REMOVING: SOLVING THE PROBLEMS OF SOLIDS IN WASTEWATER

In the world of fluid handling, we often wish "wastewater" was just that—water. But any operator or plant manager knows the reality is far more complex. Wastewater is a rugged slurry filled with rags, plastics, grit, rocks, and biological matter.

At Hayes Group, we see firsthand the havoc these solids wreak on fluid handling systems. While modern pump technology has come a long way in handling solids, sometimes the best strategy isn't just to pump them—it’s to remove them entirely.

The Toll on Your Equipment

When solids are left unchecked, they attack every component of your system. It is not a matter of if damage will occur, but when.

• Pumps: This is the most common casualty. Stringy materials (like wipes or rags) wrap around impellers, causing "ragging" that unbalances the pump, increases energy consumption, and eventually trips the motor. Meanwhile, abrasive grit wears down volutes and impellers like sandpaper, drastically shortening the pump's lifespan.

• Valves: Solids are notorious for lodging in valve seats. If a check valve can't close properly due to debris, you lose backflow prevention. If an isolation valve gets jammed by a rock or heavy solid, you lose control of your line during critical maintenance.

• Piping: Over time, heavy solids settle in low points of the piping, restricting flow and increasing head pressure. Grease and lighter solids can accumulate on pipe walls, eventually leading to full blockages that are difficult and expensive to clear.

The Strategy: Removal for Protection

The logic is simple but powerful: If the solid never reaches the equipment, it can’t damage the equipment.

By implementing a physical barrier at the headworks or collection point, you eliminate the threat before it travels downstream. Removing solids upfront protects the integrity of your pumps, instrumentation, and biological treatment processes. It shifts the maintenance focus from emergency repairs on complex machinery to routine management of screening equipment.

Solutions for Screening and Removal

Depending on the volume of flow and the nature of the solids, different technologies can be deployed.

1. Static Screens and Bar Racks

The first line of defense is often the simplest. Bar racks consist of vertical steel bars spaced at specific intervals. They catch large objects—rocks, timber, large rags—before they enter the intake channel. Static screens operate similarly but often use a curved or sloped surface where water runs through, and solids slide off.

• How it works: These are stationary collection points. As wastewater flows through the rack, large debris is physically blocked. However, these often require manual raking or cleaning to prevent the flow from backing up.

2. Automated Screening

For facilities that cannot afford the labor of manual cleaning or have high solid loads, automation is key.

• • Chain and Rake Screens: This system automates the bar rack concept. A mechanically driven chain equipped with rakes continuously cycles over the screen face. The rakes engage with the bars from the bottom up, pulling debris out of the water and depositing it into a dumpster or conveyor at the top. This ensures the screen remains open and flow is consistent without human intervention.

• • Rotary Drum Screens (Rotomat Style): This system automates the bar rack concept. A mechanically driven chain equipped with rakes continuously cycles over the screen face. The rakes engage with the bars from the bottom up, pulling debris out of the water and depositing it into a dumpster or conveyor at the top. This ensures the screen remains open and flow is consistent without human intervention.

These units are the multi-taskers of headworks. Installed directly in the channel (often at a steep angle), the system utilizes a rotating cylindrical basket to filter flow. As wastewater passes through the submerged screen, solids are trapped inside the basket. The drum's rotation lifts the debris out of the channel, where it is sprayed off into a central auger. This integrated screw conveyor doesn't just transport the waste; it washes, compacts, and dewaters the screenings as they travel upward, discharging a dry, compressed "cake" into a container. This effectively combines screening, washing, transport, and dewatering into a single, enclosed machine.

The Importance of Screen Sizing

There is no "one-size-fits-all" in wastewater. At Hayes Group, we emphasize that the screen size (or bar spacing) must be tailored to the specific collection point site.

• Too Small: If the openings are too tight for the application, the screen will "blind" (clog) almost instantly, causing overflow and backing up the system.

• Too Large: If the openings are too wide, harmful debris will pass through, damaging the pumps and valves downstream that you were trying to protect.

Setting the correct screen size requires analyzing the type of solids typical for that site (e.g., municipal sewage vs. industrial runoff) and balancing the required flow rate with the necessary level of protection.

Conclusion

Solids are an inevitable part of wastewater, but equipment failure doesn't have to be. By choosing the right screening technology - whether a simple bar rack or an advanced Rotomat style unit - you protect your downstream investment and ensure reliable operation.

Not sure which screening method is right for your facility? The experts at Hayes Group are here to help you analyze your application and find the perfect fit. Contact us today to clean up your process.