Fractionation and bioavailability of phosphorus in sludge from municipal wastewater treatment plants

Sludge samples were collected from two municipal wastewater treatment plants (WWTPs) in Shanghai. Extraction efficiencies for total phosphorus (TP) from sludge by SMT and the alkaline potassium persulfate digestion (APPD) method were compared. Variations in phosphorus fractions based on the sludge treatment process were analyzed by the SMT method. The relationship between bioavailable phosphorus and TP was also investigated. The results indicated that extraction of phosphorus by SMT was more complete than by the APPD method. The phosphorus content in ADS was considerably lower than in the other types of sludge. In all types of sludge samples, inorganic phosphorus (IP) dominated the TP (above 62%), whereas apatite phosphorus (AP) dominated the IP, especially in ADS, where AP accounted for 90% of IP. Both bioavailable phosphorus and non-apatite phosphorus had significant positive correlations with TP. The fraction of bioavailable phosphorus in ADS was 20% of TP, which was significantly lower than in the other types of sludge (from 52% to 66%). The results also indicated that phosphorus in ADS had low bioavailable potential, and therefore had low ecological risk for landfill disposal.