Real-time total organic carbon tightens effluent control at Greencore 09 February 2012

Greencore Foods plant in Selby has dramatically improved its wastewater treatment process, managed by Veolia Water Industrial Outsourcing, since installing a new continuous TOC (total organic carbon) monitor.

Greencore environment manager David Murtagh says that its BioTector, from Hach Lange, now enables the plant to respond faster to changes in influent, and so control effluent quality and minimise discharge fees to the Environment Agency.

He makes the point that effluent from the food manufacturing industry contains inorganic salts and organic components that enter the waste stream in part from the wash-down of processing tanks and lines during CIP (clean in place) procedures for product changeover.

However, overload of organics on the effluent treatment plant adversely affects the efficiency of the treatment process – so wastewater entering the facility is analysed for TOC to control its strength prior to treatment.

"In the past, samples were manually collected from the site drains pit and transported to the laboratory at a second location," explains Murtagh.

He says that led to significant waste, both in terms of time and resources – with the analyses being labour intensive and delaying feedback to the process.

Murtagh also states that impending tightening of the consent to discharge to river, by the Environment Agency, was an issue. "We needed more frequent, detailed, prompt, accurate and reliable influent TOC data to help manage the effluent treatment plant more efficiently – and provide feedback on the process that is the source of the TOC," he says.

His concern, however, was that while on-line TOC instruments typically work well on cleaner, particulate-free effluent samples, the high solids, fats, oils and greases, and variable TOC loads coming from raw influent can be "a major issue" for fine capillary tubing and valves, which, in his experience, typically cause instrument seizure.

But Hach Lange's BioTector is different. It uses a patented oxidation process to offer aggressive breakdown of organics without thermal dependence by exposing high pH reagents to ozone.

Dr Patsy Rigby, of Hach Lange UK, explains that this enables the system to handle very large sample volumes without the need for syringe -ontrolled dilution mechanisms. Indeed, a self-cleaning facility, with micro-bubbles, prevents particles becoming trapped, while an in-built salt trap allows loads as high as 30% and calcium loads of up to 12% also without dilution.

"Without the temperature resistant ceramic components of contemporary systems, where salt can easily crystallise and cause blockage, the catalyst within the BioTector is attached to the exterior of the furnace, extending lifetime and facilitating easy replacement," states Rigby.

And it's working: as Veolia's continuous improvement manager Marcus Hardiker puts it: "All previous concerns regarding the use of an on-line TOC meter were addressed... We needed the sample to be as representative as possible [so] no in-line filters were installed in the sample line. The sampling arrangement was carefully engineered ... to deal with the site's type of effluent containing high sand and silt content."

And he continues: "Signals from the BioTector unit have been integrated into both Veolia Water's effluent plant control system and Greencore's own data acquisition system. Veolia use the analysis to control the strength of feed transferred to the site effluent treatment plant.

"Any loads that exceed a pre-determined level are diverted to the site 'calamity tank'. This control has enabled the performance of the effluent treatment plant to be greatly improved."

Incidentally, Hardiker reports that signals from the TOC meter are also transmitted to Greencore's production areas, so that on-line data is also visible for process personnel, who can now see the effect of their activities on the effluent loads being discharged to the site treatment plant.

"Greencore has also linked the on-line results provided by the BioTector to an alarm syste,m so that production personnel know when the TOC levels have increased – thus enabling them to react much quicker and identify and address any issues as they arise," concludes Hardiker.

Brian Tinham

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