7 Major Stages of Water Recycling
With increasing urbanization, the number of industries is also growing in India. Moreover, as factories snowball, their wastewater production is also rising. However, many companies do not consider wastewater treatment and release untreated water into rivers, lakes, or landfills.
This untreated water pollutes natural water sources and spreads waterborne diseases among the residents.
About 37.7 million Indians suffer from waterborne diseases every year. (Source: India water portal)
Photo credit: WaterAid / Marco Betti
Owing to the fact that tons of wastewater from industries and municipalities are left untreated, the government of India is encouraging effluent and sewage treatment through various laws and awareness programs.
Industries like textile, paper & pulp, oil & gas, food & beverages, chemical, automobile, pharmaceutical highly require wastewater treatment plants because wastewater treatment removes pollutants like large solid particles, organic & inorganic compounds, toxic & hazardous waste materials, etc.
However, wastewater treatment is not a single-step process, but consecutive techniques, technologies, and methods are combined to fulfill the treatment requirement.
Screening
Screening water treatment solutions are considered a pre-treatment of wastewater that removes large floating particles like plastic, wood chips, rags, leaves, etc. These solid materials can obstruct the water flow downstream and lead to the clogging of equipment, pipes, and pumps. Screening solutions reduce the risk of breakdown due to the accumulation of large pollutants by removing them. There are two types of screens based on the pore size,
Coarse screens: Coarse screens provide a screening solution for bigger-sized particles present in wastewater. They consist of steel bars that are corrosion resistant and positioned at a 60° angle to facilitate the removal of particles ranging from 0.25 to 6 inches. Most industries and municipalities use coarse screens are the first treatment step to get efficient screening solutions.
Fine screens: Fine screens, as the name suggests, remove fine and smaller particles from wastewater and offer the best screening solutions by reducing the majority of suspended solids from water and protecting the downstream processes and equipment. They can remove particles of 1.5 to 6 mm in size.
Screening water treatment solutions are prominent to reduce equipment breakdown and maintenance costs. It also saves time and additional operational costs.
Aeration
Aeration is adding air bubbles to wastewater in two ways: air in the water or water in the air. When air bubbles enter the water, they attach themselves to suspended solids like oil & grease particles, eliminate gaseous particles, oxidize metals, and supplement bacteria to facilitate the decomposition of organic matter.
When air bubbles attach themselves to contaminants, they float on the surface together and allow froth removal, and water is sent for further treatment.
Coagulation & flocculation
Coagulants (chemicals) are added to wastewater under constant mixing, stimulating chemical reactions to neutralize suspended solids, and the neutralized particles come together to form flocs.
In the flocculation tank, water is gently stirred, which facilitates the bonding of smaller flocs to form larger flocs. Here water is mixed in a way that prevents the dispersion of the bigger flocs.
Sedimentation
When flocs are formed, they can settle in the sedimentation tank, where material accumulates at the bottom of the tank, called sludge. Then, the clear water is sent for further treatment, and sludge is scraped out for disposal.
Filtration
Filtration is one of the most essential and integral processes in wastewater treatment.
When solid particles are left out after coagulation, flocculation, and sedimentation, they are removed through filtration. Here, wastewater is passed through filters where insoluble particles are retained, and water is allowed to pass.
Generally, industries use sand filters or gravity filters. In those filters, when filters are fully loaded with solid particles, they are back-washed to unclog.
If the turbidity of the wastewater is low, it will become pollutant-free by the time it reaches the filtration process and can be reused or released. However, if it is highly turbid, it requires further treatment.
Disinfection
Disinfection removes microorganisms from water that can be harmful to humans as well as aquatic life. Generally, chlorine is used to disinfect water as it is relatively inexpensive and effective. It kills most bacteria from water, and the residual chlorine left after that prevents the further growth of microorganisms.
After disinfection, water is tested, and if it has contamination, it will be further treated until it complies with the national wastewater discharge limits.
Wastewater treatment is essential to save the environment, reduce freshwater use by providing treated water for reuse, and reduce humans’ and aquaculture’s health risks.