Dioxins and furans in biochars, hydrochars and torreficates produced by thermochemical conversion of biomass: a review

Abstract Converting raw biomass into valuable products protects the environment, improves economics, and helps tackle climate change by cutting resource demand waste production. Thermochemical treatment is a common method for producing biochars, hydrochars torreficates from organic wastes, which can also generate dioxins furans consequently limit use of thermochemically converted chars. Here we review presence in chars produced hydrothermal carbonization, torrefaction, pyrolysis processes under influence temperature, residence time, heating rate, pressure, feedstock type. Dioxins were mostly below 20 ng total toxic equivalence per kilogram (TEQ kg −1 ), with highest level 113 TEQ found over 100 samples different char types. The most sewage sludge. Processing temperature type key factors resulting high dioxin levels chars, care should be taken when at temperatures up to 300 °C or using feedstocks previously contaminated preservatives.