The possibility of using hydrolyzed urine as a new solvent for biogas upgrading was examined in a batch system. Although the upgraded CH4 content in this study is sufficient for use in boilers, additional biogas upgrading will be required for use of biogas as vehicle fuel and the natural gas replacement.
Further studies are needed to implement a continuous biogas upgrading system in which biogas is continuously upgraded along with a continuous supply of hydrolyzed urine as fertilizers such as ammonium bicarbonate and struvite are simultaneously produced, as shown in Figure 15.
Firstly, further batch mode biogas tests will be performed with more diverse volumes of applied biogas to investigate the optimal point of CO2 removal efficiency. In addition, the absorption capacity may be theoretically the same regardless of the circulation rates and applied volume ratio of biogas to solvent. However, the calculated absorption capacity was different when 10 L biogas was applied compared to when 5 L biogas was applied. It is expected that the reason for the different results will be revealed with additional batch mode experiments.
Secondly, the performance will be compared in different reactor types and conditions, such as hollow fiber membrane contactor reactors and low temperature maintenance reactors. It is expected that the efficiency under these conditions will be higher because the biogas upgrading test was conducted in batch mode with no temperature control, which mimics the conditions for the most basic type of reactor.
Lastly, ammonium bicarbonate, which is the main product in the CO2 scrubber using NH3, will be qualitatively analyzed using other analytical instruments such as FT-IR or Raman spectroscopy. For this process, quantitative analysis of ammonium bicarbonate will also be conducted.
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Figure 15. Flow diagram of continuous biogas upgrading process of using human urine
44
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