The installation of a BioTector continuous TOC (Total Organic Carbon) monitor to police the front end of Cobevco’s wastewater treatment plant has enabled tight control of the treatment process. Delivering results 20 times faster than laboratory techniques, the monitor at the Elton facility in Cheshire provides advance notice of organic overload so that the plant is able to instantly divert carbon-rich waste and protect the treatment process.
Treatment plant protected by effluent monitor at major drinks factory
QUINN Glass has been a high profile contract bottle manufacturer and filler for the food and beverage industry for over 10 years with key customers including major brands from around the world. The recently rebranded Cobevco filling division operates a state of the art bottle filling and wastewater treatment plant at their manufacturing site in Elton. The launch of Cobevco underpins a £500 million investment in its Northern Ireland and Cheshire plants to provide the most modern, hygienic and efficient manufacturing facilities in the UK.
The 21,600m2 filling hall was recently expanded to incorporate a 6th high-speed filling line giving the plant the capability to fill over 4 million litres of both bottled and bag-in-box wine, beer, cider, spirits and soft drinks per week. Since inception, the investment plans have incorporated a commitment to streamline operational throughput and minimise any impacts on the local environment through intensive green programmes.
Central to the environmental programme is a 260m3 per hour in-house biological wastewater treatment facility, operating 24/7 between 3 staggered Sequential Batch Reactors (SBR). Clear surface water from the post-treatment process is collected in an attenuation pond, filtered and discharged by consent to Hoole Pool Gutter (linking up to the river Dee). A purpose-built site laboratory working 24/7 in conjunction with all operations provides key analytical information, on-demand, for all parts of the process through to discharge.
Matt Tait the site Facilities Manager says: “It would be extremely costly to treat the effluent load externally (estimated at approximately £16million annually for the 1200m3 wastewater generated daily). The installation of the on-site treatment plant in 2005 has therefore saved a considerable amount of money; it has also enabled the management of the complete process cycle, preventing any adverse impact on the local environment.'
Treatment begins with raw process effluent water pumped 25m uphill to the SBR plant. Flow rate is measured to determine the treatment capacity needed and excess volume is diverted to a special on-site lagoon (with a capacity of up to 6000m3 wastewater). In addition to effluent flow rate, organic loading is also a measurement parameter of key importance.
Wastewater from the bottle filling process contains various organic components, most of which are sugar based compounds that can enter the waste stream from the intense clean-in-place rinsing of processing tanks and pipelines between product changeovers. All drink products have a natural background sugar level (particularly high in non-fermented soft drink products) so it is possible for the organic content of the waste stream to become elevated.
Specific bacteria are used to consume the organics as a food source; breaking them down to produce carbon dioxide gas. Bacteria however require specific conditions to thrive including temperature, pH, food source loading and oxygen levels. If any of these parameters are out of balance the bacteria can lose their efficiency, which means that the treatment cycle would have to be extended, or back-up SBR tanks would have to be employed. This would be costly and could have a serious effect on the earlier stages; for example, waste backlog could cause stoppage in the filling lines. Live data on the initial organic load is therefore extremely valuable because process managers can intervene in situations of overload, diverting the waste to a holding tank and reducing flow into the treatment process.
In the past, samples were manually collected three times per day and analysed by the on-site laboratory. Cobevco are consented by the Environment Agency on the final discharge Biological Oxygen Demand (BOD) – a parameter based on measuring the oxygen consumed by bacteria to break down the given organic load in the tank. As a 5 day test this can seriously affect the throughput of the treatment process, and is clearly impractical for active management and intervention. The alternative organic measurements of Chemical Oxygen Demand (COD) based on the amount of oxygen consumed during chemical digestion or Total Organic Carbon (TOC) which is a direct measure of the organic carbon content (both requiring application of heat to encourage bond breakage) can be achieved in less than 3 hours. Consequently, TOC or COD measurements are often used by industry to replace BOD for parts of the process where measurements are not required for consent reporting purposes.
To achieve continuous monitoring of raw influent, a BioTector TOC analyser from HACH LANGE was installed at the front end of the Cobevco treatment plant. BioTector uses a patented two-stage chemical oxidation process to aggressively break down the carbon forms without a heat supply. In a first step the reactor breaks down the inorganic carbon with acid and in a second stage the organic forms are treated with highly corrosive hydroxyl radicals (internally generated and rendered harmless afterwards) catalysed with manganese ions. Taking approximately 7 minutes from sample to result (without any sample pre-treatment or dilution) with the option of measuring up to 6 independent sample streams on a single instrument, the BioTector offers significant throughput potential. Wide-bore tubing with an integrated acidic back-clean in the presence of micro-bubbles prevents lines from clogging or cross-contamination between samples, ensuring drift-free operation without recalibration between 6 monthly services.
By linking the BioTector to a flow meter through an internal relay in advance of the feed, Cobevco only sample when there is flow to the treatment plant. This reduces reagent consumption and lowers costs.
Although there is a close relationship between TOC/COD and BOD, correlation factors vary between different waste streams. By analysing laboratory data over 1 month, Cobevco found very consistent trending between the TOC, BOD and COD of the effluent feed and entered the appropriate correlation factors into the BioTector. This has enabled all 3 parameters to be reported on-screen and saved to the datalog.
Reflecting on the advantages of a continuous monitoring system, Matt Tait said: 'The BioTector acts as a policeman on the treatment plant, helping us to improve plant efficiency by enabling us to manage the forward-feed organic and hydraulic loading to each SBR.
'We have found the BioTector to be very user-friendly; reagent levels are displayed and the instrument has not needed any recalibration or replacement parts between its 6 monthly services.'
Data is currently downloaded directly to an SD card (simple insertion on the rear of the door) and exported to Excel for integration and trending against other key parameters including flow, pH and dissolved oxygen.
Looking forward Matt says: 'The final stage of the process will be to integrate signals from the BioTector fully into the SCADA system for complete visible control. With SCADA and alarm parameter data available to individual line operatives, they will have full visibility of the effect their activities have on the treatment plant.”
Historically, the ability to measure organic load continuously has not been possible because instruments have been unable to cope with the strength of the effluent without filtration. However, the patented two-stage chemical oxidation process employed by the BioTector completely resolves this problem and opens the door to new levels of process control.