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ETH-Rektor Günther Dissertori überreicht Valentin Faust den Otto-Jaag-Gewässerschutzpreis 2024 (Foto: ETH, Alessandro Della Bella).

Otto-Jaag-Gewässerschutzpreis 2024 für Valentin Faust

18. November 2024 | Claudia Carle

Für seine Dissertation wurde der Umweltingenieur Valentin Faust am ETH-Tag vom 16. November 2024 mit dem Otto-Jaag-Gewässerschutzpreis ausgezeichnet. Seine Arbeit liefert wichtige Erkenntnisse für die Herstellung von Dünger aus menschlichem Urin.

Die ETH Zürich vergibt den Otto-Jaag-Gewässerschutzpreis für hervorragende Master- und Doktorarbeiten auf dem Gebiet des Gewässerschutzes und der Gewässerkunde. Dieses Jahr erhielt Valentin Faust diese Auszeichnung im Rahmen des ETH-Tages vom 16. November für seine Dissertation zum Thema “Effects of pH on urine nitrification: from microbial selection to process performance”.

Seine Arbeit war Teil des Weltraumforschungsprogramms MELiSSA der Europäischen Weltraumorganisation ESA. MELiSSA steht für «Micro Ecological Life Support System Alternative» und hat zum Ziel, Systeme zu entwickeln, die langfristige, bemannte Weltraummissionen ermöglichen, beispielsweise auf den Mars. Dafür braucht es regenerative Systeme, die aus den anfallenden Abfällen in Form geschlossener Kreisläufe Nahrung, Wasser und Sauerstoff produzieren. Der Dünger für die Produktion von Nahrung soll dabei aus Urin gewonnen werden.

Die Prozessstabilität erhöhen für den Einsatz im Weltraum

Die Eawag beschäftigt sich seit langem mit den dafür erforderlichen Prozessen, um die Rückgewinnung von Ressourcen aus Abwasser sowie autarke Sanitärsysteme für Orte ohne Kanalisation und Wasseranschluss zu ermöglichen. Für den Einsatz im Weltraum muss der mehrstufige Prozess zur Rückgewinnung von Stickstoff, Phosphor und anderen Nährstoffen aus Urin besonders zuverlässig und störungsfrei funktionieren. Ziel der Arbeit von Valentin Faust als Doktorand in der Abteilung Verfahrenstechnik der Eawag war es daher, die Prozessstabilität der Urinbehandlung zu erhöhen und ausserdem den CO2-Fussabdruck des Verfahrens zu senken. Er nahm dabei insbesondere den Prozessschritt der Nitrifikation unter die Lupe, in welchem Bakterien das im Urin enthaltene Ammonium in Nitrat umwandeln. Diese Reaktion ist sehr empfindlich auf Veränderungen des pH-Wertes. Faust untersuchte, wie sich der pH-Wert auf die Zusammensetzung der Mikroorganismen sowie auf die Entstehung unerwünschter Reaktionsprodukte wie Nitrit und den Klimaschädling Lachgas auswirkt.

Dafür arbeitete er unter anderem mit Nitrifikationsreaktoren im Labor- und Pilotmassstab und modellierte den Nitrifikationsprozess, um vorhersagen zu können, unter welchen Bedingungen der Prozess zum Erliegen kommt bzw. welche Betriebsstrategien eine stabile und möglichst klimafreundliche Nitrifikation ermöglichen.

Wertvolle Erkenntnisse auch für den Einsatz auf der Erde

«Die Ergebnisse von Valentin Faust liefern wichtige Erkenntnisse für den Betrieb von Nitrifikationsreaktoren zur Herstellung eines Düngemittels aus menschlichem Urin», erklärt Kai Udert, Gruppenleiter in der Abteilung Verfahrenstechnik der Eawag, der Fausts Doktorarbeit betreut hat. «Das ist sehr wertvoll für die Weiterentwicklung der ressourcenorientierten Siedlungswasserwirtschaft mit dem Ziel Nährstoffkreisläufe zu schliessen und Wasserressourcen zu schützen.»

Valentin Faust freut sich über die Auszeichnung. «Es hat mir grossen Spass gemacht, in einem internationalen Team gemeinsam an den Herausforderungen eines zirkulären Systems zu arbeiten – für den Einsatz auf der Erde oder im Weltraum». Was er mit dem Preisgeld machen wird, weiss er noch nicht. «Ein Flugticket zum Mond kaufe ich mir jedenfalls nicht». Nach einem kurzen Postdoc an der Eawag arbeitet Faust nun als Projektleiter an der Ostschweizer Fachhochschule (OST) in der Fachgruppe Angewandte Chemie im Bereich Abwasser, Wasser und Geruch.
 

Titelbild: ETH-Rektor Günther Dissertori überreicht Valentin Faust den Otto-Jaag-Gewässerschutzpreis 2024 (Foto: ETH, Alessandro Della Bella).
 

Originalpublikationen

Ammonia oxidation by novel "Candidatus Nitrosacidococcus urinae" is sensitive to process disturbances at low pH and to iron limitation at neutral pH

Acid-tolerant ammonia-oxidizing bacteria (AOB) can open the door to new applications, such as partial nitritation at low pH. However, they can also be problematic because chemical nitrite oxidation occurs at low pH, leading to the release of harmful nitrogen oxide gases. In this publication, the role of acid-tolerant AOB in urine treatment was explored. On the one hand, the technical feasibility of ammonia oxidation under acidic conditions for source-separated urine with total nitrogen concentrations up to 3.5 g-N L-1 was investigated. On the other hand, the abundance and growth of acid-tolerant AOB at more neutral pH was explored. Under acidic conditions (pH of 5), ammonia oxidation rates of 500 mg-N L-1 d-1 and 10 g-N g-VSS-1 d-1 were observed, despite high concentrations of 15 mg-N L-1 of the AOB-inhibiting compound nitrous acid and low concentration of 0.04 mg-N L-1 of the substrate ammonia. However, ammonia oxidation under acidic conditions was very sensitive to process disturbances. Even short periods of less than 12 h without oxygen or without influent resulted in a complete cessation of ammonia oxidation with a recovery time of up to two months, which is a problem for low maintenance applications such as decentralized treatment. Furthermore, undesirable nitrogen losses of about 10% were observed. Under acidic conditions, a novel AOB strain was enriched with a relative abundance of up to 80%, for which the name “Candidatus (Ca.) Nitrosacidococcus urinae” is proposed. While Nitrosacidococcus members were present only to a small extent (0.004%) in urine nitrification reactors operated at pH values between 5.8 and 7, acid-tolerant AOB were always enriched during long periods without influent, resulting in an uncontrolled drop in pH to as low as 2.5. Long-term experiments at different pH values showed that the activity of “Ca. Nitrosacidococcus urinae” decreased strongly at a pH of 7, where they were also outcompeted by the acid-sensitive AOB Nitrosomonas halophila. The experiment results showed that the decreased activity of “Ca. Nitrosacidococcus urinae” correlated with the limited availability of dissolved iron at neutral pH.
Faust, V.; van Alen, T. A.; Op den Camp, H. J. M.; Vlaeminck, S. E.; Ganigué, R.; Boon, N.; Udert, K. M. (2022) Ammonia oxidation by novel "Candidatus Nitrosacidococcus urinae" is sensitive to process disturbances at low pH and to iron limitation at neutral pH, Water Research X, 17, 100157 (11 pp.), doi:10.1016/j.wroa.2022.100157, Institutional Repository

Nitrous oxide emissions and carbon footprint of decentralized urine fertilizer production by nitrification and distillation

Combining partial nitrification, granular activated carbon (GAC) filtration, and distillation is a well-studied approach to convert urine into a fertilizer. To evaluate the environmental sustainability of a technology, the operational carbon footprint and therefore nitrous oxide (N2O) emissions should be known, but N2O emissions from urine nitrification have not been assessed yet. Therefore, N2O emissions of a decentralized urine nitrification reactor were monitored for 1 month. During nitrification, 0.4-1.2% of the total nitrogen load was emitted as N2O-N with an average N2O emission factor (EFN2O) of 0.7%. Additional N2O was produced during anoxic storage between nitrification and GAC filtration with an estimated EFN2O of 0.8%, resulting in an EFN2O of 1.5% for the treatment chain. N2O emissions during nitrification can be mitigated by 60% by avoiding low dissolved oxygen or anoxic conditions and nitrite concentrations above 5 mg-N L-1. Minimizing the hydraulic retention time between nitrification and GAC filtration can reduce N2O formation during intermediate storage by 100%. Overall, the N2O emissions accounted for 45% of the operational carbon footprint of 14 kg-CO2,equiv kg-N-1 for urine fertilizer production. Using electricity from renewable sources and applying the proposed N2O mitigation strategies could potentially lower the carbon footprint by 85%.
Faust, V.; Gruber, W.; Ganigué, R.; Vlaeminck, S. E.; Udert, K. M. (2022) Nitrous oxide emissions and carbon footprint of decentralized urine fertilizer production by nitrification and distillation, ACS ES&T Engineering, 2(9), 1745-1755, doi:10.1021/acsestengg.2c00082, Institutional Repository

Optimizing control strategies for urine nitrification: narrow pH control band enhances process stability and reduces nitrous oxide emissions

Nitrification is well-suited for urine stabilization. No base dosage is required if the pH is controlled within an appropriate operating range by urine feeding, producing an ammonium-nitrate fertilizer. However, the process is highly dependent on the selected pH set-points and is susceptible to process failures such as nitrite accumulation or the growth of acid-tolerant ammonia-oxidizing bacteria. To address the need for a robust and reliable process in decentralized applications, two different strategies were tested: operating a two-position pH controller (inflow on/off) with a narrow pH control band at 6.20/6.25 (∆pH = 0.05, narrow-pH) vs. a wider pH control band at 6.00/6.50 (∆pH = 0.50, wide-pH). These variations in pH also cause variations in the chemical speciation of ammonia and nitrite and, as shown, the microbial production of nitrite. It was hypothesized that the higher fluctuations would result in greater microbial diversity and, thus, a more robust process. The diversity of nitrifiers was higher in the wide-pH reactor, while the diversity of the entire microbiome was similar in both systems. However, the wide-pH reactor was more susceptible to tested process disturbances caused by increasing pH or temperature, decreasing dissolved oxygen, or an influent stop. In addition, with an emission factor of 0.47%, the nitrous oxide (N2O) emissions from the wide-pH reactor were twice as high as the N2O emissions from the narrow-pH reactor, most likely due to the nitrite fluctuations. Based on these results, a narrow control band is recommended for pH control in urine nitrification.
Faust, V.; Boon, N.; Ganigué, R.; Vlaeminck, S. E.; Udert, K. M. (2023) Optimizing control strategies for urine nitrification: narrow pH control band enhances process stability and reduces nitrous oxide emissions, Frontiers in Environmental Science, 11, 1275152 (14 pp.), doi:10.3389/fenvs.2023.1275152, Institutional Repository

Influence of pH on urine nitrification: community shifts of ammonia-oxidizing bacteria and inhibition of nitrite-oxidizing bacteria

Urine nitrification is pH-sensitive due to limited alkalinity and high residual ammonium concentrations. This study aimed to investigate how the pH affects nitrogen conversion and the microbial community of urine nitrification with a pH-based feeding strategy. First, kinetic parameters for NH3, HNO2, and NO2- limitation and inhibition were determined for nitrifiers from a urine nitrification reactor. The turning point for ammonia-oxidizing bacteria (AOB), i.e., the substrate concentration at which a further increase would lead to a decrease in activity due to inhibitory effects, was at an NH3 concentration of 12 mg-N L-1, which was reached only at pH values above 7. The total nitrite turning point for nitrite-oxidizing bacteria (NOB) was pH-dependent, e.g., 18 mg-N L-1 at pH 6.3. Second, four years of data from two 120 L reactors were analyzed, showing that stable nitrification with low nitrite was most likely between pH 5.8 and 6.7. And third, six 12 L urine nitrification reactors were operated at total nitrogen concentrations of 1300 and 3600 mg-N L-1 and pH values between 2.5 and 8.5. At pH 6, the AOB Nitrosomonas europaea was found, and the NOB belonged to the genus Nitrobacter. At pH 7, nitrite accumulated, and Nitrosomonas halophila was the dominant AOB. NOB were inhibited by HNO2 accumulation. At pH 8.5, the AOB Nitrosomonas stercoris became dominant, and NH3 inhibited NOB. Without influent, the pH dropped to 2.5 due to the growth of the acid-tolerant AOB “Candidatus Nitrosacidococcus urinae”. In conclusion, pH is a decisive process control parameter for urine nitrification by influencing the selection and kinetics of nitrifiers.
Faust, V.; Vlaeminck, S. E.; Ganigué, R.; Udert, K. M. (2024) Influence of pH on urine nitrification: community shifts of ammonia-oxidizing bacteria and inhibition of nitrite-oxidizing bacteria, ACS ES&T Engineering, 4(2), 342-353, doi:10.1021/acsestengg.3c00320, Institutional Repository

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