H J Heinz - Westwick Factory

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UUI managed and operated the effluent treatment plant at Westwick for several years on behalf of Heinz. As part of a general upgrade and modernisation of the ETP it was decided to add on a pesticide adsorption stage at the back end of the process to meet increasingly stringent discharge standards.

The pesticides are only present in trace quantities and are carried into the works in soil attached to the potatoes which are to be processed. The first operation in the factory is to wash the incoming potatoes with fresh water. The waste from this operation passes through grit traps and filters before the liquids combine with waste organic matter to pass to the effluent treatment plant where the organic and particulate matter is treated to provide an effluent clean enough in all but one respect to pass directly to the local river.

The final treatment stage is provided by the new GAC contactors which remove the vast majority of pesticides present by adsorption.

Description Influent Characteristics (Average)
Flow m3/day 100 m3/h
Suspended Solids mg/l 10mg/l
BOD 10mg/l
Temperature oC 6-16


The effluent from the factory is erratic caused by shift working patterns and batch production and so the flow to the river is variable depending on the time of day and the nature of the production.

Although the flows were buffered to a certain extent by the existing effluent plant it was necessary to diverted to a new, small break/buffer tank to provide the new pumps with stable suction conditions.

The discharge pumps are PLPC controlled and inverter driven to maintain the level in the break tank at within a band equivalent to 45-60% of the tank capacity. These operate as duty / standby units with dedicated 2mm basket strainers and deliver the treated effluent to the GAC Contactors over 100 metres away.

If both contactors are on line the flow passes through them both operating in parallel although each is capable of the maximum works flow of 100m3 should the other be unavailable for any reason.

Each vessel is taken off line for backwashing daily using raw water. The waste backwash water passes to a backwash water buffer tank from where it is pumped back at a controlled rate to the head of the effluent treatment works.

The filtered water (now pesticide free) passes back to the existing effluent plant discharge and out to the river.

GAC Regeneration

Eventually all available sites in the GAC will be taken up by pesticides and other organic matter and the removal capacity will be greatly reduced. Regeneration of the media must take place at a specialised facility at very high temperatures which drive off the pesticides and organics from the carbon, incinerating them at the same time.

The carbon is then ready for re-use after being topped up to the original volume (a small proportion of the carbon is destroyed during the regeneration process).

Carbon is transferred between the works and Graffham Carbons’ Regeneration Facility in the Midlands by specially adapted 20-Tonne road tankers. These are equipped with compressors which in conjunction with the motive water available at the Westwick works remove spent carbon as a slurry from the vessels and return freshly regenerated carbon to the vessel from another tanker in a similar manner – an operation taking around two hours per vessel approximately once per year.

Project Details

Client: H J Heinz - Westwick Factory, Westwick, England

Industry: Effluent polishing prior to river discharge

Application: Granular Activated Carbon (GAC) Contactors