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.

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.