More Water Out

Drum thickeners from Alfa Laval offer substantial improvement in volume reduction and major savings on handling and transportation.
More Water Out
The horizontally oriented cylindrical drum made of high-density polyethylene mesh allows liquid to drain as the solids travel through.

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Sludges are a fact of life in water treatment; the key is to handle them efficiently and cost-effectively. A major part of that is volume reduction, which can substantially reduce handling, storage and transportation costs.

Alfa Laval now offers the ALDRUM G3 drum thickener, designed to provide more thickening capacity in the same footprint as the previous version and with lower operating costs. Representatives of the company’s Environment Market Unit — Alfredo Fernandez, business manager for the Americas, and Keith Williams, vice president of municipal waste — talked about the technology in an interview with Water System Operator.

WSO: What was the motivation for this new thickener design?

Fernandez: The G3 is an improvement on the first edition of the ALDRUM thickener.

The new design increases solids load capacity by up to 30 percent within the same footprint. There are three models of the G3 in capacities from 15 gpm to 700 gpm. They fit the exact same footprint as the previous versions, the largest of which has 500 gpm capacity. Both the new and previous versions can achieve volume reduction up to 90 percent.

WSO: What determines the actual volume reduction these units can achieve in a given application?

Fernandez: That is largely determined by the type of sludge. The results can differ with sludge from a drinking water plant, a wastewater treatment plant or an industrial process.

Williams: How quickly the product drains and how much volume reduction you get depends on factors like whether the material comes from surface water or groundwater, and on the solids concentration going in. If you feed at 2 or 3 percent solids, getting 90 percent volume reduction is more challenging than if you feed at a half to one percent.

WSO: For what kinds of sludges is this equipment suitable?

Williams: It is suitable for almost any material that you can treat with a coagulant or flocculant to enable separation. It’s for any relatively dilute slurry where there is a need to reduce the volume before storing, further treating or transporting.

WSO: Mechanically speaking, how does this technology remove water from sludge?

Williams: There is a horizontally oriented, cylindrical drum made of a high-density polyethylene mesh. Internal to that is a conveyance device. As you feed the sludge in and rotate the drum, liquid drains the length of the drum through the polyethylene screen. The solids travel inside the drum to the other side and are discharged as thickened sludge.

Fernandez: The typical screen mesh size is 0.6 to 1 mm. The screens need no operator attention. A spray bar controlled with a timer sprays water on the screen to keep it clean when needed. The spray frequency is set at the time of commissioning; the customer can also adjust it to suit changing conditions. The screens last for many years, and if they do need replacing, the cost is very low.

WSO: What other advantages does this equipment have?

Fernandez: It is easy to service and is essentially maintenance-free. The cover is hinged so that it is very easy to open for service maintenance. All sprays and splashing are contained within the unit. It operates quietly. Power consumption is very low at about 7 amps for a medium-sized with 150 gpm capacity. We have also seen polymer consumption reduced on the order of 5 to 10 percent as compared to previous designs.

WSO: What accounts for the lower polymer consumption?

Fernandez: The unit is designed for gentle treatment of the sludge. When you prepare the sludge with polymer, you create flocs. If you shear those flocs or mix them in a violent manner, they break, and the polymer used to form the flocs is partially lost. Our technology treats the flocs very gently, and so polymer consumption is reduced.

Williams: The new design takes a lot of turbulence out of the feed zone. Basically, we increased the volume of the feed chamber and slowed the velocity down. We also modified the intake in the drum and took the agitator out of the floc tank. We now use inline mixing to blend the slurry and the polymer. That’s gentle treatment, and it also reduces power consumption and overall cost.

WSO: Are demonstrations of this technology available?

Fernandez: Yes. Customers appreciate how effective these machines are when they see them in operation. We have pilot units that we can use to demonstrate the technology on the prospective customer’s actual slurry. Most orders for the equipment are generated by demonstrations.



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