Wastewater has its origins from houses, business, industry as well as storm drains and rainwater. Mainly, wastewater contains around 99.9 per cent water by weight with the remaining 0.1 per cent containing dissolved solids or materials. The material may include excrement, detergent from washing clothes and dishes, food, oils, plastics, salts, sand and heavy metals.
Some wastewater from the industrial and agricultural processes may also contain chemicals that may be hazardous to the environment or the public. These chemicals need to be removed or neutralized before they can be reintroduced back to the environment as a part of the water cycle.
The process of chemical wastewater treatment
The chemical wastewater treatment process is done alongside the biological treatment and cleaning process to achieve the various water standards. The main reason for the use of chemicals is for disinfection and filtration of solid wastes.
Neutralization involves the addition of chemicals to balance the pH of the wastewater.
Acids are used to raise the pH and alkalis are used to lower the pH depending on the initial pH level of chemical.
Chemical precipitation is one of the most common methods for removing dissolved metals from wastewater that contains heavy toxic metals. To convert the dissolved metals into solid form, a precipitation reagent is added to the mixture.
Chemical coagulation involves destabilizing the wastewater particles during the chemical flocculation. The fine solid particles in the wastewater carry negative charge and chemical coagulation involves introducing positively charged particles into the mix which binds them into a larger group. After the larger group is formed, sedimentation can be used to remove the particles from the mixture.
With the introduction of the oxidizing agent during chemical oxidation, electrons are attracted to pollutants in the wastewater. The pollutants undergo structural deconstruction, becoming less toxic.
When the water is too hard, it is difficult to use to clean and often that leaves a grey residue. For example, when you wash your hands with hard water and soap, the lather on your hand is hard. An ion exchange process is used to make the hard water into soft water.
Adsorption and Chemisorption
Adsorption is the process where substances are formed on the surface of the solid waste due to Van der Waal force. When the same thing happens as a result of a chemical bond it is called chemisorption. Colour from textile dying, pharmaceutical residue, arsenic and heavy metals are examples of substances that can be removed through these process.
Precipitation is the chemical process that involves the addition of chemical agents to the wastewater to dissolve the insoluble substances.
Flocculation uses flocculants to remove very fine particles from wastewater. Flocculants help waste particles form large clumps through magnetic neutralization, which makes it easier to filter out during the process.
In chemical stabilization, an oxidant is introduced to the wastewater to slow down the growth of biological matter. The water is then separated from sludge of biological matter.
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