Laboratory Products Focus Rapid Analysis is Key to Successful Management of FOG


In some parts of the UK, the majority of sewerage blockages occur due to a build up of Fats Oil and Grease (FOG) from food-related activities, domestic homes and industry. Quantitech Managing Director, Keith Golding, believes that successful management of the problem, through best practices and effective grease interception, can only be achieved when rapid analysis tools are employed.


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Drawing on experience in the United States, Keith explains how monitoring can help to ensure that FOG related problems can be minimised, from both point and non-point sources.


Infrared analysis of oil and grease has been used in the petroleum industry on highly regulated offshore platforms for over 30 years


Author Details:


Keith Golding*, Managing Director Quantitech Ltd, Unit 3, Old Wolverton Road, Milton Keynes, MK12 5NP.


Tel: 01908 227722 Fax: 01908 227733


Email: sales@quantitech.co.uk


*(please note that a high proportion of the material was provided by Sandy Rintoul, President of Wilks Enterprise, Inc.)


Point sources have been the focus of much attention recently; however, combined sewer overflows (CSOs) are a major contributor to non-point source pollution. A recent study in the United Sates showed that FOG blockages account for 50 to 75% of all CSOs [1].


In response to this problem the US EPA, along with city and state agencies, initiated the Capacity, Management, Operation, and Maintenance (CMOM) programme in 2001 to encourage operators of sewer systems to improve maintenance. As an aid to the CMOM program, Water Environment Research Foundation (WERF) funded a report titled ‘Assessment of Grease Interceptor Performance’ [1].


The study evaluated different grease interceptor designs and tested the effluent for FOG levels with a portable infrared oil and grease monitor, the InfraCal TOG/TPH Analyser (see Photo 1) because this enabled rapid onsite analysis.


Differences begin with sample collection because it is difficult to obtain two identical grab samples from a waste stream. Another consideration is recognition of the inherent error in the EPA 1664 Method itself. As stated in the method in section 17.0 ‘Acceptance Criteria for Performance Tests’ for ongoing precision and recovery, the accepted range hexane for extractable material is 78- 132%. This means that for a 100ppm sample, an acceptable result from a laboratory using the EPA 1664 method would be 78ppm to 114ppm, or +/- 18ppm. For hexane extractable material that is treated with silica gel to remove the polar organics for a total petroleum hydrocarbon (TPH) measurement, the acceptable result range is 64ppm to 132ppm, or +/- 34ppm for a 100ppm sample.


INFRARED ANALYSIS OF FOG


Hydrocarbons such as fats, oil and grease can be extracted from water through the use of an appropriate solvent. The extracted hydrocarbons absorb infrared energy at a common infrared wavelength and the amount of energy absorbed is proportional to the concentration of the oil/grease in the solvent. The infrared absorption can be directly calibrated to the amount of oil in the original sample.


Infrared analysis of oil and grease has been used in the petroleum industry on highly regulated offshore platforms for over 30 years. EPA Methods 413.2 and 418.1 were infrared methods for oil and grease measurement that called for (now banned) Freon to extract hydrocarbons from the effluent.


InfraCal CVH


For both industrial and sewage treatment operators, waiting for remote laboratory results can take several days or even weeks, which may result in high levels of FOG entering the wastewater stream. As a consequence, accurate onsite analysis is generally preferable.


FOG ANALYSIS METHODS


FOG analysis is slightly more complicated than normal chemical analysis because the definition of FOG is dependent on the procedure and solvent used. Different test methods assess different physical properties of FOG, so there can be differences in the result.


In essence, infrared analysis counts CH2 groups, so infrared absorbance rises with the length of hydrocarbon chain which correlates with the weight of the hydrocarbon. Therefore, the EPA 1664 hexane/gravimetric method and infrared analysis typically correlate well with each other. Table 1 shows two sets of data comparing the hexane/infrared method to the hexane/gravimetric method. One data set is from a meat packing plant and the other from tests conducted on a grease trap at a restaurant.


Table 1: Comparison of the Hexane/infrared Method to the Hexane/gravimetric Method


Sample 1 Sample 2


Sample 1 Sample 2 Sample 3 Sample 4 Sample 5


Meat Packing Plant Infrared Gravimetric 67 ppm 1990


70 ppm 2020


After Grease Trap at a Restaurant 423 332 103 157 67


415 300 130 170 74


EPA Method 1664 using hexane as the extraction solvent and gravimetric analysis is now the standard method replacing Freon methods. This gravimetric procedure requires a skilled laboratory technician, a considerable amount of time and specialist equipment. So, to accommodate those that need fast, simple analysis, the ASTM passed a new method using a Freon replacement solvent, and simplified infrared analysis. There is also a simplified infrared method using hexane extraction and evaporation.


MEASUREMENT OF FOG USING INFRARED ABSORPTION AND A HYDROCARBON FREE SOLVENT


For an infrared measurement, FOG is measured at the C-H absorption band at 2930 cm- [1]. S-316 solvent (called for in the new ASTM method D 7066-04) and hydrocarbon- free perchloroethylene are good infrared solvents as they totally lack a C-H absorption band. The solvent extract is placed directly in a quartz cuvette and a beam of infrared light goes through the cuvette with the extract for an infrared transmission measurement (Figure 1). A detector


Figure 1: The measurement of IR absorption of an oil sample with a cuvette


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