Calcium-rich biochar from the pyrolysis of crab shell for phosphorus removal.

Calcium-rich biochars (CRB) prepared through pyrolysis of crab shell at various temperatures were characterized for physicochemical properties and P removal potential. Elemental analysis showed that CRB was rich in calcium (22.91%-36.14%), while poor in carbon (25.21%-9.08%). FTIR, XRD and TG analyses showed that calcite-based CRB was prepared at temperature ≤600 °C, while lime-based CRB was prepared at temperature ≥700 °C. Phosphorus removal experiment showed that P removal efficiencies in 80 mg P/L phosphate solution and biogas effluent ranged from 26% to 11%, respectively, to about 100% and 63%, respectively, depending on the pyrolysis temperature of the resulting biochar. Specifically, compared to common used CaCO3 and Ca(OH)2, P removal potential of calcite-based CRB was much higher than that of CaCO3; while that of lime-based CRB was close to that of Ca(OH)2. These results suggested that CRB was competent for P removal/recovery from wastewater.