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Agricultural sludge

Eberhardt Josué Friedrich Kernahan and Enrique Rodríguez Cañas

Download this image from Wellcome Collection.

Scanning electron micrograph of waste (sludge) from an industrial farming process, after having been burned. In the foreground, silver oxide structures (coloured pink, purple and green) and structures rich in calcium carbonate (coloured brown) can be seen. The background (coloured blue) shows the surface of a zirconia crucible (a container that can withstand very high temperatures), which was used to hold the sample as it burned. The sludge was burned to measure how much carbon, hydrogen, nitrogen and sulphur it contained. A wide range of organic and inorganic samples can be analysed in this way, including soils, sludge, water, fuels, polymers, cosmetics and pharmaceuticals. This technique can also be used in environmental studies to verify the quality or contamination of fuels and soils. The width of the image is 155 micrometres (0.155 mm).

How was this image coloured?

Scanning electron microscopy, as the name suggests, uses electrons instead of a light source to capture an image. A focused beam of electrons moves or scans across the sample being imaged in a regular pattern. This produces images (or micrographs) of the sample's surface in shades of grey, as electrons do not carry information about colour. Micrographs are then digitally coloured to add colour back into the image, for example to clarify structures and enhance visual discrimination between them (or simply for artistic effect). In this image, silver oxide structures (the flower-like shapes) have been coloured pink, violet and green to make them stand out from the calcium carbonate residues (the branch-like structures), which have been coloured brown. The background, coloured blue, highlights the surface of the container in which the sample was burned.

Why was this sample being analysed?

This type of analysis is called elemental analysis. In elemental analysis, the constituent parts or building blocks (chemical elements) that make up a substance are analysed and measured. This can help determine the purity of a substance or the structure of an unknown material. One form of elemental analysis (seen here) involves burning a sample in an atmosphere of excess oxygen (combustion). The sample is placed inside a silver capsule and then into a furnace, where it is burned. The resulting gases and other combustion products are then collected and analysed. The sludge sample shown here was being analysed in order to measure its total carbon, hydrogen, nitrogen and sulphur content.