Recovery of Struvite from Sewage Sludge Using Pulsed Electric Field Technique and Process Optimization

In this paper, nutrient recovery from sewage sludge as struvite using pulsed electric field (PEF) technique was performed. Box-Behnken response surface methodology (BBD) was used to determine the best struvite formation conditions. NH4-N removal efficiency (Y-1) and PO4-P removal efficiency (Y-2) were considered response functions, while the pH (X-1), magnesium concentration (X-2, mM), and phosphate concentration (X-3, mM) were considered independent variables in the BBD. The best struvite formation conditions by using BBD optimization was found for pH 8.5 and Mg+2/NH4+/PO4- molar ratio of 1.2:1:1.2 at 89.83% NH4-N and 80.30% PO4-P removal efficiency. The predicted dates for response functions determined by regression analysis exhibited excellent agreement with the experimental results. The obtained precipitation contained 61.7% struvite (MgNH4PO4 center dot 6H(2)O) and 38.3% nahpoite (Na2HPO4). The goodness of fit (GOF) was found as 1.67 and Bragg factor was calculated as 47.4% for this match in Rietveld refinement. Ammonia loss was calculated as 13% at optimum operation conditions using Visual Minteq. Saturation index (SI) value calculated by Visual Minteq was above zero, which means that the struvite can occur to the liquid phase of sludge pre-treated by PEF. After PEF pre-treatment, the heavy metals in liquid phase of WAS were below detection limit, except Cr and Ni. In study in evaluation of the obtained struvite, the heavy metal contents of the sediment were founded below the limit value, except Cr.