Statistical modeling of phosphorus solubilization from chemical sludge and evaluation of optimal sodium hydroxide dose

Abstract

Phosphorus (P) recovery from sludge has drawn widespread attention across the world to minimize the P load to the watershed, a concern for eutrophication, and to meet the stringent effluent discharge regulations in some countries. Waste activated sludge (WAS) and dewatered sludge (DS) were treated with a wide range of NaOH doses (0–0.75 g g−1 TS). The WAS sludge was diluted to 4.5%–2.25% of TS before the treatment to make comparable amount of TS as of DS (2.25%–1.5%). The kinetic study illustrated that P solubilization reached equilibrium within the first 20 min of treatment duration. Significant positive correlation was found between solution pH and P solubilization, whereas effect of TS was mostly insignificant. The experimental data was well fitted to the exponential models and exhibited maximum P solubilization of about 67% and 56% from the DS and WAS at NaOH doses of 0.71 and 0.27 g g−1 TS, respectively. The optimal NaOH application dose of 0.36 g g−1 TS for DS and 0.20 g g−1 TS for WAS were obtained with 64% and 48% of P solubilization, respectively. The modeling approach and the optimal dose of NaOH illustrated in this study could be utilized for other types of sludges having similar P to TS ratio and P solubilization mechanisms could be further extended to other type of P recovery techniques.