02-15 - Disposal of an Organic Waste into an Aqueous...

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Disposal of an Organic Waste into an Aqueous System: Nature of the problem : Aqueous systems can accommodate a finite amount of oxygen. This O 2 is used by fish and other organisms, including bacteria, and is replenished from the atmosphere. In the absence of oxygen - fish die and other anaerobic (without O 2 ) bacteria take over. These may produce smelly by-products (Ex. H 2 S) which (along with the death of fish) are considered undesirable. For a number of reasons we want to keep aquatic systems aerobic (i.e ., oxygenated).
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The aerobic bacteria which consume organic wastes use up oxygen in the process. If we are going to discharge an organic waste we need to be able to predict the effect on stream D.O., so that we do not exceed the assimilative capacity of the receiving water. Must quantify reactions of dissolved oxygen. Possible reactions: Sinks : Sources : Microbial “demand” for O 2 in the stream and sediments (benthos), and respiration of plants and algae (in the dark). Atmospheric reaeration, and photosynthesis of plants and algae (in the light).
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With respect to each reaction need to consider: a. extent (how much) b. rate (how fast) We'll begin with microorganisms and try to come to grips with what they do. Objective here is to do better than a "black box" approach to the problem, i.e. , to develop a fundamental (and, therefore, generally applicable) concept of what's going on. chemical equilibrium chemical kinetics What we referred to previously as a “phenomenological” model
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Microbial Growth and Oxygen Utilization Most organic compounds represent a high energetic state relative to the inorganic matter (CO 2 ) from which they are formed. Microorganisms can capture this energy by converting the material back (or part way back) to the inorganic starting materials. This reaction is referred to as respiration . The energy captured is used in synthesis of more cells. These reactions fall into the general class of what are termed oxidation - reduction reactions. REDOX, for short An energy yielding reaction An energy consuming process .
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Define : Oxidation - Reduction - Ex. , Oxidation of ferrous iron to ferric iron coupled with reduction of O 2 (O = zero) to H 2 O (O = -II) balanced reaction: 2 Fe+ 2 + 1/2 O 2 (g)+2H + 2Fe +3 +H 2 O oxidation #'s +II 0 +I +III +I -II Simple rules for assigning oxidation numbers: - same as valence for an element in a monatomic ion Ex. , Fe +2 has +II oxidation number.
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02-15 - Disposal of an Organic Waste into an Aqueous...

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