Physicochemical properties and sorption capacities of sludge-sawdust based biochars towards the removal of synthetic dyes in wastewater

Biological sludge is a widely available waste material of high environmental concern, the disposal of which involves a high cost, whereas its reuse is in line with the modern approach to the waste management and the circular economy. It should also be noted that thermal conversion of biological sludge for biochar production allows inhibiting the intrinsic toxicity related to the presence in this matrix of poorly biodegradable organic micropollutants and potentially pathogenic organisms. It is therefore evident that the conversion of biological sludge into biochar as a sorbent for wastewater treatment seems to be a ‘‘win–win’’ solution for both improving sludge management and protecting the environment. Based on the above- mentioned considerations, the objective of this research was the production of biochars from mixtures of biological sludge and waste woody biomass, their in-depth product characterization, the assessment of their environmental compatibility towards European Standards, and the evaluation of their applicability for the removal of selected synthetic dyes.