Wastewater Treatment Plant – It is of utmost importance currently to have fresh water and eco-friendly industrial practices. Companies utilize water for their operations in some form or other. Post usage, the wastewater should be treated so that it does not harm our surroundings, either by being released into nature or sewers. To guard against legal fallout, the physical and chemical traits of said effluent must be observed in place.
1. Wastewater Treatment Plant (WWTP)
Domestic, agricultural, industrial, medical, and transport activities generate wastewater.
Wastewater can be divided into two categories:
Sewage Water: Water that comes from domestic activities such as toilets, showers, or sinks is known as sewage water.
Industrial Wastewater: Water from manufacturing, industrial, and commercial activities, on the other hand, has a completely different composition from sewage water.
How does it work?
- In this water treatment plant, wastewater drains by gravity through the main sewer system to the plant.
- In the pre-treatment stage, the water moves through a gravel chamber to remove any grit from the water. A gravel dump is then used to dispose of the gravel. After the water moves through the bar screens, which remove large objects, the fine screens remove smaller objects like undigested foods, matches, etc.
- Grit in wastewater settles in the bottle in the grit chamber, which is then removed from the tank and disposed of in a landfill.
- During the sedimentation stage, also referred to as primary treatment, the water flowed to the primary settling tanks, also called pre-settling basins. These tanks have hoppers located in their bases where the water flows. A hopper moves around the edges of a tank, causing the treated water to remain at the edges while the particulates in wastewater that are most sedimentation-prone settle on the bottom.
- Following the primary treatment, the secondary treatment takes place. This is also known as the biological stage, as it utilizes natural processes and bacteria that consume contaminants in the water, such as biodegradable organic compounds, carbon, and phosphorus. Sludge is then formed by dead bacteria and organic residues.
- The sludge is pumped out and moved to the settling tanks. Once settled, the sludge moves to the digestion tanks.
- Another important thing that occurs in the digestion tanks is the mixing of the sludge and the production of biogas, which can be used by wastewater treatment plant to produce electricity or thermal energy.
- When the sludge reaches an optimal level in the digestion tank, the next digestion takes place in the storage tanks. By doing so, water can be separated from semi-solid sludge, while the remaining sludge is processed mechanically for dewatering, which involves removing as much water as possible.
- Finally, after the digestion and dewatering processes are completed, the sludge left behind is disposed of in the landfill. Moreover, if it complies with all agricultural standards, this sludge can be used as fertilizer for industrial crops in about a month.
There is a large amount of wastewater produced by petroleum refineries, petrochemical plants, and chemical plants, as well as paper and pulp manufacturing.
2. Sewage Treatment Plants (STPs)
It can also receive rainwater and debris from sewers. These plants remove contaminants/sewage waste from households, and commercial buildings, and sometimes even receive commercial wastewater. In addition to cleaning wastewater with a bunch of chemical, physical, and biological procedures before disposing of it into the environment, STPs play a critical role in keeping residents healthy and safe.
How does it work?
The wastewater that enters a sewage treatment plant undergoes a pre-treatment process. It flows through screens and into settlement basins that can remove large amounts of debris.
As stated above, it acts as a pre-treatment before three more aggressive stages- primary, secondary, and tertiary.
Primary Treatment: After passing through the clarifiers, wastewater flows into the aeration basins. This design results in the settling of the organic material, where the heavier matter collects at the bottom while the lighter particles rise to the surface for easier removal. The sediment that accumulates is known as a primary sludge blanket. Afterward, this sludge moves on to undergo the activated sludge process, which takes place in the aeration basins.
Secondary Treatment: This treatment phase involves the use of aerobic aeration, with aeration basins containing aerators that have piping or tubing with holes formed by ceramic or rubber membranes. This air flowing through the aerators creates bubbles when mixed with the water column, bringing beneficial bacteria in contact with the organic matter present in the wastewater and transforming it into something else entirely. As well as this, it is also effective in eliminating noxious chemicals. Once aeration is complete, it flows further into secondary clarification tanks, where bacteria form a sludge blanket and settle for one or two days until pumped out. This sludge is called return-activated sludge (RAS), which then cycles back to primary clarification tanks to help break down any remaining organic material.
Tertiary Treatment: After primary and secondary processes, tertiary treatment is employed to maximize safety. This more advanced process involves sand filtration to remove fine particulates and exposure to UV lights to disinfect organisms and clear any infections. Ultimately, the treated water is securely dispensed into the environment as effluent.
Applications: Residential houses, commercial buildings, municipal wastewater, etc., are all examples of STPs.
On the other hand, effluent treatment plants treat industrial effluent, the wastewater produced by the flow of byproducts from industries.
How does it work?
Preliminary treatment: Screening, sedimentation, filtration, clarification, and other physical techniques are employed to remove as much solid physical matter as possible before sending the effluent on to the next stage.
Primary treatment: Solid waste and organic matter are removed in this phase, and chemicals are added to break down any solid or chemical waste. To control the pH level, sodium carbonate or hydrochloric acid can be added, or chemical coagulation, chemical precipitation, or chemical precipitation can be used.
Secondary treatment: Several chemical and biological processes are used here to remove suspended particles and biodegradable matter.
Tertiary treatment: An industrial effluent is tertiary treated using a combination of physical, chemical, and biological processes.
Applications: Chemical industries, such as textile and dye manufacturing, use ETPs to treat wastewater that has high levels of chemical contamination.
For industrial water treatment, demineralization involves removing dissolved solids or minerals from feedwater or process streams.
How Does It Work?
This water treatment plant works on the principle of ion exchange, making use of two types of resins – an anion one and a cation one. The anion resin releases hydroxyl ions with a negative charge, while the cation resin generates hydrogen ions that are positively charged. This process enables softening of the water, removing nitrate from wastewater; and ultimately deionizing it to produce water of excellent quality.
Application: A demineralization process removes all minerals from the water completely and is generally used to produce water of high purity for industries such as makeup and feed water in high-pressure boilers, food and beverage manufacturing, and electronics manufacturing. As well as generating steam, power, and cooling, they are also used in industries.
RO Water Treatment:
By applying pressure to wastewater while it is on one side of a membrane, reverse osmosis (RO) removes many pollutants and contaminants.
How does it work?
This water treatment plant functions using a high-pressure pump, increasing the pressure on the salt side of the RO to compel the water through the semipermeable RO membrane. The membrane permits only certain atoms and molecules to pass, and others are not granted passage and are discarded into the reject stream (or brine or concentrate stream). Ultimately, almost 95%-99% of dissolved salts can be removed from wastewater.
In industries such as mechanical, boiler feed, semiconductor manufacturing, and metal finishing for food and beverage, reverse osmosis water treatment plants are widely used.