Human urine is considered a major
stream of nitrogen
mass flow
in domestic wastewater, which is widely available and rich in valuable
nutrient resources for hydroponic cultivation. In this study, a promising
concept of nutrient recovery from real urine was proposed, including
urine alkalinization by Ca(OH)2, full nitrification in
a trickling filter, and chemical supplementations. The steady performance
of urine nitrification among different urine-collecting batches indicates
the robustness of the trickling filter. An optimal hydraulic loading
rate of 2.1 m3 m–2 h–1 sufficed the dissolved oxygen and urine circulation in the trickling
filter, achieving a nitrate production rate of 223 ± 2 mg N L–1 d–1 with an efficiency of 90 ±
2% at pH 6 and 21 °C. The electrical energy consumption was only
1.15 kWh kg–1 NO3
–-N
production at a short hydraulic retention time of 1 day. Among all
of the three types of pH control reagents (i.e., Ca(OH)2, CaCO3, and K2CO3), K2CO3 could enhance the activity of ammonium-oxidizing bacteria
by raising the inorganic carbon level in the trickling filter and
subsequently result in the lowest supplementation of extra macronutrients
(i.e., nitrogen, phosphorus, and magnesium) to the urine-sourced nutrient
solution. Batch tests showed that the highest activity of ammonium-oxidizing
and nitrite-oxidizing bacteria was in the bottom compartment of the
trickling filter, consistent with the vertical stratification of their
relative abundance. Overall, the proposed novel concept was demonstrated
to be robust and energy-efficient in nutrient recovery from real urine
for hydroponics.