Chemisty of Wastewater Treatment (Essay Sample)

Chemisty of Wastewater Treatment
Name of Student
Institutional Affiliation
Introduction
Waste water refers to water which cannot be used in its current state. Water is a renewable resource, thus, various methods are used to make water safe for human and animal use (Gupta et al, 2012). One of the means used to clean waste water is chemical methods. In this case, reactive species are made to react with the contaminant species in the water, resulting in their removal. Chemical reactions used include precipitation, oxidation, chelating, ion exchange, and neutralization. Impurities found in waste water ranges from trace metal ions, dissolved carbon dioxide gas, inorganic acids, halides, and nitrates (Gupta et al, 2012). These impurities pose a health risk to humans, and hence, their removal. However, there are other water impurities that cannot be removed using chemical means such as dirt particles. Thus, for total purification of wastewater, a combination of mechanical, biological, and chemical methods is required.
Chemical methods of wastewater cleaning
Precipitation reactions
In precipitation reactions, coagulating and flocculating reagents are added into the water that is being treated (Gupta et al, 2012). A chemical reaction takes place and the precipitating agents bind with the impurities causing them to form insoluble masses that can be easily removed. This is commonly used to treat water that is unpurified with heavy metals such as lead and zinc. A precipitating agent such as sodium hydroxide solution is added to the water. The hydroxyl ions will precipitate the heavy metals present by the formation of insoluble metal hydroxides that can be filtered off. Silver ions are also commonly used to precipitate most metals and halides found in wastewater. Precipitation of various metals is dependent on the total hydrogen concentration in the water. For maximum precipitation to take place, one may be required to keep adjusting the pH of the water.
M2+(aq) + OH-(aq) → M(OH)2 (S)
Chelating Treatment
This involves the formation of coordination complexes by use of a chelating agent. One of the commonly used chelating agents used is ethlylenediaminetetracetic acid (EDTA) (Henze, 2002). Chelating is useful for removal of both heavy metals from wastewater and removal of other metals such as calcium and sodium. Chelating agents are used chemically to soften hard water through the removal of calcium ions. The chelating agent binds to the metal ions through the formation of coordinate bonds. The resulting complex can then be easily separated from the water either through distillation. PH is also a major factor in chelating treatment (Gupta et al, 2012). Some metals bind more strongly than others to the chelating agent as varying pH levels. Thus, at an optimal PH many metals can be bound by the EDTA solution added, allowing for the formation of many complexes at the same time,s which is economical.
Ca2+(aq) + EDTA4-(aq) → CaEDTA2-
Other Chemical methods
Oxidation reactions involve using an electron rich species, which can donate electrons to the impurity oxidizing it and thus, causing its degradation (Henze, 2002). An example is the use of alkalinized chlorine to neutralize cyanide. Activated carbon is also commonly used to remove...