Water Quality Essay

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Introduction
Water pollution is always one of the major concerns for environmental engineering. Toxic water sources can be a critical problem, it will endanger some species or even the whole eco-system. Also, it might cause various problem of human's health. Water pollution can be caused by different reasons such as acid rain, runoff of fertilizer, industrial wastes etc. Treatment of water is necessary to prevent such pollutants. Engineers have several ways to measure the quality of water
- Measuring the pH level of the water
- Measuring the level of dissolved oxygen chemically and biologically (COD, BOD)
- Measuring the amount of bacteria
- Biological sample
There are so many other ways to measure water quality. In this lab report, we are going to discuss BOD, biochemical oxygen demand.

What is BOD ?
BOD determines the quality of water by measuring the amount of dissolved oxygen in the samples. The oxygen in the water is usually from photosynthesis of aquatic plants and oxygen from the air that dissolved into the water. Bacteria uses the dissolved oxygen to degrade the organic matters and produce energy for cell maintenance and growth. The Bacteria/micro- organisms will stop growing until the organic matters run out hence the less the organic matters, the better the water quality. The BOD experiment can measure change of dissolved oxygen level and calculate the amount of micro-organism in each sample. [1]
BOD and COD
There is always a strong correlation between the BOD and the COD experiment results. Both methods are used to measure the amount of organic matter in water. COD measures the amount of oxygen needed to completely oxidise all organic matters in the sample. COD is more accurate than the BOD and it is also fa...

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...se due to the acidic environment. The BOD result will be less than it should be. The pH level should be monitored as well as the temperature. [4]
At last, nutrients play a key role of the decomposition. If the nutrients are deficient, the bacteria will lose its ability to consume microorganisms. This error is fairly simple to solve, we just have to make sure the seeded water contain enough nutrient for the bacteria for 7 days.

Conclusion
After we conducted the experiment, we found out the sample with the least dilution factor has the biggest BOD value. We also found out BOD value is inversely proportional fraction of waste water volume and total combined volume. In conclusion, the biggest dilution factor, the more BOD value and the worse water quality. There are some errors in the experiments but most of them can be eliminated to produce a more accurate result.

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