Sludge Thickening and Dewatering – A Comparison of Relative Technologies and Performances

Basgallop, R. and Willoughby, N., Andritz UK, Ltd



The industrial world over, at any one time, many types of process technology are being promoted, tested, purchased and installed. The definition of selection criteria for a particular application can be simple, apparently simple or obviously difficult.

The only realistic option for end users to evaluate even generic types of equipment is by employing one of the manufacturers of the equipment under consideration to run tests using their test rigs. This brings to the fore a number of questions which the end user must ask:

Are other types of generic equipment available?

  • How familiar is the end user with the equipment on the test rig?
  • How representative are the test conditions of the future process scenario for the plant such as sludge characteristics, types of flocculating agents available and at what price?
  • How reliable is the automation regime in a full sized installation?

This paper sets out to consider the above issues in greater detail using the example of test work carried out at Anglian Water’s Cotton Valley Sewage Treatment Works (STW) which follows on with work originally reported by Panter (Panter 2009).

The main equipment cited is that of belt filter presses and decanter centrifuges with comments on the development of common types of dewatering equipment.

Keywords: Dewatering, belt press, decanter centrifuge, test work, biosolids, sludge, polymer, thermal hydrolysis, digestion, THP


Over the years many new and enhanced processes for the treatment of municipal sludge have been developed and come to market. The aims of these processes and techniques vary from simply producing the driest possible dewatered cake in order to reduce the cost of landfill through to regarding sludge as a raw material from which great economic and sustainability benefits can be realised.

The latter view has become increasingly important in our climate change-savvy culture. In fairness to the industry, the economics of the various disposal routes have changed both in terms of the cost of simply dumping sludge to the possibility of generating income from what was once a waste material.

Equipment too has been developed, and continues to develop, both in respect of the invention of new machines and making significant improvements to existing technology platforms. As in other industries, there are a number of companies who continue to manufacture standard forms of equipment with little research and development taking place and other companies who place great store by developing their product base to respond both to the changing requirements of their existing customer base and develop into other industrial areas.

Selection of the appropriate equipment for a process is very difficult for the end user or specifying engineer. Although usually aware of the actual generic types of equipment to be used for the process, the task of identifying competent suppliers of the technology and understanding their agendas is a thankless one. This is made even more difficult by the fact that tests of generic equipment usually have to be carried out by the potential suppliers themselves.

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