There are various types of wastewater treatment screens. Consequently, when you are looking to purchase a screen, there are key features you should consider to ensure you get the best screen.Such features include:

• Size of the screen openings – First, you need to know the particle sizes you intend to trap using the screen. With this knowledge, you should look at the micron ratings of the various wastewater treatment screens and select the ideal for your plant.
• Self-Cleaning Feature – The screens are prone to clogging due to material accumulation on the screen’s surface over time. Thus, selecting a wastewater screen that features self-cleaning will make the wastewater treatment process efficient and reduce the maintenance cost.

A Self Screening Screen

• Screening Type – Most screens offer either coarse or fine screening. However, newer screens provide both coarse and fine screening. Installing a screen that offers fine and coarse screens is a plus since the screening will be more efficient.
• Technology Applied – Ideally, with constant technological advancements, a vital feature to consider in a screen is the level of technology. Screens that feature modern technology designs will improve the screening process.
• Flow Rate – Wastewater screens differ in terms of the flow rate they can accommodate. Considering the flow rate of a screen will ensure that you get the right screen for your specific application. Higher flow rates (than the screen’s rating) may potentially damage the screen.
• Customization – If a screen can be customized for your specific application, without a doubt, the screen will function efficiently.
• Screen Design – Preferably, the screen should feature a resistance welding design to guarantee its strength and durability.
• Capture Rate – At the end of the day, the main reason for the screening is to capture potentially hazardous materials. Consequently, you should ensure that the screen has a high capture rate for it to carry out the screening effectively.
• Construction Material – Most screens are constructed with either stainless steel or carbon steel to ensure durability.

Screening is a vital process in industrial or municipal wastewater treatment. Screening removes objects such as plastic, metals, fabric, debris, etc.

The main reasons for screening are to:

• Prevent damage to the downstream equipment.
• Reduce the chances of blockage of the downstream equipment.
• Minimize the contamination of the water discharged from the water treatment plant.
• Make the treatment process more effective and reliable.

The above reasons double up as the key benefits of wastewater treatment screens. Some additional benefits of using a wastewater treatment screen include:

• Versatility due to a wide range of wire profiles to fit various applications.
• Most screens can be customized as per your specifications.
• Replacing wastewater screens is easy and fast, preventing any lengthy downtime.
• Modern screens feature a self-cleaning design, significantly cutting on the maintenance cost and time.
• Wastewater screens have a resistance welding design making them stronger and durable.
• Also, the wastewater screens have a simple design that excludes components such as guides, sprockets, or bushings.
• Several wastewater screens have a higher capture rate.
• If the screen is correctly installed in the right application, it will offer less flow resistance. This, in turn, ensures continuous wastewater flow through the screen.
• Lastly, the slots or openings for the screens are made with high precision to ensure that the screening process is effective.

Wastewater Treatment Screen Minimize The Chance Of Blockage Downstream

Wastewater treatment screens have a few limitations, but these do not overshadow their overwhelming benefits.

The commonly highlighted disadvantages include:

• Some modern complex screens are difficult to install and may require expert help.
• Manually cleaned screens require regular cleaning, increasing the need for maintenance.
• The high precision required in making the openings in the screen may be demanding on the manufacturer’s side. Inaccurate slots will make the screen inefficient.

You know what they say about variety; it is the spice of life. Putting this in context, variety in terms of wastewater treatment screens makes the screening process more efficient.

Let’s look at the various types of screens used in wastewater treatment and how they compare.

Perforated Plate Screen For Wastewater

As the name suggests, the screening media for a perforated plate screen is simply a plate panel that has perforations (openings).

Modern perforated plate screens have a step design, allowing for the automatic cleaning of the screens at the discharge point.

These types of screens capture solids from the wastewater.

Next, the step design transport the captured solid to the rear of the unit for disposal.

Upon discharge of the solids, the screens are automatically cleaned by a brush and a spray.

Perforated Plate Screen

Band Screen For Waste Water

Band screens comprise a series of perforated plates. This makes these types of screens have a high capture rate of up to 80 percent.

Notably, band screens remove various objects and materials for the wastewater, including fine materials, rags, metals, bags, etc.

Additionally, wipers can be integrated into a band screen to aid in the removal of large objects such as cans or bottles.

Band Screen For Wastewater

Bar Screen For Wastewater

Bar screens can be categorized under coarse screens.

Structure-wise, bar screens are made up of vertical bars – spaced between 1 to 3 inches apart.

Generally, bar screens help in removing large objects such as plastics and rags from the wastewater.

If the screens are sequentially placed, the bar screen comes ahead of the other screens.

In screening, the large objects are first removed, followed by the remaining finer materials.

Depending on the design, bar screens can be automatically cleaned or manually cleaned using a hard rake.

Bar Screen

Mechanical Bar Screen For Waste Water

A bar screen is a piece of heavy-duty screening equipment with a rake that constantly removes the debris or the materials trapped on the screen.

Mechanical bar screens are typically classified into two:

1. Single Rake Mechanical Bar Screen – It features a fixed bar rack anchored within the channel, with openings greater than 1 inch. The screening materials are lifted out of the channel by a rake arm.

One major advantage of the single rake mechanical bar screen is removing screening materials from deep channels. However, it is prone to jam, and maintenance is not easy due to the inaccessibility of some parts.

Single Bar Mechanical Screen

2.Multi-Rake Bar Screen – This is the modern-day mechanical bar screen featuring multiple rakes for increased efficiency.

This specific mechanical bar screen is easier to maintain, durable, and has a more effective raking system.

Regardless, it is also prone to jam, and some parts are also inaccessible making maintenance difficult.

Multi Bar Screen

Inlet Screen For Wastewater

An inlet screen essentially acts as a pre-treatment device in a wastewater treatment plant. This is not specifically a type of screen but is instead a broader category of the screens located at the wastewater treatment plant’s inlet.

Screens such as drum screens and screw screens can be classified as inlet screens. It’s worth noting that most inlet screens are coarse screens.

Coarse Screen For Waste Water Treatment

Wastewater comprises a number of objects that vary in size; there are larger materials and smaller/fine materials.

The coarse screen majorly traps the larger objects and removes them from the wastewater. Also, the main materials it removes include debris, metals, rags, and any other larger solids.

Typically, they have openings measuring not less than 0.25 inches.

If you are to arrange the screens sequentially, you will start with the coarse screen, the fine screen then the micro screen

Fine Screens For Wastewater Treatment.

Unlike the coarse screens, these types of screens have openings ranging from 0.06 to 0.25 inches. They trap objects that the coarse screen permitted to pass.

Micro Screens For Wastewater Treatment

The openings on the micro screens are less than 0.06 inches. These screens trap the finest materials that either coarse or fine screens couldn’t trap.

Inclined Rotary Drum Screen

 Inclined Rotary Drum Screen

As the name implies, a rotary drum screen is a drum-shaped screening device.

It is hollow (has openings on its top and bottom parts), while the sides are fitted with sieves.

The rotary drum screen is usually horizontally placed in the system.

Wastewater is channeled into the drum, which is in a constant rotating motion. Inside the drum, water is allowed to pass through the sieves while the solids are screened out.

Commonly, rotary drums are fitted with an auger that carries the trapped solid waste to the end of the drum.

Consequently, the solid waste is emptied from the rotary drum.

Alternatively, other rotary drums are cleaned by spraying water from the outside of the screen.

The advantages of a rotary drum screen include:

• High capture rate
• Minimal maintenance
• Simple and efficient

Continuous Filter Screen

The continuous filter screen is ideal for fine screening. It has a belt screen that filter the wastewater.

This screen can feature either a single belt or a double belt design.

Typically, the continuous filter screen is suspended using a crane system.

The filter screen has filter elements (made out of special plastic) placed on a stainless steel shaft- supported to the frame. Consequently, wastewater is screened as it flows through the screen.

Notably, this specific filter screen has no moving parts; thus, it is easy to use and maintain.

Coanda Screen

A Coanda screen uses a slanted design to filter raw or wastewater. For a better understanding, below is a simple diagram of the Coanda screen.

A Coanda Screen

From the above diagram,

Typically, the approach plate channels the water to the filter screen. As the wastewater flows onto the filter screen, water goes below the filter screen while the debris remains on the filter screen.

The filtered water will then exit the Coanda screen via the outlet. For the debris, they will slide down the filter screen.

Notably, the coanda screen’s efficiency depends on the mounting angle and the span or length of the filter screen.

Also, these screens are widely used in flowing water bodies such as rivers.

Some key benefits of Coanda screens include;

• Constant supply of screened water.
• The screens are self-cleaning, thus reducing the maintenance cost.
• Lack of moving parts which also lowers the maintenance cost.
• High corrosion resistance

Sieve Bend Screen

The sieve bend screen is a concave curved screen. Generally, v-shaped wires are welded to support rods to construct a sieve bend screen.

In a way, the operation of the sieve bend screen is similar to that of the Coanda screens.

The wastewater flows against the sieve bend screen in the direction indicated by the arrow. Consequently, the water is sieved, and the debris is collected in the lower part (Part A).

The common advantages of these types of screens include:

• High dewatering capacity
• Low clogging probability
• Durability
• Low maintenance requirement
• High rust and corrosion resistance

Spiral Screw Screen

The spiral screw screen has a simple design comprising a trough fitted with a perforated basket and a rotating screw.

Besides, the perforated basket permits water to pass through while the solid materials remain on the upper surface.

After which, the rotating screw transports the solid materials to the compaction zone, thereby automatically cleaning the screen.

Although this type of screening device is cost-effective, it does not have a high capture rate, plus the spiral cleaning mechanism can push the debris through the screen.

The main reasons you may want to replace your wastewater treatment screen are:

• If it is ineffective – no longer carrying out adequate screening on the wastewater
• You want to generally make your screening more efficient.
• If the screen is way too old.
• You want to be at par with the advancements in the screening industry.
• If your screen is damaged beyond repair.

You can either replace the screen with another screen of the same type or entirely go for a completely different type of screen. Your choice will mainly depend on:

• The capture rate of the current screen
• Modifications you will make if you were to install a new type of screen.
• The water supply and pressure – whether the new screen type will work efficiently at the prevailing conditions.

Bar Screen

Bar screens are made by spacing vertical bars within 1 to 3 inches apart. These screens have large openings due to their design.

They are used in the first level of filtration to remove large solids like rags, plastics, and pumps. The removal of such objects is essential to prevent any clogging in the system.

Most bar screens are fitted with upward moving rakes to remove the materials trapped by the bar screen.

In terms of classification, you can place the bar screen under the coarse screen category.

Wedge Screen

In the case of wedge wire screens, they are made by arranging wedge wires in a triangular shape at regular intervals.

Their design makes them be able to trap finer materials from the wastewater. Also, the triangle shape makes it difficult for the screen to clog.

However, if by any chance the screen does clog, these types of screens usually feature a strong backwash effect.

Classification-wise, the wedge screen falls under the fine screen category.

The simple difference of the two lies in their definitions.  Perforations are holes on a solid material, while the mesh is evenly spaced wires.

Difference Between Plate And Mesh Screen

Thus deductively, a perforated plate screen is made by drilling or making holes on a metal plate.

Also, the hole sizes may vary depending on the specific application of the screen.

On the other hand, the mesh screens are constructed by equally spacing wires to permit water flow but trap solids.

Depending on the diameter of the wire, the solids can either be smaller or larger. If the wire used has a small diameter, the opening will be larger, permitting larger solids to pass through.

Notably, mesh screens are graded according to the number of holes per square inch.

When looking at the size of the wastewater screen, we place a major focus on the openings on the screens.

Ideally, the screen openings are categorized into three:

• Coarse Screens – These remove rags, large solids, and debris. Typically, they have openings measuring not less than 0.25 inches.
• Fine Screens – Unlike coarse screens, these types of screens have openings ranging from 0.06 to 0.25 inches.
• Micro Screens – However, there are finer screens (with openings less than 0.06 inches) placed after the less fine or coarse screens.

Most wastewater plants have all of these screens for more efficient screening. Notably, most modern design skins have all of these screen types to the screen installation.

The size of the screen will also depend on the specific water treatment application. For example;

• Membrane Bioreactors (MBRs) and Integrated Fixed-film Activated Sludge (IFAS) need screens with finer openings.
• Systems with pumps need mechanical rake-type screens, which are primarily coarse screens.
• While water intakes and wastewater plants headworks will require finer screens with a high screening removal rate.

The material used for wastewater treatment screen differs depending on the manufacturers.

Also, the type of screen will affect the choice of material.

Regardless, most screens are made out of stainless steel. However, the grades of stainless steel used also differ.

Some key reasons why stainless steel is preferred include:

• Durability
• Versatility
• High corrosion resistance
• Stainless steel is a relatively strong metal

Stainless Steel Is The best Material To Make Wastewater Screens

Yes, the flow rate is among the factors that determine the design of wastewater treatment screens. The recommended flow rates of the various screens differ depending on the type of the screens.

Below are recommended flow rates for the major types of wastewater screens:

• Bar screens – The optimum velocity required is 0.6m/s. Also, the maximum velocity should range between 0.75 to 1.0 m/s to prevent any forceful passage of materials through the screen. Moreover, the minimum velocity should be 0.4 m/s to avoid any build-up of the materials.
• Drum and disc screens – Most of these screens require a velocity of around 0.05 m/s for efficient functioning.
• Coarse screens – These will require a velocity of not more than 0.9 m/s and not less than 0.4m/s to prohibit any solid deposition.

Usually, the wastewater treatment screen should be installed at the inlet of an industrial or municipal wastewater treatment plant.

This is so because screening ought to be the first step in wastewater treatment.

Commonly, the screens can be installed in series forms for efficiency.

The first screen is usually the coarse screens (commonly bar screens).

This screen has fairly large openings, and its central role is to retain large solid materials such as rags, metals, and bottles.

From the coarse screen, the wastewater moves to the fine screen. The fine screens have smaller openings compared to the coarse screen.

Consequently, they trap smaller materials that pass through the coarse screen.

Finally, the wastewater passes through the micro screens. These screens have the smallest openings between the three-screen types.

They trap the finest materials from the wastewater.

Commonly wastewater treatment screens are used in municipal and industrial wastewater treatment plants. The typical industries using these screens are:

• Sewage treatment plants
• Water-intake stations
• Sewage pumping stations.

Bar screens are the common type of screens that feature mechanical cleaning designs.

Mechanically cleaned wastewater treatment screens differ in terms of design.

Below we highlight the common mechanical designs and their respective functioning.

• Chain driven Wastewater Treatment Screens – These feature a back and forth moving raked chain that cleans the screen with every movement. This design can use multiple rakes.
• Catenary Wastewater Treatment Screen – Comprises rakes suspended against the rack by the chain’s weight. Typically, it features a front clean, front return chain that cleans in continuous motion.

The rakes are not that rigid since they can pass over heavy objects jammed between bars, thus preventing further jamming.

• Continuous Belt Wastewater Treatment Screen – As the name suggests, this design features continuously moving chains having multiple rakes attached to them. This design is ideal for both fine and coarse screenings.
• Reciprocating rake / Climber Wastewater Treatment Screen – This is a simple design where the rake drives itself to the bottom of the screen, then carries the screenings as it moves back up. Once up, the screenings are removed.

Unlike the previous three mechanical designs, the climber design uses only one rake. As such, it has a significant drawback of not being efficient in applications with heavy screenings.

When looking to purchase a quality wastewater treatment screen, there are some key elements that will help you gauge if the screen is quality. These include:

• Capture efficiency – This shows how effective the screen is in capturing materials. A high capture rate translates to a quality screen.
• Versatile – Versatility, in this case, is with regard to the ability of the screen to handle the variation in the medium velocity and screening concentration. A quality screen should function efficiently despite these variations.
• Robust – Ideally, a quality wastewater treatment screen should be strong. This enables the screen to withstand any peak variations of the inflow pressure and the screening concentration.
• Diversity – Finally, a screen that can be used in a number of applications is a quality one. Although specialization of a screen is regarded as more efficient, diversity remains ideal.

Wastewater treatment screens not only ensure efficient screening but also contribute to the durability of the wastewater screen.

As such, you should carry out regular maintenance on the wastewater treatment screen to ensure the optimal operation of your wastewater treatment plant.

Below are some critical maintenance practices for most if not all wastewater treatment screens:

• Regular lubrication of the moving parts.
• Recording and reviewing readings.
• Inspect the screens for any damage or corrosion.
• Cleaning the screens regularly to clear the debris – for the manually cleaned screens.
• Greasing the bearings if the screen parts are movable.

To sum it all up, regular inspection is key in maintenance. It will help you catch any problem with the screen in time.

Additionally, adhering to the manufacturer’s manual when carrying out routine maintenance practice is also important to prevent any damage to the screen.

Wastewater treatment screens usually have a simple structure. Hence they do not have many parts.

Below are the typical components of a wastewater treatment screen.

• Frame/Body – It is the part that holds the screen in place. For example, in the mesh screen, the frame holds the mesh.
• Screen – This is the part that does the actual screening. It can be made from various materials, primarily wedge wires and metal bars. The screen has openings to permit water flow but restrict materials.
• Cleaning mechanism – Most modern bar wastewater treatment screens have a mechanical cleaning system comprising of rakes and chains. For the other screens, there may be sprays to clean the screen.

The operating mechanism of a wastewater treatment screen is quite straightforward.

Usually, the screen is either installed on the inlet of the wastewater plant or in a strategic path of flow of the wastewater.

As such, the screen obstructs the flow of water, forcing the wastewater to pass through it. As the water passes through the screens, materials larger than the screen’s opening are restrained.

Depending on the cleaning mechanism of the screen, the captured screenings are either removed from the screen manually or mechanically.

The efficiency of a wastewater treatment screen is dependent on some key factors, including:

• Application of the screen
• The speed of flow or velocity of the water
• Size of the screenings
• Composition of the screenings

The above-mentioned factors will help you choose the correct screen and also ensure that the screen operates efficiently.

Additionally, regular maintenance also contributes greatly to the efficient operation of a wastewater treatment screen.

Yes, you can repair certain parts of a wastewater treatment screen including the spray nozzles, brushes, rakes, grid panels, and wiper blades.

However, when repairing such parts, ensure you use parts that your screen’s manufacturer has approved.

In some instances where the screening material is totally damaged, you will purchase a new screen.

There is no precise pricing for all the wastewater treatment screens. The price variation depends on the:

• Type of screen
• Sophistication or technology employed on the screen
• Materials used to make the screen
• The size of the entire screen

Generally, a wastewater treatment screen price can be as low as $800 to a peak of $50,000.

Coarse and fine screens differ in terms of the size of their openings. Coarse wastewater treatment screens have slots not measuring less than 0.25 inches. They capture large solids present in the wastewater, such as rags, bottles, etc.

On the other hand, fine screens have openings with sizes ranging between 0.06 to 0.25 inches.

The other difference between the two screens is concerning the structure or design. Fine screens are mostly perforated or have wire mesh, while coarse screens are made of steel bars.

Other Related Products:

• DSM Screen
• Gravel Pack Screen
• Rotary Drum Screen
• Coanda Screen
• Johnson Screen

For all your wastewater treatment screens, contact us now.