National University of Singapore Department of Civil and Environmental Engineering

ESE2401 Water Science and Technology

Session 2014/2015

Laboratory Manual

for

Experiment E1 & E2

Venue: EW2 03-14 ESE Teaching Lab.

Name_________________________________________

Group_________________________________________

Date of Experiment ______________________________

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Laboratory Hazards: A Warning Many reagents require handling with the utmost care, either in their original state or in solution or both. This is to protect the health and safety of the user. Reagents bearing labels with the word POISON, DANGER, CAUTION, FLAMMABLE, or comparable warnings must be handled with special care. Concentrated acids and bases may cause chemicals burns and are especially hazardous if spilled or splashed into the eyes. Always handle with extreme care to avoid contact. In diluting concentrated acids, always add acid to water to prevent local overheating and possible injury; never add water to acid. Students are advised to use face shields or safety glasses and to familiarize themselves with the positions of the eye wash fountains. Mercury and its compounds are used to prepare standards, displace gases and preserve samples. These compounds must always be handled with extreme caution as they are very toxic. Sodium azide (APHA) is toxic and reacts with acid to produce more toxic hydrazoic acid. Avoid inhalation, ingestion and skin exposure. The samples provided may also contain pathogenic organisms. Students must wash their hands before leaving the laboratory and are advised to leave their belongings well away from the work benches to avoid possible contamination. Food should not be brought into the laboratory. Eating, drinking and smoking are not allowed in the laboratory. Students are required to wear shoes which cover their feet. Students are expected to clean up all the equipment used during their experiments before leaving the laboratory.

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Experiment E1 & E2

The purpose of these experiments is to illustrate some of the tests used to assess selected properties of water and wastewater. Experiment E1

Purpose To determine the various categories of solids that are commonly defined in water and wastewater analyses and to investigate the nature of the materials that these solids categories define.

1a) Gravimetric Analysis Introduction Gravimetric analysis is based on the determination of constituents by measurements of their weights. In addition to weighing, gravimetric analysis involves three other techniques. These are filtration which separates suspended or particulate fractions from the dissolved fractions, evaporation which separates water from the material dissolved or suspended in it and combustion which separates the inorganic material from organic matter by destroying the latter. Total Solids and Total Volatile Solids This includes both dissolved and suspended material. Apparatus: 1. Porcelain or nickel dishes 2. Steam Bath 3. Oven 4. Furnace 5. Analytical balance 6. Dessicator Procedure: 1. Weigh an ignited nickel or porcelain dish, W1. 2. Add 25 mL of sample (more is sample contains little suspended material). 3. Evaporate to dryness on a steam bath. 4. Further drying of samples for 1 hr at 103oC (due to time constraint, students may

dry samples for ½ hr at 103oC) in an oven. 5. Cool samples in a dessicator and weigh, W2. 6. Place dishes into a furnace at 500oC for 20 min. 7. Remove from furnace and allow dishes to cool slightly before further cooling in a

dessicator. Reweigh., W3.

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Calculations

Total solids, (mg/L): sampleofVolWWTS 12 −=

Total volatile solid, (mg/L): sampleofVolWWTVS 32 −=

Total fixed solid, (mg/L): sampleofVolWWTFS 13 −=

Suspended Solids and Volatile Suspended Solids Apparatus: 1. Filter apparatus 2. Vacuum pump 3. Drying oven 4. Muffle furnace 5. Analytical balance 6. Glass fibre disks 7. Dessicator Procedure: 1. Weigh pretreated fibre disk (stored in dessicators) and container, W1.

(Warning: do not remove more than one disk for weighing at any given time. Disks absorb moisture from fingers and the atmosphere very quickly resulting in erroneous values of W1. Weigh disks must not be marked).

2. Carefully place glass-fibre disk in the filter apparatus. 3. Apply a vacuum and wet the disk with distilled water. 4. Add 25 mL of sample (more if sample contains little suspended material). 5. Remove the disk from the filter apparatus and transfer to its container, dry at

103oC for 1 hr; cool to room temperature in a dessicator then weigh, W2. 6. Place dishes into a furnace at 500oC for 20 min. (Warning: do not use aluminum

dishes). 7. Remove from furnace and allow dishes to cool slightly before further cooling in a

dessicator. Reweigh, W3. (Warning: when loading or removing samples from a furnace or oven use protective gloves and tongs).

Calculations

Suspended solids, (mg/L): sampleofVolWWSS 12 −=

Volatile suspended solid, (mg/L): sampleofVolWWVSS 32 −=

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Fixed suspended solid or residue, (mg/L): sampleofVolWWFSS 13 −=

1b) Turbidity Introduction The technique used is based on nephelometry (i.e., the measurement of the forward scattering of light at 90o to the path of an incandescent light beam). Suspended particles in a water sample reflect a portion of the incident light. A photoelectric detector measures the light reflected at 90o and compares this against light reflected by a reference standard. The higher the turbidity the higher is the intensity of scattered light. Formazin polymer is used as the reference turbidity standard suspension. Turbidimeters are usually calibrated to read directly in nephelometric turbidity units (NTU). Apparatus: 1. Turbidimeter 2. Formazin reference standards Procedure: 1. Switch machine on to warm-up. 2. Place reference standard into sample well and follow calibration instructions (Hold reference standard tubes only by the top. Glass surfaces must be kept clean.

Wipe surfaces with the lens tissue provided.). 3. Thoroughly mix samples provided and collect approximately 200 mL of each. 4. Rinse a clean sample tube with the sample; then fill the tube ¾ full. 5. Tap the tube to remove any air bubbles. Wipe glass surface clean. (Hold reference standard tubes only by the top). 6. Place sample tube into sample well and cover with shield. Read the scale and

report turbidity in NTU. 1c) Conductivity Introduction The ability of an aqueous solution to carry an electric current depends on the presence of ions and on the temperature of measurement. A numerical expression of this ability is conductivity. Solutions of most inorganic acids, bases and salts will have relatively high conductivities but solutions or organic compounds will not conduct a current well. The conductance of a solution is the reciprocal of its resistance and is given the units of mhos (i.e. reciprocal ohms). The specific conductance, K, of a solution is the conductance of 1 cc of solution between electrodes of 1 sq cm area which are 1 cm apart and has units mho/cm. In a conductivity meter, resistance measurements are made and converted to conductance on the instrument read out. Since conductivity cells used do not have electrodes exactly 1 sq cm. in area and 1 cm apart, readings must be corrected to standard conditions by using a cell constant. The conductivity of a particular sample can usually be related to the dissolved solids content.

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Apparatus: 1. Conductivity meter Procedure: 1. Rinse cell with sample to be tested. 2. Collect about 100 mL of sample in a beaker. 3. Measure the conductivity of the sample with the cell. Also record the temperature

of the sample. Calculation (if standard conditions do not apply to the electrodes) Conductivity = mq where m = specific conductance q = cell constant (Note: The instrument gives a direct reading from the scale and does not require the above calculation) 1d) pH Introduction pH or hydrogen ion activity indicates the intensity of the acidic or basic character of a solution. Measurement of pH is important because almost every phase of water and wastewater treatment is pH dependant. The pH of a sample is measured electrometrically by potentiometric measurement using a glass electrode and a reference electrode (calomel). Apparatus: 1. Buffer solution pH 4.0 2. Buffer solution pH 7.0 3. pH meter Procedure: 1. Check pH meter calibration with Buffer solutions provided. (Note: Always rinse

probe with distilled water before immersing it into a solution. On completion, place probe back into a beaker of distilled water.)

2. Collect samples in beakers and measure pH with probe. To provide gentle mixing during pH measurement, drop a magnetic bar into the beaker. Adjust magnetic stirrer so that there is only gentle mixing.

3. Read the meter and record results. 4. On completion leave probe in a beaker of water.

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1e) Chloride Introduction In costal areas, the presence of large amounts of chloride in wastewater indicates salt water infiltration of the collection system. Zeolite and ion exchange water softeners add chloride from regeneration. Human excretions also add chlorides. The chloride content should remain constant through the plant and have no significance in interpreting process changes or efficiencies. With a low pH they indicate industrial waste containing muriatic acid. Volumetric Techniques This depends on the measurement of volumes of liquid reagents of known strength. The requirements of this mode of analysis are: (i) Equipment to measure the sample volume accurately e.g. pipette. (ii) A standard solution of suitable strength. (iii) An indicator to show when stoichiometric end point has been reached. (iv) A graduated burette for accurate measurement of the volume of standard solution

necessary to reach end point. Apparatus: 1. Burette, 25 mL 2. Beakers 3. 5 mL pipette 4. Silver nitrate, 0.0141 N 5. Sodium Chloride, 0.0141 N 6. Potassium Chromate indicator Procedure: 1. Standardize silver nitrate solution. Add exactly 20 mL of sodium chloride to 1 mL of potassium chromate in a beaker.

Titrate as in step 4. Then,

Normality Constant, 3

N AgNOmLNaCl)(mLNaCl)of(NC =

2. Place 100 mL sample or a smaller amount diluted to 100 mL with distilled water

into a beaker. 3. Add 1 mL of potassium chromate. 4. Add silver nitrate solution from burette agitating the sample constantly until a

uniform pinkish-yellow end point is reached. Record volume of silver nitrate used, M1.

5. Repeat steps 2, 3 and 4 using 100 mL distilled water as sample. Record volume of AgNO3 used, M2.

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Calculations

mg/L Cl = sample ml

C x 1000 x 35.45 x )MM( N21 −

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Experiment E2

Measurement of Organic Strength The standard methods used for the measurement of the organic strength of samples (eg wastewaters and effluents) are COD, BOD and TOC. To enable the tests to be completed during the laboratory period the reaction times for the COD test have been reduced from the standard method. All of the determinations (except TOC) involve the measurement of the difference between initial and final amounts of an oxidizing agent and thus the sample must not exert such a high oxygen demand that no oxidizing agent remains at the end of the test.

3a) Chemical Oxygen Demand (COD)

(Closed Reflux Titrimetric Method) Overall objective Determine the oxygen equivalent required to completely oxidize organic matter contained in a sample of interest. Background Most types of organic matter are oxidized by a boiling mixture of chromic and sulfuric acids. The sample is refluxed in strongly acid solution with a known excess of potassium dichromate. After the digestion, the unreduced potassium dichromate is titrated with ferrous ammonium sulfate to determine the amount of potassium dichromate consumed and the oxidizable organic matter is calculated in terms of oxygen equivalent. COD is used as a measure of the concentration of organic matter in a sample of interest. It is a common means of expressing the strength of wastewater streams, especially as it relates to biological treatment. Typical applications Measuring COD of feed solutions or reactor contents for biological systems. Typically used for carbon or oxygen mass balances. Equipment and reagents required: Block Digester or oven at 150 °C Reflux Tubes, 16X100 mm Tube Rack Small TFE-covered magnetic stirring bar Magnetic Stir Bar Plate 0.0167 M Standard Potassium Dichromate Digestion Sulfuric Acid Reagent Ferroin Indicator Solution Standard Ferrous Ammounium Sulfate Titrant (FAS)

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Method 1. Add 2.5 ml of sample to reflux tube. Use distilled water for the blank. 2. Add 1.5 ml of digestion solution to samples. 3. Add 3.5 ml of sulfuric acid reagent to samples. 4. Tightly cap the tubes and shake. Be sure to wear face shield, gloves, and mitts

when shaking tubes, which become hot. 5. Digest tubes for 2 hours 6. Remove test tubes and cool to room temperature in a test tube rack 7. Add 2 drop of ferroin indicator and a magnetic stir bar 8. On a magnetic stir bar plate, titrate to red/orange endpoint with 0.2M FAS. The

endpoint is a sharp endpoint. 9. Dump waste into a hazardous waste container. Rinse the tubes with small amount

of distilled water, and pour into hazardous waste container. 10. Calculate COD as follows:

COD as mg O2 per L = (A - B) x M x 8000 / ml sample where: A = ml FAS used for blank B = ml FAS used for sample

M = molarity of FAS Notes, tips and caveats: Interferences may result from the presence of straight-chain aliphatic compounds, or nitrite. 3b) Biochemical Oxygen Demand: 5 day-BOD

A water sample is incubated for 5 days at 20°C. The reduction in dissolved oxygen content after the incubation period yields a measure of the biochemical oxygen demand. To obtain a reliable result the DO in the incubated sample should be a residual of at least 0.5 mg/l. Thus if a sample has a BOD higher than 7 mg/l, it will require dilution to prevent excessive oxygen consumption in the BOD bottle. It is usual to set up 3 dilutions to straddle a sample’s estimated BOD and the table below details the dilutions suitable for various BOD ranges.

PERCENT MIXTURE BOD COVERED

100 2-7 mg/l 50 4-14 20 10-35 10 20-70 5 40-140 2 100-350 1 200-700

0.5 400-1400 0.2 1000-3500 0.1 2000-7000

Apparatus and Reagents 1. DO meter + BOD self-stirring probe

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2. BOD incubator 3. Pipettes, beakers and 1 l measuring cylinders 4. Buffer solution (i.e. distilled water containing trace elements and phosphate

buffer). Procedure 1. Decide on dilution required 2. Using a 1 l cylinder prepare the desired dilutions for each sample. Make up 750 ml. 3. Carefully fill 2 BOD bottles to the brim (avoid the introduction of air bubbles

while pouring sample into the bottle) 4. Immediately determine the DO using the probe (DOSI) 5. On removal of the probe use a little distilled water to fill the bottle again and then

gently stopper it. Ensure that no air bubbles are trapped beneath the stopper. Also fill flare tops of bottle with distilled water.

6. Also incubate two bottles of dilution water after determining initial DO, DOBI. These are your blanks.

7. Determine final DO values in bottles after 5 days of incubation i.e. DOSF and DOBF.

Calculations

BOD mg/l = used sample offraction c volumetridecimal p,

)DO - (DO - )DO - (DO BFBISFSI

Eg. p = 0.1 if a 10% mixture is used. (3c) Total Organic Carbon: - Combustion-Infrared Method

The organic carbon in water and wastewater represents many compounds and oxidation states. Biological or chemical processes may oxidize some of these further but because there are organic compounds that do not respond to either COD or BOD, these tests may not be a satisfactory measure of total organic carbon (TOC). TOC, however, does not provide the same kind of information as either BOD or COD although it can be related to the latter two parameters if a sufficiently constant empirical relationship can be established. TOC analyzers offer a means of measuring total organic carbon in the range normally found in water and wastewater. Organic carbon is oxidized to CO2 by heat and oxygen and the CO2 is measured directly by a nondispersive infrared analyzer. Inorganic carbon must be compensated for since it usually forms a significant portion of the total carbon. Total organic carbon is commonly estimated by subtracting from total carbon the total inorganic portion.

Apparatus and Reagents: 1. Sample blender or homogenizer 2. Magnetic stirrer 3. Hypodermic Syringe

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4. Total Organic Carbon Analyzer 5. Redistilled water for preparation of blanks and standard solutions 6. Standard carbon solution 7. Air, dry and CO2 – free Procedure: Warning – Students should consult the technician in attendance before they operate the

Total Carbon Analyzer 1. If sample contains gross solids or other insoluble matter, homogenize. 2. Continuously stir sample with a magnetic stirrer following 1. 3. Withdraw a portion using the hypodermic syringe. 4. Inject into the analyzer and obtain peak height reading.

Repeat until 3 consecutive peaks are obtained that are reproducible to within ±10%.

5. From calibration curve provided obtain TOC readings. References 1. Standard Methods for the Examination of Water and Wastewater, 20th edition,

American Public Health Association, 1998. 2. Chemistry for Environmental Engineering, Sawyer, C.N., McCarty, P.L., 4th

edition, McGraw-Hill. 3. Environmental Chemistry, De, A.K., Wiley Eastern Ltd., 1987.

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Report for E1 and E2 Each student undertaking the two laboratory classes will have to submit two separate detailed formal reports – one on each experiment. Each report is due exactly two weeks after your laboratory class. Reports are to be submitted to the Water and Science Laboratory (WS2 02-32). Each report should include the following:

(i) Results neatly tabulated (ii) All calculations performed clearly set out (iii) A brief discussion on the sources of errors and ways to reduce them (iv) A brief discussion of the parameters investigated

− outlining their relationship with each other and − their importance in water quality analysis

(v) Conclusion The following questions may be found useful when preparing the formal report. The report, however, must not be seen to consist of a series of answers to the questions below: (i) Discuss the importance of the two temperatures used in gravimetric analysis. (ii) Tabulate TSS, TVS and TFS. Comment on their relative sources abundance with

reference to the possible of sources of the three samples provided. (iii) Discuss the relationship between turbidity and the gravimetric results and that

between conductivity and TFS. (iv) With reference to the possible sample sources, comment on your pH data. (v) From your chloride test, is there any sample which contains enough to affect the

COD test? Are you adding sufficient mercuric sulphate?

(vi) Discuss the significance of reflux time on COD yield using the dichromate oxidation method.

(vii) Tabulate BOD, COD and TOC values determined and calculate the ratios of BOD/COD, BOD/TOC and COD/TOC, comment on the samples’ relative biodegradability.

(viii) When considering the analysis of industrial wastes, it is imperative to evaluate the BOD, COD and TOC values for various classes of compounds and to attempt to correlate BOD and COD with TOC. Discuss the factors which might constrain or negate these correlations.

(ix) Discuss the effect of high dissolved solids on the results of COD tests. (x) Identify the most likely sources of the given samples.