Water & Wastewater Treatment

INDUSTRIAL TREATMENT 19 February 2014 Water & Wastewater Treatment 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. This would mean that the treatment cycle would have to be extended, or back-up SBR tanks would have to be employed. Such measures 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. Consents In the past, samples were manually collected three times per day and analysed on-site. Cobevco is consented by the Environment Agency on the final discharge BOD. As a five- day test, BOD monitoring can seriously affect the throughput of the treatment process and is clearly impractical for active management and intervention. The alternative organic measurements of COD or TOC can be achieved in less than three 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 was installed at the front-end of the treatment plant. BioTector uses a patented two-stage chemical oxidation process to aggressively break down the carbon forms without a heat supply. Taking approximately seven minutes from sample to result, with the option of measuring up to six 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 six-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. Correlation Although there is a close relationship between TOC/COD and BOD, correlation factors vary between different waste streams. By analysing laboratory data over one 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 three parameters to be reported on-screen and saved to the datalog. 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. "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." The installation of a BioTector continuous TOC 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 provides advance notice of organic overload so that the plant is able to instantly divert carbon-rich waste and protect the treatment process. nnn Jargonbuster: BOD, COD and TOC BOD, COD and TOC are measures of organic (carbon-based) compounds in a given load in a tank. They are used to determine wastewater quality in order to establish the relative 'strength' of wastewaters. • Biological oxygen demand (BOD) – a parameter based on measuring the oxygen consumed by bacteria • Chemical oxygen demand (COD) - based on the amount of oxygen consumed during chemical digestion • Total organic carbon (TOC) - a direct measure of the organic carbon content BOD requires a five-day incubation to determine the quantity of oxygen consumed. COD and TOC traditionally require the application of heat to encourage bond breakage and measurement can be achieved in less than three 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. HUBER TECHNOLOGY Sludge Treatment Solutions Sludge screening. Sludge thickening. Sludge dewatering. Sludge drying. The Biotector installation and integrated online flow meter Utilities engineer Rob Lawson evaluating results from the BioTector

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