Electrochemically induced precipitation enables fresh urine stabilization and facilitates source separation

Source separation of urine can enable nutrient recycling, facilitate wastewater management, and conserve water. Without stabilization of the urine, urea is quickly hydrolyzed into ammonia and (bi)carbonate, causing nutrient loss, clogging of collection systems, ammonia volatilization, and odor nuisance. In this study, electrochemically induced precipitation and stabilization of fresh urine was successfully demonstrated. By recirculating the urine over the cathodic compartment of an electrochemical cell, the pH was increased due to the production of hydroxyl ions at the cathode. The pH increased to 11-12, decreasing calcium and magnesium concentrations by >80%, and minimizing scaling and clogging during downstream processing. At pH 11, urine could be stabilized for one week, while an increase to pH 12 allowed urine storage without urea hydrolysis for >18 months. By a smart selection of membranes [anion exchange membrane (AEM) with a cation exchange membrane (CEM) or a bipolar membrane (BPM)], no chemical input was required in the electrochemical cell and an acidic stream was produced that can be used to periodically rinse the electrochemical cell and toilet. On-site electrochemical treatment, close to the toilet, is a promising new concept to minimize clogging in collection systems by forcing controlled precipitation and to inhibit urea hydrolysis during storage until further treatment in more centralized nutrient recovery plants

An appraisal of urine derivatives integrated in the nitrogen and phosphorus inputs of a lettuce soilless cultivation system

Reinforcing and optimizing sustainable food production is an urgent contemporary issue. The depletion of natural mineral resources is a key problem that is addressed by recycling mined potassium and phosphorus, and nitrogen, whose production depends on very high energy input. A closed-loop approach of fertilizer use asserts the necessity for efficient management and practices of organic waste rich in minerals. Human-derived urine is an underutilized yet excellent source for nitrogen fertilizer, and, in this study, processed urine fertilizer was applied to greenhouse soilless cultivation of lettuce (Lactuca sativa L.) cv. Grand Rapids. Biomass increase, biometric parameters, soil plant analysis development (SPAD) index, minerals, and organic acids content of lettuce were analyzed. From eight different urine fertilizer products generated, K-struvite, urine precipitate-CaO, and the liquid electrodialysis (ED) concentrate supported the growth of lettuce similar to that of commercial mineral fertilizer. ED concentrate application led to the accumulation of potassium (+17.2%), calcium (+82.9%), malate (+185.3%), citrate (+114.4%), and isocitrate (+185.7%); K-struvite augmented the accumulation of magnesium (+44.9%); and urine precipitate-CaO induced the highest accumulation of calcium (+100.5%) when compared to the control, which is an added value when supplemented in daily diet. The results underlined the potential of nitrogen- and phosphate-rich human urine as a sustainable source for the fertilization of lettuce in soilless systems

Nitrogen recovery from urine in Space : a case for nitrification

C

A five-stage treatment train for water recovery from urine and shower water for long-term human Space missions

Long-term human Space missions will rely on regenerative life support as resupply of water, oxygen and food comes with constraints. The International Space Station (ISS) relies on an evaporation/condensation system to recover 74-85% of the water in urine, yet suffers from repetitive scaling and biofouling while employing hazardous chemicals. In this study, an alternative non-sanitary five-stage treatment train for one "astronaut" was integrated through a sophisticated monitoring and control system. This so-called Water Treatment Unit Breadboard (WTUB) successfully treated urine (1.2-L-d with crystallisation, COD-removal, ammonification, nitrification and electrodialysis, before it was mixed with shower water (3.4-L-d(-1)). Subsequently, ceramic nanofiltration and single-pass flat-sheet RO were used. A four-months proof-of-concept period yielded: (i) chemical water quality meeting the hygienic standards of the European Space Agency, (ii) a 87- +/- -5% permeate recovery with an estimated theoretical primary energy requirement of 0.2-kWh p -L-1, (iii) reduced scaling potential without anti-scalant addition and (iv) and a significant biological reduction in biofouling potential resulted in stable but biofouling-limited RO permeability of 0.5 L-m(-2)-h(-1)-bar(-1). Estimated mass breakeven dates and a comparison with the ISS Water Recovery System for a hypothetical Mars transit mission show that WTUB is a promising biological membrane-based alternative to heat-based systems for manned Space missions

Urine recycling technologies for a circular future within and beyond terrestrial boundaries

L'objectiu d'aquesta tesi és el desenvolupament de tecnologies per al reciclat d'orina que siguin eficients en la utilització de recursos i que i) es puguin implementar en sistemes de suport de vida, com el Micro-Ecological Life Support System Alternative de l'Agència Europea de l'Espai o ii) que puguin ser emprats a la Terra com a sistemes de tractament d' orina locals/distribuïts. Com que els recursos són limitats a l'Espai, l'objectiu ha sigut assolir la màxima recuperació de nutrients amb el mínim cost energètic i l'ús dels materials per reduir les càrregues màssiques i minimitzar la necessitat de re-abastiment. Per això s' han investigat i posat a punt diverses alternatives de procés combinant etapes biològiques i fisicoquímiques.El objetivo de esta tesis es el desarrollo de tecnologías para el reciclado de orina que sean eficientes en el uso de recursos y que i) se puedan implementar en sistemas de soporte de vida, como el Micro-Ecological Life Support System Alternative de la Agencia Europea del Espacio o ii) que puedan ser utilizados en la Tierra como sistemas de tratamiento de orina locales/distribuidos. Como los recursos son limitados en el Espacio, el objetivo ha sido alcanzar la máxima recuperación de nutrientes con el mínimo coste energético y la utilización de los materiales para reducir las cargas másicas y minimizar la necesidad de reabastecimiento. Para ello se han investigado y puesto a punto distintas alternativas de proceso combinando etapas biológicas y físico-químicas.Human presence in outer space is currently supported by regular resupply of life support consumables from Earth. However, deep-space exploration or space habitation will depend on regenerative life support systems (RLSS) for in-situ oxygen, water and food production and waste management as resupply becomes practically impossible due to the long distance and transit time. Urine recycling is of key interest in RLSS to recover water and nutrients, which can serve as a fertiliser for plants and microalgae. Urine source separation and recycling also gains attention on Earth to shorten terrestrial nutrient cycles, which play a pivotal role in our food supply, but are currently pushed to their planetary boundaries by extensive synthetic fertiliser production and use. Nutrient recovery from waste streams could reduce the need for energy intensive ammonia production and mining of non-renewable phosphorus and potassium, and obviate the need for advanced nutrient removal to protect the environment. Amongst other streams, urine is targeted, as it presents the major nutrient source in domestic wastewater and has good fertilising properties. Other benefits stemming from urine source separation include the reduced water consumption for flushing and the decreased nutrient load and better effluent quality of wastewater treatment plants. The goal of this PhD thesis was to develop resource-efficient urine recycling technologies that i) can be implemented in RLSS, such as the Micro-Ecological Life Support System Alternative from the European Space Agency or, ii) used for on-site/decentralised urine treatment on Earth. As resources are scarce in space, the goal was to achieve maximum nutrient recovery with minimum energy expenditure and use of consumables in order to reduce payloads and to minimise the need for resupply. Different urine treatment trains combining biological and physico-chemical processes were investigated. Urine contains many valuable compounds, but the compositional complexity and instability present challenges for urine collection and treatment. Urea, the main nitrogen compound in urine, quickly hydrolyses into ammonia and (bi)carbonate, causing nutrient losses, odour nuisance, scaling and clogging by uncontrolled precipitation, and ammonia volatilisation. Therefore, an alkalinisation step was included to prevent ureolysis and to remove calcium and magnesium by controlled precipitation, thereby minimising the risk for scaling in the following treatment steps. In Chapter 2 and 3, NaOH was used to increase the pH of fresh urine, whereas Chapter 4 investigated the use of an electrochemical cell to avoid base consumption, the logistics associated with base storage and dosing, and the associated increase in salinity. Nitrification was applied to convert instable urea and/or volatile and toxic TAN into non-volatile nitrate in Chapter 2, 3 and 5. Three different reactors were employed: a pilot scale MBBR, a bench scale MABR and a bench scale MBBR. The MABR was preceded by a microbial electrolysis cell to remove the COD prior to nitrification. Full urine nitrification is preferred over partial nitrification because of the higher process stability and safety, but requires additional alkalinity to compensate for the proton release by nitrification. In Chapter 5, the nitrification reactor was coupled to a dynamically controlled electrochemical cell for in-situ OH- production as an alternative to base addition, enabling full nitrification. Nitrified urine can be applied as a fertiliser, but the nutrient concentrations are low compared to synthetic fertilisers. Hence, for terrestrial applications, a concentration step is preferred. Chapter 2 explored the feasibility of ED to concentrate nutrients, whereas, in Chapter 5, the electrochemical cell for pH control also functioned as concentration technology. Alternatively, nitrified urine can be valorised as culture medium for microalgae, which was investigated in Chapter 6.Universitat Autònoma de Barcelona. Programa de Doctorat en Biotecnologi

Urine treatment technologies for a circular future within and beyond terrestrial boundaries

Human presence in outer space is currently supported by a regular resupply of life support consumables from Earth. Deep-space exploration or space habitation will, however, depend on regenerative life support systems (RLSS) for in-situ oxygen, water and food production and waste management as resupply becomes practically impossible due to the long distance. Urine recycling is of key interest in RLSS to recover water and macro-/micronutrients, which can serve as a fertilizer for plants and microalgae. Urine source separation and recycling also gains attention on Earth to close and/or shorten the terrestrial nutrient cycles, which play a pivotal role in our food supply, but are currently pushed to their planetary boundaries by extensive synthetic fertilizer production and use. Nutrient recovery from waste streams could i) reduce the need for energy intensive ammonia production using the Haber-Bosch process and mining of non-renewable phosphorus and potassium, and ii) obviate the need for advanced nutrient removal to protect the environment. Amongst other streams, urine is targeted, as it presents the major nutrient source in domestic wastewater and has good fertilizing properties (i.e., contains all macro- and micronutrients required for plant growth). Other benefits stemming from urine source separation and recycling include the reduced water consumption for flushing and the decreased nutrient load and better effluent quality of wastewater treatment plants. The goal of this PhD thesis was to develop resource-efficient urine treatment technologies that i) can be implemented in RLSS, such as the Micro-Ecological Life Support System Alternative (MELiSSA) from the European Space Agency (ESA) or, ii) used for on-site/decentralized urine treatment on Earth. As resources are scarce in space, the goal was to achieve maximum nutrient recovery with minimum energy expenditure and use of consumables in order to reduce payloads and to minimize the need for resupply. Different urine treatment trains combining biological and physicochemical processes were investigated. Three main treatment steps were considered: (i) Alkalinization through chemical or electrochemical hydroxide addition to prevent urea hydrolysis during collection and storage, (ii) Biostabilization in a microbial electrolysis cell (MEC) and membrane-aerated biofilm reactor (MABR) or moving bed biofilm reactor (MBBR) to transform urine into a stable nitrate-rich urine solution low in organics, which is suitable for plant or microalgae cultivation, (iii) Concentration of the nitrified urine through electrodialysis or an electrochemical cell or valorization through microalgae cultivation in a photobioreactor. Urine contains many valuable compounds, but the compositional complexity and instability of urine presents a challenge for urine collection, treatment and reuse. Urea, the main nitrogen compound in urine, quickly hydrolyses into ammonia, ammonium and (bi)carbonate, causing nutrient losses, odor nuisance, scaling and clogging by uncontrolled precipitation, and ammonia volatilization. The latter can pose a health risk to the crew in a small space cabin, as ammonia is a toxic gas. Clogging of pipes by the precipitating salts is a common problem in nonwater urinals and urine-diverting toilets, and it is believed to be one of the major barriers for the widespread implementation of source separation. Therefore, an alkalinization step was included to prevent urea hydrolysis during collection and storage and to remove calcium and magnesium by controlled precipitation, thereby minimizing the risk for scaling in the following treatment steps. In Chapter 2 and 3, sodium hydroxide was used to increase the pH of fresh urine, whereas Chapter 4 investigated the use of an electrochemical cell to avoid base consumption, the logistics associated with base storage and dosing, and the associated increase in salinity. Sodium hydroxide addition or electrochemical OH− addition both yielded 80-90% of calcium and magnesium removal. About 30% to 80% of the phosphate was captured in the precipitates, which could be valorized as a slow-release P fertilizer in agriculture or as a resource for the phosphate industry. Alkalinization, followed by nitrification, also proved to be an effective strategy to safeguard the downstream units from excessive scaling. The alkalinized urine could be stored for several months without urea hydrolysis. Yet, urine is only temporarily stabilized by increasing the pH and still contains i) urea, which can easily hydrolyse when the pH is lowered or urease is added, and ii) biodegradable organics, which can cause biofouling. Therefore, the urine was further processed using bacteria, oxidizing organics (COD, chemical oxygen demand) and urea into CO2 and nitrate. Chapter 3 evaluated COD removal in a MEC. Up to 85% of the COD was removed at a COD loading rate of about 30 g COD m−2 d−1 in the MEC, which was dominated by (strictly) anaerobic genera, such as Geobacter (electroactive bacteria), Thiopseudomonas, a Lentimicrobiaceae member, Alcaligenes and Proteiniphilum. Electroactive bacteria transferred the electrons obtained by COD oxidation to the anode, generating an electric current of 0.5 and 2 A m−2, which was about 27-46% of the current that was expected based on the observed COD removal. Apart from COD removal, urea hydrolysis took place in the MEC, increasing the TAN/TN ratio from <10% (influent) to 100% (effluent). Overall, MEC treatment reduces the oxygen demand and limits biomass production in subsequent aerobic treatment, increases the urine alkalinity and can convert the chemical energy contained in organics into electrical energy. Nitrification was applied to convert instable urea and/or volatile and toxic TAN into non-volatile nitrate in Chapter 2, 3 and 5. Besides nitrification, treatment in the aerobic bioreactor yielded 90% COD removal in Chapter 2 and 5, whereas almost all biodegradable COD had been removed by a MEC prior to nitrification in Chapter 3. Three different reactors were employed: a pilot scale MBBR (Chapter 2), a bench scale MABR (Chapter 3) and a bench scale MBBR (Chapter 5). MABR reactors have a high oxygen utilization efficiency, compact design and are compatible with the reduced gravity conditions in space, but, due to their counter-diffusional biofilm, there is a higher risk for denitrification. Indeed, feeding the MABR directly with raw urine in Chapter 3 resulted in N loss (18%) due to denitrification, whereas pre-treatment in the MEC yielded full N recovery in the MABR. Due to the release of protons by nitritation and the limited alkalinity in urine, only about half of the TAN in urine can be converted into nitrate. Full nitrification can be achieved by hydroxide addition, typically using a base (e.g., NaOH), and is usually preferred over partial nitrification because of the higher process stability and safety. The alkalinization step provided some additional alkalinity, but this was not sufficient to obtain complete TAN conversion (Chapter 5). Therefore, the nitrification reactors in Chapter 2 and 3 were equipped with pH control (NaOH addition). In Chapter 5, the nitrification reactor was coupled to a dynamically controlled electrochemical cell to study in-situ electrochemical hydroxide production as an alternative to base addition, enabling full nitrification. Overall, stable, full urine nitrification was obtained in all nitrification reactors at urine concentrations of 17% to 40% (i.e., urine dilution factors of 6 to 2.5) and maximum loading rates between 200 and 300 mg N L−1 d−1 without substantial N loss. Nitrified urine can be applied as a fertilizer, but the nutrient concentrations are relatively low compared to synthetic fertilizers. Hence, for terrestrial applications, a concentration step is preferred in order to reduce the storage and transportation volumes. Chapter 2 explored the feasibility of electrodialysis (ED) to concentrate nutrients. About 70% of the ions were captured in 15% of the initial volume when the pilot installation was operated using a 20% urine solution at a volumetric salt loading rate of 240 mmol NaCl-eq L−1 d−1. Nitrate, phosphate and potassium were concentrated by factors 4.3, 2.6 and 4.6, respectively. Doubling the urine concentration from 20% to 40% further increased the ED recovery efficiency by 10% and decreased the volume ratio of diluate to concentrate from 5.8 to 4. Besides providing alkalinity to enable full nitrification, the electrochemical cell installed in the bioreactor in Chapter 5 functioned as concentration technology, yielding a clean acidic nitrate-rich side stream and a nitrate-depleted urine stream. Similar to ED, 70% of the nitrate could be recovered and a concentration factor of 3 was obtained. Alternatively, nitrified urine can be valorized as culture medium for microalgae. Chapter 6 provided a proof of concept for Limnospira indica cultivation on the nitrified urine produced in Chapter 5. Dilution proved to be important to obtain high N utilization efficiencies, as the N uptake is limited by the biomass concentration which is in turn limited by the light availability. Furthermore, supplementation with chemicals was required to obtain a high yield and N uptake. Nitrified urine supplemented with phosphorus, magnesium, calcium, iron, EDTA and trace elements was as effective as standard synthetic medium in terms of biomass production, nutrient uptake and protein yield. Urine precipitates harvested in the alkalinization step could potentially supply enough phosphorus, calcium and magnesium, requiring only external addition of inorganic carbon, iron, EDTA and (possibly) trace elements. Overall, this research opens opportunities for efficient resource recovery from urine during deep-space missions and for on-site/decentralized treatment on Earth. The process configuration of the treatment train can be tailored, offering versatility for applications on Earth and in space

Environmental and economic sustainability of the nitrogen recovery paradigm : evidence from a structured literature review

Our economy drives on reactive nitrogen (Nr); while Nr emissions to the environment surpass the planetary boundary. Increasingly, it is advocated to recover Nr contained in waste streams and to reuse it 'directly' in the agri-food chain. Alternatively, Nr in waste streams may be removed as N2 and refixed via the Haber-Bosch process in an 'indirect' reuse loop. As a systematic sustainability analysis of 'direct' Nr reuse and its comparison to the 'indirect' reuse loop is lacking, this structured review aimed to analyze literature determining the environmental and economic sustainability of Nr recovery technologies. Bibliometric records were queried from 2000 to 2020 using Boolean search strings, and manual text coding. In total, 63 studies were selected for the review. Results suggest that 'direct' Nr reuse using Nr recovery technologies is the preferred paradigm as the majority of studies concluded that it is sustainable or that it can be sustainable depending on technological assumptions and other scenario variables. Only 17 studies compared the 'direct' with the 'indirect' Nr reuse route, therefore a system perspective in Nr recovery sustainability assessments should be more widely adopted. Furthermore, Nr reuse should also be analyzed in the context of a 'new Nr economy' that relies on decentralized Nr production from renewable energy. It is also recommended that on-par technology readiness level comparisons should be carried out, making use of technology development and technology learning methodologies. Finally, by-products of Nr recovery are important to be accounted for as they are reducing the environmental burdens through avoided impacts

Combining (bio)electrochemical processes and nitrification for urine recycling in Space

Urine is an essential resource in regenerative life support systems (RLSS), as it presents a major flux of water and nutrients (e.g. nitrogen and phosphorus). Currently, on board of the International Space Station, only water is recovered from urine using physical-chemical processes and hazardous chemicals, while the nutrients are concentrated in a toxic brine. In this study, a novel treatment train for water and nutrient recovery from urine was investigated, combining (bio)electrochemical processes and nitrification. Since ammonia volatilization can pose a hazard to the crew, the urine (33% dilution) was first stabilized to prevent urea hydrolysis into NH3/NH4+ (total ammoniacal nitrogen, TAN) during storage. By recirculating the fresh urine over the cathodic compartment of an electrochemical cell, the pH was increased to 12 due to water reduction at the cathode (7 kC L-1 urine to reach pH 12). The high pH inhibited urea hydrolysis for over 18 months and triggered precipitation of bivalent cations (>85% Ca2+ and Mg2+ removal), reducing the downstream scaling potential. Subsequently, stabilized urine was treated in a microbial electrolysis cell (MEC) in order to remove the organics (chemical oxygen demand, COD). Up to 85% of the COD was removed, generating energy in the form of hydrogen gas at the cathode. A current production of 6-20 mA was obtained at COD loads of 200-340 mg COD d-1 and HRT between 2.5-6.7 days, corresponding to coulombic efficiencies of 25-45%. The MEC community was dominated by, amongst others, members to the genera Geobacter, Pseudomonas, Arcobacter and Comamonas, known to comprise electroactive bacteria, i.e., bacteria capable of transporting electrons to an electrode. Besides COD oxidation, the MEC hydrolysed 80-100% of the organic nitrogen, resulting in a TAN-rich COD-low stream, which was fed into a membrane aerated biofilm reactor (MABR) composed of three parallel modules with hollow fiber membranes in order to convert TAN into non-volatile and non-toxic nitrate by nitrification. Full nitrification (effluent TAN and NO2--N <10 mg N L-1) was obtained at a loading of 200-230 mg N L-1 d-1 (HRT between 5.5-8.8 days), without N loss when the MABR was operated on MEC effluent, whereas denitrification and partial nitrification occurred when the MABR was operated at the same N loading rate on raw stabilized urine without a MEC pre-treatment. In-situ electrochemical pH control was implemented in the recirculation loop of a nitrification reactor in order to enable full nitrification without base addition. Hydroxyl production at the cathode compensated for the acidification by nitrification. The treatment train yielded a stable nitrate-rich nutrient solution, suitable for microbial protein production based on microalgae, for instance belonging to the cyanobacterial genus Limnospira, previously described as Arthrospira (‘Spirulina’). Supplementation with phosphorus and micronutrients yielded a >80% conversion of nitrate-N into edible biomass. Since the oxidation of COD and N in the MEC and MABR is not based on bubble-dependent gas/liquid mass transfer, the concept is compatible with microgravity conditions. Moreover, by integrating electrochemical cells in the treatment train, the use of chemicals and the logistics related to their storage can be minimized. As a highly N- and resource-efficient technology train, the concept can be useful for MELiSSA (micro-ecological life support system alternative), the RLSS programme from the European Space Agency (ESA), as well as for other RLSS