In the water treatment process, the water treatment grille bar screen is the initial purification step, responsible for blocking and removing various impurities in the water. Whether you are a professional water resource manager, environmental engineer, or a friend who has a keen interest in the water cleaning process, it is very necessary to have a deep understanding of the working mechanism of the bar screen.

Inflow

The first stop for wastewater entering a treatment facility is a screen. Wastewater flows through large pipes or channels from a variety of sources, such as residential areas, industrial areas, or rainwater collection systems.

When wastewater reaches the screen, its composition can vary depending on its source. For example, municipal wastewater may contain organic matter, household cleaning chemicals, and solid impurities, while industrial wastewater may contain industry-specific contaminants. Regardless of where the wastewater comes from, the screen must handle these impurities.

The design of the inflow channel is critical to the operation of the screen.The channel design needs to ensure that the water flow can evenly cover the full width of the screen. Turbulence can be reduced and the flow rate can be maintained evenly by installing flow adjustment devices or special inlets.

Today's water treatment plants generally use precision sensors and control systems to monitor the water inflow, measure flow, water level and wastewater composition, and optimize the performance of the screen and subsequent processes.

Faced with high-speed water flow, such as during heavy rain, the treatment is more difficult. The screen must be able to handle peak flow rates to prevent overload and avoid large amounts of raw water passing directly.

Some advanced screen systems integrate flow control devices at the water inflow stage, such as adjustable weirs or gates, to adjust the water flow rate and ensure efficient operation under various water inflow conditions.

Screening

Screening is the main task of water treatment grille bar screens, which can separate larger debris from wastewater. As wastewater passes through the screen, it encounters vertical or inclined bars made of durable materials such as stainless steel or high-strength polymers.

The spacing between the bars is important and determines how large debris can be retained. Typically, the bars are spaced between 6 mm and 150 mm, depending on the needs of the treatment station. Smaller spacing can retain more debris, but requires frequent cleaning and may cause a drop in water pressure.

As water flows through the bars, it can retain a variety of solids, such as leaves, branches, rags, plastic bags, bottles, gravel, sand, and sometimes toys or household items.

The screening effect depends on several factors: water flow speed, fence angle, etc. If the water flows too fast, debris may rush through; if it is too slow, debris may sink to the bottom before the water reaches the screen. The inclined screen allows debris to float to the surface more easily when the water level rises.

Modern screens are more complex, with specially shaped bars, devices to reduce water pressure loss, and vibration mechanisms to prevent debris accumulation.

However, screens are mainly used to block large debris, and cannot block dissolved pollutants or very small particles. These problems will be solved in the later treatment stages.

As the screening continues, debris will accumulate. More accumulation can improve the screening efficiency because the debris itself becomes a filter. However, too much accumulation will affect the water flow and increase the water level upstream, so it needs to be cleaned regularly.

Separation

The separation stage is where the grille bar screen truly demonstrates its value in the water treatment process. As debris is captured by the bars, it begins to accumulate, forming what's often referred to as a "screenings mat" or "debris layer." This accumulation is a dynamic process that plays a crucial role in the overall efficiency of the screening operation.

Initially, larger objects are caught directly by the bars. However, as these objects build up, they create a more complex filtration surface. This surface can often trap smaller particles that might otherwise have passed through the bars, effectively improving the screen's filtration capability over time. It's a delicate balance, though, as excessive buildup can impede water flow and reduce overall system efficiency.

The composition of this debris layer can vary widely depending on the source of the wastewater. In municipal systems, it often consists of a mix of organic matter (food waste, leaves, etc.) and inorganic materials (plastics, paper products, etc.). Industrial wastewater might result in more specialized types of debris accumulation.

As the debris accumulates, the water must find its way through or around these obstacles. This creates a complex flow pattern, with water seeking the path of least resistance through the screen. In well-designed systems, this flow pattern helps to distribute the screening effect more evenly across the entire screen surface.

The clarified water that passes through the screen is not completely clean, but it is free of the larger, more problematic debris that could damage or interfere with downstream treatment processes. This "pre-treated" water typically still contains dissolved contaminants, smaller suspended particles, and microscopic organisms, all of which are addressed in subsequent treatment stages.

It's worth noting that the separation process isn't just about removing visible debris. By removing larger organic materials at this stage, the water treatment grille bar screen also helps to reduce the biochemical oxygen demand (BOD) of the wastewater. This can have significant benefits for the efficiency and effectiveness of biological treatment processes that often follow the screening stage.

The accumulation of debris on the screen necessitates regular cleaning to maintain optimal performance. In many modern facilities, this cleaning is automated, with mechanical rakes or brushes periodically sweeping the screen to remove accumulated material. The removed screenings are typically collected for disposal, often involving dewatering and compaction to reduce volume.

Outflow

The outflow stage is the end of the work of the screen bars, when the clear water leaves the screen and enters the next treatment stage. Although this stage may seem simple, it is critical to the overall efficiency of water treatment and needs to be designed carefully.

When the water leaves the screen, it is best to maintain uniform flow across the full width of the channel, which is critical for downstream processes, many of which rely on stable water flow conditions. Outflow channel design often includes features to promote uniform flow, such as gradual widening or flow straightening vanes.

The velocity of the outflow water needs to be monitored. Too high a flow rate may allow small pieces of debris to flow into the downstream treatment system; too low a flow rate may cause sedimentation in the outflow channel. Many facilities install flow control structures downstream of the screen to manage flow rate.

Advanced treatment plants monitor multiple parameters of the effluent, such as flow rate, compared with the inflow rate to detect whether the screen is seriously leaking or plugged. Some facilities also have sampling points to evaluate the screening effect.

Although the effluent water is clearer than the influent water, it still contains many contaminants, such as dissolved matter, fine suspended particles, and microorganisms. Removing large pieces of debris can reduce the burden of downstream treatment and improve efficiency.

Some treatment plants use multiple stages of screening. In this case, the effluent from one screen goes directly to a finer screen or other preliminary treatment stage. Staged treatment provides a more complete removal of debris of all sizes.

The outflow stage also affects the overall hydraulic curve of the treatment plant. The water level at the screen outlet affects the upstream water level, which in turn affects the head that drives the water through the screen. Therefore, the correct design of the outflow structure is critical to maintaining optimal hydraulic conditions for the screening process.

About Us

Tianjin Kairun is a preferred manufacturer of water treatment grille bar screens, and they offer a comprehensive warranty to ensure product quality and durability for peace of mind.

Warranty terms vary depending on the product model and conditions of use, but Tianjin Kairun generally provides a limited period of warranty against manufacturing defects and performance issues, covering key components such as screen bars, frames and cleaning mechanisms. For the most accurate and up-to-date warranty details, it is recommended to contact Tianjin Kairun directly.

When choosing a water treatment screen bar manufacturer, consider Tianjin Kairun, we will provide more product information, warranty service details, and customized solutions to meet your needs. You can contact us at catherine@kairunpump.com to discuss your requirements or for more information.

References

1. Tchobanoglous, G., Stensel, H. D., Tsuchihashi, R., & Burton, F. (2013). Wastewater Engineering: Treatment and Resource Recovery (5th ed.). McGraw-Hill Education.

2. Spellman, F. R. (2013). Handbook of Water and Wastewater Treatment Plant Operations (3rd ed.). CRC Press.

3. American Water Works Association. (2011). Water Treatment Plant Design (5th ed.). McGraw-Hill Professional.

4. Davis, M. L. (2010). Water and Wastewater Engineering: Design Principles and Practice. McGraw-Hill Education.

5. Vesilind, P. A., Morgan, S. M., & Heine, L. G. (2010). Introduction to Environmental Engineering (3rd ed.). Cengage Learning.