Optimization of phosphorus leaching from sludge of rubber-latex processing wastewater-treatment plant in Vietnam

Abstract
In this study, optimal parameters for P leaching from sludges of a rubber-latex processing wastewater-treatment plant were carried out. The process optimization is based on laboratory experiments and simulation with a MATLAB program. The optimal P-leaching parameters for dried sludges were found to be as follows: dried sludge particle size below 2.5 mm, leaching time of 60 min, a phase ratio of 10 mL g−1 with 2 M H2SO4 for chemical sludge, a phase ratio of 5 mL g−1 with 1.7 M H2SO4 for biological sludge. At these conditions, P leaching efficiency reaches 90% on average for chemical as well as biological sludge. The equilibrium pH of the leached liquid was found to affect formation of mineral precipitates, such as gypsum (CaSO4), which leads to significant reduction in the dissolved Ca content in the leached liquid. Simulation results from the solid–liquid-liquid thermodynamic equilibrium tool also show the formation of other precipitated minerals such as AlPO4, FePO4, or Al(OH)3 at different equilibrium pH. The highest dissolved P and lowest dissolved Ca contents were observed at equilibrium pH less than 0.3.