Desorption characteristics of phosphate and ammonium from sludge-based biochar

It is effective to adsorb phosphate and ammonium from water by sludge-based biochar, while the desorption performance has not been studied systematically. Biochar in this study was prepared through the co-pyrolysis of sludge and walnut shells to remove $$ and $$ from water. The desorption characteristics of $$ and $$ from the post-adsorption sludge-based biochar were investigated. The effects of the adsorption condition (concentration of adsorption solution) and desorption conditions (pH value of desorption solution and desorption temperature and time) on desorption performance were examined. Several techniques were performed to characterise the properties of the post-adsorption sludge-based biochar. The adsorption amount of the pure sewage sludge biochar (SBC) for $$ and the biochar derived from the co-pyrolysis of sewage sludge and walnut shell with the mixing ratio of 3:1 (MBC3-1) for $$ were 14.19/ 23.75 mg/g and 9.28/ 16.23 mg/g, respectively, when the concentrations of the adsorbates were 100 and 500 mg/L. The desorption experiments showed that the acidic condition (pH = 2) was beneficial for $$ and $$ desorption. The highest desorption ratio reached 7.58% for $$ and 2.18% for $$. The desorption of $$ was endothermic, whereas that of $$ was exothermic. The desorption amounts of $$ and $$ decreased and increased, respectively, with the increase in desorption time. This study of the desorption characteristics of $$ and $$ in sludge-based biochar provides a theoretical basis for the subsequent utilisation of sludge-based biochar.