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Struvite Production from Dairy Processing Waste
Journal article   Open access   Peer reviewed

Struvite Production from Dairy Processing Waste

Shane McIntosh, Louise Hunt, Emma Thompson Brewster, Andrew Rose, Aaron Thornton and Dirk Erler
Sustainability (Basel, Switzerland), Vol.14(23), pp.1-15
28/11/2022
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Abstract

Agriculture Ammonium Anaerobic processes Calcium Chemical precipitation Coprecipitation Dairy industry wastewaters Dairy products Dairy wastes Effluents Experiments Fertilizer applications Fertilizer industry wastewater Fertilizers Food processing Food security Hydroxyapatite Mineralization Nutrient removal pH effects Phosphorus Phosphorus removal Ratios Recovery Response surface methodology Rock phosphate Security Stoichiometry Struvite Wastewater
Food security depends on sustainable phosphorus (P) fertilisers, which at present are mostly supplied from a finite rock phosphate source. Phosphate (PO43−) and ammonium (NH4+) in dairy processing wastewater can be recovered as struvite (Mg + NH4+ + PO43− 6H20), a nutrient rich mineral for fertiliser application. The objectives of this study were to (1) quantify the effects of, pH, temperature and Mg: PO43− dosing rates on nutrient (PO43− and NH4+) removal and struvite precipitation from post anaerobic digested dairy processing wastewater, and (2) co-blend different dairy processing wastewaters to improve the reactant stoichiometry of NH4+ and PO43− for optimal struvite recovery and NH4+ removal. Phosphate removal (>90%) and struvite production (>60%) was achieved across a range of synthesis conditions, and was significantly impacted by pH as determined by response surface modelling. A combination of disproportionate molar ratios of PO43− and NH4+, presence of calcium and the apparent mineralisation of organic N, resulted in co-precipitation of hydroxyapatite and elevated levels of residual aqueous NH4+. In the second phase of this study, struvite was successfully precipitated and NH4+ removal was improved (~17%) however, higher concentrations of calcium in the wastewater blends resulted in greater hydroxyapatite co-precipitation (up to 30%). While struvite was the desired product in this study the formation of multiple heterogenous P-rich products (struvite and hydroxyapatite) has the potential to improve P recovery from dairy processing wastewaters and produce a fertiliser blend with amenity and value in agricultural systems.

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