Dissolved oxygen disturbances

Figure 9.11. Disturbed equilibrium for the determination of the coefficients K a and Css-DO is dissolved oxygen concentration, and Csat is the saturation concentration at equilibrium with the atmosphere, which is generally below Css-...

Some reasons for screening samples in the field are to improve the selection of samples for laboratory analysis, to avoid excessive site disturbance, to map the site, and to perform the required on-site analysis ( immediates , like pH, EC, and dissolved oxygen). 

Raw water may contain floating impurities organic impurities, dissolved calcium and magnesium bicarbonates, chlorides, and sulphates, as well as dissolved oxygen, etc. These can cause both temporary and permanent hardness. Untreated water can affect the product quality, cause corrosion of equipments, form scales in boilers (can consume excess fuel and affect their performance), and disturb process reactor temperature due to scales in the cooling jackets. 

The fate of chemicals in the environment depends not only on processes taking place within compartments, but also by chemical partitioning between compartments. For example, there may be exchange of chemicals between air and water or soil. Movement from the water or soil into the air is accomplished by volatilization and evaporation of volatile or semivolatile compounds. Movement of chemicals from the air to water or soil is accomplished by deposition or diffusion into the water. Chemicals can also move from water to soil or sediment and vice versa. If a solid chemical in the soil or sediment dissolves into the water, this is called dissolution , while the opposite is called precipitation . If a chemical dissolved in water attaches to a soil or sediment particle, this is called adsorption , while the opposite is called desorption . The fugacity of a chemical, that is, its tendency to remain within a compartment, is affected by the properties of that chemical, as well as the chemical and physical properties of the environments such as temperature, pFF, and amount of oxygen in water and soil. Wind or water currents, wave action, water turbulence, or disturbance of soil or sediment (through the action of air or water currents, animals, or human activities) may also affect partitioning of chemicals. 

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