Kai M. Udert

Last Name

Udert

First Name

Kai M.

ORCID

0000-0002-8051-7362

Organisational unit

01109 - Lehre Bau, Umwelt und Geomatik

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Publications 1 - 10 of 12

Influence of pH on Urine Nitrification: Community Shifts of Ammonia-Oxidizing Bacteria and Inhibition of Nitrite-Oxidizing Bacteria
Faust, Valentin; Vlaeminck, Siegfried E.; Ganigué, Ramon; et al. (2024)
ACS ES&T Engineering
Aurin, ein Dünger aus menschlichem Urin im Praxistest auf Sportrasen
Akert, Franziska; Aebischer, Philippe; Udert, Kai M.; et al. (2024)
Rasen - Turf - Gazon: European Journal of Turfgrass Science
Electrochemical Treatment of Urine
Udert, Kai M. (2014)
Encyclopedia of Applied Electrochemistry
Comparing the adsorption of micropollutants on activated carbon from anaerobically stored, organics-depleted, and nitrified urine
Heusser, Aurea; Dax, Anne; McArdell, Christa S.; et al. (2024)
Water Research
Separate collection and treatment of urine optimizes nutrient recovery and enhances micropollutant removal from municipal wastewater. One typical urine treatment train includes nutrient recovery in three biological processes: anaerobic storage, followed by aerobic organics degradation concurrently with nitrification. These are usually followed by activated carbon adsorption to remove micropollutants. However, removing micropollutants prior to nitrification would protect nitrifiers from potential inhibition by pharmaceuticals. In addition, combining simplified biological treatment with activated carbon adsorption could offer a cheap and robust process for removing micropollutants where nutrient recovery is not the first priority, as a partial loss of ammonia occurs without nitrification. In this study, we investigated whether activated carbon adsorption could also take place between the three biological treatment steps. We tested the effectiveness of micropollutant removal with activated carbon after each biological treatment step by conducting experiments with anaerobically stored urine, organics-depleted urine, and nitrified urine. The urine solutions were spiked with 19 pharmaceuticals: amisulpride, atenolol, atenolol acid, candesartan, carbamazepine, citalopram, clarithromycin, darunavir, diclofenac, emtricitabine, fexofenadine, hydrochlorothiazide, irbesartan, lidocaine, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole, trimethoprim, venlafaxine, and two artificial sweeteners, acesulfame and sucralose. Batch experiments were conducted with powdered activated carbon (PAC) to determine how much activated carbon achieve which degree of micropollutant removal and how organics, pH, and speciation change from ammonium to nitrate influence adsorption. Micropollutant removal was also tested in granular activated carbon (GAC) columns, which is the preferred technology for micropollutant removal from urine. The carbon usage rates (CUR) per person were lower for all urine solutions than for municipal wastewater. The results showed that organics depletion would be needed when micropollutant removal was the sole aim of urine treatment, as the degradation of easily biodegradable organics prevented clogging of GAC columns. However, CUR did hardly improve with organics-depleted urine compared to stored urine. The lowest CUR was achieved with nitrified urine. This resulted from the additional organics removal during nitrification and not the lower pH or the partial conversion of ammonium to nitrate. In addition, we showed that the relative pharmaceutical removal in all solutions was independent of the initial pharmaceutical concentration unless the background organics matrix changed considerably. We conclude that removal of micropollutants in GAC columns from organics-depleted urine can be performed without clogging, but with the drawback of a higher carbon usage compared to removal from nitrified urine.
Increasing urine nitrification performance with sequential membrane aerated biofilm reactors
Heusser, Aurea; Wackernagel, Isolde; Reinmann, Mauro; et al. (2024)
Water Research
This study aimed to investigate whether separating organics depletion from nitrification increases the overall performance of urine nitrification. Separate organics depletion was facilitated with membrane aerated biofilm reactors (MABRs). The high pH and ammonia concentration in stored urine inhibited nitrification in the first stage and therewith allowed the separation of organics depletion from nitrification. An organics removal of 70 % was achieved at organic loading rates in the influent of 3.7 gCOD d−1 m−2. Organics depletion in a continuous flow stirred tank reactor (CSTR) for organics depletion led to ammonia stripping through diffused aeration of up to 13 %. Using an MABR, diffusion into the lumen amounted for 4 % ammonia loss only. In the MABR, headspace volume and therefore ammonia loss through the headspace was negligible. By aerating the downstream MABR for nitrification with the off-gas of the MABR for organics depletion, 96 % of the ammonia stripped in the first stage could be recovered in the second stage, so that the overall ammonia loss was negligibly low. Nitrification of the organics-depleted urine was studied in MABRs, CSTRs, and sequencing batch reactors in fed batch mode (FBRs), the latter two operated with suspended biomass. The experiments demonstrated that upstream organics depletion can double the nitrification rate. In a laboratory-scale MABR, nitrification rates were recorded of up to 830 mgN L−1 d−1 (3.1 gN m−2 d−1) with ambient air and over 1500 mgN L−1 d−1 (6.7 gN m−2 d−1) with oxygen-enriched air. Experiments with a laboratory-scale MABR showed that increasing operational parameters such as pH, recirculation flow, scouring frequency, and oxygen content increased the nitrification rate. The nitrification in the MABR was robust even at high pH setpoints of 6.9 and was robust against process failures arising from operational mistakes. The hydraulic retention time (HRT) required for nitrification was only 1 to 2 days. With the preceding organics depletion, the HRT for our system requires 2 to 3 days in total, whereas a combined activated sludge system requires 4 to 8 days. The N2O concentration in the off-gas increases with increasing nitrification rates; however, the N2O emission factor was 2.8 % on average and independent of nitrification rates. These results indicate that the MABR technology has a high potential for efficient and robust production of ammonium nitrate from source-separated urine.
Optimizing control strategies for urine nitrification: narrow pH control band enhances process stability and reduces nitrous oxide emissions
Faust, Valentin; Boon, Nico; Ganigué, Ramon; et al. (2023)
Frontiers in Environmental Science
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.
Andere Wege für das Abwasser
Maurer, Max; Tilley, Elizabeth; Udert, Kai M. (2023)
Globe ~ Wasser
Die Wasserwirtschaft mit Kanalisation und zentralen Kläranlagen ist nicht mehr zukunftsfähig und global keine Lösung. Umweltingenieur:innen der ETH Zürich und der Eawag bereiten den Weg zu einer kreislauffähigen und dezentraleren Wasserinfrastruktur.
Resource-Efficient Nitrogen Removal from Source-Separated Urine with Partial Nitritation/Anammox in a Membrane-Aerated Biofilm Reactor
Timmer, Marijn J.; De Paepe, Jolien; Van Winckel, Tim; et al. (2024)
ACS ES&T Engineering
Source separation and decentralized urine treatment can cut costs in centralized wastewater treatment by diverting 80% of the nitrogen load in sewage. One promising approach for nitrogen removal from source-separated urine is partial nitritation/anammox (PN/A), reducing the aeration demand by 67% and organic dosage by 100% compared to nitrification/denitrification. While previous studies with suspended biomass have encountered stability issues during PN/A treatment of urine, a PN/A biofilm was hypothesized to be more resilient. Its use for urine treatment has been pioneered here for maximum rates and efficiencies in an energy-efficient membrane-aerated biofilm reactor (MABR). Nitrogen removal rates of 1.0 g N L⁻¹ d⁻¹ and removal efficiencies of 80–95% were achieved during a 335-day operational period at 28 °C on stabilized (pH > 11.5), diluted urine (10%). A balance between N2 and NO₃⁻ formation was observed while optimizing the supply of O₂ through intermittent aeration and was rate limiting for the conversion toward N2. A short-term operation on less- and undiluted urine yielded N removal rates of 0.6–0.8 g N L⁻¹ d⁻¹ and removal efficiencies of 93% on 66% urine and 85% on undiluted urine. Metataxonomic analysis and fluorescence in situ hybridization confirmed the presence in the biofilm of nitrifiers (Nitrosomonas, Nitrospira) at the membrane side and anammox bacteria (“Candidatus Brocadia”) at the anoxic bulk side. The findings suggest that a biofilm approach to PN/A treatment of urine overcomes stability issues and that a PN/A-MABR has significant potential for resource-efficient decentralized urine treatment. In human long-duration deep-space missions, this gravity-independent technology could produce N2 to compensate artificial atmosphere losses while facilitating water recovery from urine.
Conditions for successful nitrogen removal from source-separated urine by partial nitritation/anammox
Faust, Valentin; Markus, Philipp; Schielke-Jenni, Sarina; et al. (2024)
PLOS Water
Partial nitritation/anammox (PN/A) of source-separated urine is less energy-intensive and potentially cheaper and more environmentally friendly than conventional nitrogen removal from mixed sewage. However, PN/A of undiluted source-separated urine has not yet been established. In this study, the feasibility of PN/A for source-separated urine (total nitrogen ≈ 2 to 3 g-N L-1). To evaluate the influence of different factors, one- and two-stage configurations were operated using different influents, i.e. source-separated urine, synthetic urine, and urine with additional divalent cations. While partial nitritation was successfully achieved in both configurations with digester supernatant and urine, anammox activity was lost shortly after switching from digester supernatant to the urine influents. Toxic organic compounds or pharmaceuticals and the high monovalent to divalent cation ratio were suspected as causes of anammox failure, but were ruled out due to the different reactor configurations and influent compositions tested. Other suspected factors such as COD/N ratio, phosphate and sulfate inhibition, nitrogen compound inhibition, metal inhibition, pH and dissolved oxygen were also systematically excluded. Instead, the high salt concentration in urine compared to the digester supernatant most likely caused the reactor to fail due to the disintegration of large flocs, and the resulting challenge of biomass retention. The shortcomings of the floccular sludge system were overcome by using biofilm carriers, resulting in successful PN/A. This hybrid system ran for 140 days with nitrogen removal rates of up to 1000 mg-N L-1 d-1 with an average of 410 ± 220 mg-N L-1 d-1, and a nitrogen removal efficiency of 93 ± 3% at 30°C.
Environmental impact of integrating decentralized urine treatment in the urban wastewater management system: A comparative life cycle assessment
Appiah-Twum, Hanson; Van Winckel, Tim; Santolin, Julia; et al. (2025)
Water Research
As municipal wastewater treatment regulations become more stringent, integrating source-separated urine treatment into centralized urban wastewater management offers a ‘hybrid’ solution. However, it is not clear how the environmental impacts of such hybrid systems compare to highly efficient centralized wastewater treatment plants (WWTPs) with low N2O emissions and electricity use. In this study, a consequential life cycle assessment was used to compare the environmental impact of three urine separation hybrid wastewater treatment systems – which combine decentralized urine treatment with a highly efficient central WWTP– to a centralized WWTP treating mixed wastewater (baseline). The studied urine treatment systems include partial nitrification & distillation, struvite precipitation & stripping/scrubbing, and partial nitritation/anammox. Additionally, the environmental impact of urine pre-treatment by calcium hydroxide and electrochemical alkalinization methods on the partial nitrification & distillation system was evaluated. The results show that all hybrid scenarios have a lower environmental impact in the freshwater ecotoxicity, marine toxicity, freshwater eutrophication, and marine eutrophication categories compared to the baseline. However, all hybrid scenarios resulted in higher impacts on global warming compared to the baseline, with direct N₂O emissions being a key variable. Additionally, it was identified that urine alkalinization increased the environmental impact of the treatment system in 7 out of the 10 impact categories. A Pareto frontier analysis was developed to guide decision makers on where hybrid solutions could be used as a strategy to reduce the global warming impacts of conventional WWTPs. Using N₂O-N emission factors of 75 WWTPs, 87 % of centralized WWTPs had a lower global warming impact compared to partial nitrification & distillation, and 91 % compared to partial nitritation/anammox hybrid solutions. However, at electricity demands of 1 kWh/PE/day and 1.5 kWh/PE/day at the central WWTP, both hybrid solutions showed lower global warming impact than all the studied WWTPs. The study highlights the potential of hybrid wastewater treatment solutions as a strategy to reduce global warming impacts in WWTPs with high N₂O emissions and electricity use as well as a means to reduce marine eutrophication (i.e. nitrogen pollution).

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Kai M. Udert

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