Dewatering of source-separated human urine for nitrogen recovery by membrane distillation

• DCMD was operated as a dewatering process for source-separated human urine.
• High temperature promoted higher flux of water rather than ammonia.
• Acidification prevented ammonia transfer from ammonia-rich solution.
• Filtration (1.2 µm) improved the water flux of acidified human urine.

The nitrogen content of a synthetic ammonia wastewater was concentrated using direct contact membrane distillation (DCMD). The ratio of transferred ammonia to water (i.e., specific ammonia transfer: SAT) was controlled by operational conditions. With 20 °C on the permeate side, and a high temperature of 70 °C on the feed side, the process exhibited low SAT values for PTFE/PP (PTF045LD0A), PTFE/PP (TF-450), and PVDF (HVHP-14250) membranes. This was because the increase in water flux (>24 L/m2 h) was greater than that of ammonia transfer. A positive relationship between SAT and free ammonia concentration was identified under different total ammoniacal nitrogen concentration and pH. The acidification pretreatment to pH 5 led to further reduction in the SAT value (as low as 6.91×10−5 g-N/g-H2O). As a practical application, the dewatering process of source-separated human urine by DCMD required an additional filtration step to prevent fouling, but the filtration had an insignificant effect on the SAT. For the acidified and filtered source-separated human urine, total ammoniacal nitrogen was successfully concentrated with a low SAT value (<2.06×10−3 g-N/g-H2O).

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