The recovery of struvite in sewage treatment plants provides a useful fertilizer while preventing costly operational problems from precipitation in pipes, pumps and digesters. Currently, however, the sale of struvite as a fertilizer is hampered by low revenues. A higher value of struvite is its use in phosphorus-based flame retardants, in which phosphoric acids released at elevated temperatures react catalytically with organic substrates to form layers of carbon that suffocate the flame. In this thesis we evaluated the fire retardant performance of sewage derived struvite suspended in an inexpensive viscoelastic hydrogel carrier (0.68% hydroxyethyl cellulose, 0.12% methyl cellulose and 5% colloidal silicon dioxide nanoparticles). The effectiveness of this formulation was compared with that of a conventional flame retardant based on polyphosphate in thermogravimetric analyzes of wood samples and combustion tests on dry grass on a laboratory scale. The struvite-based formulation performed comparable to the polyphosphate retarder while requiring 60% less total phosphorus. Since struvite is extracted from wastewater, applications of struvite in flame retardants can also offset the demand for depleted phosphorus, a finite resource. Analysis of the supply and demand for conventional flame retardants in the US shows that sewage treatment plants could produce sufficient amounts of struvite-based flame retardants to meet US demand for forest fire fighting while significantly improving revenues compared to direct sales of struvite fertilizers. We conclude that struvite-derived from wastewater is a promising green chemical agent for flame retardants and can help save global phosphorus.


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