Why is a biological wastewater treatment process so important? Every gallon of water brought to a wastewater treatment plant is contaminated. If it comes from a residential septic tank, it’s filled with urine, feces, and dirty water from laundry, dishes, and showers/baths. The same is true for water that is piped in from sewers. Even industrial wastewater is going to contain contaminants.

It’s important to properly clean water before releasing it into natural water sources. Too much phosphorus can cause algae blooms to take over the lake or pond. Algae will end up depleting the stores of oxygen fish and other aquatic creatures rely on. As many lakes are becoming overrun with blue-green algae, states are all taking measures to limit the chemicals, minerals, and bacteria by making sure water treatment plants meet requirements that remove these items from water.

Primary vs. Secondary Treatments

Before this water returns to lakes, streams, or public water systems, it has to be cleaned and disinfected. That’s done through several steps that include biological wastewater treatment, but there are also primary measures. You have screens that remove items that won’t break down. Many of these items should be trashed, but it doesn’t always happen. People don’t realize the problem it’s posing when they flush things that aren’t meant to be flushed. Tampon applicators, plastic wrappers, toy cars, and baby wipes are just a few of the things that make it to a wastewater treatment plant.

There are two main types of wastewater treatment: primary and secondary. Primary treatment is a fairly basic process that is used to remove suspended solid waste and reduce its biochemical oxygen demand in order to increase dissolved oxygen in the water. Primary is the use of screens and trash rakes to remove larger items. It’s also the grit removal system.

It’s estimated that primary treatment only reduces biochemical oxygen demand by about 30% and suspended solids by up to 60%. Therefore, the water needs to be treated again in order to remove additional contaminants. That’s where secondary treatment comes in.

Secondary treatment involves complex biological processes that are used to remove organic matter that was not removed during primary treatment. You’re using biology and microorganisms to devour and remove other contaminants. There are many different kinds of biological wastewater treatments, however, each treatment can be classified as either an aerobic, anaerobic, or anoxic treatment depending on whether or not oxygen is present. Here’s a quick look at the three.

What Are Biological Aerobic Treatments?

If a treatment is classified as a biological aerobic treatment, it means it takes place in the presence of oxygen. Aeration is needed to oxygenate the wastewater through the use of mixers and aerators. Aerobic treatments work faster and result in cleaner water than anaerobic treatments, which is why they are preferred.

The most popular aerobic treatment is the activated sludge process. At the start of the activated sludge process, wastewater moves into an aeration tank that is pumped full of oxygen. Aerating the wastewater increases microbial growth, which speeds up the decomposition of the organic matter that is still in the water. Then, this wastewater is transferred into a secondary clarifier, which is also known as a secondary settler or settling tank.

The sludge, or waste, within the water will start to separate, leaving only the clean and treated water behind. Remaining sludge can then be converted into a mixture of methane and carbon dioxide that can be used for heat and electricity. Any remaining sludge is dewatered (dried) and composted or sent to a landfill. The activated sludge process is one of the most efficient ways to biologically treat wastewater and it’s effective.

Another popular aerobic treatment is the trickling filter process. During the trickling filter process, wastewater flows over a bed of rocks, gravel, ceramic, peat moss, coconut fibers, or plastic. As the wastewater flows, the microorganisms in the water quickly start to attach to the bed. A layer of microbial film will soon start to grow over the bed. Over time, the aerobic microorganisms found in this layer of microbial film will start to break down the organic matter found in the water. If needed, oxygen can be infused or splashed into the wastewater to maintain aerobic conditions.

The trickling filter process can rapidly reduce high concentrations of organic matter in the water, however, there are disadvantages to this method as well. A trained professional will need to watch over this process from the start to finish, so this may not be the best choice for facilities with limited resources. Clogs are also fairly common, so the trained professional will need to know how to identify and fix this issue.

Some facilities use aerated lagoons as opposed to the activated sludge process. With this method, the wastewater sits in a treatment pond, where it is mechanically aerated. Pumping oxygen into the pond will increase microbial growth and speed up the decomposition of organic matter. However, unlike the activated sludge process, the water is not moved into another tank after it has been aerated. Instead, the separation of the sludge and the clean water happens within the treatment pond.

Using an oxidation pond is another way to biologically treat the wastewater. This process involves removing the organic matter from wastewater using an interaction between bacteria, algae, and other microorganisms. This method may seem similar to an aerated lagoon, but it is far more complex and it takes much longer to achieve the desired results. This process also requires a lot more land space than the others, so it is typically not used in areas that are densely populated.

What Are Biological Anaerobic Treatments?

Biological anaerobic treatments take place in the absence of oxygen. Aerobic treatments are usually preferred, however, it is best to use an anaerobic treatment when dealing with highly concentrated wastewater.

The upflow anaerobic sludge blanket reactor is a single-tank anaerobic treatment, which means it takes place in one tank. This process begins with the wastewater entering through the bottom of the reactor tank. As the wastewater naturally starts to flow upwards, it encounters a sludge blanket that is suspended within the tank.

The sludge blanket consists of microbial microorganisms that break down organic matter within the wastewater. When the wastewater encounters the sludge blanket, the microorganisms quickly break down the organic matter, leaving clean water behind to rise to the top of the tank. There are other similar anaerobic treatments, including the anaerobic filter, which involves a filter that has microbial microorganisms on its surface.

What About Biological Anoxic Treatments?

You also have anoxic treatments. In this case, the microorganisms use other molecules to multiply. There may not be oxygen, but nitrates and nitrates act in its place. Anoxic treatments help remove nitrates and nitrites, selenates and selenites, and sulfates from the wastewater.

People are seeing this more in areas where nitrates and sulfates are a concern. It’s the best way to remove as many of them as possible. Anoxic treatments work without adding additional chemicals.

While many states stopped using laundry detergents that contained phosphates, you still see shampoos and soaps with sulfates and nitrates. High levels of sulfates can give water an unpleasant taste and can be dehydrating. High levels of nitrates can impact how oxygen moves around the bloodstream. While it takes a lot to affect a person’s health, it’s still important for water districts to make sure water is safe for everyone.

What Happens After Wastewater is Biologically Treated?

It’s estimated that biological treatments can remove up to 90% of the wastewater’s contaminants. Because all of the contaminants have not been removed, the wastewater is usually sent through a tertiary treatment process after the biological treatment. During this stage, heavy metals, nutrients, and other impurities are removed from the wastewater.

The most common type of tertiary treatment involves the use of chlorine, which is a powerful disinfectant. Small amounts of chlorine are added to the water to remove the remaining impurities before the water is discharged into the environment. There are other ways to disinfect the water that do not involve chemicals. Many facilities avoid the use of chlorine by using UV light to treat the water.

Regardless of which method is used, it is estimated that about 99% of all contaminants have been removed from the wastewater after it has completed this treatment. Once the chlorine is at safe levels, the water can be released back into water sources or moved to storage tanks that supply homes and businesses with water.

What Equipment Is Needed?

The equipment that’s needed for biological treatment systems depends on the area and load. A large city processes far more wastewater than a small town. Systems may want to put a lot of focus on being energy efficient. So many have strict discharge restrictions that must be adhered to. Take a look at some of the equipment that’s used in biological treatments.

#1 – Closed Loop Reactor (CLR) Process

The CLR Process is ideal for its consistency and performance whether you’re in a cold climate or a warm one. It’s designed in a closed loop like a circle or extended oval like you’d see at a race track. Aerators and multi-basin designs complete the system. Because this system is customized for simple, effective operation, it can handle increased loads with ease and doesn’t require a lot of attention from workers in a wastewater treatment plant.

Not only can you save money with the CLR Process, but it also helps lower energy costs. It’s adept at removing phosphorus and nitrogen. If you need a system that works well at cleaning water without driving up costs for the members of your district.

#2 – Extended Aeration/Complete Mix Process

An economical solution biologically processing of wastewater is a package treatment plant. It’s a smaller design that’s ideal when space is limited. Choose an E.A. Aerotor Plant or a Packaged Extended Aeration Plant. What are the differences?

An E.A. Aerotor Plant uses the design from a CLR Process for aeration and mixing and a Spiraflo Clarifier to help the sludge settle. The addition of oxygen in the aeration/mixing process aides biological processing and helps remove more sludge. You add other components as needed to create a custom wastewater treatment design.

You could choose the Package Extended Aeration Plant to have an all-in-one system in a single steel tank. It is designed for low usage and includes your screens, aeration, clarification, sludge tank, and disinfection in one. You don’t need a lot of manpower to effectively operate this system.

#3 – Sequencing Batch Reactors

Treat wastewater in one basin using the Sequencing Batch Reactor or Continuous Feed Sequencing Batch Reactor. This system works by aerating and mixing wastewater to create a lot of oxygen. It then “decants” so that the water is discharged without needing activated sludge pumping or external clarifiers. It allows biological wastewater processing to process for an extended period.

#4 – Magna Rotors

If you’re relying on a system that does add oxygen to help with biological wastewater treatment, Magna Rotors are one of the leading choices. Think of them as large mixers that add oxygen. The benefit is that the rotors have a fiberglass cover that does not get too cold in the winter. You’re not as likely to see the equipment stop working in the winter. The stainless steel blades are also durable and not likely to become bent or dented.

#5 – SharpBNR Process Control

This is an add-on that can help with overall energy consumption and performance. The process control can be programmed to measure things like dissolved oxygen and aeration. Adjust them as needed to meet your goals using a computer or the Human Machine Interface on the control panel. You can link it to a SCADA system, too.

Since 1928, Lakeside Equipment Corporation has been committed to providing clean and healthy water to people around the world using innovative biological treatment processes. Contact Lakeside Equipment Corporation to learn more about our biological treatment systems. Call 630-837-5640 or visit our website to connect with one of our knowledgeable representatives today.

Within a wastewater treatment or water treatment plant, a screw pump moves all of that liquid at a constant speed in the most efficient way possible. Screw pumps are designed to avoid clogging and excessive wear. They don’t require much maintenance, but that doesn’t mean they never experience issues. Here’s a list of common screw pump problems and how to resolve them.

What Is a Screw Pump?

Before getting into common screw pump problems, it helps to know how they work. There’s a giant screw inside a trough or pipe that continually rotates. As it does, water pushes from the bottom of the screw to the top with the help of momentum, the screw’s ridges, and the sides of the trough or pipe. This moves liquids from a lower point like a pool or wet well to a higher point like a basin or tank.

What Issues Are Common?

What are the most common issues people experience with their plants’ screw pumps? These six issues are the most likely to occur.

Cavitation

Sometimes, pressure changes in liquid form small cavities, and then allow vapor and gases to fill those pockets that implode. This is known as cavitation and occurs when the static pressure is lower than the liquid’s vapor pressure. 

Why does cavitation occur? If there is insufficient suction pressure, it’s common. Having high fluid viscosity or gas and air in the fluid are other causes.

When cavitation happens, it creates vibrations that can damage the mechanics within the pump and lead to the failure of the bearings, seals, or shaft. It’s important for the pressure at the suction portion of the pump to remain steady. Reduce the pump’s speed and increase the level of fluid in the suction tank. If gas or air are present, remove them before the liquid makes it to the screw pump.

High Pressure With the Discharge of Liquids

A high discharge pressure is often tied to a blockage in the discharge line. It also occurs if the valve is closed. Those can be easy fixes. Find the blockage or open the valve. It also occurs if the pump speed is set too high. Again, it’s an easy fix. 

Leaks

Leaks also create noises as the fluid levels being moved through the screw pump aren’t adequate. You should notice leaks as you’ll find fluid where it shouldn’t be. They usually occur when seals are worn or fittings are loose. The repairs for leaks involve replacing worn or damaged seals and tightening or replacing loose or broken fittings.

Loss of Flow or No Flow

If your system is not pushing water at all or the flow rate has greatly diminished, it’s often a sign that your motor is working too slowly or is overloaded. It can be tied to a loose belt if the pump is belt-driven. It can also be tied to insufficient suction or the suction pipe being inadequately sized. If the fluid pressure is too close to or matches the vapor pressure, it can lead to issues with flow. If the viscosity of the liquid is too high or the liquid is too hot, flow rates are also impacted.

When any of this is happening, the motor needs to be examined. Make sure everything is lubricated correctly, that belts are tight, and that a variable frequency drive is set correctly. Check the fluid’s temperature and viscosity, and change speed and suction rates if needed.

Loud or Excessive Noise

Is your screw pump making loud rattles, bangs, or grinding noises? Those are not normal noises and need to be investigated. A screw pump makes noise, but excessive or extremely loud noises are not okay.

Loud or excessive screw pump noise is a sign of a clog, cavitation, blocked suction or discharge, misalignment, or worn or damaged bearings. If there are problems, have the repairs made ASAP. Alignment may need to be adjusted. Any blockages need to be cleared.

Make it a point to know how a maintained, properly functioning screw pump sounds. The easier it is to identify the normal noises, the easier it is to determine when a noise isn’t the same. 

Overheating

While the maintenance of a screw pump is minimal, you still need to make sure the pump components are lubricated and working properly. When there is too much friction, overheating is possible and damages a pump in a short time.

Overheating is often linked to operating pumps at too high a speed, clogged lines, or air leaks within the system. All three of these possible causes have to be addressed. 

If you are running your pump faster than is needed, slow it down and see if the problem goes away. Check the lines for clogs, and look for air leaks. Finally, check the lubrication levels and make sure there is adequate lubrication within the pump.

Don’t Delay Troubleshooting Issues

Never delay your attempts to troubleshoot issues. If there is a problem and you wait too long, the repairs could become far more costly. Identifying issues in the earliest stages can save money in the long run. Especially if you have a screw pump expert like Lakeside Equipment to help with the repairs.

Most problems are avoidable if you perform routine maintenance on your screw pumps. You should always keep an eye out for leaks or unusual noises. If there are any concerns, call in an expert. It’s better to pay for an inspection and learn nothing is wrong than to wait and have your pump fail and need to be replaced.

Two Types of Screw Pumps

When you’re investing in screw pumps in your plant, there are open and enclosed screw pumps. Enclosed screw pumps have the screw installed within a solid pipe. Open screw pumps are in a concrete or steel trough. 

Lakeside Equipment offers two types of enclosed screw pumps: Type C or Type S. Type C has a smaller horizontal footprint and an outer rotating tube, while Type S has a stationary tube with a pivot feature to reduce the maintenance needs on the lower bearing. There’s no grouting work required, so installation costs are lower.

Open screw pumps don’t clog, so you don’t need to pre-screen your wastewater. Installation doesn’t require a wet well, and maintenance is minimal. But, they’re going to require a lot of concrete, steel, and possibly grout to build the troughs. 

Which is right for your plant’s needs? Talk to the experts at Lakeside Equipment about your goals and plant design and we’ll help you figure out the right solutions for your budget, volume, and space.

The importance of removing contaminants from wastewater cannot be understated. If wastewater is not properly treated before it is returned to the environment, it could harm the environment or negatively impact the health of people in the community.

The wastewater goes through a lengthy treatment process that involves a number of different steps. Early on in the process, the water is pushed through a screen, which filters out large pieces of debris. The debris must be cleaned off of these screens periodically, otherwise the screens will be less effective. To clean these screens, it’s best to use a trash rake.

What is a Trash Rake?

Trash rakes are heavy devices that are used to remove large pieces of debris from screens at hydropower facilities. Most trash rakes are designed with long arms that reach into the bottom of the basin. The arm of the trash rake then moves upwards across the screen, picking up pieces of debris along the way.

Some trash rakes simply drop the debris that is collected on a nearby deck so it can be manually removed by workers at the facility. Other types of trash rake move the debris away from the deck and drop it into a bin designated for this type of waste.

What Are Cable Operated Rakes?

There are two main categories of trash rakes: cable operated rakes and hydraulically operated rakes. A cable operated rake system consists of a cable winch and rake arm. The rake arm scrapes across the screen to remove large pieces of debris, which is then deposited in a dumpster.

The Catronic Series trash rack sits on the deck located above the screens. It can be used as a stationery unit to clean a single screen or as a moving unit that is capable of cleaning multiple screens. Another cable operated rake system is the Monorail Series trash rake. Instead of sitting on the deck, this type of trash rake moves back and forth along a monorail structure that is built above the screens. Because it moves along the monorail, this trash rake can be used to clean multiple screens within the same general area.

There are benefits to both the Catronic Series and Monorail Series trash rake systems. One benefit of the Monorail Series trash rake is it does not take up space on the deck, whereas the Catronic Series trash rake does. Both of these systems use low maintenance energy efficient equipment that can easily be repaired and cleaned away from the water that is being treated. The install for these raking systems is easy, too. This means facilities can install either one of these systems without having to replace their existing screens or make any other modifications.

What Are Hydraulically Operated Rakes?

Lakeside’s hydraulically operated rakes are ideal for hydropower plants, pumping stations, wastewater treatment plants, and other industrial applications.

The Hydronic T Series trash rake system features a telescoping design that can clean at inclinations of up to 90 degrees. This system can run without the use of chains, guides, and sprockets, which makes it easier to operate. The pressure that the rake applies to the screen can also be adjusted to minimize the wear and tear.

The Hydronic K Series trash rake system is designed with a long arm that can reach depths of up to 100 feet. The arm is also capable of removing larger objects from the water such as trees and rootstocks. Depending on your facility’s needs, the K Series system can remain stationary to clean a single screen or it can swivel or travel to reach other screens.

Another hydraulically operated raking system is the Hydronic Multifunctional (M) Series. The M Series is designed with an articulating arm and a telescoping rake that can reach depths of up to 150 feet. There are several different rake heads that can be used on this system, including a triple jaw gripper that is capable of lifting more debris, and an orange peel grapple that is ideal for removing debris from the bottom of the screen.

Although this system can be semi-automatic or fully automatic, there is also the option of manually operating it out of the driver cab. It is best to manually operate the system to remove large pieces of debris from the surface.

Finally, there is the Hydronic H Series trash rake system. The other systems mentioned above are designed to clean screens that feature vertical bars. However, the H Series trash rake system is specifically designed to clean screens with horizontal bars. This rake starts at one side of the screen and pushes the debris caught between the bars to the other side of the screen. Then, the debris that has been collected can either be removed manually or with a grab rake.

Self-Cleaning Screens

Trash rake systems are used to clean screens, however it’s important to note that there are also self-cleaning screens available. The CO-TEC screen, for example, is designed with rake teeth that can be extended between the bars on the screen. Once extended, the rake teeth can then be lifted upwards, dragging debris in the same way that a trash rake does. If the screens at a facility need to be replaced, this type of product should be considered. However, facilities that are not interested in replacing their existing screens should stick to a trash rake system instead.

To learn more about hydropower trash rakes or to place an order, contact Lakeside Equipment Corporation today. Lakeside Equipment Corporation has been committed to improving the quality of water resources for decades. We currently provide high quality products and reliable services to municipalities and companies around the world. Call 630-837-5640 or visit our website to connect with one of our knowledgeable representatives today.

One of the first steps a wastewater treatment plant takes to treat water is to run it through a static screen. If your plant isn’t performing this preliminary treatment step, it’s worth your consideration as they’re a cost-effective way to get a jump start on wastewater treatment.

What Does a Static Screen Do?

When wastewater flows into a treatment plant, a static screen sits in front of the remaining wastewater equipment. Wastewater enters the system, passing through a stationary static screen first to remove as many solids as possible.

Think of it like a mesh screen that keeps bugs from entering your window at home. In this case, it’s a durable screen that catches particles like plastics, feminine products, foods that weren’t digested, hardened particles of grease, and paper products. 

Items that get captured are composted or removed and taken to a landfill. Many plants compost them over time, and that compost can be used in forests. This makes it easier for the next stages of wastewater treatment, such as grit removal.

In addition to a municipal wastewater treatment system, static screens benefit businesses that are under orders to pre-treat industrial wastewater or who want to do their part. It includes companies like chemical processing plants, paper mills, breweries, food processing plants, and plastic and metal processing plants. If you have a stormwater system, they are fantastic for removing plastics, trash, and fallen sticks and branches after a storm.

Learn About the Different Types of Static Screens

There are different types of static screens, including two primary ones that most plants use. The options include:

Band Screens

Band screens are typically installed at the start of a single flow or direct flow channel. It has guides along each edge of the screen panels to ensure movement and alignment remain steady as the chains move around the system to keep the static screens in constant motion. 

The filter mesh is welded and has a frame that acts as a bucket that deposits materials into a collection area. As materials are deposited, spray nozzles clear the grills of debris.

Step Screens

Step screens have different stainless-steel bars with the screen that moves upward to the top, depositing the solids they collect. It almost resembles an escalator. If you can imagine an escalator with mesh that catches the materials instead of solid steps, you have a good understanding of what step screens look like.  

Wedge Wire Screens

Wire wedge screens are self-supporting and either a cylinder or flat panel. Wastewater travels onto the panel or cylinder and falls through the mesh, while solids go over the top to the collection area. It’s usually made from stainless steel due to its durability and anti-corrosion qualities. 

Step and wedge wire screens are the most commonly used static screens, but it’s important to consider what’s best for your wastewater treatment plant. The current design, space, and budgetary constrictions all influence your final decision.

Advantages of Static Screens in Wastewater Treatment

What are the advantages of static screens in wastewater treatment? One of the first benefits is that they’re cost-effective. They do not require electricity, and the purchase and installation costs are not out of reach, especially when you consider that they help make the rest of the wastewater treatment process a little easier to manage. Static screens also require very little maintenance, so you won’t need to spend a lot of time training or hiring additional workers to keep the screens maintained.

They clean themselves with water spray or bar rakes that clear the screen’s bars as the system moves around with the water’s current. Some are also self-reversing to clear any jams that may occur after a storm where large branches enter systems that combine wastewater and stormwater runoff.

Static screens do their job effectively. The mesh screens capture a lot. They can remove small particles of solidified grease, corn skins that are harder for a body to digest, or bone particles from animals that get into a sewer and end up in wastewater. With these items removed before the remaining wastewater treatment measures take place, it eases wear and tear on equipment and gets the treatment process started faster.

With a static screen, they don’t need ideal conditions in order to work correctly. It doesn’t matter if flow rates increase or decrease or if temperatures are colder or hotter than usual. Static screens will work effectively in any condition.

Because static screens come in a variety of sizes and formats, it’s easy to fit one into your existing system. Some require very little headroom. When you’re shopping for the best static screen, finding a variety of sizes ends up helping out if you have little space.

Tips for Choosing the Right Static Screen for Your Facility

The best static screen for wastewater treatment depends on your current setup. Work with an expert in wastewater treatment equipment to learn more about your options, the costs, and how to incorporate static screens in your plant.

Lakeside Equipment brings decades of expertise in water treatment to the table. We offer a variety of screens to ensure every customer gets the right equipment for their needs. Our line-up includes:

• Raptor® FalconRake Bar Screen: This step system doesn’t require much space and is a cost-effective and low-maintenance option. Bars can be spaced as close as ¼ inch.
• Raptor® Fine Screen: The Fine Screen is a cylinder static mesh screen that’s angled and has a rotating rake that travels around the screen to clean between the bars, which prevents clogs.
• Raptor® Micro Strainer: The Micro Strainer is meant for lower use in a smaller facility. It’s a great option for a business that wants to pre-treat wastewater or for a smaller municipality. Stainless steel components and thicker baskets and tubes increase the system’s durability and lifespan.
• Raptor® Multi-Rake Bar Screen: Stainless steel construction, including the roller chain, with rectangular or trapezoidal bars that act as steps and capture solids. This system has an auto-reverse to prevent jams.
• Raptor® Rotary Strainer Screen: This wedge wire system is designed with mesh openings of 0.01 to 0.1 inches. It’s in a self-contained unit with stainless-steel construction to prevent corrosion. 
• Raptor® Rotating Drum Screen: Wedge screen systems can use the cylinder mesh system, and that’s what this rotating drum screen does. The stainless-steel drum captures solids, while the liquids pass through. It’s a multi-purpose system that screens, washes, compacts, and dewaters.

Ask us about our line of Raptor® screens for your larger wastewater treatment plant or the Raptor® Micro Strainer for small facilities. Our wastewater equipment specialists help you make the right choice that’s in your budget and does everything you expect.

The pumps that are used to treat wastewater can be classified as either a centrifugal or positive displacement pump. There are pros and cons to both of these types of pumps, so it’s not always easy to determine which one is right for your needs. To make the right choice, it’s important to learn the differences between centrifugal and positive displacement pumps.

How Centrifugal and Positive Displacement Pumps Operate

To understand how these pumps are different, you must first learn how each pump operates. Positive displacement pumps draw a fixed volume of liquid into the pump through the suction valve, trapping it within a cavity found inside the pump, then forcing it out through the outlet valve. The manner in which the liquid is forced out through the outlet valve will vary depending on the type of positive displacement pump. For example, a piston positive displacement pump is designed to force liquid out using a piston that moves up and down through the body of the pump. Other positive displacement pump models, such as screw pumps and gear pumps, do not have components that move up and down. Instead, these pumps use rotating components to force liquid from one side of the pump to the other.

Centrifugal pumps are known for their simplistic design. The most important component of a centrifugal pump is the impeller, which is a rotating device that moves fluid through the pump. The impeller rotates to draw fluid into the pump, then transfers kinetic energy from the motor to the fluid, which moves through the pump and exits through the discharge valve.

How Pressure Affects the Flow Rate

One of the main advantages of a positive displacement pump is its ability to produce a consistent flow rate. The flow rate of a positive displacement pump will remain constant when there are changes in pressure.

However, this is not the case with centrifugal pumps, which are designed to react to changes in pressure. The efficiency of a centrifugal pump peaks at a specific level of pressure. Whenever the pressure is not at this specific level, the efficiency of this pump will decrease. Therefore, the flow rate of centrifugal pumps will be affected by changes in pressure.

How Viscosity Affects the Flow Rate

Another difference between centrifugal and positive displacement pumps is the way the viscosity of the fluid affects the flow rate. As viscosity increases, the flow rate of a centrifugal pump will begin to rapidly decrease. The exact opposite is true of positive displacement pumps. As the viscosity increases, the flow rate of a positive displacement pump increases as well. This is because highly viscous liquids quickly fill the internal clearances of a positive displacement pump, which produces a greater volumetric efficiency. For this reason, it is important to choose a positive displacement pump to handle liquids that are highly viscous.

Shearing of Liquids

The speed of the spinning impeller found within the centrifugal pump design makes it less than ideal for handling shear sensitive mediums. Positive displacement pumps are not designed with any high-speed components, which means these pumps will not apply a great deal of shear to mediums. Because of this, it is best to choose a positive displacement pump when handling mediums that are shear sensitive.

Suction Lift Capabilities

Some centrifugal pumps will have suction lift capabilities, however the standard models do not. Positive displacement pumps do have suction lift capabilities. Consider the piston pump, which is a traditional positive displacement pump model. The piston is the component that moves up and down to force water from one side of the pump to the other. When the piston moves upwards, the pressure in the body of the pump goes down, which will open the suction valve and allow water to flow freely into the pump. The suction valve will close when the piston moves downward and increases the pressure inside the body of the pump, which pushes the water out of the pump.

When to Use Centrifugal and Positive Displacement Pumps

When choosing a pump, it’s important to consider the conditions in which the pump will operate. It is best to use a centrifugal pump to handle a large volume of low viscosity fluid in a low pressure environment. The centrifugal pump works best when it is transferring water, however it can also handle the transfer of low viscosity chemicals and fuels.

Because of its simplistic design, centrifugal pumps can be made out of a number of different materials, including plastic, stainless steel, and cast iron. This makes it more versatile since its design can be adjusted to fit your needs. This type of pump is also very compact, which makes it the ideal choice when there is not much space for a pump.

Positive displacement pumps are often installed to pump oil, sewage, and slurry. Positive displacement pumps are also ideal for pumping fluids that contain solid materials. In general, positive displacement pumps are used whenever the conditions are not ideal for centrifugal pumps. For example, the flow rate of a centrifugal pump is greatly affected by changes in pressure. Therefore, it is best to use a positive displacement pump when there will be changes in pressure, since this will not impact the flow rate of this type of pump.

To learn more about centrifugal and positive displacement pumps or to place an order, contact Lakeside Equipment Corporation today. For decades, Lakeside Equipment Corporation has been committed to providing high quality and reliable products and services to customers around the world. Let us guide you through the process of finding the right centrifugal or positive displacement pump for your needs. Call 630-837-5640 or visit our website to connect with one of our knowledgeable representatives today.

Any wastewater treatment plant will deal with sludge on a daily basis. Sludge is a semi-solid material resulting from wastewater treatment, water treatment, and other industrial processes. When it comes to wastewater treatment, sludge is often made up of fecal matter, food particles, microorganisms, and inorganic solids from things like medications people take or toilet paper pulp.

As part of the wastewater treatment process, sludge needs to be screened. The more that’s removed, the better it is for the remaining processes. Sludge screening systems are the key to removing as much sludge as possible before the other sewage sludge treatment steps.

What Does a Sludge Screening System Do?

A sludge screening system is the first step in removing solids from wastewater as it comes in from a sewer or is hauled in by trucks from residential septic systems. The screens can remove items that never should have been flushed, such as baby wipes or plastic wrappers, and help remove fats, oil, and grease (FOG), hard food particles like corn, bones, and pieces of nuts. Hair is another issue as it goes down the drain in a shower, bath, or sink and ends up in the wastewater.

These solids are removed by pumping the sludge through fine screens. Sludge is washed and compacted to remove any excess water. When the compacted sludge has been processed, It’s moved to another area for composting or further processing. Eventually, it can be used for fertilizer once it’s composted and mixed with lime, if needed, or incinerated to convert it to a fine ash that’s added to a landfill.

What Are the Benefits of Sludge Screening?

If sludge isn’t removed, it makes it harder to clean wastewater for release to a river, pond, lake, or ocean. Sludge contains phosphorus, and phosphorus feeds algal blooms in water. In a lake, algal blooms can impact the health of wildlife and aquatic animals.

Sludge can also create clogs in pipes. That’s not ideal as it can slow or stop wastewater’s movement from one area to the next. It can lead to disastrous and costly overflows or backups. Pressure from a clog can damage pumps and valves, so sludge screening helps prevent damage and emergency repairs.

Digestion that takes place during sludge treatment is handled with or without oxygen. Anaerobic is the form that uses oxygen. It’s more affordable and helps create biogas that can be used for heating and electricity. The biogas resulting from anaerobic digestion can also be converted into biomethane for use in the natural gas grid or fuel for certain vehicles.

You can also take sludge and mix it with lime to compost it. Once it’s composted, it can be used as a fertilizer. Sludge can also be incinerated to ash and added to a landfill. It creates a new way to use materials that could otherwise become a health risk in that community.

What Can Impact Sludge Screening?

What impacts sludge screening? Your wastewater treatment plant’s flow rates impact it. If the flow rate is faster than a screen handles, there are going to be problems. You need to have screens that are equipped for your highest flow rate.

The screen sizes also impact how well your system works. If the screen is too fine, it may take too long to process things. If it’s too wide, you might not effectively capture as much sludge as you were hoping. 

The contents of the sludge coming into your treatment plant also impact sludge screening. If you live in an area with a lot of restaurants, the sludge coming into your plant may have more food particles and FOG than a plant with nothing more than residential homes.

How Do You Choose the Best Sludge Screening System For Your Wastewater Treatment Plant?

How are you supposed to choose? It’s going to require you to consider a few factors. First, what are your flow rates, and what are the solids usually composed of? Do you end up with more paper pulp than food waste or more FOG than other areas? 

You don’t want a sludge screening system that leads to head loss. Head loss is a situation where pressure in a pipe decreases due to friction. You need to avoid that when possible.

Do you have a large maintenance team or do you need a system that takes care of itself for the most part? With a small maintenance crew or maybe just one maintenance worker, you should consider a low-maintenance system. 

Screens usually need to have the chains inspected and tension adjusted when needed, bearings need to be greased, solenoid valves may need adjustments, and a periodic inspection is important. It’s always a good idea to check fasteners and make sure the vibrations of the machine haven’t loosened any connectors. If you can get a system that is above water vs. below water, these maintenance tasks are easier to manage.

What Are the Different Types of Sludge Screening Systems?

Lakeside Equipment offers a variety of Raptor® screening products for grease traps, industrial wastewater, scum, sludge, and wastewater. Our options include:

FalconRake Bar Screen: Stainless steel, corrosion-resistant construction that requires minimal headroom. This system is a low-maintenance option where bars travel up through the incoming wastewater and over the arm in a continual loop. As bars hit the top of the arm, the sludge drops to a container and the fluids drop through the wastewater screen to move to the next step in processing.

Fine Screen: The Fine Screen uses rotating rake teeth to get in between the screen’s bars to keep pushing sludge through these options. While the sludge is removed, it’s also dewatered and washed to remove organic materials. The sludge is drier and weighs less.

Micro Strainer: For lower volumes, a Micro Strainer may be ideal. It has a thicker screening basket and transport and polymer bearings to extend the equipment’s life. It’s made from corrosion-resistant stainless steel. This four-in-one system has screens to filter and remove solids, a washing system, a compactor, and a dewaterer to get as much wastewater out of the sludge as possible before moving it to the next step. The sludge ends up in a barrel.

Multi-Rake Bar Screen: A multi-rake bar screen looks like a big ladder with wide rungs that are controlled by a drive assembly. Rakes capture the sludge and bring it up to the top where the sludge is collected and pushed to a container for processing while wastewater drops into the trough to continue through the wastewater treatment process.

Rotary Strainer Screen: Wastewater comes into a cylinder and water drops through the rotating wire screen cylinder with the sludge removed using an auto-cleaning blade as the solid sludge passes through a discharge suit.

Rotating Drum Screen: A rotating drum screen is ideal for smaller particles, so it’s typically used more to remove scum from wastewater.

Ask a professional for advice. Wastewater treatment equipment specialists can talk about your current system, what you hope to achieve, and work on the best way to upgrade your wastewater equipment to get the best performance possible. Our team at Lakeside Equipment is happy to go over the different sludge screens available and what the benefits are for each one.

For decades, engineers have used screw pumps for wastewater plant lift stations, storm water pumping, and other industrial applications. These pumps are used to move large volumes of liquid, but their design also makes it easy for large objects to pass through without clogging the system. This means water that is contaminated with various objects can be pumped with ease.

Screw pumps can also be operated when no water is present. This means there is no need to install additional parts to stop the pump from running in dry conditions. The pump can continue to operate regardless of how little water is present.

Screw pumps are not only efficient, they are also low maintenance. The pumps are designed with very few moving parts, and these parts constantly run at a slow speed. This innovative design minimizes wear and tear and the need for repairs.

Screw pumps can be used in a variety of industrial settings. However, there are two main types of screw pumps that engineers must choose between: open and enclosed. Before placing an order, it’s important to understand the differences between these two designs.

An Introduction to Open and Enclosed Screw Pumps

Before learning about the benefits of both open and enclosed screw pumps, it’s best to learn the differences between their designs.

An open screw pump has four components: a spiral screw, upper bearings, lower bearings, and a drive assembly. Open screw pumps are placed within concrete or steel troughs at a slight angle, leaving their screw-shaped design exposed.

Enclosed screw pumps are very similar to open screw pumps, however they are encased within a tube so their screw-shaped design is not exposed. Because the pump lies within a tube, it does not need to be placed within a cement or steel trough.

There are two types of enclosed screw pumps: Type S and Type C. Both of these types are enclosed within tubes, however the tube in a Type S design is stationary, whereas the tube in a Type C is not. Type C pumps are designed with two spiral flights welded to the inside of the pump’s tube, which rotates as it operates.

The Benefits of Open Screw Pumps

The open screw pump is known for its simplicity and reliability. These pumps are incredibly low maintenance as it is, however they can become even more durable. If the lower bearing is designed with a permanently greased lubricated roller bearing or a sleeve bearing, this will minimize the wear and tear even further.

If a repair is needed, it may be easier to identify the issue on an open screw pump than it would be on an enclosed pump. This is because the open design of an open screw pump makes it possible to see all of the moving parts.

The bottom of an open screw pump can operate in both submerged and non-submerged conditions, which makes it more versatile than other screw pumps.

The Benefits of Enclosed Screw Pumps

As previously mentioned, enclosed screw pumps are encased within a tube, which eliminates the need for a steel or concrete trough. Because it does not need a trough, it is considered easier to install than an open screw pump. It’s also a better choice for clients who are in need of a quick replacement and do not have the time to install a trough.

Both open and enclosed screw pumps are efficient, however the Type C pump operates at the highest efficiency. In fact, it is estimated that the Type C pump is between 5-10% more efficient than the open screw pump, which is why it has become a popular choice.

The Type C enclosed pump has a maximum inclination of 45 degrees, whereas the open screw pump and Type S enclosed pump both have a maximum inclination of 40 degrees. The difference between 40 and 45 degrees may not seem significant, but it results in the Type C enclosed pump leaving a much smaller footprint.

There are benefits to the Type S enclosed screw pump, too. The top of Type S enclosed pumps can be fixed in place or mounted onto a pivot. If it is mounted onto a pivot, the tube can be repositioned to adjust the pumping rate. Both the open and Type C designs do not have this flexibility.

How to Choose the Right Type of Screw Pump

There are benefits to both open and enclosed screw pumps, which can make it difficult to determine which is right for your needs. Instead of focusing on the design of the pump, think about how the pump will be used. These are the factors that should be taken into consideration when selecting a screw pump:

• Capacity
• Speed
• Inclination
• Number of Flights
• Horsepower

For example, the number of flights in a screw pump will have an impact on the output capacity of the system. This is because each additional flight increases the output capacity of the pump by about 25%. Therefore, it’s important to calculate the maximum output capacity needed so you can determine how many flights you will need. By approaching the decision in this manner, you will be able to select the perfect open or enclosed screw pump for your needs.

To learn more about open and enclosed screw pumps or to place an order, contact Lakeside Equipment Corporation today. At Lakeside Equipment Corporation, we are committed to treating water so it can be used as drinking water or safely returned to the environment. Since 1928, we have provided local governments and corporations with the high quality services and top-of-the-line equipment they need to help us achieve this goal. Call 630-837-5640 or visit our website to connect with a representative today.

As wastewater comes into a plant, one of the very first steps is to remove large solids. A bar screen is important for that reason. Despite ads, printed media, and other warnings that people stop flushing plastic wrappers, rags, baby wipes, and plastic applicators, it still happens. 

When a wastewater treatment plant is intertwined with storm drains, twigs, leaves, branches, cans, bottles, and plastic bags get into the wastewater. Bar screens remove these items to prevent clogs and damage to wastewater equipment. However, there are always challenges with wastewater bar screen operations that need to be considered.

Six Common Challenges of Wastewater Bar Screens and How to Overcome Them

What are some of the most common challenges with the operation and maintenance of wastewater bar screens? There are six at the top of our list.

The Accumulation of FOG

Fats, oils, and grease, aka FOG, are an annoyance that wastewater treatment plant operators deal with regularly. When FOG clings to trash rake bars, it builds up and solidifies into a stuck-on mess. Talk to city officials about requiring grease traps in restaurants and commercial kitchens in your municipality. Grease traps catch FOG for easy removal and keep it out of sewer lines. 

That will cut down on FOG, but it won’t remove it all. You need to degrease your bar screen regularly to keep it from creating clogs and slowing flow rates. Ask a wastewater treatment equipment specialist about the best screening materials for plants that get high quantities of FOG.

Clogs From Debris

Debris like branches, cans, bottles, and plastic bags are problems when they get stuck and reduce wastewater flow rates. While the role of a bar screen is to remove them, no system is foolproof. Items can get stuck and need clearing. 

Prevent debris accumulation by checking that the bars in your screen are sized appropriately for the most common materials you have to remove. If you get a lot of bottles and cans because your system is connected to stormwater, you might find wider spacing is fine. But, you get a lot of plastic applicators and they slip right past wider bars, so you need spacing that’s better at catching the smaller items.

You can also look into bar rakes that automatically reverse if there is a jam. By going into reverse, it helps clear the items that caused the obstruction and ensures the system works efficiently and effectively.

Corrosion

Wastewater can be corrosive, and even stainless-steel construction is susceptible to corrosion over time. You can apply coatings to bar screens to limit the damage. Regular inspections of the bars to check for corrosion help alert you to problems before they become a major headache.

If your wastewater treatment plant is in an industrial area, talk to city officials about requiring factories to have industrial wastewater treatment plants and treat their water before releasing it to the sewer system.

Mechanical Wear and Tear

Wear and tear from regular use is bound to happen. With planned maintenance and routine inspections, you can catch damaged or worn parts before the damage becomes a major inconvenience. Make sure your wastewater treatment plant has the appropriate screens in place to prevent damage. Look for durable construction, too. You might find that composite parts last longer than metal or plastic ones. 

Sand and grit also wear out components. A grit collection system is an essential part of a wastewater treatment plant, so make sure it’s part of your system.

Ragging

Rags are a headache. Look into rag catchers placed before your bar screens to catch rags, baby wipes, pads, and other fibrous materials before they get into your bar screen. When they reach a bar screen, they can wrap around components and get snagged, which creates extra work for your maintenance team.

Weather and the Unexpected

Not every system is connected to a stormwater system, but some still are. The U.S. is working hard to get cities and municipalities to separate systems and come up with ways to help with unexpected rainfall that leads to flooding of storm drains and wastewater treatment plants.

When weather creates high flow rates, your system may not be prepared. Have protocols in place for weather events, power outages, or unexpected equipment breakdowns. Measures that automatically adjust flow rates and help avoid overworking bar screens are essential.

Setting up a lot of green spaces between sidewalks and roadways provides one way to use up water. Adding rooftop gardens, turning concrete lots into parks and playgrounds, and tree-lined streets all help keep stormwater from rushing to storm drains. It also helps lower the risk of erosion.

What Does a Bar Screen Do?

Think of a bar screen like an escalator. It has steps that travel upward from wastewater areas and collect items on the bars as the steps move upward. At the top of that bar screen, the items get raked into a collection bin for composting or incineration, and the steps go back down to the wastewater to repeat the process.

Tips for Keeping Your Equipment in the Best Shape

Once you’ve installed wastewater bar screens, you need a regular preventative maintenance plan in place. That includes regular inspections and procedures that ensure your employees focus on efficient bar screen operations.

While a bar screen and trash rake do a great job, you need to have someone monitoring the controls. The ability to check performance remotely helps a lot, but there still needs to be someone performing basic maintenance. Some of the things that require basic maintenance are:

• Adjust and clean solenoid valves
• Check and adjust brushes and scrapers
• Check roller chains for wear and adjust tension as needed
• Inspect and grease the bearings and rack and pinion gears, if needed
• Inspect the tracking system and tighten any loose fasteners
• Periodically check for heavier debris like rocks
• Testing the motor for vibrations and amperage

When you have new wastewater bar screens installed, ask the experts what the best maintenance plan is and if there are any special considerations. Lakeside Equipment’s expertise with water treatment solutions dates back to 1928, so your municipal or industrial wastewater needs are addressed by a professional team with the insights you need.

We recommend two bar screens. The Raptor Multi-Rake Bar Screen excels at removing inorganic solids with low headloss. The FalconRake Bar Screen, also from Raptor, has a heavy-duty design that stands up to severe conditions and doesn’t rely on lower bearings, bushings, guides, or sprockets for minimal maintenance. Ask Lakeside Equipment about the pros and cons of these bar screens and find the right equipment for your plant’s needs.