The Stuttgart Process (Germany)

Abstract

The Stuttgart Process for nutrient recovery aims to produce struvite as fertilizer from digested sewage sludge from wastewater treatment plants (WWTP) with chemical phosphorus removal. This chapter deals with the detailed description of the experiences with a pilot-scale test plant and its process operation, the latest process optimizations, as well as operational performance data, i.e., phosphorus recovery rates, recyclate product quality, required operational supplements, and costs. The results show that depending on the chemicals used for phosphorus elimination and on the process boundary conditions (especially pH value for dissolving phosphorus from the sewage sludge), different amounts of phosphorus can be recovered. With acidic leaching at pH of approximately 3, it is possible to gain recovery rates of more than 65% as struvite with high purity and very low contents of heavy metals and recalcitrant organic compounds. Additional operating costs for the Stuttgarter process would increase wastewater feed of about 0.15 €/m3.