4.7 Article

Nitrogen recovery from pig slurry by struvite precipitation using a low-cost magnesium oxide

Journal

SCIENCE OF THE TOTAL ENVIRONMENT
Volume 768, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.scitotenv.2020.144284

Keywords

Nutrient recovery; Magnesium ammonium phosphate; Pig manure; Magnesium oxide; Magnesium by-products

Funding

  1. Rural Development Program of the Government of Catalonia - European Agricultural Fund for Rural Development (FEADER) [5621 002 2016 P4, GO. 16.01.01]
  2. Spanish Ministry of Science and Innovation [RTC2019-007257-5]
  3. Spanish Ministry of Science, Innovation and Universities [RYC-201722372]
  4. Government of Catalonia [APIF-DGR 2018]
  5. University of Barcelona [APIF-DGR 2018]

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Our research successfully optimized the technology for recovering ammonia nitrogen from pig manure by using a stabilizing agent synthesized from LG-MgO and phosphoric acid. The experimental results showed that the H3PO4/LG-MgO ratio controlled the magnesium phosphate mineral phase of the stabilizing agent.
Ammonia nitrogen management is a recurrent problem in intensive livestock areas. Struvite precipitation stands as a mature technology to recover ammonia nitrogen and prevent associated environmental problems. However, the feasibility of struvite technology to recover ammonia nitrogen from pig manure is limited by the reagents cost. This research aimed to optimise the formulation of a stabilizing agent (SA) synthesised using an industrial low-grade MgO by-product (LG-MgO) and phosphoric acid for efficient TAN recovery via struvite precipitation. Experimental results showed that the H3PO4/LG-MgO ratio controls the magnesium phosphate mineral phase of the SA (bobierrite and/or newberyite). Newberyite-rich SA showed the highest TAN removal efficiency from pig manure (66-73%) compared to the SA formed by a mixture of newberyite and bobierrite (51-59%) and by bobierrite (26%). Particle size reduction of LG-MgO did not improve the SA's TAN removal efficiency, although XRD patterns showed that the precipitates from the TAN removal experiments contained some unreacted newberyite. The economic analysis showed that the higher reactivity of the SA formulated using higher H3PO4/LG-MgO ratios compensated reagent costs. The SA synthesised with a H3PO4/LG-MgO ratio of 0.98 showed the most economical treatment cost, which was estimated at 7.5 (sic) per kg of ammonia nitrogen from pig manure. Finally, the optimum SA was successfully synthesised in a 200-L pilot plant, with a TAN removal capacity only 10% lower than the one synthesised at lab-scale. (C) 2020 Elsevier B.V. All rights reserved.

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