Study of biochar impregnated with Al recovered from water sludge for phosphate adsorption/desorption

Aluminum ions extracted from water sludge and waste biomass (Korean pine residue) were utilized to develop a biochar for phosphate removal. The biochar impregnated with the extracted aluminum ions adsorbed phosphate from wastewater up to 11.9 mg P/g which is comparable to those of Al2(SO4)3 impregnated biochar (14.3 mg P/g) and AlCl3 impregnated biochar (2.26 mg P/g). Co-existence of anions (HCO3−) deteriorates phosphate adsorption about 15% followed by SO42−, NO3− and Cl−. Phosphate desorption and aluminum ion release from the phosphate saturated Al-biochar were less than 5% in distilled water while they were 65 and 15% in citric acid solution (2%), respectively, in 48 h. Al-biochar also showed the characteristics of slow release P fertilizer which is helpful to protect water environment from eutrophication. Al-biochar using waste KPR and Al ions extracted from water sludge was very effective in removing phosphate from wastewater. In addition, the phosphate saturated biochar showed very high potential for agricultural application as an eco-friendly P fertilizer.