Real-time TOC tightens effluent control at Greencore (14/02/12)
A food manufacturing facility in Selby, north-east UK, has installed a new continuous TOC (Total Organic Carbon) monitor, ‘the BioTector’ which has dramatically improved the site’s capability to refine and improve the plant’s wastewater treatment process, says the monitor’s manufacturer, Hach Lange. As a result the plant is better able to quickly respond to changes in the influent.
The Selby site is operated on a continuous improvement basis with its own dedicated wastewater treatment plant to monitor and control effluent quality and minimise discharge fees. Effluent from the food manufacturing industry contains an array of inorganic salts and organic components which enter the waste stream in part from the wash down of processing tanks and lines during clean in place procedures for product changeover. Overload of organics on the effluent treatment plant adversely affects the efficiency of the treatment process. If the waste is not treated to the required standard, then the site will be unable to achieve the river discharge parameters that have been set by the Environment Agency.
The effluent treatment plant at the Selby facility is managed by a specialist team from Veolia Water Industrial Outsourcing Ltd. Raw feed water entering the facility is analysed for TOC to control the strength of the feed transferred to the site effluent treatment plant.
As Greencore Environment Manager David Murtagh explains: ‘In the past, samples were manually collected from the site drains pit and transported to the laboratory at a second location. Given the geographical distance between sites this led to significant waste, both in terms of time and resources. We had a small team in the laboratory who performed a number of analyses on the delivered samples, which was quite labour intensive and delayed results. Even state of the art laboratory techniques still took too long for pragmatic purposes, preventing prompt feedback on the process. Overall, this was not 21st century and provided no direct information to control the effluent plant or provide an early warning of process issues. An alternative needed to be sought.
‘A further key driver was the impending tightening of the consent to discharge to river by the Environment Agency. We needed more frequent, more detailed, prompt, accurate and reliable influent TOC data to help manage the effluent treatment plant more efficiently and provide feedback on the process which is the source of the TOC. We were wary of on-line TOC instruments due to poor experiences in the past; while they worked well on cleaner, particulate-free effluent samples, the high solids, fats, oils and greases, and variable TOC loads coming from raw influent was a major issue for delicate fine capillary tubing and valves, which typically caused instrument seizure.’
To achieve continuous functioning in harsh process environments the BioTector uses an advanced oxidation process to offer aggressive breakdown of organics without thermal dependence. This is achieved by exposing high pH reagents to ozone. Highly corrosive unstable hydroxyl radicals are generated and by a Two Stage Advanced Oxidation. This enables the system to handle very large sample volumes without the need for syringe controlled dilution. A self-cleaning facility with micro-bubbles prevents particles becoming trapped and an inbuilt salt trap allows salt loads as high as 30% and calcium loads of up to 12% 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.
Unaffected by fats (internal tubing is protected by back wash), greases, salts and particulates up to 2mm diameter, a representative sample is achieved without pre-filtering allowing in excess of 80,000 continuous measurements per year.
Veolia’s Continuous Improvement Manager Marcus Hardiker explains: ‘All previous concerns regarding the use of an on-line TOC meter were addressed with practical solutions. The instrument takes samples from the raw effluent that is fed to the site’s treatment plant. However, we needed the sample to be as representative as possible and therefore no in-line filters were installed in the sample line. The sampling arrangement was very carefully engineered by the specialist team in order to deal with the site’s unique type of effluent containing high sand and silt content.
‘The 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 uses 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.
‘The signals from the TOC meter are also transmitted to Greencore’s production areas, and the on-line data is visible for process personnel who can now see the effect that their activities are having 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 system so that production personnel know when the TOC levels have increased – thus enabling them to react much quicker and thereby identify and address any issues as they arise.
