Dairy reduces effluent and increases yield with TOC analysis

The Murray Goulburn dairy factory in Maffra, Victoria, processes four million litres of raw milk per year into intermediate products including butter, cream, anhydrous milk fat and milk powders. The Environment, Yield and Waste Manager for the Maffra plant, David Lambert, confirms that there have been significant financial benefits achieved as a result of reducing waste in the plant effluent and therefore also increasing yield. Reduced waste also reduces plant operating costs by minimising or even avoiding excess chemical oxygen demand (COD) penalties on discharges.

Murray Goulburn's plant effluent is processed by United Group's EGSB anaerobic reactor and associated treatment plant prior to discharge into the Macalister River. Four years ago, a BioTector total organic carbon (TOC) analyser was installed at the plant, which samples the plant effluent on a 24/7 basis, every 12 minutes. Since its installation it has paid back its investment several times over by limiting COD discharge levels outside the trade waste agreement, thus minimising additional charges previously incurred.

The TOC analyser at Murray Goulburn is designed for industrial use and has been installed as part of a SCADA system controlling plant effluent. Samples are taken via large bore tubing to the instrument, therefore permitting reliable analysis of sample volumes to 8 mL, and containing particulate matter to 2 mm. Thus problems associated with the use of laboratory instrumentation when applied industrially, are avoided. TOC analysis is a far more reliable method of analysis than milk-water interface (turbidity) analysers, as the latter do not respond to dissolved substances such as proteins, lactose or sugars.

The instrumentation makes rapid measurements of total inorganic carbon (TIC) and TOC within an eight-minute analysis cycle (plus purging and cleaning), in readiness for the next sample (a total cycle time of 12 minutes). The plant discharge control comprises a 100-kilolitre discharge pit with direct connection to the wastewater treatment plant. There is a 500-kilolitre capacity buffer tank into which the contents of the discharge pit are pumped when the TOC analysis readings indicate a higher than permissible level of milk solids and dissolved material. In addition to the TOC analyser, a pH meter and a turbidity analyser are installed in line so that a high level of suspended solids, or a variation of pH outside permissible limits, will trigger a discharge to the buffer tank. The buffer tank discharges slowly back to the effluent pit, and in this way the TOC/COD levels are stabilised to a large degree. The effectively continuous measurement by the turbidity meter also allows for the control and draining of incidental spills that may occur within the cycle time of the TOC analyser. The measurement of pH allows for the control of low pH wastewater, which is not directly amenable to the TOC analysis but may concurrently exhibit elevated TOC levels.

The BioTector TIC/TOC analyser in Murray Goulburn's factory actually measures CO₂ derived from inorganic carbon/acid reactions (TIC). Organic carbon is measured through oxidation (utilising base/ozone reactions producing highly reactive, hydroxyl radicals) to form carbonates, which are then converted to CO₂ by means of acid reactions. The CO₂ gas is measured by infrared spectrometry. The technology has significant advantages, including suitability for samples with a high level of particulates and fats as well as other dissolved substances, and is also tolerant of high salt concentrations. The BioTector self-cleaning procedure between sampling is also essential for an instrument processing industrial effluents.

The experiences at Murray Goulburn's Maffra plant with the BioTector TIC/TOC analyser have proved the economic value to be derived from an industrial, on-stream analysis procedure. Corrective action on discharges can be taken in virtual real time instead of having to rely on laboratory procedures, which can take some days using wet chemical methodologies or offline spectrometry that requires sample processing to remove particulate matter.

In addition to effluent analysis, the BioTector is also useful in tracing product leakages in specific plant areas through correlation with events such as cleaning cycles and milk-water interface measurements. Correlation, however, is not a simple task as there are many effluent points in the production process, feeding two main discharge pipes. Thus, in order to improve production uptime and minimise the time involved in solving leakages, a number of TOC analysers could be monitoring in-plant effluent points. Murray Goulburn is considering extending the use of the BioTector for this purpose, because it is hoped that the capital outlay, with appropriate changes involved, will be paid for through increased yield from waste reduction.

Pryde Measurement Pty Ltd
www.pryde.com.au