Each year in Australia over 85 million tons of biosolids (sludge) are dewatered at municipal Sewage Treatment Plants (STPs) into around 1.65 million tons of dewatered biosolids, also called wet biosolids, which is trucked offsite for reuse in agriculture and composting.

Dewatering takes place via a variety of methods, with centrifuges being most commonly used (39 per cent), followed up closely by belt filter presses and drying beds (24 per cent and 23 per cent respectively).

Biosolids dewatering takes place in most of the 2400 sewage treatment plants in Australia.

Regionally there have always been trends in dewatering technology with centrifuges favoured by most large NSW utilities and belt filter presses being favoured in Queensland and Victoria, along with rural New South Wales.

There is however a new trend emerging and it has become the primary choice of major utilities in Brisbane and Western Australia – dewatering via screw press.

This is an interesting development, as like most of the dewatering technology used, screw presses are not new and in fact may well be one of the oldest technologies.

The first centrifuges were used to separate dairy products around 1860 and belt filter presses were originally used in Europe in the early 1900’s for pulp and paper, while screw presses were first used in Roman times for pressing wine.

This new trend is being driven by changes in our economy and concerns over the environment and sustainability as well as a need for municipalities to continually improve their efficiency and operating costs.

Large increases in operational and maintenance labour and power costs as well as the unsustainability of processes that use large quantities of washwater have forced municipalities to look seriously at their current dewatering technology and search for better alternatives.

Add odour generation, either around the dewatering process or in the dewatered biomass, noise and other environmental concerns and the reason for the trend away from belt filter presses and centrifuges to screw presses becomes patently obvious.

Add to this the major advances in screw press technology in the last 10 years, enabling screw presses to now successfully dewater Waste Activated Sludge (WAS) and the trend becomes one that is certainly here to stay.

In fact it is safe to say that we can expect that most medium to large municipal dewatering facilities will make the change to screw press based dewatering in the near future.

About the author

John Koumoukelis is a Board Member of the Hydroflux Group. His career in the water industry spans more than 16 years. John’s professional roles are based on business development and technical sales management for process equipment and design/build contracts, within the wastewater sector.

For more information, visit www.hydroflux.com.au. 

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