Biochar and hydrochar as adsorbents for the removal of contaminants of emerging concern from wastewater

Carbon materials have been used extensively in water treatment, and among them, biochar (BC) and hydrochar (HC) have been studied in recent decades as eco-friendly adsorbents in water treatment. Specific physicochemical characteristics of chars allow for the effective removal of a wide range of water contaminants, including emerging contaminants (e.g. pharmaceutically active compounds, agro-chemicals, and endocrine disrupting compounds). BC and HC can be synthesized from different biomass sources, even from biowaste, which makes them low-cost materials. In fact, the application of waste biomass for char production can be designated as a promising way towards achieving sustainable development goals concerning solid waste management. The selection of feedstock material and optimization of the reaction conditions of the carbonization process (pyrolysis, hydro-thermal carbonisation, etc.) influence the performances of char-based materials leading to the products with desired characteristics suitable for the removal of a certain group of compounds. The objective of this review is to provide an overview of the current status of research regarding the use of BC and HC as adsorbents in the removal of contaminants of emerging concern (CECs) from wastewater. The physicochemical properties of the substrates, types of synthesis, characterization techniques, as well as mechanism and influence of process parameters in the removal of selected CECs from wastewater, will also be addressed.