Turning hazardous waste into value-added products: production and characterization of struvite from ammoniacal waste with new approaches

Ammonium nitrogen present in high concentration in ammoniacal waste was recovered through chemical precipitation as magnesium ammonium phosphate hexahydrate known as struvite with new approaches. For the first time, in such investigations, a central composite design of response surface methodology was adopted to optimise the process parameters in terms of pH, concentration of ammonium nitrogen, phosphate and magnesium salts during precipitation and recovery of struvite. A new membrane-integrated continuous approach ensured very efficient downstream separation and recovery (95%) of struvite and simultaneous purification of water for reuse. This ensured protection of surface water from chemical contamination by a hazardous waste stream. Exhaustive characterisation of the product struvite was done from different angles using scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, thermo-gravimetric analysis and electron diffraction spectroscopy. Findings indicate that with appropriate approaches, hazardous ammoniacal waste under response surface optimised conditions can be efficiently converted simultaneously into a pure, value-added struvite by-product and reusable water. Investigations culminated in an environmentally benign process towards tackling an environmental problem of the industries that generate ammoniacal waste.

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► Novel process developed for conversion of waste nitrogen into useful struvite.
► Response surface optimisation turned the chemical process very efficient.
► Downstream cross flow nanofiltration ensured recovery and reuse of quality water.
► The process developed is environmentally benign.