Nutrient recovery from anaerobically digested chicken slurry via struvite: Performance optimization and interactions with heavy metals and pathogens

The aim of this studywas to assess the potential of struvite precipitation to recover nutrients fromanaerobicallyprocessed poultry slurry and struvite's interactions with heavy metals (Zn, Cu, Pb, Cr, and Ni) and pathogens (total coliforms and Escherichia coli). The impacts of pH, Mg, N, and P molar proportion, reaction time, and mixing rate and durationwere explored to determine the optimal conditions for nutrient recovery through struvite precipitation. A pH range of 9.5 to 10.5, was ideal for P and N removal and recovery, with a molar ratio of 1: 1: 1 for Mg: N: P. A mixing rate of 150 rpmfor 10min could allownutrient recoverywith little loss (3.32%) of NH3 through volatilization, and also achieve an optimal struvite crystal size (50-60 mu m). The results of X-ray diffractometry and scanning electronmicroscopy confirmed that the precipitates generated at pH 9 and 10 were orthorhombic struvite. Moreover, along with the recovery of nutrients, 40, 45, 66, 30, and 20% of Zn, Cu, Pb, Cr, and Ni, respectively, and 70% total coliforms and E. coli were removed by struvite precipitation from poultry slurry. This was observed despite that the levels of contaminants (heavymetals) detected in struvitewerewell belowthe permissible limits and free of pathogens. Consequently, itwas inferred that the struvite qualitywas reasonable by virtue of its heavy metal and pathogen content, and therefore appropriate for application in the field. Similarly, struvite precipitation has multiple benefits as it can effectively recover nutrients as well as reducing pathogenic populations. (C) 2018 Elsevier B.V. All rights reserved.