Date of Publication :15th March 2017

Abstract: Natural receiving waters including rivers, streams, and tidal areas sustain a background population of microorganisms including bacteria, fungi, and algae. These organisms require energy for respiration and organic carbon food sources in order to synthesize new cells using the following general equation: In the above equation, the microbes occur naturally and consume organic food sources that are naturally present in the water. Some of the carbon matter in the food is biodegraded to release energy that drives the reaction. Energy is released through the biodegradation process by combining part of the organic food source's carbon compounds with oxygen. The by products of this reaction are additional microbial cells and carbon dioxide. Nutrients, primarily nitrogen and phosphorus, complete the reaction and are needed as part of the building blocks used to form new microbial cell tissue. In a clean water environment, the amounts of available organic food supplies are limited. This places a restriction on how fast the above reactions proceeds and also on how many microbes are able to grow. In general, the population of microbes in a clean water environment is restricted to a low background level by the limited amount of organic food that is present. While periodic fluctuations in the food supply may cause brief periods of population swings or declines, the number of microbes in the ecosystem will achieve an equilibrium condition over time that is based on the steady state amount of organic food present. If an artificial organic food supply is allowed to enter the ecosystem, the number of microbes that can be sustained will increase in response to the added food. If the amount of additional food is large, the population of microbes may increase exponentially and will continue to grow up to the point that the amount of food again becomes limiting for the elevated population. Raw sewage contains a high organic carbon content that provides an excellent supply of food for waterborne microbes. If raw sewage is discharged into receiving water, the bacteria population will become elevated in response to the new addition of food. This causes the above biodegradation reaction to proceed rapidly and, in the process, to create larger amounts of new microbes and carbon dioxide. This requires that more oxygen be available for use by the microbes. If sufficient extra food is added by the sewage discharge, the population of microorganisms and the resulting oxygen consumption may proceed so rapidly that all of the receiving water's oxygen is depleted.

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