Tests of a revolutionary filtration medium have proved beneficial for a North Yorkshire vegetable producer eager to improve the quality of its effluent discharges.
JE Hartley has been has been supplying frozen vegetables to the wholesale manufacturing and retail trades for more than 20 years. Its plant handles vegetables such as carrots, turnips, peas, beans, potatoes and celery. It was encouraged by interim results of independent trials investigating the potential of recycled glass filtration media (RGFM) as an alternative to traditional sand for effluent filtration at its site in Thorganby, near York.
Altough the company’s treatment process has a long history of compliance with environmental standards, discharging up to 350m3/d with a maximum suspended solids concentration of 30mg/l, suspended solids reduction is important to discourage excessive growth of blanket weed, leading to a de-oxygenation of water, with a consequent detrimental impact on fish habitat. Blanket weed can also affect river flows, as silt and other particles build up when they are caught in it.
To date RGFM has outperformed sand as a filtration medium, removing 80 per cent of suspended solids compared to 32 per cent for sand.
John Pick, site manager at JE Hartley, said: “The results to date are very encouraging and, provided we maintain the improved performance level through different crop changes - the products we process and washings we produce vary seasonally - we’ll seriously consider upgrading our filtration process to include recycled glass.
“During trials carried out between November 2004 and February 2005, RGFM improved removal rates for suspended solids and the efficiency of backwashing -the pumping of clean water backwards through the filters, flushing them clean of sludge - increased. A reduction in the requirement to do this will undoubtedly lead to cost savings.
“The tests also revealed the most effective size of glass media varied according to the type of crop being processed.”
Two-stage pilot scale filters are being tested on-site, so the advantages of using different-sized glass media over a single stage sand filter can be gauged. Initial results are promising: the combination of coarse and medium grade glass is polishing the final effluent effectively.
Pick said: “Full-scale trials are now imminent, during which we will optimise the operating cycles for different crops in terms of backwash frequency. We will also continue to monitor the performance of the recycled glass filters and compare this to that of the existing sand filtration unit.
“The full results should be available before the year-end and we hope they continue to be positive about the new material. We’re always trying to improve our impact on the environment and see this filtration medium using recycled glass as a plus, because it will help us contribute further to sustainability.”
Hartleys’ trial is being funded by WRAP (the Waste & Resources Action Programme) and undertaken by consultant Aqua Enviro Ltd.
The tests are part of a wider initiative by WRAP, a government-funded, not-for-profit organisation established to improve the UK’s recycling performance and promote resource efficiency, to encourage the use of materials made from recycled glass across a variety of industry sectors. These include brick and tile fluxing, grit blasting and sports turf.
WRAP’S campaign is intended to push the UK towards its target under the European Union packaging directive, which says 60 per cent of used glass must be recycled by 2008. The current UK percentage is 42 per cent.
Bronnie Allen, materials development manager (glass) with WRAP, said: “We’re
delighted with the initial feedback from Hartleys, which appears to support the findings of other WRAP funded trials being run at other sites. These indicated RGFM is viable commercially and offers performance benefits over traditional filtration materials.”
Any companies interested in setting up a trial or learning more about recycled glass applications should contact WRAP www.wrap.org.uk
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