Sewage Effects on Rivers
When an organic material, such as raw sewage, is poured into the river, dramatic changes occur at the bottom of the river from the sewage entrance. Organic wastewater is mixed with oxygenated oxygen as a result of the consumption of oxygen much more than when it is not contaminated and its dissolved oxygen decreases. The air velocity or dissolution of airborne oxygen in the water will also increase. But the dissolution of oxygen is not enough to prevent the reduction of oxygen in the river. In such a situation, the river is said to be anaerobic. However, the concentration of water oxygen is often not reduced to zero, and the river returns to the first state without being in anaerobic conditions.
The effect of sewage in the concentration of river oxygen can be estimated by mathematical formulas. It is assumed that there is an oxygen balance at each point of the river, and this balance is determined by the amount of oxygen consumed by microorganisms and the dissolution of airborne oxygen in the water. The rate of consumption or reduction of oxygen is determined by the following equation.
(L – Y) = K 1 : Dissolving or Dissolving Oxidation Rate (DO)
So that L is the amount of oxygen needed to decompose organic matter in milligrams per liter, called the amount of oxygen required for biochemical reactions (BOD), Y is the amount of oxygen consumed by microorganisms at any given time, expressed in mg The liter is expressed and K 1 is the constant daily oxygen consumption and is assumed to be constant for a particular sewage, and it depends on excess compounds, temperatures, and so on.
When the anaerobic conditions are provided in the river, gases such as hydrogen sulfide and methane form and move in bubbles to the surface, while bubbles cling to the large particles of black solids called slime and place them on the surface Floats water. Therefore, the smell of hydrogen sulfide gas is clear from a distant distance, which indicates the anaerobic conditions of the river.
The color of the river is usually black and the presence of long strands sticking to the rocks and usually encountered in the form of slender and gelatinous masses facing downstream of the river are two distinct signs of other anaerobic conditions in the river.
Sewage also affects aquatic organisms, so that their type and number varies after the arrival of wastewater into the river. Increasing opacity, sediment, and low concentration of dissolved oxygen can reduce fish life. Only a few special fish species can survive in these conditions, and as the food is abundant, so their numbers are greatly increased. Carp and catfish fish can survive in completely polluted waters, and even if necessary, they can use oxygen from the surface of the water. On the other hand, lyric fish salmon in ultrapure water, pure and cooling requirements, and is very sensitive to air pollution.
The river’s response is proportional to the type of incoming wastewater. The above-mentioned reactions occur when contaminated organic matter is rapidly decomposed and if pollutant compounds are toxic to aquatic organisms, the number and type of microorganisms at the point below the entry point of the river pollution also decreases. The oxygen dissolved in water is not diminished and may even become colder. In general, there are different types of contamination and the river reacts differently to each contamination
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