Express your results in mg/L. Show all your work in your lab notebook. For the samples you combusted at 550 C, calculate the VSS. VSS is the mass of dry solids that

volatilized (left) the filter after combustion at 550 C divided by the volume of sample passed through the filter. Express the VSS in mg/L and as a percentage of the TSS. For the samples you filtered, calculate the percentage of solids captured on the filter based on the percentage change in the turbidity. How does this value compare with the ratio of TSS to TS based on mass measurements? If there is a difference, explain why.

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Discussion Questions

1. Calculate the total volume of the samples used in the TS test based on a calculation of the sample mass from measurements made on the analytical balance and on an assumption that sample density is 1.00 kg/Liter. Compare the gravimetric-based calculated volume with the volumetric measurement. Which method is more accurate? Why? Under what circumstances would you use one method rather than the other?

2. Knowing what you do about the source of the water sample tested, and the nature of the particles in the sample, do your lab results make sense? Explain why or why not. (For instance, are the relative TSS and VSS values what you expected, or were there any surprises?)

3. What fraction of the turbidity was removed on the glass fiber filter? If that fraction is less than 100%, discuss why all the turbidity wasn't removed. (Hint: What was in the filtrate?)

4. Do the TSS and turbidity tests measure the same thing? When would you use one type of measurement and when the other? (Second hint: Think about mass vs. number.)

5. Would you expect the analytical results to be higher than, lower than, or the same as the true value under following conditions, and why?

a. Weighing a warm crucible? b. Estimate the organic content by volatile-solids analysis of a sample containing a large

quantity of organic materials having high vapor pressure. c. Estimate the organic content of a sample by combustion at 800oC

Lab Write-up 1. Report your data and the results of your calculations in your lab notebook.

1. Provide sample calculations for every different kind of calculation done. Be sure to check for appropriate significant figures.

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Example data table format:

Water Sample Identification Table Sample ID Description of Sample

Total Solids (TS) data and calculated results. Sample

No. Mass

boat (g) Mass boat + sample

before drying (g) Mass boat + solids

after drying (g) Vol. of

sample (mL) Mass of

sample (b) Total Solids

(mg/L)

Total Suspended Solids (TSS) and Volatile Suspended Solids (VSS) data 1 Sample

No. ID Number

on Boat Mass of clean

filter and boat (g) Mass of filter, boat, and solids after drying (g)

Mass of filter, boat, and solids after combustion (g)

Total Susp. Solids (TSS) and Volatile Susp. Solids (VSS) data 2 and calculated results. Sample

No. Volume of sample

filtered (mL) Total Suspended Solids (mg/L)

Volatile Suspended Solids (mg/L)

VSS/TSS ratio (expressed as %)

Turbidity data and calculated results Sample

No. Turbidity of sample

(NTU)

Turbidity of filtrate

(NTU)

Percent of turbidity removed by filtering (%)

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LAB 6: CHEMICAL COAGULATION JAR TESTING INTRODUCTION Coagulation is accomplished through neutralization of negatively charged colloidal (clay size) particles. This is necessary since the repelling forces between the particles, due to their negative surface charge, is greater than the attractive body forces when the particles are separated. For this reason, without the neutralization process, particles do not collide, stick together and grow into larger particles that would settle to the bottom, thus, the small particles remain in suspension.

The purpose of chemical coagulation is to condition the water such that small particle growth is promoted, thus increasing particle size and density. The physical process in which the particles actually group together forming “flocs”, is known as flocculation. This increase in size and density of the particles facilitates removal in gravity sedimentation and water filtration processes. Coagulation and flocculation are two separate stages. They play a vital role in improving the aesthetics of drinking water and also remove microorganisms and other contaminants that can be harmful to our health.

BACKGROUND

Coagulation refers to the chemical alteration of the suspended particles that allows the particles stick together in larger clumps called flocs. Flocculation refers to the physical process that collects these flocs into even larger clumps that easily settle out by means of gravity. Particles in water can be classified into two different size groups: colloidal and suspended solids. Colloidal particles, also referred to as colloids range in size from 1 micrometer to 5 nanometers while suspended solids generally consist of particles larger than 0.5 micrometers. These particles can also be differentiated by the nature of how they react with water molecules. Hydrophobic particles are defined by having a low attraction to water and are generally inorganic in origin. Hydrophilic particles react more readily with water and often consist of organisms both living and dead such as bacteria, algae and viruses. Regardless of which group these particles may fit into it is their chemical properties and not their size that dictates the way in which they will react during the coagulation and flocculation processes.

Almost all colloidal particles have a negative charge, meaning that they will be attracted to particles holding a positive charge and repel other particles that are also negative. This tendency to repel other negatively charged ions slows the process of gravity induced settling considerably. Due to this slow rate of settling it is necessary to artificially expedite the rate at which the particles can be separated.