If the world was truly in critical need of phosphate for agricultural fertilizer to prevent so-called “critical food shortages”, WHY not use the readily available over-abundance of sewage sludge rather than destroying sensitive and pristine ecological environments/towns to MINE for it?
Is it as simple as the fact that “sh!t doesn’t SELL” and mine magnates won’t be able to profit?
Phosphorus in Manure and Sewage Sludge More Recyclable than in Soluble Inorganic Fertilizer
Sewage sludge could make great sustainable fertilizer
Turning sewage sludge safely into fertilizer
Drivers of Plant-Availability of Phosphorus from Thermally Conditioned Sewage Sludge as Assessed by Isotopic Labeling
Ashes from sewage sludge incineration are rich in phosphorus content, ranging between 4% and 9%. Due to the current methods of disposal used for these ashes, phosphorus, which is a valuable plant nutrient, is removed from biological cycling. This article proposes the possible three-stage processing of SSA, whereby more than 90% of phosphorus can be extracted to make an adequate phosphate fertilizer. SSA from two Swiss sewage sludge incinerators was used for laboratory investigations. In an initial step, SSA was leached with sulfuric acid using a liquid-to-solid ratio of 2. The leaching time and pH required for high phosphorus dissolution were determined. Inevitably, dissolution of heavy metals takes place that would contaminate the fertilizer. Thus in a second step, leach solution has to be purified by having the heavy metals removed. Both ion exchange using chelating resins and sulfide precipitation turned out to be suitable for removing critical Cu, Ni and Cd. Thirdly, phosphates were precipitated as calcium phosphates with lime water. The resulting phosphate sludge was dewatered, dried and ground to get a powdery fertilizer whose efficacy was demonstrated by plant tests in a greenhouse. By measuring the weight of plants after 6 weeks of growth, fertilized in part with conventional phosphate fertilizer, fertilizer made from SSA was proven to be equal in its plant uptake efficiency.