Highly effective removal of malachite green from aqueous solution by hydrochar derived from phycocyanin-extracted algal bloom residues through hydrothermal carbonization

Huge volumes of harmful algal bloom residues (ABR) are collected during emergency treatment of cyanobacteria blooms, and phycocyanin-extracted algal bloom residues (PE-ABR) are produced after extraction of phycocyanin from ABR. To utilize them in a more efficient way, we propose a new approach to prepare hydrochars from PE-ABR through hydrothermal carbonization (HTC). The physical characters of as-prepared hydrochars were analyzed by SEM, FTIR and Raman spectroscopy. The PE-ABR hydrochar showed remarkable adsorption capability for removal malachite green (MG), with the maximum adsorption capacity of PE-ABR hydrochar for MG was 89.05 mg g(-1). The adsorption equilibrium is consistent with Langmuir's model, and the adsorption kinetics follows the pseudo-second-order equation. Therefore, this work have demonstrated that harmful ABR can be utilized not only as a potential material for production of phycocyanin, but also an excellent source for hydrochar for removal dyes in contaminated wastewater with high adsorption efficiency.