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A wastewater treatment plant is an important part of the American landscape, protecting communities and ecosystems while keeping the water cycle moving. But how does a wastewater treatment plant work? Read on to discover more as we explore the ins and outs of these critical pieces of infrastructure.

The Input

The input to a wastewater treatment plant – more technically referred to as the ‘influent’ – is essentially any water that is expelled by residential properties and qualifying businesses within the plant’s catchment area. In an urban setting, this water will be collected over a small but highly concentrated area, due to the more built-up nature of these regions. In more rural locations – where properties are more spread out – the wastewater may be collected across a broader catchment area.

This influent may consist of water that has been flushed into the sewage system, along with all the organic and inorganic matter this water carries. It may also consist of stormwater, which washes material into storm drains after periods of heavy weather.

Not all of the influent will be raw. Some types of businesses may be required to carry out processes of pretreatment, rather than simply releasing the water into the municipal system. However, water from residential properties will be largely untreated. We’ll discuss this process of pretreatment in a later article.

Primary Treatment

As the influent enters the wastewater treatment plant, it passes through a screen. This screen is an important component as we understand how wastewater treatment plants work, as it removes any larger solids that the plant’s infrastructure will find difficult to break down. Solid debris can actually damage plant equipment if it is not removed, so the screen is vital.

The next phase is the grit chamber, where water is allowed to settle so that smaller solids can sink to the bottom. These solids are then removed from the wastewater as it passes through the plant.

The final phase of primary treatment is the sedimentation tank. Here, the speed of the water flow is reduced, giving the mixture more time to settle and separate. Smaller particles can sink to the bottom of the sedimentation tank, ready for removal. Pumping is used to remove the grit and the sediment from their respective tanks.

Once primary treatment is completed, the wastewater can be considered ‘treated’ because most of its potentially harmful content has been removed. However, primary treatment alone is generally not enough to achieve the high levels of water quality required by modern communities and municipalities. To prevent the human and environmental issues caused by incomplete treatment of water, the waste will typically be passed to a secondary stage of treatment.

Secondary Treatment

The wastewater now passes through an activated sludge tank – which has largely replaced the trickling beds or secondary filtration media that were once used in this phase. As the waste passes through the sludge, bacteria within the tank consumes the organic matter suspended in the water, providing another step in the treatment process.

The ‘activation’ element is key to understanding how wastewater treatment plants work. Activation typically means pumping air into the sludge mixture via an aeration tank. This process accelerates the work of the bacteria, making it easier for these microorganisms to consume the organic matter. Even with this acceleration, wastewater will typically remain in the activated sludge tank for a number of hours.

As the sludge is significantly denser than water, it will settle at the bottom of the tank after this process. From here, the aerated and bacteria-laden sludge is pumped back to the beginning of the secondary treatment phase, ready to interact with more wastewater as it is pumped through the plant.

While the sludge is pumped back to the beginning of the secondary phase, the less dense water moves through to the next stage, which is usually another sedimentation tank. Here, the leftover bacteria from the activated sludge stage is removed. Disinfection with chlorination may also be used to kill and remove harmful bacteria and pathogens. The chlorine itself may also be harmful, so this will be followed by a process of dechlorination in some cases.

The Output

Once both the primary and secondary treatment phases are complete, the wastewater flows out of the treatment plant. This water is known as ‘effluent’ – the opposite of the influent that flows into the plant. It’s worth bearing in mind that each treatment phase has its own influent and effluent. In other words, the effluent that flows out of the first treatment phase will be the same as the influent flowing into the secondary phase.

Up to 99% of harmful materials are removed during the various stages of treatment. Any potentially harmful materials that remain within the water are at very low concentrations, which means they should not pose a risk to human communities or to local ecosystems. Currently, there is no perfect method deployed in wastewater treatment plants. There will always be some material left over, but testing and analysis show that the effluent water is no longer harmful.

After treatment, the effluent water is released into receiving channels and distributed among the local water table. The aim of a wastewater treatment plant is not to break the natural water cycle, but instead to keep this cycle moving in a safe, viable, and environmentally sound manner. The plant and the treatment infrastructure simply represent another step in the ongoing journey of water as it is used and recycled.

Find Wastewater Treatment Plant Solutions in the Chemtech Range

When treated in the right way, wastewater effluent should not pollute the local water table, damage nearby ecosystems, or put human communities at risk. The phases of pretreatment, primary treatment, and secondary treatment are highly effective in removing harmful pathogens and other materials from the water, but only if wastewater treatment plants have the right products on their side. Here at Chemtech, we offer the product range and the solutions you need, so take a look at our product listings to discover more. If you have any questions or queries, simply reach out to our team today.