Struvite is a hydrated phosphate magnesium-ammonium, chemical formula MgNH₄PO₄ ∙ 6H₂O. It is a mineral which is often formed in an uncontrolled manner in sewage treatment plants, especially in pipes discharging effluent sludge dewatering presses from fermentation tanks. In earlier laboratory tests carried out in static conditions [Czajkowska and Siwiec 2011, Czajkowska 2012] demonstrated a significant effect of pH and concentrations of phosphate, magnesium and ammonium compounds on the formation of struvite. Investigations were carried out methodically for 6 values of pH, 5 concentrations of phosphate and 10 concentrations of ammonium. For those conditions sought magnesium concentrations at which precipitation of struvite. Both of laconic literature data and with information from facing the problem of struvite treatment plants shows that there is a possibility there are other stimulants formation of struvite. The most serious of which is calcium. For this reason, it was carried out studies designed to determine the significance of the impact on the precipitation of calcium deposits. Studies designed to answer the question whether the presence of calcium accelerates the crystallization from solution in cases where the specified concentrations of other components such crystallization does not occur. Practical significance of this research is to give ability to specify ranges of concentrations of individual components, including calcium, at which the settlement will precipitate struvite or mixtures of similar compounds.

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