Application of sludge-derived KOH-activated hydrochar in the adsorptive removal of orthophosphate

Hydrochar, a hydrothermally carbonized product, has gained attention recently as an adsorbent, among its wide environmental applications. In this study, sludge from the paper recycling industry, having a lower pollution load, was used to produce hydrochar, followed by pre-activation and post-activation using KOH. Characterizations were performed for structural morphology (SEM and TEM), molecular functionalities (FTIR) and textural features (BET surface area). Furthermore, Response Surface Methodology (RSM) was used to optimize the adsorption parameters for the removal of orthophosphate with different hydrochars. This study aimed at a low-cost, waste-to-wealth, and negative emission technology for simultaneous solid waste management and orthophosphate removal in aqueous solution. It was predicted from the adsorption experiment that an orthophosphate dose of 100 mg L(−1) at substrate pH 5.11 will result in the adsorption of 9.59 mg orthophosphate per g of post-activated hydrochar after 28.6 h, which was validated using further confirmation study.