Phosphorus adsorption characteristics of alum sludge: Adsorption capacity and the forms of phosphorus retained in alum sludge

Adsorption is an effective method for phosphorus removal from eutrophic waters. Phosphorus adsorption is affected by various factors, such as the nature of the adsorbent, the characteristics of the raw water, etc. This study investigated the effect of alum sludge chemical components on adsorption capacity and the forms of P retained in alum sludge. Results showed that alum sludge can be used as a good candidate material for P adsorption, and components of Al, Ca and initial concentration of P had a significant effect on P adsorption. All the sampled sludges had high P adsorption capacity ranging from 2.06 to 6.06 mg P g−1 sludge. Derived from four different water treatment plants in Shandong province, Yu Qing alum sludge had the largest P adsorption capacity (6.06 mg P g−1), followed by Xue Shan and Que Hua, while San He sludge had the least. Sequential P extraction test indicated that most of the P forms stored in the sludges are in the inorganic forms, and the relative proportion illustrated that most of the P fractions bound to Ca (AP) and P-Al, Fe (NAIP) in all samples. Utilization of alum sludge as P adsorbent has become a win-win technology for water treatment and waste management.