Abstract
Several technologies have aimed to recover nitrogen directly from urine. Nitrogen recovery in these technologies was limited by the mismatch of the nitrogen-phosphorus molar ratio (N:P) of urine, being 30–46:1, and that of the final product, e.g., 1:1 in struvite and 16–22:1 in microalgae biomass. Additionally, the high nitrogen concentrations found in urine can be inhibitive for growth of microorganisms. Cyanobacteria were expected to overcome phosphorus (P) limitation in urine given their ability to store an N-rich polymer called cyanophycin. In this study, it was found that the model cyanobacterium Synechocystis sp. PCC6803 did not experience significant growth inhibition when cultivated in synthetic medium with concentrations of 0.5 g ammonium-N L−1. In the case of urea, no inhibition was observed when having it as sole nitrogen source, but it resulted in chlorosis of the cultures when the process reached stationary phase. Synechocystis was successfully cultivated in a medium with 0.5 g ammonium-N L−1 and a N:P ratio of 276:1, showing the N:P flexibility of this biomass, reaching biomass N:P ratios up to 92:1. Phosphorus starvation resulted in cyanophycin accumulation up to 4%. Dilution of the culture in fresh medium with the addition of 118 mg N L−1 and 1.5 mg P L−1 (N:P of 174:1) resulted in a rapid and transient cyanophycin accumulation up to 11%, after which cyanophycin levels rapidly decreased to 3%.
Highlights
IntroductionThe development of the Haber–Bosch process (artificial fixation of nitrogen) has resulted in a 35–55% addition of reactive nitrogen to the natural nitrogen fixation rates
The development of the Haber–Bosch process has resulted in a 35–55% addition of reactive nitrogen to the natural nitrogen fixation rates
Synechocystis 6803 grew linearly between O D720 values of 0.3 and 0.6 on either ammonium (NH4+) or urea; growth rates are presented in terms of OD720 day−1 (Fig. 2)
Summary
The development of the Haber–Bosch process (artificial fixation of nitrogen) has resulted in a 35–55% addition of reactive nitrogen to the natural nitrogen fixation rates This process requires a lot of energy (37 kJ g N−1) and a hydrogen source, generally natural gas, and cannot be considered very sustainable Nitrogen is removed from wastewater by subsequent nitrification and denitrification and is released back to the atmosphere as dinitrogen gas This process requires a lot of energy (45 kJ gN−1) for aeration during nitrification and consumption of valuable carbon sources for denitrification (Maurer et al 2003; Morales et al 2013). Sustainable technologies to reduce the environmental impact related to nitrogen should focus on its recovery and reuse
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