Effective dewatering is important to biosolids management. Drier cake reduces volume and helps cut the cost of hauling to a land application site or landfill.

But dewatering can be tricky because wastewater treatment facilities face changeable influent and biosolids characteristics that can change over time and even day to day.

Now press manufacturer Alfa Laval and process belt producer GKD have combined to develop a belt press that’s designed to give operators more control over dewatering and enable them to produce drier material, or significantly increase throughput.

The Alfa Laval AS-H Belt Press KPZ combines proven press technology with GKD belt weaving technology to create a press that is low-maintenance, long-lasting, flexible and easily upgraded as facility needs change.

It’s designed to be suitable for municipal facilities and for several industrial applications. It is available in a wide size range and with modular options to meet specific requirements. Ken Medlin, managing director-Ashbrook Simon-Hartley with Alfa Laval, and Linden Swann, technical sales manager for process belts with GKD-USA, talked about the technology in an interview with Treatment Plant Operator.

How would you describe the working relationship between Alfa Laval and GKD? 

Swann:  The 20-year partnership between GKD and Alfa Laval makes the system whole. GKD supplies woven synthetic mesh to Alfa Laval, which designed the KPZ press.

What would you say is the most essential benefit of this new design?

Medlin: We’ve created a press that allows for variability in the process. Our machine can change and move depending on biosolids characteristics. So we have variability from a mechanical standpoint, and we also have variability with the belt weave. They are separate pieces, but together allow for the most control over the dewatering process.

What in particular provides the flexibility operators need?

Medlin: The control comes from speed of the belts. One is the gravity section, and the other is through the pressure section on the tower. Operators can run those at different speeds; they have the ability to control the belt speeds independently. And we have a variable tension system. We also have a wedge plate that can be adjusted to ensure proper entry into the pressure section. In addition, the chicanes are all independently operated.  

How does the belt design contribute to operating flexibility?

Swann: We have a number of mesh designs that can range from 50-micron to 3,000-micron woven synthetic mesh. Based on the process and the biosolids characteristics, we can alter our mesh specification to provide the most suitable belt. We offer a standard product that is suited for the majority of applications, but we also provide solutions for challenging conditions.

What level of solids content can this press achieve?

Medlin: We can produce dry cake at 21-24% solids. With a typical waste activated sludge, we can typically get 2-3% higher solids content than a traditional belt press. But beyond that, we can accommodate a higher hydraulic loading of solids. The throughput is about one-third higher than with any of our other belt presses.

What needs in the market drove development of this belt press?

Medlin: Market drivers around removal of phosphorus and other components of sludge are affecting things like the addition of polymer. We wanted to give operators as much flexibility as possible to deal with the conditions they face. We provide that flexibility through our tension rollers and our hydraulic process, or we can use our adjustable wedge plate, which allows them to even and thin the material as it goes into the pressure section. Our Dri-Boost Plow enables to increase throughput or increase cake solids.

How does the Dri-Boost Plow function?

Medlin: The normal belt press chicane is a wedge or a panel that sits on the belt and it moves the material back and forth across the belt so that the water can drain. The Dri-Boost Plow has an arrow/spear profile. It’s a wide device sitting on the belt, so it creates a wider area on the belt for the water to drain. In addition to this, it turns the material over, so we get a drier cake at the end of the gravity deck.

What are some of the unique features of the belts?

Swann:  It has a low-profile seam. There is no transition; it’s virtually the same thickness as the belt. This allows the chicanes and the scraper blades to pass smoothly over the seam area, which is typically the fail point of a belt. There is also a wear indicator. Our belts are blue, but the core of the monofilament polyester is white. So as the belt wears during the process, the white starts to come through. That indicates the need to change out the belt very soon.

What makes this press easy to maintain?

Medlin: The gravity deck is where about 80% of belt press maintenance is done. With our low profile, there is no need for scaffolding or other structures to provide access to the deck area. In addition, a wash box continuously washes the belts to clean the polymer and excess material. This keeps the belts clean and allows for optimal operation without oversight.