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Cleaner carrots from waste water.

WHEN 17,000 tonnes of freshly harvested carrots need to be washed before being packed for the supermarkets, there is an awful lot of water required -- and a great deal of waste water to be treated before it can be re-used or safely discharged.

Haith Industrial Ltd came up with the solution in the design and development of a brand new carrot washing and packing plant for H S & D Burgess Ltd of Yaxley, near Peterborough in Cambridgeshire, whose farming operation provides the crop in question.

The Company became involved when an engineering solution to the waste water disposal problem was needed, as the original plant had to be relocated to a new greenfield site. Previously the operation had taken clean water from the Fenland dyke network, and discharged the waste water through a simplified filtration system back into a ditch.

At the new site, all the clean water had to come from the mains supply, so it was essential to both keep demand on the supply to a minimum, and to ensure the discharge would meet the levels specified by the National Rivers Authority.

In addition, the site was close to a village, so that environmental considerations were important; there could be no unsightly, large lagoons, and the treatment system had to be instantaneous.

Main civil engineering contractors Thurlow Nunn Standen Ltd had sub-contracted the construction of the main part of the new vegetable packing station to the Haith Tickhill Group, who also drew up a plan for the design and contruction of the waste treatment plant, through their subsidiary Haith Industrial.

The Government's regional Agricultural Development and Advisory Service (ADAS) office, based in Cambridge, advised on the installation, to ensure that the treatment system met the necessary requirements and objectives. They subsequently carried out test sampling on the pilot system provided by Haith Industrial, to assess the levels of reduction in BOD (biological oxygen demand) and suspended solids that were possible.

Although water input to the new plant was variable, virtually 99% reduction in suspended solids was achieved, and BOD reduced by around 75%.

The treatment system was designed for virtually automatic, year-round operation, recirculating the initial washing water to keep overall demand as low as possible. Fresh water is used only for the final rinsing, with the periodic overflow passing through the treatment system and sand filter before going to discharge.

After initial washing of the carrots and stone removal, the water is transferred into a settlement area, where heavy soil and leafy fractions or other vegetable matter are removed. It then passes through a clarifier, like a large funnel, which uses a flocculant to settle out the remaining solid fraction quickly.

This sludge is removed for spreading safely back onto the land, while the clarified water passes to a self-cleaning gravel filter for further separation. The water then return to the washing plant, and the cycle begins again.

The major advantage of recirculating the water in this way is that less is used overall for washing the carrots, so that costs are kept to a minimum, and the risk of a severe fine for pollution of water courses is eliminated. Since the successful establishment of the plant last summer, throughputs of harvested crop and, therefore, soil have increased to the extent that a second clarifier unit is due to be commissioned to handle the extra water required.

A complete service

The Haith Tickhill Group of Companies -- including Haith Engineers Ltd, Tickhill Engineering Co, Ltd, Ramsey Engineers (Armthorpe) Ltd and Haith Industrial Ltd -- have been involved with the food processing and agricultural industries for over 40 years, providing design and manufacturing solutions to a wide range of mechanical handling problems in the food industry. Major clients include Walkers Crisps, KP, Allied Lyons and Unilever.

The introduction, and enforcement, of tighter legislation throughout the EC has meant a growing need to tackle the major problem of effluent treatment and disposal, in both industry and agriculture.

There are two options for the safe disposal of such effluent: it can either be treated to a very high degree, to meet NRA and other standards for direct discharge; or passed on in a suitable form for final treatment at a sewage works, for which there is a charge -- the more creatment required, the higher the charge.

This is the area where Haith Industrial's specialised experience has become more in demand, typified by the example of the Burgess washing and packing plant.

Whereas this plant's waste water was treated by simple clarification, removing the suspended solids to reach the required standard, other applications may require a more sophisticated, tailored approach, using biological solutions.

For example, the Company is currently working on a project, together with ADAS, for a large dairy farming business, to provide an effluent treatment plant. This will need to handle wash water and run-off from yard areas, together with an element of silage effluent, which is too expensive to treat individually, but which can be handled effectively in diluted form.

To this end Haith Industrial have developed their own, patented biological treatment plant, called a submerged filter. This is basically a vessel where a regime of bacteria, supplied with oxygen, are maintained in a medium; these are developed to suit individual requirements, and can be established on site in a matter of three to four days to meet a variety of BOD reduction standards.

As with the clarifier used on the Burgess scheme, the submerged filter is available as a pilot plant for trials work at different sites, to show the treatment principal in action. it can also be hired to provide a temporary solution EO an individual problem -- such as in seasonal vegetable harvesting and packing work, covering anything from mushrooms to large field vegetables, or to replace existing plant that fails or does not work efficiently.

For example, Haith Industrial put their clarifier system into a Norfolk plant handling parsnips, after it had been discovered that unfiltered sandy grit had remained in the washing system and was effectively "shotblasting" the vegetables.

The new clarifier not only solved the mechanical problem, but also saved money on further maintenance to the old system, and improved the quality of the end product.

In this particular case, the water was partially treated to solve the plane's immediate effluent problem. Having begun to deal with the situation in this way, the company is now better equipped to deal with any future imposition of specific quality standards, should this be required.

From their own design and production facilities at Worksop, Nottinghamshire, Haith Industrial are well equipped to continue providing a complete and comprehensive effluent treatment service to the food industry. Further details are available from Ivor Schofield at Haith Industrial Ltd, Carlton-in-Lindrick, Worksop, Notts S81 9LB. Tel:0909 730836. Fax:0909 730768.
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Publication:Food Trade Review
Date:Apr 1, 1993
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