In pilot trials, the new system for Australian Hardboards Limited (AHL) reduced industrial water consumption by 65% and enabled the recycling of close to 100% of the process effluent, along with offering energy savings.

The results of the pilot trials were presented at the fifth Membranes in Drinking and Industrial Water Production conference held recently in Germany, arousing the interest of industry professionals from across the globe.

The System, jointly developed by AHL and leading consulting firm Sinclair Knight Merz, is expected to be adaptable to other liquid?solid separation applications in the timber, pulp and paper, water and wastewater, mine tailings, minerals and other wet process related industries.

AHL’s Queensland manufacturing plant uses mixed eucalyptus species as the principal raw material in the wet process manufacture of a hardboard product known as ‘Masonite’.

The Plant produces around one megalitre per day of effluent consisting principally of suspended fibre, colloidal and dissolved organic and inorganic materials, which are generated during the pulping and digestion process.

AHL Managing Director, Rex Hills, said that the thermo-mechanical pulping process at the Plant was largely unchanged from an original late-1950s design, and that process water effluent had been treated and recycled using the traditional methods of settling ponds and land irrigation.

“Recognising that these processes could provide significant opportunities to reduce water and energy use without adversely affecting product quality, we commissioned Sinclair Knight Merz to examine a variety of technologies for upgrading the treatment and recycling processes,” Mr Hills said.

“We are very pleased with the outcome,” he said.

“Because of the resulting increases in process efficiency, we look set not only to achieve cost savings on our operations, but also to make a contribution to environmental sustainability on behalf of our industry,” Mr Hills added.

Sinclair Knight Merz Process Engineer, Lee Foster, said that a range of key technology choices was investigated for the upgrade.

These included standard cross-flow membranes, the Vibrating Shear Enhancement Process (VSEP) membrane system, a membrane bioreactor, evaporation and standard biological systems.

“Our feasibility work involved a literature study of relevant industry practice and an extensive economic analysis to compare each technology option, including the impact of any process modifications,” Ms Foster said.

“The economic analysis demonstrated that the VSEP membrane technology offered the lowest capital and operating costs of all the systems investigated, while producing the best results,” she said.

VSEP is a relatively recent innovation in membrane-based liquid-solid separation technology.

It uses intense vibratory shear waves on the face of the membrane to stop the buildup of contaminants and to overcome the negative separation performance issues associated with conventional cross-flow membranes.

The vibration also improves fouling resistance and allows for filtration rates up to 10 times higher than is achievable with conventional cross-flow systems.

“Following the favourable economic analysis, and having also identified a number of other key processing advantages, we carried out extensive laboratory and pilot plant trials on a VSEP based system,” Ms Foster said.

“In addition to superior cost, footprint and reliability considerations, the System demonstrated an ability to produce a high solids concentrate which, in the AHL context, had a positive calorific value because it was produced as wood molasses,” she said.

“This made it potentially suitable for reuse as boiler fuel, for composting or as a supplement for animal feedstock,” she added.

In addition, the cleaned permeate water was shown to be suitable for recycling back to the Plant and, treated further with reverse osmosis, to be suitable for boiler use.

With the addition of the reverse osmosis treatment, the System would increase the boiler feed-water temperature from ambient to about 60oC, resulting in significant energy savings.

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