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Feature: Solutions for sludge

A research project into the recyclability and reuse opportunities of paper mill sludge has just been launched at Aylesford Newsprint's Kent plant.

Funded by the Waste and Resources Action Programme (WRAP) and using state-of-the-art technology developed in Canada, the six-month project to assess the economic viability of processing paper mill sludge into usable materials came on-stream in earlier this month.

Paper mill sludge is the main waste product from the manufacture of white recycled papers, and can represent as much as 40% of the material input in the production of higher quality paper grades.

In total, UK mills generate around one million tonnes of sludge each year and end uses for this material are limited - most is either landfilled, landspread or incinerated.

Aylesford Newsprint's commercial manager Chris White says: "While 80% of the sludge produced as a by-product of the recycling process at Aylesford Newsprint is burnt to produce 17% of the mill's energy needs, the remaining 30,000 tonnes are either composted, landfilled or landspread.

This is a significant cost to the mill and so solving this problem by generating markets for this sludge would be of enormous benefit."

David Powlson, WRAP's technical manager for paper, says: "With higher quality requirements for paper and rising landfill costs, the volume and cost of sludge disposal is becoming an inhibiting commercial factor for the further expansion of recycled paper manufacture. This project will use technology to explore the potential for overcoming this barrier and improving the economics of producing paper products from recycled fibre."

Central to the success of this latest WRAP project is a KDS Micronex sludge processing plant developed by First American Scientific (FASC). Sited at Aylesford Newsprint's mill, the demonstration plant is the first of its kind in Europe.

Brian Nichols, president of FASC, is certain that this plant will be a valuable resource for paper mills using recovered fibre: "The stringent environmental legislation, high disposal costs for waste and high energy costs in the UK and the EU create a significant opportunity for this type of technology."

"The problem with sludge is its composition," adds White.

"It is made up of 50% fibre and 50% fillers - both can be recycled individually but the task becomes more challenging when they are combined."

The FASC equipment will dry the sludge into a fluff which allows fibre and fillers to be separated.

Initially, the sludge's moisture content is reduced from 50% to 10% by the KDS Micronex.

The resulting sludge fluff can then be split into its fibre and filler constituents using screening equipment, and the materials assessed for their recycling potential.

Possible end uses for the fibre include insulation, lower grade paper applications and fuel briquettes, while the filler material has potential for use in a range of products, particularly for in construction.

This is not the first WRAP-led research project into the use of paper mill sludge.

In 2004, the organisation released the results of a two-year study into the use of paper mill sludge in the manufacture of construction products.

Working with the Building Research Establishment (BRE), the Biocomposites Centre at the University of Wales and the Bridgewater Paper Company, the project demonstrated the technical and commercial feasibility of recycling de-inked recycled paper mill sludge to manufacture construction products that would

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