Metcalf and eddy wastewater engineering pdf

Tests selected and desired test metcalf and eddy wastewater engineering pdf vary with the intended use or discharge location. Tests measure physical, chemical, and biological characteristics of the waste water. Tests will determine the quality of this wastewater.

Aquatic organisms cannot survive outside of specific temperature ranges. Solid material in wastewater may be dissolved, suspended, or settled. Imhoff cone after water has settled for one hour. Finely divided material is readily available to microorganisms whose populations will increase to digest the amount of food available. Digestion of this food requires oxygen, so the oxygen content of the water will ultimately be decreased by the amount required to digest the dissolved or suspended food. Oxygen concentrations may fall below the minimum required by aquatic animals if the rate of oxygen utilization exceeds replacement by atmospheric oxygen. Both the BOD and COD tests are a measure of the relative oxygen-depletion effect of a waste contaminant.

Both have been widely adopted as a measure of pollution effect. COD test measures the oxygen demand of biodegradable pollutants plus the oxygen demand of non-biodegradable oxidizable pollutants. The so-called 5-day BOD measures the amount of oxygen consumed by biochemical oxidation of waste contaminants in a 5-day period. The total amount of oxygen consumed when the biochemical reaction is allowed to proceed to completion is called the Ultimate BOD. Because the Ultimate BOD is so time consuming, the 5-day BOD has been almost universally adopted as a measure of relative pollution effect. There are also many different COD tests of which the 4-hour COD is probably the most common. There is no generalized correlation between the 5-day BOD and the ultimate BOD.

Similarly there is no generalized correlation between BOD and COD. It is possible to develop such correlations for specific waste contaminants in a specific wastewater stream but such correlations cannot be generalized for use with any other waste contaminants or wastewater streams. This is because the composition of any wastewater stream is different. In such a case, the 5 day BOD and the ultimate BOD would be very similar since there would be very little organic material left after 5 days. However a final effluent of a sewage treatment works serving a large industrialised area might have a discharge where the ultimate BOD was much greater than the 5 day BOD because much of the easily degraded material would have been removed in the sewage treatment process and many industrial processes discharge difficult to degrade organic molecules.