Phosphorus extraction and sludge dissolution by acid and alkali treatments of polyaluminum chloride (PAC) treated wastewater sludge

• P release characteristics of PAC treated wastewater sludge were studied.
• Highest P release was found with 2 N HCl and 1 N NaOH concentrations at 2 h.
• Kinetic studies of P release and sludge dissolution follow the first order reaction.
• Sequential extraction with NaOH/HCl give maximum P release (91.7%).

Phosphorus (P) leaching characteristics of polyaluminium chlorides (PAC) treated wastewater sludge was investigated by wet chemicals (acid and alkali). Sludge fractionation showed non-apatite inorganic P was the dominant P (90.9% of TP) while apatite P only accounted for 3.7%. After 2 h extraction with 1 N NaOH or 2 N HCl, 80.5% and 77.9% of total P was leached, while sludge dissolution reached 72.7% and 75.6%, respectively. Kinetic study with HCl and NaOH showed that P release and sludge dissolution follow first order reaction with rate constants of 0.50 and 0.35 min−1 (P release) and 0.47 × 10−2 and 0.15 × 10−2 min−1 (sludge dissolution), respectively. Sequential extraction by NaOH/HCl leached 91.7% of the total P. This study will help in understanding the P release behavior of the PAC treated wastewater sludge.