Question

Discuss the purpose of the following chemicals used in industrial waste treatment:

3.1 Hydrogen Sulphide

3.2 Carbon Dioxide

3.3 Chromium

3.4 Carbon Monoxide

Answer 1

Solution:

The purpose of the following chemicals used in industrial waste treatment are. Following are not chemicals but the gases which having wide applications in different fields. Some of them are also used in waste treatment. Let's discuss one by one.

1. Hydrogen Sulphide: H2S is the gas which is formed from hydrogen and sulphide. Hydrogen sulfide (H2S) gas typically is formed in wastewater collection systems that are conducive to creating septic conditions. Collection systems in warm climates that have a flat grade or do not have the flow through velocities to prevent the stagnation of fluid, allow the septic conditions to occur. In general, septic conditions occur when bacteria use all of the available oxygen while decomposing organic matter in wastewater for energy. Sewers with low velocities encourage the growth of anaerobic bacteria in a slime layer coating the sewer. These bacteria reduce sulfur compounds such as sulfate (SO4), thereby producing sulfides (SO2). These compounds occur naturally in domestic wastewater but also can be concentrated in industrial waste streams. Under anaerobic (septic) wastewater conditions, sulfides cannot be oxidized. Therefore, they combine with hydrogen to produce hydrogen sulfide gas, creating the "rotten egg" or decayed egg odor associated with septic wastewater. Hydrogen sulfide plays important role in waste treatment especially waste water treatment.

2. Carbon Dioxide: Carbon dioxide gas is used for pH control. If the waste water having higher pH it can be reduced quickly by carbon dioxide. When carbon dioxide (CO2) gas is dissolved in water in forms carbonic acid. The reaction is,

CO2 + H2O = H2CO3

CO2 is also used for Re-carbonation for two purposes in a lime-softening plant:

(1) for pH adjustment and (2) for the neutralization and precipitation of the calcium hydroxide in the primary basin effluent in cases where high-magnesium waters are softened by application of excess lime followed by re-carbonation. Instead of sulphuric acid carbonic acid is preferred which can easily modify conditions in waste water treatment. There are many sources of carbon dioxide and wide uses.

3. Chromium : It is the metal which is very harmful when intake excess. Basically chromium is essential to human but in very less quantity from foods. Hence chromium is the metal which cannot actively involve in waste treatment. Hence it is not a chemical which can remove any waste material but it is the waste from steel industry. Waste water from steel industry is treated to remove chromium. So it does not take part in waste treatment.

4. Carbon monoxide : It is the poisonous gas which do not play any role in waste treatment. Carbon monoxide is basically an gas produced from different sources like coke from the electrochemical industry which contains aluminum and polycyclic aromatic hydrocarbons. Hence it is the gas which dissolve in water but makes poisonous nature.

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