Assessment of alternative phosphorus fertilizers for organic farming: Sewage precipitation products

The application of sewage sludge to agricultural land is currently prohibited in organic farming due to the risk of soil contamination from harmful compounds. Incineration or disposal to landfill of sludge is costly, leads to increased greenhouse gas emissions, and neglects the possibility of nutrient recovery. There are various technologies to recover P by crystallization or precipitation from waste water and sewage sludge. Depending on the input material, nutrient concentrations and concentration of contaminants can vary widely. Regarding the content of potentially toxic elements, the trade-offs between (potentially) toxic element concentrations and potential benefits may be more favorable for treated sewage products than for several natural phosphate rocks or even animal manures or bio waste compost. This fact sheet describes the most important aspects to assess the suitability of sewage sludge precipitation products for use in organic farming.