Choosing the right screening method is an important part of protecting the rest of your treatment system
Protecting downstream pump facilities requires operators to think strategically about their needs in order to identify the best solution for their specific challenges. Buying a headworks system is arguably one of the most important purchasing decisions a public works engineer will make, and innovative systems offer unique options to choose from.
Some operators find that vertical screening systems, which can retrofit into smaller facilities, are ideal for their needs. But if your debris removal needs involve high-solids loading situations, a fine screen coupled with a grinder might be the best fit.
Screening traditional methods
Fine screens help remove smaller pieces of trash, such as rags, wipes, cotton swabs, plastics and latex, that can easily pass through traditional bar screens. Such trash quickly becomes problematic, as it collects on aerators, causes scum blanket accumulation in digesters, and clogs pumps and floats in final clarifiers. Increased removal of inorganic solids can benefit treatment processes from activated sludge to oxidation ditches, as well as membrane bioreactor facilities and lagoons.
Fine screens are solids removal devices with openings of 6 mm (1/4 inch) or less. They can be further categorized into straight-through or in-to-out designs. Straight-through products screen wastewater in two directions and are typically constructed using a round-hole perforated plate design. This configuration offers superior capture performance when compared to bar screens or step screens, which screen in only one direction. In-to-out fine screen layouts offer the best capture of solids due to their non-carry-over design, and are constructed as either perforated plate band screens or cylindrical drum screens.
While fine screening technology offers superior solids removal and downstream protection, it can be damaged from heavy debris such as stones and irregular objects often carried by stormwater in combined sewer overflow systems. This heavy debris can damage the screening panels or overload removal systems. One way to prevent this is to have a coarse screening device, such as a bar screen, precede the fine screen to remove larger, potentially damaging debris. This arrangement creates a second solids removal area that will need to be addressed with a washer-compactor.
Placing a grinder before your fine screen offers an additional layer of protection for your downstream equipment. Grinders resolve tough debris issues, such as rocks, wood, rags and wipes before they reach the fine screen. Often, grinders function as an alternative to coarse screens, offering an innovative option to reduce debris loads before the solids are sifted through the fine screen.
Incorporating a grinder with a dual-shaft design is especially useful, as the dual shafts actively pull material into and through the cutters. This means the grinder can handle a wider variety of debris compared to single-shaft macerators and grinders. A dual-shafted grinder is also helpful in breaking down essential soft organics so that they pass more easily through the fine screen. Leaving these organics in the waste stream is important, as the biological process in the treatment facility is more effective in treating these solids than releasing at a landfill.
An ideal grinder solution for many headworks facilities is JWC Environmental’s Channel Monster. The patented Channel Monster uses rotating drums to capture solids and matches them with the proven Muffin Monster dual shafted grinder technology. The result is a high flow capacity system that will shred rags, rocks, wood and other trash in to small pieces that can pass harmlessly through pumps, pipes and process systems.
Channel Monsters are a perfect fit for pump stations where solids need to be ground up before flowing through the fine screen. They are capable of handling tough solids such as disposable wipe balls and first flush loading that can overwhelm even the best pump. High flows at the headworks are easily handled by the grinder, which can effectively grind down debris and rags before they enter the treatment facility – even during storm flows. The innovative cutter profile pulverizes heavy solids down to a size that will not damage fine screens, protecting equipment and downstream processes. As an alternative to coarse screens, the Channel Monster offers headworks facilities the opportunity to simplify their system.
Consumer wipes have seen a surge in popularity over the last decade and are an enormous burden on treatment plant operators because of the clogs and safety issues related to pump deragging. In 2013, JWC investigated a wipes phenomenon occurring inside pump stations called “reweaving” – parts of wipes and hair were combining into large rag balls. The rag balls would then slow the flow of wastewater or completely clog sewer pumps.
Their research uncovered an issue where strips of wipes were roping together in the swirling action of a sewer system. To prevent this, the Channel Monster with Wipes Ready technology uses new cutters, screening drums and operating technologies to improve debris capture rate and cut wipes into smaller squares. This eliminated the formation of long strips and rag balls in test environments.
The Channel Monster with Wipes Ready technology comprises rotating screening drums with 12 mm perforated openings, feeding debris into a dual-shafted grinder to shred solids effectively and completely, while maintaining proper flow rates so capacities at pump stations are not compromised by clogs and equipment breakdowns. The system is also a durable, cost-effective and versatile solution to protect valuable pumps, pipelines and other treatment equipment from the harmful effects of wipes and other debris.
Incorporating a grinder, like the Channel Monster, ahead of your fine screen can resolve issues before they begin. Allowing the grinder to shred difficult debris before it flows through your fine screen enhances the screen’s capabilities and protects your equipment, time, operators and facility. The two units work together to create the answer to high-solids loading problems.
A solution for overloaded screens
Nearly 25 million gallons of influent flows through the Moygashel Waste Water Treatment Plant in Dungannon, Ireland, each day. When the rains are heavy, particularly in the winter, the flush surcharge from the gravity main flows immediately onto the 1/4-inch inlet band screens, overloading and blinding them, sometimes as often as three times a week.
Tired of maintenance call-outs and manually cleaning the screens, Moygashel contacted JWC Environmental to find a solution for their ineffective headworks screens. JWC recommended installing Channel Monsters ahead of the fine screen to precondition the debris in the flow and protect the screens from overload and damage by acting as a control buffer.
Grinding the solids controls the rate at which they hit the screen and reduces them to a smaller, more uniform particle size, while leaving soft organics in the water. Before installing the grinders, solid organics were removed by the screens and dropped into dumpsters – generating inconvenience and foul odors.
Installing the Channel Monsters ahead of the fine screens provided Moygashel an easy-to-install solution to their solids loading issue. “In Moygashel, JWC has more than met my expectations and provided my team with a simple solution in the form of their grinders,” says Michael McAlary, functional manager for Northern Ireland Water Limited.
Headworks facilities facing similar challenges to those in Moygashel, should consider a grinder and fine screen combination to solve their solids-loading issues.