Optimum technical operating conditions and treatments for the production of high-purity struvite fertilizer from livestock wastewater.

Inadequate treatment of nutrient-rich waste streams originating from human activities such as agriculture, animal breeding, urbanization, and industrialization causes an array of environmental problems. Among them are eutrophication of surface water, nutrients and pathogens leaching into groundwater, soil acidification, and destruction of fragile ecosystems. Moreover, food security will be jeopardized, since industrial P-fertilizers are manufactured using phosphate rocks which is non-renewable resource that is constantly depleting. Nutrient recovery (N and P) from wastewater matrices could be a sustainable solution to mitigate this problem. Struvite is a crystalline mineral, which constitutes a slow-release high-value organic fertilizer, containing equal molar concentrations (1:1:1) of magnesium, ammonium, and phosphate (struvite MgNH4PO4·6H2O), that can be recovered from nutrient-rich wastewater streams. This presentation will focus on the optimum operating conditions that should be applied, in order to produce high-quality struvite fertilizer from livestock wastewater. The tested experimental conditions for struvite crystallization included: solution pH, molar ratio Mg2+: N-NH4+: P-PO43-, temperature, added Mg-sources, retention time, and seeding-material addition. Moreover, the effect of matrix composition is discussed. The produced struvite from each process was analyzed for its quality and purity, which was higher than 90%, and in most of the cases the precipitate was complying with the legislative requirements for fertilizers.