Prickly pear cactus (Opuntia ficus-indica) grows on dry, marginal land, and represents a sustainable source of both biofuels and carbonaceous materials for water treatment. The raw plant was hydrothermally carbonized between 180 and 250 °C at various times and biomass to water ratios. These hydrochars could be used as a solid fuel, but upgrading the carbon for use as a sustainable water treatment material may represent a more beneficial use. When the hydrochars are pyrolyzed to 600°C in nitrogen, a series of furfurals, phenols, aliphatic and aromatic hydrocarbons can be recovered, followed by physical activation of the char using carbon dioxide. Importantly, low-temperature hydrochars (180°C) produced the highest surface area materials upon activation at 250 m2/g, as compared to ~150 m2/g for both the raw and 250°C carbonized then activated samples. The 180°C sample also adsorbed the greatest amount of heavy metals from water. In a simulated test case representing natural waters of Sicily that pose a health threat for their high levels of Mg, V, Mn, Fe and Cu, the activated hydrochars adsorbed (from a equimass solution of each metal) upwards of 87 mg/g of Mg, 100 of Mn, 140 of Cu, and 182 mg/g of Fe. Interestingly, the adsorption of these metals prohibited adsorption of the V to the char surface.

Sustainable water treatment materials via hydrothermal carbonization, secondary biofuel extraction, and activation of prickly pear cactus

255th National Meeting (2018)

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