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Background Of Study




Water is the main natural resources on Earth. According to Prakash (2005), “Water is essential to continue normal life”. Water can be found in many forms such as in liquid state, solid state, and gaseous state. The Earth is covered by water as much as 71%. Water can be obtained from various natural sources such as rivers, lakes, wells, and atmosphere. Water is also a renewable natural source as the water on Earth is evaporated and will be poured back to Earth by raining.

Water pollution is the contamination of water bodies. It occurs when pollutants are directly or indirectly discharged into water bodies without adequate treatment to remove harmful compounds. There are many sources of water pollution such as wastes from industrial area, farms, and also agricultural activities. According to World Health Organisation (WHO), the quality of fresh water is important for drinking water, food production, and recreational water activities.

Reservoir Park’s Lake is selected for the study. Reservoir Park is a recreational park where the public can use it for recreational activities such as jogging, picnic, and hawking. This park is located at the city centre. It is not located nearby housing areas, but people around Kuching would go to the Reservoir Park for a jog especially after working hours, and also during the weekends. The lake is populated by aquatic lives such as fishes and tortoises. The public is allowed to feed them with breads and fish-food.

The focus of this study is to analyse and determine the Biochemical Oxygen Demand (BOD) and the Dissolved Oxygen (DO) content of the lake. With this data, I could determine whether the lake water is clean and safe not only for the aquatic lives, but also to the surrounding.


Although water is limited in certain areas of the world, for example, in the South Africa, water is actually one of the renewable sources. Every living organism needs water to accomplish their daily routine; drinking, cleaning, and growth. A good water quality is essential to all living things as bad water quality can harm the digestive systems of both humans and animals. Not only humans and animals depend on clean water, aquatic lives do, too. Polluted water cannot be used for cleaning, drinking, and even cooking.

A bad water quality does not only bring negative effect on human health and the ecosystem, it will also affect the economy. In the economic sector, polluted water is not good for the national tourism. Beautiful water for example, blue sea water and clean rivers, would attract visitors as they can enjoy the clean water while having quality time with each other. On the other hand, a dirty and polluted water body would give negative feedback from the visitors thus would affect its profit in the economic sector. In this case, Reservoir Park’s is one of the most well-known parks in Kuching, Sarawak. It is important to maintain a clean lake so visitors would still enjoy having picnics and also jog around the park. A dirty lake would endanger the health of the public using the park, especially the ones who is having picnic in that area, Reservoir Park specifically.


The main objectives of this study are to:

Determine the biochemical oxygen demand (BOD) of the water samples from Reservoir Park’s lake

Determine the dissolved oxygen (DO) of the samples

Find a way to maintain or improve the lake’s water quality


Studies will be done on the Reservoir Park’s lake. It is a man-made lake located in the heart of Kuching City. Reservoir Park is a recreational park used by the public to have picnics, jogs, and walks.

The quality of the lake water in this study is determined by parameters; Biochemical Oxygen Demand (BOD) and Dissolved Oxygen (DO). The level of the water quality of this lake is determined by using the data provided by the Department of Environment (DOE) and Alam Sekitar Malaysia (ASMA).




According to Seng (2011), the Water Quality Index (WQI) is calculated from six water quality parameters: pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and ammoniacal nitrogen, NH3-N (AN). All these parameters are called chemical parameters. “Early humans could judge water only through the physical senses of sight, taste, and smell. Not until the biological, chemical, and medical sciences developed were methods available to measure water quality and to determine its effect on human health and well-being (Peavy, H.S., Rowe, D.R.,1985).


Water quality parameters are divided into 3 categories, mainly chemical, biological, and physical parameters. Chemical parameters consists of pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), and ammoniacal nitrogen (AN). Meanwhile physical parameters consists of total suspended solids, colour, taste, and temperature. Biological parameters are the presence of pathogens. Of all these parameters, only BOD and DO are chosen for this study.


Biochemical oxygen demand is the amount of oxygen consumed during microbial utilisation of organics (Peavy, et al, 1985). When organic matters are present in water bodies, natural existing microorganisms will consume them through a biochemical process. The BOD is measured by determining the oxygen consumed from a sample placed in an air-tight container and kept in a controlled environment for a selected period of time. The higher the BOD value, the higher the water quality. A high BOD level indicates that tere are living organisms present in the water body, which then shows that the water quality is good enough for living orgnanisms.


Oxygen is needed for humans and the ecosystem to go through respiration. Si it is important to aquatic lives. “Atmospheric oxygen dissolved in surface water aerobic organism could breathe in the oxygen molecules”, (Seng, 2011). Seng also stated that a swift flowing river will have higher DO due to the continuous mixing of oxygen and water, while stagnant pond will have lower DO.


Water quality can be observed physically through sign and odour. Complete analysis of the river will identify the quality and quantity of the water.

In Malaysia, Water Quality Index (WQI) and Interim National Water Quality Standards (INWQS) are used to classify water quality.

Table 2.1: National Water Quality Standards

(Source: EQR2006)




Nitrogen mg/l 0.1 0.3 0.3 0.9 2.7 > 2.7

Biochemical Oxygen Demand mg/l 1 3 3 6 12 > 12

Chemical Oxygen Demand mg/l 10 25 25 50 100 > 100

Dissolved Oxygen mg/l 7 5 – 7 5 – 7 3 – 5 < 3 < 1

pH – 6.5 – 8.5 6.0 – 9.0 6.0 – 9.0 5.0 – 9.0 5.0 – 9.0 –

Colour TCU 15 150 150 – – –

Electrical Conductivity* µS/cm 1000 1000 – – 6000 –

Floatables – N N N – – –

Odour – N N N – – –

Salinity % 0.5 1.0 – – 2.0 –

Taste – N N N – – –

Total Dissolved Solids mg/l 500 1000 – – 4000 –

Total Suspended Solids mg/l 25 50 50 250 300 300

Temperature ˚C – Normal + 2˚C – Normal + 2˚C – –

Turbidity NTU 5 50 50 – – –

Faecal Coliform* count/ 100ml 10 100 400 5000 (20000)a 5000 (20000)a –

Total Coliform count/ 100ml 100 5,000 5,000 50,000 50,000 > 50,000

Table 2.2: Department of Environment Water Index Classification

(Source: WEPA)



Ammoniacal Nitrogen mg/l < 0.1 0.1 -0.3 0.3 – 0.9 0.9 – 2.7 > 2.7

Biochemical Oxygen Demand mg/l < 1 1 -3 3 – 6 6 – 12 > 12

Chemical Oxygen Demand mg/l < 10 10 – 25 25 – 50 50 – 100 > 100

Dissolved Oxygen mg/l > 7 5 – 7 3 – 5 1 – 3 < 1

pH – > 7 6 – 7 5 – 6 < 5 > 5

Total Suspended Solids mg/l < 25 25 – 50 50 – 150 150 – 300 > 300

Water Quality Index – < 92.7 76.5 – 92.7 51.9 – 76.5 31.0 – 51.9 > 31.0

Table 2.3: Water Classes and Uses

(Source: EQR2006)


CLASS I Conservation of natural environment.

Water Supply I – Practically no treatment necessary.

Fishery I – Very sensitive aquatic species.


CLASS IIB Water Supply II – Conventional treatment.

Fishery II – Sensitive aquatic species.

Recreational use body contact

CLASS III Water Supply III – Extensive treatment required.

Fishery III – Common of economic value and tolerant species; livestock drinking.

CLASS IV Irrigation

CLASS V None of the above

Table 2.4: DOE Water Classification Based on WQI

(Source: EQR2006)



Biochemical Oxygen Demand 91 – 100 80 – 90 0 – 79

Ammoniacal Nitrogen 92 – 100 72 – 91 0 -70

Suspended Solids 76 – 100 70 – 75 0 – 69

Water Quality Index 81 – 100 60 – 80 0 – 59



WQI = (0.22 × SIDO) + (0.19 × SIBOD) + (0.16 × SICOD) + (0.15 × SIAN) +

(0.16 × SISS) + (0.12 × SIpH)

Where :

SIDO = Sub-Index dissolved oxygen (DO)

SIBOD = Sub-Index biochemical oxygen demand (BOD)

SICOD = Sub-Index chemical oxygen demand (COD)

SIAN = Sub-Index ammoniacal nitrogen (AN)

SISS = Sub-Index suspended solids

SIpH = Sub-Index pH

0 ≤ WQI ≤ 100


Sub-Index for dissolved oxygen (DO) (In % Saturation)

SIDO = 0 For 8

SIDO = 100 For 92

SIDO = -0.395 + 0.0302 – 0.000203 For 8 92

Sub-Index for biochemical oxygen demand (BOD)

SIBOD = 100.4 – 4.23 For 5

SIBOD = 108-0.055x – 0.1 For 5

Sub-Index for chemical oxygen demand (COD)

SICOD = -1.33 + 99.1 For 20

SICOD = 103-0.0157x – 0.04 For 20

Sub-Index for Ammoniacal Nitrogen

SIAN = 100.5 – 105 For 0.3

SIAN = 94-0.573x – 5 × I – 2I For 0.3 4.0

SIAN = 0 For 4.0

Sub-Index for suspended solids

SISS = 97.5-0.00676x + 0.05 For 100

SISS = 71-0.0061 + 0.015 For 100 1000

SISS = 0 For 1000

Sub-Index for pH

SIpH = 17.02 – 17.2 + 5.022 For 5.50

SIpH = -242 + 95.5 – 6.672 For 5.50 7.00

SIpH = -181 + 82.4 – 6.052 For 7.00 8.75

SIpH = 536 – 77.0 + 2.762 For 8.75




Reservoir Park’s Lake is chosen for my study of water quality. The study is to determine the water quality of the lake. In addition, the study of water quality will be based on water quality index (WQI) and the interim national water quality standard (INWQS). Water sample was taken, and the experiment has been undergone.

The physical parameters of the water sample were the colour of water while the chemical parameters are the Biochemical Oxygen Demand (BOD) and the content of the Dissolved Oxygen (DO). The DO value can be used to determine the BOD count of the water sample. The test for BOD is a bioassay procedure that measures the oxygen consumed by bacteria from the decomposition of organic matter.


3.3 AIM

To measure the Biochemical oxygen Demand (BOD) and the value of the Dissolved Oxygen (DO) of the Reservoir Park’s Lake.




1.BOD Incubator

2.BOD Bottles

3.BOD Sensor

4.Graduated Cylinder



7.Sample Bottles

Chemical reagents and preparation of dilution water

1.Calcium Chloride

2.Dilution Water

3.Ferric Chloride

4.Magnesium Sulfate

5.Phosphate Buffer Solution

Figure 3.1: BOD incubator

Figure 3.2: BOD bottles



The following preparations are needed before implementing the BOD5 test procedure:

1. Dilution water was prepared 3 to 5 days before initiating BOD5 tests to ensure that the BOD of the dilution water is less than 0.2 mg/L. Dilution water is to be discarded if there is any sign of biological growth.

2. Sample pH is determined. The sample is to be adjusted to a pH between 6.5 and 7.5, if necessary, using sulfuric acid (H2SO4) for samples with pH greater than 7.5 or sodium hydroxide (NaOH) for samples with pH less than 6.5 (American Public Health Association and others, 1995).

3. Sodium sulfite (Na2SO3) is added to remove residual chlorine, if necessary. Samples containing toxic metals, arsenic, or cyanide often require special study and pretreatment (American Public Health Association and others, 1995). Samples must be seeded after pretreatment.


1. The amount of sample that is to be analysed are determined; if available, use the historical results of a previous test of BOD5 for a particular sampling site.

2. A clean calibrated thermometer is placed into the constant temperature chamber.

3. Constant temperature chamber is turned on to allow the controlled temperature to stabilize at 20°C ±1°C.

4. The DO instrument is turned on, but not the stirring attachment. Some DO instruments need to be turned on 30 to 60 minutes before calibration.

5. Dilution water was aerated before adding nutrient solutions.

6. After aeration,

a. Add to dilution water

• 1 mL each of the potassium phosphate, magnesium sulfate, calcium chloride, and ferric chloride solutions per 1 L of dilution water.

b. The container of dilution water is shaken for about 1 minute to dissolve the slurry and to saturate the water with oxygen.

c. Dilution water is placed in the constant temperature chamber to maintain a temperature of 20°C until sample dilutions and analyses begin.

d. The initial and final (after 5 days ± 4 hours) DO tests of the dilution water is determined and recorded simultaneously with each batch of environmental samples.

7. The temperature of the BOD incubator is checked using a laboratory thermometer to ensure that the temperature has been maintained at 20° ± 1°C. A minimum/maximum recording thermometer can be used to audit the temperature during times when checks cannot be made.

8. The sample container is placed in the constant-temperature chamber or water bath to begin warming the sample to 20°C ± 1°C. While the sample is warming, insert the air diffusion stone into the container and aerate the sample for about 15 minutes. After removing the air diffusion stone, excess air bubbles are allowed for several minutes to dissipate. The initial DO of the BOD sample needs to be at or slightly below saturation.

9. Dilutions are prepared as required by measure the appropriate amounts of sample necessary for the analysis. BOD5 dilutions should result in a DO residual of at least 1 mg/L and a DO depletion of at least 2 mg/L after a 5-day incubation to produce the most reliable results. The dilutions are prepared to obtain a DO uptake in this range using the dilution water prepared earlier.

a. For each subsample, mix thoroughly by inverting 20 times.

• Large-bore pipet is used for sample volumes less than 50 mL. A subsample that is representative of all the particle sizes present was withdrawn.

• A graduated cylinder is used for sample volumes greater than or equal to 50 mL.

b. Two additional samples were diluted to bracket the appropriate dilution by a factor of two to three. At least three samples diluted were prepared according to volumes specified.

c. The sample from the pipet or graduated cylinder was poured into a clean BOD bottle.

• The dilution water was agitated and filled the remaining portion of the BOD bottle with dilution water.

• Three samples containing only dilution water were prepared. These samples serve as blanks for quality control. If two of the three samples meet the blank-water criterion, accept the data.

10. The DO instrument was calibrated.

11. After bringing the samples to saturation and preparing the dilutions (steps 8 and 9 above), the initial DO concentration (D1) of each sample and each dilution blank were measured.

a. The self-stirring sensor was carefully inserted into the BOD bottle, avoiding air entrapment.

b. Turn on the stirrer was turned on and the DO and temperature readings were allowed stabilize for about 1 to 2 minutes.

12. The bottle number, date, time, and D1 were recorded on a form similar.

13. The stirrer was turned off and remove the sensor from the BOD bottle. The sensor and stirrer were rinsed with deionized water from a wash bottle. Rinse water was discarded into a waste container.

14. Glass beads were added to the BOD bottle, if necessary, to displace the sample up to the neck of the bottle so that inserting a glass stopper will displace all air, leaving no bubbles.

15. The BOD bottle was carefully capped with the ground-glass stopper. The bottle was tipped to one side and check for an air bubble.

• If an air bubble is present, add glass beads to the bottle until the bubble is removed. The bottle is capped and checked again for an air bubble. Repeat if necessary.

• If no bubble is present in the sample, a water seal was created by adding distilled or deionized water to the top of the BOD bottle around the glass stopper. The overcap was then placed over the stopper on the BOD bottle to minimize evaporation from the water seal.

16. The sealed BOD sample was placed in the BOD incubator and incubate the sample at 20°C ± 1°C for 5 days.

17. At the end of 5 days ± 4 hours, the BOD bottles were removed from the incubator, the overcasps were removed, the water seals were poured off, the ground-glass stoppers were removed, and the final DO concentration (D2) were measured.

• The DO uptake (DO0 days – DO5 days) in the dilution water should not be greater than 0.2 mg/L and preferably not more than 0.1 mg/L. Exceeding the 0.2-mg/L criterion could be grounds for rejecting results of the BOD analysis of the environmental sample.

• Dilution water of poor quality will cause an oxygen demand and appear as sample BOD. Improve purification or get the dilution water from another source if DO uptake exceeds 0.2 mg/L.

18. The field form was completed by recording the date, time, and D2 for each respective sample bottle.




The location chosen for the water quality research was the Reservoir Park’s Lake. Physical water quality parameter method has been used to determine the colour of the water samples. For chemical water quality parameter method, the experiments were conduct to identify the biochemical oxygen demand (BOD) and the dissolved oxygen (DO) of the water samples from the lake.


From the observation, the colour of the water samples was light brown. The lake is located in a recreational area where pass-byers might litter into the lake. Some would feed the aquatic lives living in the lake with crumbs of bread and even fish-food.


Two trials of experiments have been conducted to identify and analysis the results of the water samples from the lake. The results of the (BOD) of the water samples are based on the Table 5.1 and Table 5.4.


For the dissolved oxygen (DO), two trials have also been conducted to identify and analyse the (DO) of the water samples. The Table 5.2, Table 5.3, Table 5.5, and Table 5.6 shows the results of the experiments.



Table 4.1: First trial of BOD results

Bottle number Sample size Initial BOD readings Date/time of readings Final BOD readings Date/time of readings

1 Dilution

blanks 0.00 18/02/15

02:45pm 0.00 23/2/15


2 50ml 2.50 18/02/15

02:45pm 29.50 23/2/15


3 100ml 0.50 18/02/15

02:45pm 31.00 23/2/15


Table 4.2: First trial of DO of Dilution Blanks

Dilution Water Blanks

Bottle Number Initial DO Readings

(D1) Date/Time of Reading Final DO



Date/Time of Reading D1 – D2

1 4.51 18/02/15

02:45pm 3.35 23/2/15

12:11pm 1.16

Table 4.3: First trials of DO of water samples

Environmental Sample

Bottle Number Sample size (ml)

Initial DO


Date/Time of Reading Final DO



Date/Time of Reading D1 – D2

2 50 5.10 18/02/15

02:45pm 4.98 23/2/15

12:11pm 0.12

3 100 4.80 18/02/15

02:45pm 3.74 23/2/15

12:11pm 1.06


Table 4.4: Second trial of BOD Results

Bottle number Sample size Initial BOD readings Date/time of readings Final BOD readings Date/time of readings

1 Dilution

blanks 0.00 04/03/15

02:45pm 0.00 09/03/15


2 50ml 6.00 04/03/15

02:45pm 31.80 09/03/15


3 100ml 1.60 04/03/15

02:45pm 32.50 09/03/15


Table 4.5: Second trial of DO of Dilution Blanks

Dilution Water Blanks

Bottle Number Initial DO Readings

(D1) Date/Time of Reading Final DO



Date/Time of Reading D1 – D2

1 5.35 04/03/15

02:45pm 5.01 09/03/15

10:10am 0.34

Table 4.6: Second trials of DO of water samples

Environmental Sample

Bottle Number Sample size (ml)

Initial DO


Date/Time of Reading Final DO



Date/Time of Reading D1 – D2

2 50 5.63 04/03/15

02:30pm 5.06 09/03/15

09:54am 0.57

3 100 5.65 04/03/15

02:30pm 5.39 09/03/15

09:54am 0.26



BOD5 (mg/L) = D1 – D2



D1 = initial sample dissolved-oxygen (DO) concentration (in mg/L)

D2 = sample DO (in mg/L) after 5 days

P = decimal volumetric fraction of sample used

If 100 mL of sample are diluted to 300 mL, then P = 0.33.

Notice that if no dilution was necessary, P = 1.0 and the BOD5 is determined by D1 – D2.


Theoretical BOD for 50ml Water Sample = = 3.4193

Actual BOD for 50ml Water Sample = 31.80

In this experiment, the theoretical biochemical oxygen demand (BOD) is different from the actual BOD. This may be because of the fault of the BOD sensor and the DO sensor.


The biochemical oxygen demand (BOD) of the Reservoir Park’s lake is determined by using a BOD sensor. The sensor shows that the readings of the BOD is from 1 to 3mg/l and according to the Department of the Environment (DOE) the class of water (based on table 2.2) is Class II. Thus, only conventional treatment is needed. But for the second trial, the BOD of the lake slightly increase with the highest BOD count recorded is 6.00. Based on table 2.2, the water sample is classified under Class III. Thus, the water needs an extensive treatment. The increasing BOD level is because of the increase of human activities around the lake. During the first trial, it was rainy season. Reservoir Park was quite unattended as it was raining for the whole week. On the other hand, during the second trial, the weather changed to sunny. This affects the usage of the park surrounding the lake, and human activities increased. More people use the park during the second trial. Litters and organic wastes are thrown into the lake. The quantity of fish-food increased, which resulted the condition of the aquatic lives. More organisms undergone respiration, which explains the increase in the BOD level.

The dissolved oxygen (DO) content is slightly the same for both trials. This is because the lake is stagnant which causes the rate mixing of water and oxygen low.

After 5 days, the BOD level for both samples increase. The activity of microorganisms in the water samples causes the demand of oxygen increase. On the other hand, the dissolved oxygen content decreases because oxygen has been consumed by microorganisms in the water samples. “The significance of this parameter is that, when BOD is high, DO in the water sample will be depleted and this will eventually suffocate all aquatic life”, (Lau, 2011)




Firstly, the objectives of the study are fully achieved. The biochemical oxygen demand (BOD) and the Dissolved oxygen (DO) of the water can be identified by conducting two (2) number of trials of the experiments. The BOD of the lake at the Reservoir Park is in good condition which is class II or class III (based on the Department of Environment (DOE) water index classifications).

The theoretical and actual BOD is different. This is because of some faults and will be discussed in recommendation.

The lake is stagnant. Moreover, it is located in the city centre, and available for public. In order to conserve its good quality, the public should not litter into the lake. Litters including food wrapping, waste water, trash, and oil.

The stagnant lake will affect its biochemical oxygen demand (BOD) and its dissolved oxygen (DO). This is because a swift flowing water body mixes the oxygen with the water body. Stagnant lake does not mix well with the surface oxygen thus would affect its BOD level.


Other chemical parameters experiment can be done to this lake. Chemical parameters including pH, chemical oxygen demand, and ammoniacal nitrogen.

As stated in my discussions, the theoretical biochemical oxygen demand (BOD) is different from the actual BOD. This may be because of the fault of the BOD sensor and the DO sensor. The laboratory should prepare well functioning equipments for accurate reading of results.

Secondly, water samples used should be fresh and must not be kept too long. For best result, newly taken samples should be taken straight to the laboratory. Fresh water samples reduce its probability of it getting contaminated. Water samples should also be sealed air-tight to avoid water samples from contaminated. References

Delzer G.C. & Mackenzie S.W., 2003 “Five Day Biochemical oxygen Demand.” Adapted from USGS TWRI Book (third Edition).

Department of Environment, (DOE) 1994. Interim Water Quality Standard for Malaysia Gov. Malaysia.

DOE, progress in Malaysia Towards Environmentally sound and sustainable development 1976-1990, Department of Environment, Ministry of science, Technology and the environment, Malaysia 1991, p.4.

DOE, Environmental Quality Report, 1985- 1986, Department of Environment, Ministry of Science, Technology and the Environment, Malaysia, 1986.

DOE, Environmental Quality Report, 1987, Department of Environment, Ministry of Science, Technology and the Environment, Malaysia, 1987.

DOE, Environmental Quality Report, 1988, Department of Environment, Ministry of Science, Technology and the Environment, Malaysia, 1988.

DOE, Environmental Quality Report, 1989, Department of Environment, Ministry of Science, Technology and the Environment, Malaysia, 1989.

Lau. S “Water in the Environment: Tainted Life Source Hungers for Cures.” 2011.

Peavy. H.S, Rowe D.R. Tchobanoglous.G. (1985), “environmental Engineering,” McGRAW-HILL INTERNATIONAL EDITION.

World Health Organizations (WHO), 2012 “the effect of the water pollution towards

human health”