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  2. 2. Title : Biochemical Oxygen Demand (B.O.D)Objectives : 1. To identify the BOD using data logger. 2. To determine biochemical oxygen demand in the given water sample. 3. To perform a basic experiment to determine the water quality of a given system based on biochemical oxygen demand (BOD). 4. To determine most polluted water sample.Hypothesis:The higher B.O.D value, the more polluted the source of water.Variables: 1. Manipulated : Sample of water 2. Responding : Dissolved oxygen value 3. Constant : Volume of water sampleIntroduction: Data logger is a device such as lab instrument to record all data generated or the datapassing through a particular point in a networked computer system. It can record a wide varietyof energy and environmental measurements including temperature, relative humidity, lightintensity, oxygen dissolve (DO), water level and soil moisture. Data loggers are used in a broadrange of indoor, outdoor and underwater environments that essentially anywhere data is neededand the convenience of battery power is preferred. Figure 1: BOD data logger
  3. 3. Biochemical oxygen demand or B.O.D is a chemical procedure for determining theamount of dissolved oxygen needed by aerobic organisms in a water body to break the organicmaterials present in the given water sample at certain temperature over a specific period of time.It is not a precise quantitative test, although it is widely used as an indication of the quality ofwater. BOD of water or polluted water is the amount of oxygen required for the biologicaldecomposition of dissolved organic matter to occur under standard condition at a standardizedtime and temperature. Usually, the time is taken as 5 days and the temperature is 20 °C. The test measures the molecular oxygen utilized during a specified incubation period forthe biochemical degradation of organic material (carbonaceous demand) and the oxygen used tooxidize material such as sulfides and ferrous ion. It also may measure the amount of oxygen usedto oxidize reduced forms of nitrogen (nitrogenous demand). The BOD test is widely used to determine the pollution strength of domestic andindustrial wastewaters in terms of the oxygen that they will require if discharged into naturalwatercourses in which aerobic conditions exist. The test is one of the most important both inregulatory work and in studies designed to evaluate the purification capacity of receiving waterbodies. We take sample of water at pond water, drain water, distilled water, aquarium water andpipe water. So we use data logger to get the result from the entire water sample. Therefore, BODvalue is determined by the following formula:BOD value in mg/l = [(D1-D2) – (B1-B2)] /PWhere;D1= initial DO in a sampleD2= final DO in a sampleB1= initial DO in blankB2= final DO in blankP= fraction of the BOD bottle that is represented by the sample
  4. 4. Apparatus:Beaker, D.O Probes @ Dissolves oxygen meter (sensor), Computer with Data LoggerSpreadsheet Program.Materials:Pond water, drain water, distilled water, aquarium water and pipe waterEMPOWERProcedure: 1) 5 beakers were labeling with A, B, C, D and E. 2) 100 mL of pond water are collected and pour into beaker A. 3) *The D.O probe was placed in the beaker A to read the initial D.O concentration directly. 4) The result was recorded in Data Logger Spreadsheet Program. 5) Steps 1 to 4 were repeated by using different samples of water which are drain water, distilled water, aquarium water and pipe water which the samples of water is poured into beaker B, C, D and E respectively. 6) The samples were let until 5 days and D.O probes was placed again in these samples to read the final D.O concentration. 7) BOD value was determined by the following formula: B.O.D value = Final D.O – Initial D.O p *Note that, before put the sensor into the next sample of water, rinse the sensor with distilled water.
  5. 5. Results and Data: Beaker Water samples Initial D.O (mg/L) Final D.O (mg/L) B.O.D value (mg/L) A Drain water 3.6 4.563 0.963 B Distilled water 4.263 4.675 0.412 C Pond water 3.975 4.625 0.65 D Aquarium 3.725 4.588 0.863 water
  6. 6. E Pipe water 4.1 4.638 0.538Analysis: From the graph above, there are five different colour lines of graph means that, it has fivedifferent water samples. The blue line represents drain water. The red line represents aquarium water. Thepink line represents pond water. The green line represents pipe water. The last purple line representsdistilled water. This graph shows the BOD (Biological Oxygen Demand) level of the water sampleagainst time. From this graph, it shows the drain water have the highest BOD level which is 0.963mg/l. While,the lowest BOD level is distilled water which have 0.42 mg/l. This shows that the most polluted watersample is drain water followed by aquarium water sample, pond water, pipe water and the less pollutedwater sample is distilled water. Beside that, from the graph shows the BOD level will increase over thetime. It can be said that the BOD level is directly proportional to the time.
  7. 7. Discussion: Biological Oxygen Demand (BOD) is a measure of the amount of oxygen that bacteria willconsume while decomposing organic matter under aerobic conditions. BOD is determined by incubating asealed sample of water for five days and measuring the loss of oxygen from the beginning to the end ofthe test. Samples often must be diluted prior to incubation or the bacteria will deplete all of the oxygen inthe bottle before the test is complete. The very important thing to know is the dissolve oxygen (DO) content of the sample to measuringthe BOD of a water sample. The amount of DO in water affects natural biochemical processes in twoways where by limiting the amount of oxygen available for respiration and by affecting the solubility ofessential nutrient in the water sample. The decomposition of organic matter is the greatest factor in thedepletion of available oxygen in water body. As the organic content in water increase, there is acorresponding increase in bacterial activity and decrease the dissolved oxygen content. The microorganisms such as bacteria are responsible for decomposing organic waste. When theorganic matter such as dead plants, leaves, grass clippings, manure, sewage, and food waste also presentin a water supply. This will support the bacteria to begin process of breaking down the waste. Thissituation can cause more available dissolve oxygen was consumed by aerobic bacteria, robbing otheraquatic organisms that need oxygen to live. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteriapresent working to decompose this waste. In this case, the demand for oxygen will be high in the watersample due to the bacteria will cause the BOD level will be high. As the waste was consumed ordispersed through the water sample, BOD level will begin to decline. In this experiment, drain water have been identified have high BOD level may be due to the largeamount of the microorganisms to decompose waste. In drain have a lot of waste from many differentsources such as waste from house and farming area. All this types of microorganism working together todecompose waste and will cause large number of oxygen demand. On the other hand, the distilled watershows low BOD level. This case was due to the small amount of microorganisms and causes the oxygendemand to be low. In the farming area, there presents the inorganic substances like nitrates and phosphates from thefertilizer that was used by the farmer. The nitrates and phosphorus in a body of water can contribute tohigh BOD levels. These nutrients are essential for the growth of algae and other plants. Aquatic life isdependent upon these photosynthesizers, which usually occur in low levels in surface water. Excessive
  8. 8. concentrations of nutrients can over stimulate aquatic plant and algae growth. Bacterial respiration andorganic decomposition can use up dissolved oxygen. Fertilizers, failing septic systems, waste water treatment plant discharges, and wastes from petsand farm animals are typical sources of excess nutrients in surface waters. In aquatic ecosystems, becausephosphorous is available in the lowest amount, it is usually the limiting nutrient for plant growth. Thismeans that excessive amounts of phosphorous in a system can lead to an abundant supply of vegetationand cause low DO. Increased nitrogen levels adversely affect cold-water fish more than they do warmwater fish. In addition, metabolic rate and the reproductive activities of aquatic life are controlled by watertemperature. Metabolic activity increases with a rise in temperature, thus increasing a fish demand foroxygen. Temperature of water also can increase and cause to high BOD level. Therefore, warmer waterusually has high BOD level than colder water. When the water temperature increases, the rate ofphotosynthesis by algae and other plant life in the water also increases. When this situation happens, itcan make plant die faster and they will fall to the bottom of the water body so that they can bedecomposed by bacteria. Therefore, increased water temperatures will speed up bacterial decompositionand result to high BOD levels. A rise in temperature also can provide conditions for the growth of diseasecausing organisms. As the BOD level is high, dissolved oxygen (DO) level will decrease because the oxygenavailable in water is being consumed by microorganisms in the water. Since less dissolved oxygen isavailable in the water, organisms such as fish, caddisfly larvae and mayfly nymphs and other aquaticorganisms cannot survive. This will cause the aquatic organisms become extinct over the time. At highBOD levels, organisms such as macroinvertebrates that are more tolerant of lower dissolved oxygen suchas leeches and sludge worms may appear and become numerous. Therefore, from the result obtained the most polluted water is drain water which have high levelof BOD compare to the other water sample. Drainage water is no different from any other water supplyand is always usable for some purpose within certain quality ranges. Beyond these limits, drainage watermust be disposed of in a manner that safeguards the usability or quality of the receiving water for presentestablished and potential uses. Surface and subsurface drainage water from agriculture is normally degraded comparedwith the quality of the original water supply. Drainage water that flows over or through the soilwill pick up a variety of dissolved and suspended substances including salts, organic compounds
  9. 9. and soil particles. Management for safe reuse and disposal requires an understanding of thecharacteristics of the drainage water, and a matching of those characteristics to the environmentalprotection needs of the reuse or disposal area. Sometimes, characteristics of drainage water havea potential on environmental contaminant.Conclusion: The drain water has high BOD level which is 0.963 mg/L while, the lowest BOD level is distilledwater with the value 0.412 mg/L. It can be identified that the high BOD level of water is the mostpolluted.ENHANCE The chemical, physical, and biological aspects of water quality are interrelated and must beconsidered together. For example, higher water temperature reduces the solubility of dissolved oxygen,and may cause a dissolved oxygen shortage that kills more sensitive fish species. The rotting fishcarcasses may contribute to a bacterial bloom that makes some human swimmers or boaters ill. Water quality is highly variable over time due to both natural and human factors. Watertemperature, photosynthetic activity, and flows vary with season. Therefore, the flow and suspendedsediment can vary daily with rainfall. Nutrients loads can vary with season like homeowners fertilizing inthe spring flow from the runoff mechanisms affect pollutant washoff and human management likenitrogen is released after a clear cut.Question: Figure 1 Figure 2
  10. 10. 1. From the picture above, what are the phenomenon occurred? Oil spill in the sea.2. What are the sources of pollution? -Careless discharge of water heated, for example industrial places. -Removal of shading vegetation.3. What are the effects of this phenomenon? -The effect on this phenomenon is oil spills can have widespread effects on nearly all Creatures that come into contact with it, from algae to migratory birds, to marine mammals. -The main problem caused by water pollution is that it kills life that inhabits water-based ecosystems. Dead fish, birds, dolphins, and many other animals often wind up on beaches, killed by pollutants in their habitat. -Pollution disrupts the natural food chain as well. Pollutants such as lead and cadmium are eaten by tiny animals. Later, these animals are consumed by fish and shellfish, and the food chain continues to be disrupted at all higher levels. -Eventually, humans are affected by this process as well. People can get diseases such as Hepatitis by eating seafood that has been poisoned. -Ecosystems can be severely changed or destroyed by water pollution. Many areas are now being affected by careless human pollution, and this pollution is coming back to hurt humans. 4. Give one way to solve the problem. Bioremediation is the process that uses microorganisms, fungi, green plants or their enzymes to return the natural environment altered by contaminants to its original condition. In general approach is the cleanup of oil spills by the addition of nitrate or sulfate fertilizers to facilitate the decompositions of crude oil by bacteria.
  11. 11. References: Delft (1999). Understanding biochemical oxygen demand test. New Delhi: India. G.C Delzer and S.W. McKenzie (2003). Five days biochemical oxygen demand. United States. 45