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Bio-electrochemical pre-treatment and membrane aeration to intensify full nitrogen recovery for Spaceflight urine nitrification

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Abstract
Nitrogen (re)cycling is essential in regenerative life support systems (RLSS) (Clauwaert et al. 2017). Urine presents a major flux of nitrogen in a RLSS and contains additional macro- and micro-nutrients, in an optimal ratio to sustain plant growth (Clauwaert et al. 2017, Larsen et al. 2013). Instability of raw urine can result in ammonia volatilisation posing a hazard to the crew and causing considerable nitrogen loss. Urine nitrification is a microbial process to preserve the urine nutrient content while converting urea into nitrate, a non-volatile, non-toxic molecule and in most cases the preferred nitrogen source for plants in a RLSS. Nitrification is challenged by the high nitrogen, organic compounds (COD) and salt concentrations and limited alkalinity of urine. The reduced gravity in Space further adds to the complexity, by limiting the convection-driven oxygen transport to the obligate aerobic microbial community, requiring ~50 g O2/L urine to oxidize all ammonium and COD. One way of maximizing oxygen transfer in Space, is to intensify diffusion and dissolution of oxygen through the use of gas permeable membranes in so-called membrane aerated biofilm reactors (MABR). As heterotrophic bacteria oxidize the organic compounds present in urine, the biofilm thickness on the membrane aeration surface is expected to increase. Avoiding the combination of anoxic zones and COD is critical in preventing denitrification and hence a loss of nitrogen from the RLSS. Bio-anodic oxidation in a bio-electrochemical system (BES) was proposed as a pre-treatment to remove the rapidly biodegradable COD prior to membrane-aerated nitrification. As a consequence, the BES allows to operate the MABR at a high loading rate, reducing the reactor volume, and in addition, produces energy. A two-stage BES-MABR set-up was designed that could possibly be integrated in the MELiSSA concept, the RLSS system developed for the European Space Agency (ESA). The BES consisted of a bio-anode containing graphite granules, carbon felt and a stainless steel current collector, acting as an electron acceptor for the electrons generated by electroactive bacteria. At a 1:3 dilution, stabilized urine was dosed (HRT of 6-7 days) and stable operation was obtained, characterized by 80-90% COD removal, which corresponds to the rapidly biodegradable COD fraction in urine. Besides COD oxidation, 80-90% of the organic nitrogen was hydrolyzed into TAN (total ammonium nitrogen), resulting in a pH around 8.5 and an increased electrical conductivity in the bio-anode (25 mS/cm, compared to 10 mS/cm in the influent). The bio-anodic effluent was then fed into the nitrification MABR, composed of three parallel modules with hollow fibre membranes (total reactor volume 700 mL, total membrane surface area 0.18 m²). Prior to inoculation, the standard oxygen transfer rate (SOTR) equalled ~500 mg O2/module/day, providing enough oxygen to nitrify at high rate (~1.3 g N/L/d or 2 g N/m2/d). The effective coupling of the BES and the MABR without nitrogen loss through denitrification will be demonstrated to deliver a proof-of-concept and the BES operation will be further optimized in order to increase the coulombic efficiency. Acknowledgements: The authors would like to acknowledge the MELiSSA Foundation to support JDP via the POMP1 (Pool Of MELiSSA PhD) program. References: Clauwaert, P., Muys, M., Alloul, A., De Paepe, J., Luther, A., Sun, X.Y., Ilgrande, C., Christiaens, M.E.R., Hu, X.N., Zhang, D.D., Lindeboom, R.E.F., Sas, B., Rabaey, K., Boon, N., Ronsse, F., Geelen, D. and Vlaeminck, S.E. (2017) Nitrogen cycling in Bioregenerative Life Support Systems: Challenges for waste refinery and food production processes. Progress in Aerospace Sciences 91, 87-98. Larsen, T.A., Udert, K.M. and Lienert, J. (2013) Source separation and decentralization for wastewater management. IWA Publishing.
Keywords
MELiSSA, urine nitrification, microgravity, membrane aerated biofilm reactor (MABR), bio-electrochemical system (BES)

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MLA
De Paepe, Jolien, Siegfried Vlaeminck, Korneel Rabaey, et al. “Bio-electrochemical Pre-treatment and Membrane Aeration to Intensify Full Nitrogen Recovery for Spaceflight Urine Nitrification.” AgroSpace-MELiSSA, 1st Joint Workshop, Abstracts. 2018. Print.
APA
De Paepe, J., Vlaeminck, S., Rabaey, K., Gòdia, F., & Clauwaert, P. (2018). Bio-electrochemical pre-treatment and membrane aeration to intensify full nitrogen recovery for Spaceflight urine nitrification. AgroSpace-MELiSSA, 1st Joint workshop, Abstracts. Presented at the 1st Joint AgroSpace-MELiSSA workshop.
Chicago author-date
De Paepe, Jolien, Siegfried Vlaeminck, Korneel Rabaey, Francesc Gòdia, and Peter Clauwaert. 2018. “Bio-electrochemical Pre-treatment and Membrane Aeration to Intensify Full Nitrogen Recovery for Spaceflight Urine Nitrification.” In AgroSpace-MELiSSA, 1st Joint Workshop, Abstracts.
Chicago author-date (all authors)
De Paepe, Jolien, Siegfried Vlaeminck, Korneel Rabaey, Francesc Gòdia, and Peter Clauwaert. 2018. “Bio-electrochemical Pre-treatment and Membrane Aeration to Intensify Full Nitrogen Recovery for Spaceflight Urine Nitrification.” In AgroSpace-MELiSSA, 1st Joint Workshop, Abstracts.
Vancouver
1.
De Paepe J, Vlaeminck S, Rabaey K, Gòdia F, Clauwaert P. Bio-electrochemical pre-treatment and membrane aeration to intensify full nitrogen recovery for Spaceflight urine nitrification. AgroSpace-MELiSSA, 1st Joint workshop, Abstracts. 2018.
IEEE
[1]
J. De Paepe, S. Vlaeminck, K. Rabaey, F. Gòdia, and P. Clauwaert, “Bio-electrochemical pre-treatment and membrane aeration to intensify full nitrogen recovery for Spaceflight urine nitrification,” in AgroSpace-MELiSSA, 1st Joint workshop, Abstracts, Rome, Italy, 2018.
@inproceedings{8558663,
  abstract     = {Nitrogen (re)cycling is essential in regenerative life support systems (RLSS) (Clauwaert et al. 2017). Urine presents a major flux of nitrogen in a RLSS and contains additional macro- and micro-nutrients, in an optimal ratio to sustain plant growth (Clauwaert et al. 2017, Larsen et al. 2013). Instability of raw urine can result in ammonia volatilisation posing a hazard to the crew and causing considerable nitrogen loss. Urine nitrification is a microbial process to preserve the urine nutrient content while converting urea into nitrate, a non-volatile, non-toxic molecule and in most cases the preferred nitrogen source for plants in a RLSS. 
Nitrification is challenged by the high nitrogen, organic compounds (COD) and salt concentrations and limited alkalinity of urine. The reduced gravity in Space further adds to the complexity, by limiting the convection-driven oxygen transport to the obligate aerobic microbial community, requiring ~50 g O2/L urine to oxidize all ammonium and COD. One way of maximizing oxygen transfer in Space, is to intensify diffusion and dissolution of oxygen through the use of gas permeable membranes in so-called membrane aerated biofilm reactors (MABR). As heterotrophic bacteria oxidize the organic compounds present in urine, the biofilm thickness on the membrane aeration surface is expected to increase. Avoiding the combination of anoxic zones and COD is critical in preventing denitrification and hence a loss of nitrogen from the RLSS. Bio-anodic oxidation in a bio-electrochemical system (BES) was proposed as a pre-treatment to remove the rapidly biodegradable COD prior to membrane-aerated nitrification. As a consequence, the BES allows to operate the MABR at a high loading rate, reducing the reactor volume, and in addition, produces energy. 
A two-stage BES-MABR set-up was designed that could possibly be integrated in the MELiSSA concept, the RLSS system developed for the European Space Agency (ESA). The BES consisted of a bio-anode containing graphite granules, carbon felt and a stainless steel current collector, acting as an electron acceptor for the electrons generated by electroactive bacteria. At a 1:3 dilution, stabilized urine was dosed (HRT of 6-7 days) and stable operation was obtained, characterized by 80-90% COD removal, which corresponds to the rapidly biodegradable COD fraction in urine. Besides COD oxidation, 80-90% of the organic nitrogen was hydrolyzed into TAN (total ammonium nitrogen), resulting in a pH around 8.5 and an increased electrical conductivity in the bio-anode (25 mS/cm, compared to 10 mS/cm in the influent). The bio-anodic effluent was then fed into the nitrification MABR, composed of three parallel modules with hollow fibre membranes (total reactor volume 700 mL, total membrane surface area 0.18 m²). Prior to inoculation, the standard oxygen transfer rate (SOTR) equalled ~500 mg O2/module/day, providing enough oxygen to nitrify at high rate (~1.3 g N/L/d or 2 g N/m2/d). The effective coupling of the BES and the MABR without nitrogen loss through denitrification will be demonstrated to deliver a proof-of-concept and the BES operation will be further optimized in order to increase the coulombic efficiency. 
Acknowledgements:
The authors would like to acknowledge the MELiSSA Foundation to support JDP via the POMP1 (Pool Of MELiSSA PhD) program.
References:
Clauwaert, P., Muys, M., Alloul, A., De Paepe, J., Luther, A., Sun, X.Y., Ilgrande, C., Christiaens, M.E.R., Hu, X.N., Zhang, D.D., Lindeboom, R.E.F., Sas, B., Rabaey, K., Boon, N., Ronsse, F., Geelen, D. and Vlaeminck, S.E. (2017) Nitrogen cycling in Bioregenerative Life Support Systems: Challenges for waste refinery and food production processes. Progress in Aerospace Sciences 91, 87-98.
Larsen, T.A., Udert, K.M. and Lienert, J. (2013) Source separation and decentralization for wastewater management. IWA Publishing.},
  author       = {De Paepe, Jolien and Vlaeminck, Siegfried and Rabaey, Korneel and Gòdia, Francesc and Clauwaert, Peter},
  booktitle    = {AgroSpace-MELiSSA, 1st Joint workshop, Abstracts},
  keywords     = {MELiSSA,urine nitrification,microgravity,membrane aerated biofilm reactor (MABR),bio-electrochemical system (BES)},
  language     = {eng},
  location     = {Rome, Italy},
  title        = {Bio-electrochemical pre-treatment and membrane aeration to intensify full nitrogen recovery for Spaceflight urine nitrification},
  year         = {2018},
}