Glass shows promise as filtration medium

Trials taking place at Europe's largest integrated turkey producer show that an innovative reed-bed design, using recycled glass in place of quarried gravel, is successful at treating effluent.

Bernard Matthews is enthusiastic about interim results of a five-month trial, funded by the Waste and Resources Action Programme (WRAP).

This investigated the potential of recycled glass as an alternative to traditional washed gravel as the base material for a reed bed at its site in Great Witchingham, Norfolk. The new medium, made from 100% recycled bottle glass, was found to have performed successfully in comparison with quarried gravel in removing suspended solids and biological oxygen demand (BOD) from effluent at the turkey production site, before it was discharged into the local watercourse.

Mark Lowe, Operations director with consultants Aqua Enviro, which conducted the trial, explained: “We used the glass to support reeds and filter out suspended solids in a vertical, or down-flow, bed at the site.

“The tests demonstrated that fine particles in the media can impede the flow of liquid through the bed. But they also indicated that two of the three products we tested – those from Krysteline and the Glass Recycling Company – were perfectly suitable for reed-bed applications and are an entirely appropriate substitute for 5-10mm and 6-12mm washed gravel.”

The reed bed trails removed, on average, 63% of BOD and 57% of suspended solids. Further work is now taking place, partly because mature, fully performing reed beds can take up to 12 months to develop, depending on the rate at which the root or rhizome structure emerges.

Bernard Matthews is now examining different process applications. Many different configurations are possible, and the process capabilities of glass in achieving the best solution are being examined. More testing of flow rates, the nature of the wastewater and solid loadings will also help it develop detailed design criteria.

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