title: Struvite recovery from swine waste biogas digester effluent through a stainless steel device under constant pH conditions.
abstract: OBJECTIVE
  To investigate the struvite precipitation under constant and non-constant pH conditions and to test a stainless steel device under different operating regimes to maximize the recovery of struvite.
  
  
  METHODS
  The molar ratio of NH4+: Mg2+: PO4(3-) was adjusted to 1: 1.2: 1.2 and pH was elevated to 9.0. The absorbance measurement was used to trace the process of struvite crystallization. Wastewater and precipitate analysis was done by standard analytical methods.
  
  
  RESULTS
  The pH constant experiment reported a significantly higher struvite precipitation (24.6 +/- 0.86 g) than the non-constant pH experiment (19.8 +/- 1.86 g). The SAR ranged from 5.6 to 8.2 g m(-2) h(-1) to 3.6-4.8 g m(-2) h(-1) in pH constant and non-constant experiments, respectively. The highest struvite deposit on the device was found in regime 3 followed by in regimes 2 and 4. The highest PO4(3-) (97.2%) and NH4+ (71%) removal was reported in the R1 regime. None of the influent Cu2+ or Zn2+ was precipitated on the device.
  
  
  CONCLUSIONS
  A higher struvite yield is evident in pH constant experiments. Moreover, the stainless steel device facilitates the isolation of heavy metal free pure (around 96%) struvite from swine waste biogas digester effluent contaminated with cu2+ and Zn2+ and the highest yield is attainable with the device operating at 50 rpm with agitation by a magnetic stirrer.
authors.affiliation: College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310029, Zhejiang, China. pwaperera@yahoo.com
authors.forename: P W Anton
authors.initials: PW
authors.lastname: Perera
authors.forename: Wei-Xiang
authors.initials: WX
authors.lastname: Wu
authors.forename: Ying-Xu
authors.initials: YX
authors.lastname: Chen
authors.forename: Zhi-Ying
authors.initials: ZY
authors.lastname: Han
mesh_terms: D000818:Animals; D019149:Bioreactors; D011232:Chemical Precipitation; D006863:Hydrogen-Ion Concentration; D017616:Magnesium Compounds / Q000737:chemistry*; D008372:Manure; D010710:Phosphates / Q000737:chemistry*; D013193:Stainless Steel; D000069877:Struvite; D013552:Swine; D013997:Time Factors; D014865:Waste Disposal, Fluid / Q000295:instrumentation* / Q000379:methods
chemical_list: D017616:Magnesium Compounds; D008372:Manure; D010710:Phosphates; D013193:Stainless Steel; D000069877:Struvite