Recovery of Phosphorus from Sewage Sludge

In the following, a method to recover phosphorus from sewage sludge as MAP (magnesium-ammonium-phosphate, also called struvite) is to be presented. The process uses sulfuric acid to leach phosphorus out of digested sewage sludge. After solid-/liquid-separation, interfering metal ions in the liquid phase are inactivated through complexation. For the subsequent precipitation of the phosphorus, MgCl2 is added. This article describes the results of half-technical experiments (reactor volumes ∼ 1m3) and compares them with results of laboratory scale experiments.The quality of the produced MAP is comparable to that of commercial mineral fertilizers in terms of heavy metal concentration. Field experiments to determine the fertilizer value are currently being undertaken.