- 16 October 2006 -

Dewatering and thickening solutions optimize wastewater treatment efficiency

Dewatering is a vital part of sludge treatment. The process reduces transportation and disposal or drying costs, while at the same time limiting any adverse effects on the environment. Decanter technology is a proven way to dewater the sludge fast and efficiently. Noreen Comerford of Alfa Laval discusses a new technology aiming to increase capacity in the dewatering process of wastewater treatment.

Facilities are faced with the on-going challenge of reducing the volume of the sludge through dry sludge cake. For this reason, dewatering and thickening of sludge are vital parts of sludge treatment processes. Dewatering reduces transportation and disposal or drying costs, while at the same time limiting any adverse effects on the environment. Reliable, predetermined thickening concentration reduces maintenance costs and power consumption, ensuring greatest cost efficiencies in the overall process.

Decanter technology, using centrifugal force to separate the solids, is the optimal process for dewatering and thickening the sludge fast and efficiently. Alfa Laval decanters feature low installation, operating, and disposal costs. Since they minimize odours, water consumption and sludge volume, they are also an environmentally friendly method.

Dewatering
The Aldec G2 decanter is designed to address these challenges by achieving up to 30 % more efficiency in the dewatering process of sludge treatment.

Alfa Laval has used its know-how expertise in the field of decanter technology and sludge treatment to develop a new generation of decanters that aims to improve performance and economy in sludge dewatering processes. Aldec G2, the second generation, is designed to offer a higher performance than earlier generations. This means a dryer quality of the final sludge cake or the capacity to treat up to 30% more sludge.

Not only does the new design aim to transport and treat higher volumes of sludge, but also provide a cleaner centrate (separated water in the dewatering process), with minimum polymer consumption and higher cake dryness. The new decanter is equipped with a control module with operator-friendly graphic user interface. Control panels cover the full range of functions. In the Aldec G2, the sludge is fed into the decanter without destroying the polymer flocs produced, which is mixed at the right place and time by the polymer. The dewatered sludge is not discharged until it has been exposed to high G force in the bowl.

Dryer sludge
The Aldec G2 enables the sludge treatment plant to decide the dryness of the final sludge cake, and thus the volume of sludge it needs to dispose of. The dryer the sludge, the lower the disposal and drying costs. Polymer consumption is minimized as well. It adds up to major savings and also less impact on the environment.

Much thought has been given to servicing and maintenance. The decanter has full erosion protection and replaceable wear parts, it may require only a small amount of maintenance.

The drive system allows the bowl speed and the conveyor speed to be varied independently of each other. This ensures a full operational range and lowest installed power, resulting in possibly the lowest power consumption of any decanter on the market without the need for regeneration.

Thickening
Another development from Alfa Laval is the Aldrum Drum Thickener. This is a range of mechanical sludge thickeners. The Aldrum Drum Thickener works on the principle of conveying polyelectrolyte treated (flocculated) sludge through a slowly rotating drum filter. The sludge moves along in the drum, while the water phase passes through the filter cloth. Adjusting the feed rate, angle and speed of the drum can thus regulate the sludge concentration.

These Drum Thickeners are equipped with a drum cleaning system consisting of a spray bar for water. The water consumption is low due to intermittent cleaning of the drum using either potable water, final effluent or treated filtrate. The Aldrum Drum Thickener comes in four sizes. They are all available as separate components or as complete sludge thickening modules. The Aldrum Drum Thickener is designed to handle sludge extremely gently, which means it gives exceptionally high recovery for nearly all sludge types.

An Aldrum Drum Thickener is usually combined with an Aldrum Flocculation Reactor. In this combination Alfa Laval is offering five different capacities, Mini, Midi, Maxi, Mega and Mega Duo, i.e. 7-120 m3/h / 30-530 gpm on the basis of 1% DS WAS.

Optimization
The Aldrum Drum Thickeners can be adjusted to suit individual sludge thickening needs. Optimal thickening is found by varying the feed rate, the polymer type and dosage, flocculation mixer speed; drum speed, angle of the drum and the spraying interval. There is also a wide range of different filter cloths available for new applications.

In order to optimize costs and process efficiencies, companies are looking for vendors offering total single-source solutions. Alfa Laval offers customer service availability 24 hours a day. Local and global service operations centers and field service mean service available wherever and whenever you need it. Performance Service agreements allow the systems to meet stringent standards and to optimize cost efficiencies.

www.alfa laval.com

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