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Experiment 10 Comparison Of Biological Oxygen Demand In Various Water Samples| 25/5/2012
Aim: To investigate the Biological Oxygen Demand in water samples from a range of sources. Introduction
One form of water pollution is by organic wastes which serve as food for micro-organisms. The micro-organisms multiply on this food supply and use up oxygen in the water, which then is unavailable for other forms of life. Biological Oxygen Demand (BOD) is a measure of the rate at which oxygen is being removed from sample of water. This is the standard test used at Sewerage Treatment Plants. Biochemical oxygen demand or biological oxygen demand is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. It is one of the most common measures of pollutant organic material in water. BOD indicates the amount of organic matter present in water. Therefore, a low BOD is an indicator of good quality water, while a high BOD indicates polluted water. Dissolved oxygen (DO - amount of dissolved oxygen in water) is consumed by bacteria when large amounts of organic matter from sewage or other discharges are present in the water. When Organic matter such as dead plants, leaves, grass clippings, manure, sewage, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need to live. When the DO becomes too low, the aquatic organisms in that water are unable to continue at a normal rate.

The decrease in the oxygen supply in the water has negative effect on the fish and other aquatic life. Fish kills or migration and an invasion and growth of certain types of weeds can cause dramatic changes in a stream or other body of water, eventually...