Measurement of activated carbon and other black carbons in sediments

Black carbon in sediment, present natively or added as a treatment amendment in the form of activated carbon, reduces contaminant bioavailability. Field evaluation of activated carbon effectiveness in reducing contaminant bioavailability requires accurate methods to measure the amendment in sediments. The most commonly used method to separate black carbon from natural organic matter in soils and sediments is low temperature (375 °C) thermal oxidation which resulted in significant losses of activated carbons. A method was developed to isolate activated carbon using a solution of concentrated sulfuric acid and potassium dichromate to oxidize the natural organic matter while preserving the activated carbon. The chemical oxidation method was applied to assess the delivery of activated carbon to sediments in a pilot-scale demonstration project carried out in Grasse River, NY. Using this method on sediment from the Grasse River, over 98% of the natural organic matter was removed while preserving at least 95% of the activated carbon. The method was also demonstrated on other carbonaceous geosorbents and native black carbon in several sediment samples.