IntroductionWater pollution is always a major concern for environmental engineering. Toxic water sources can pose a critical problem, as they will endanger some species or even the entire ecosystem. Furthermore, it could cause various human health problems. Water pollution can be caused by several reasons, such as acid rain, fertilizer runoff, industrial waste, etc. Water treatment is necessary to prevent such pollutants. Engineers have several ways to measure water quality - Measure the pH level of the water - Measure the level of chemically and biologically dissolved oxygen (COD, BOD) - Measure the amount of bacteria - Biological sample There are many other ways to measure water quality. In this lab report we will talk about BOD, or biochemical oxygen demand. What is BOD? BOD determines water quality by measuring the amount of dissolved oxygen in samples. Oxygen in water usually comes from photosynthesis of aquatic plants and oxygen from the air dissolving in the water. Bacteria use dissolved oxygen to degrade organic substances and produce energy for the maintenance and growth of cells. The bacteria/microorganisms will stop growing until the organics run out, so the less organic matter, the better the water quality. The BOD experiment can measure the change in dissolved oxygen level and calculate the amount of microorganisms in each sample. [1]BOD and CODCThere is always a strong correlation between the BOD and 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 oxidize all organic substances in the sample. COD is more accurate than BOD and is also fa...... middle of paper ......if due to the acidic environment. The BOD result will be lower than it should be. The pH level should be monitored as well as the temperature. [4]Finally, nutrients play a key role in decomposition. If nutrients are deficient, bacteria will lose the ability to consume microorganisms. This error is quite simple to fix, we just need to make sure that the seeded water contains enough nutrients for the bacteria for 7 days. Conclusion After conducting the experiment, we found that the sample with the smallest dilution factor has the highest BOD value. We also found that the BOD value is an inversely proportional fraction of the wastewater volume and the total combined volume. Bottom line, the higher the dilution factor, the higher the BOD value and the worse the water quality. There are some errors in the experiments, but most of them can be eliminated to produce a more accurate result.