ABSTRACT

The objective of this experiment is to determine the amount of oxygen required to

determine the pollution and purification strength of waste and receiving bodies of water.

Through this experiment, the BOD is determined to be -160 mg/L and 7.6 mg/L, the TSS is

determined to be 490 mg/L and 54 mg/L and the VSS is determined to 410 mg/L and 28

mg/L for influent and effluent accordingly. After water treatment of influent, the effluent

amount is below the 20mg/L of BOD and 500mg/L of TSS standards set by Canadian

wastewater control, and therefore is acceptable to flow back into natural water resources.

TABLE OF CONTENTS

TABLE OF CONTENTS ……………………………………………….…………………………………….…1

INTRODUCTION ……….…………………………………………………………………….……………….…2

OBJECTIVE ………………………………………………………….……………………….………….2

BACKGROUND …………………………………………………….…………………………………..2

METHODS AND MATERIALS ………………………………………………….……………….……….….3

APPARATUS ………………………………………………………….…………………………………3

METHODS ………………………………………………………….…………………………………….3

RESULTS ……………………………….…………………………………………………………………..……….4

DATA RESULTS …………………………….…………………………………………………...….….4

SAMPLE CALCULATIONS ………………………………………………..……………….………..6

DISCUSSION …………………………….………………………………………………………………………….7

CONCLUSION …………………………….…………..…………………………………………………………….8

REFERENCES …………………………….…………………………………..…………………………………….8

APPENDICES…………………………….………………………………………………………………………….9

APPENDIX A …………………………….………………………………….……………………….....10

INTRODUCTION

OBJECTIVE

The purpose of this experiment is to:

a) determine the BOD concentration and percentage depletion from the difference of

dissolved oxygen amount of no incubation and a seven day incubation at 20°C

b) determine the total and volatile suspended solids by filtration and drying.

This experiment will focus on the methods of taking BOD tests. The Winkler test will

also be carried out to observe & determine the depletion of dissolved oxygen.

BACKGROUND

Biochemical oxygen demand (BOD) is defined as the amount of oxygen required by

bacteria, while stabilizing decomposable organic matter under aerobic conditions.

The significance of a BOD test is to examine the amount of oxygen required to

determine the pollutional strength of domestic and industrial wastes & purity of water

bodies. It is one of the most important tests in regulating stream-pollution-control

activities. The BOD test looks at the amount of oxygen consumed by living organisms

that are feeding off organic matter present in waste. The test is generally performed in

such a manner as similar to naturalistic conditions as possible, since the test ultimately

studies the pollution of water bodies in everyday conditions. In order for the test to be

quantitative, the samples must be protected from air to prevent the reaeration as the

dissolved oxygen level diminishes. Also, since oxygen has limited solubility in water (9

mg/L @ 20 degrees celsius), it is necessary to dilute the wastewater samples as the test

is performed.

The Winkler test is a procedure in determining the amount of oxygen that dissolves in

water. The significance of dissolved oxygen (in wastewaters) allows for one to

determine the environmental changes brought about by aerobic and anaerobic

organisms. Dissolved-oxygen measurements are necessary in maintaining the aerobic

conditions in natural waters that receive pollutional matter in aerobic treatment

processes intended to purify domestic and industrial wastewaters.

METHODS AND MATERIALS

PROCEDURE

Please refer to CHEM 2560 – Water Quality Analysis for Engineers 2010 Laboratory

manual – Experiment 4 for the detailed procedure this experiment followed

APPARATUS

Please refer to CHEM 2560 – Water Quality Analysis for Engineers 2010 laboratory

manual – Experiment 4 for a list of materials used in this experiment

RESULTS

DATA RESULTS

TABLE 1 - Dilution Factor, DO1 and DO2 for Dilution Water, Influent and Effluent

DF DO1 (mg/L) DO7 (mg/L)

Dilution water 0 4.60 5.10 Influent 70 4.01 6.30 Effluent 10 4.23 1.03

Note: DO1- dissolved oxygen with no incubation

Note: DO7- dissolved oxygen with 7 days of incubation at 20°C

TABLE 2: BOD and Percentage Depletion for Dilution Water, Influent and Effluent

BOD (mg/L) % DepletionDilution water 0 -10.9 %Influent -160.3 -50.4 %Effluent 7.565 17.9 %

TABLE 3 - Weight of Crucible, Total and Volatile Suspended Solids for Influent and Effluent

W1 (g) W2 (g) W3 (g) OS volume (mL)Influent (V 4) 17.7240 17.7289 17.7248 10 Effluent (V 7) 17.3837 17.3864 17.3850 50

Note: W1 – weight of crucible by it selfNote: W2 – weight of crucible plus total suspended solids Note: W3 – weight of crucible plus volatile suspended solids

Note: OS – original sample volume

TABLE 4: Total Suspended and Volatile Suspended Solids for Influent and EffluentTSS (mg/L) VSS (mg/L)

Influent (V 4) 490 410Effluent (V 7) 54 28

SAMPLE CALCULATIONS

Part 1: Winkler Titration for BOD

Calculating Dilution Factor (DF)

Dilution Factor = Volume of Dilution Water / Volume of SampleDF of Influent = 700ml / 10ml DF of Influent = 70

Calculating BOD Milligram per Litre

BOD (mg/L) = (DO1-DO7) x DFBOD of Influent = (4.01 – 6.03) mg/L x 70BOD of Influent = -160.3 mg/L

Calculating Percentage Depletion

% Depletion = (DO1-DO7) / DO1

% Depletion of Influent = (DO1-DO7) / DO1

% Depletion of Influent = (4.01-6.03)/4.01 %% Depletion of Influent = -50.4 %

PART 2 – SUSPENDED SOLIDS PROCEDURE

Calculating Total Suspended Solids (TSS) Milligram per Litre

TSS (mg/L) = (W2 – W1) x / Original Sample VolumeTSS of influent = (17.7289 – 17.7240) x 106 / 10 TSS of influent = 490 mg/L

Calculating Volatile Suspended Solids (VSS) Milligram per Litre

VSS (mg/L) = (W2 – W3) x / Original Sample VolumeVSS of influent = (17.7289 – 17.7248) x / 10 VSS of influent = 410 mg/L

DISCUSSION

From this experiment, the BOD of the wastewater sample analyzed was determined to be -160.3 mg/L for the solution diluted with influent and 7.565 mg/L for the sample diluted with effluent. Also from the same wastewater sample, the TSS & VSS were determined to be in concentrations of 490 mg/L & 410 mg/L for influent and 54 mg/L & 28 mg/L for effluent, respectively.

In the Winkler test, the observations made did not verify with the theory of the dissolved oxygen’s depletion over a 7-day period. In fact, it was observed that more titrant was necessary after solutions sat for 7 days, for the influent samples. As seen from the % depletion of our blank sample of dilution water & influent sample, we see that oxygen concentration actually increases. This suggests that an error was present in our experiment. Such possible sources of error may have risen from the improper sealing of the crucibles, which would have allowed for air to enter the samples. This causes error in the data since outside sources of oxygen might contribute to reaeration in the solutions. Other possible sources of error would include the loss of dissolved oxygen during transfer from its package to the BOD bottles. It was also observed that the stoppers used in this experiment were not perfectly aligned to fit to the BOD bottles used, causing for an inevitable bubble to be present in the solution. This might have allowed for air to enter the solution, hence allowing for outside oxygen to add to the system. To improve this error, one should have used extra precaution in closing the system. Such measures of preventing this error include:

a) Sealing the flask with water and leaving the bottles in a closed fumehood or oven (set at 20 degrees Celsius) for the duration of the 7-day period.

b) Making sure the bottle stopper is aligned properly or using a vacuum to leave the systems (bottles) in.

The Canadian wastewaters regulation of BOD in a wastewater sample is 20 mg/L over a 5-day incubation period. Neglecting the samples we analyzed which gave inaccurate results, we will only consider the sample diluted with effluent (treated sample), since it gives reasonable results. The sample was found to be 7.6 mg/L BOD. Since this falls under the standard accepted BOD concentration, it could be said that the wastewater sample we analyzed is acceptable to flow back into the streams after being treated with effluent and will not be considered a hazard to the environment and aqua life. The sample containing influent, had the results been accurate according to theory, should give a result that contains a BOD concentration higher than that which was treated with effluent, since effluent is a treatment source that feeds the microorganisms.

It should also be noted that the sample BOD concentration is not completely precisely accurate in comparison to the Canadian wastewater standard of BOD level. This is because the sample that was analyzed was left under a 7-day incubation period, where as the standard

is suggested to be studied after a 5-day incubation period. For this reason, it should be noted that more time is given for the sample to be depleted of oxygen, and thus giving a BOD result that is likely to be lower (after a 7-day incubation period than a 5-day period). With this said, it is hard to say whether or not the results obtained from this laboratory experiment provides sufficient data to make an accurate conclusion for the wastewater sample analyzed.

APPENDICES

APPENDIX A – SUSPENDED SOLIDS DATA

Source: http://angel.cc.umanitoba.ca - Posted November 24th, 2010 by Victor Wei, lab instructor for CHEM 2560 – Water Quality Analysis for Engineers