WO2023286090A1

WO2023286090A1 - Bioreactor system and process for nitrate production

Info

Publication number: WO2023286090A1
Application number: PCT/IS2022/050004
Authority: WO
Inventors: Amanda Key LUTHER; Hakon Örn BIRGISSON; James Edward MCDANIEL; Helga Dögg FLOSADOTTIR
Original assignee: Atmonia Ehf.
Priority date: 2021-07-16
Filing date: 2022-07-08
Publication date: 2023-01-19

Abstract

A process and system are provided to carry out continuous conversion of ammonia to nitrate, delivering a high-concentration nitrate solution and makes possible to bypass conventional processes with substantial reduction of greenhouse emission equivalents. The process and system of the present invention is robust and simple and can advantageously be operated on small scale such as on individual farms for on-site use but also in large scale facilities.

Description

Bioreactor System and Process for Nitrate Production

FIELD OF INVENTION

The invention is within the field of nitrate fertilizer production and specifically relates to bioreactor systems and processes for making nitrate fertilizer from ammonia, which systems can be operated on large or small-scale, for example at individual small farms. The systems can operate at high salinity and provide high-concentration fertilizer solutions that are ready for use or can be concentrated/processed further.

TECHNICAL BACKGROUND AND PRIOR ART

Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate, typically and most frequently carried out by separate organisms, which may include ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA), and nitrite oxidizing bacteria (NOB), but can also take place through direct ammonia oxidation to nitrate in comammox (Complete Ammonia Oxidation) bacteria. In the context of this application, the term “nitrifiers” is used to refer to any one or combination of these microorganisms. Nitrification is an important step in the nitrogen cycle in soil.

Synthetic fertiliser is a key component of modern agriculture but the production thereof by conventional processes is very energy demanding. It is estimated that industrial production of ammonia through the Haber process accounts for about 2% of man-made carbon emissions and 3-5% of natural gas use:

N₂ + 3H₂ ® 2 NH₃

Ammonia is typically converted industrially to ammonium nitrate via the Oswald process that converts ammonia to nitric acid, the overall reaction can be described as:

NH_3(g) + 20_2(g) ® H₂0 + HN0_{3 (}aq)

The process involves high -temperature oxidation of ammonia over a catalyst to form nitric oxide, followed by oxidation of the nitric oxide to nitrogen dioxide and absorption in water to produce and aqueous solution of nitric acid. This process however has a high carbon footprint as it releases greenhouse gas emissions which include unreacted nitrogen oxides, mainly NO and N₂0. Nitrous oxide (N₂0) is a powerful greenhouse gas, being about 300 times more potent than carbon dioxide. While these emissions can be reduced by emission reduction technologies e.g. by alkaline scrubbing or other abatement technologies, these have yet to be generally applied widely in nitric acid plants. According to the IPCC (2006 IPCC Guidelines for National Greenhouse Gas Inventories, ed. Eggelston et al.) high pressure nitric acid plants generally have the highest emission factor (~12 kg N₂0/tonne nitric acid), ahead of medium (~7 kg N₂0/tonne nitric acid) and atmospheric ammonia combustion plants (~5 kg N₂0/tonne nitric acid). Although atmospheric plants have attractively low N₂0 emissions they are not considered to be state of the art for other reasons, in particular their high capital investment cost and higher NOx emissions. (Grovers & Sasonow, J Integrative Env. Sci, Vol. 7, No. S1 , 2010, pp. 211-222.)

To obtain ammonium nitrate the nitric acid is reacted with ammonia in an acid base reaction. HNOs + NH₃ ® NH4NO3

Potassium nitrate can likewise be formed by neutralizing nitric acid with potassium hydroxide:

On industrial scale it is however generally prepared by displacement reaction between sodium nitrate and potassium chloride

NaN0₃ <aq) + KCI (aq) ® NaCI (aq) + KNO3 (aq)

Processes and systems have been disclosed in the recent prior art for producing ammonia via less energy intensive processes based on electrolysis, converting N₂ to ammonia, see WO 2015/189865.

Processes for making nitrate fertiliser with less environmental impact and in particular with less carbon footprint, or even more preferably with negative carbon footprint, would be highly beneficial.

SUMMARY

This invention provides a process and system to carry out continuous conversion of ammonia to nitrate, delivering a high-concentration nitrate solution and makes possible to bypass conventional processes with substantial reduction of greenhouse emission equivalents. The process and system of the present invention is robust and simple and can advantageously be operated on small scale such as on individual farms for on-site use but also in large-scale facilities. The system can receive ammonia produced electrolytically, e.g., by applicant’s prior art system as disclosed in WO 2015/189865, but is not limited thereto.

With the system and process of the invention ready-for-use liquid fertilizer can be produced with nitrate concentration that can be 3% or higher and preferably 4% or higher such as 5% or higher such as 6% or 7% or 8% or 10%. Percentages of nitrate as used herein refer to w/v based on the weight of the nitrate ion NO3-. When “salinity” is used herein we refer to % (w/v) total salt concentration, Thus, for KNO3 solutions, 3% salinity is a 3% KNO3 (w/v) solution, which has a molarity of 0,30M. (This corresponds to a nitrate concentration, %(w/v) NO3^·, of 1 ,84%.) The obtained high nitrate concentrations in the reactor output stream makes possible effective distribution of the fertilizer solution directly onto fields. If desired, the product effluent from the system can be further concentrated to obtain an even more concentrated fertiliser solution. These ranges of salinity comprise such concentrations that the nitrifiers used in the process must have some level of halotolerance, i.e., are adapted, e.g., through selective growth (environmental enrichment) in laboratories, through genetic selection, or through natural adaptation, to grow in a halophilic environment. The term halophilic environment is a term known in the art and generally refers to a high-saline environment, typically in the context of discussing microorganisms found in said environment. Furthermore, the nitrifiers in the present invention must be halotolerantto specific nitrate-based salts, which may or may not require different or additional adaptive traits compared to halotolerant microorganisms adapted to saline environments based on, for example, sodium chloride.

An aspect of the invention provides a system for producing nitrate from ammonia, comprising at least one bioreactor comprising carrier with immobilized nitrifier organisms that are able to carry out conversion of ammonia to nitrate, aqueous reactor medium, and one or more aerator. The aqueous reactor medium is chemically pure and defined, meaning that it comprises desired known and suitably adjusted concentration of ingredients (salts, essential minerals, eventual buffering components etc.) and is not comprised of wastewater or other ill-defined medium with potential contamination of other microbes.

The bioreactor can be any of various types known as such in the art and which are suited for immobilised nitrifier microorganism and effective ammonia conversion. Such reactors include but are not limited to moving bed biofilm reactors (MBBR), continuous stirred tank reactors (CSTRs), packed bed reactors (PBRs), fluidized bed reactors (FBRs), airlift reactors (ALRs), upflow anaerobic sludge blanket (UASB) reactors, and expanded granular sludge bed (EGSB) reactors. The nitrifier microorganisms are preferably provided as a biofilm immobilized on synthetic carrier. Such carrier can be comprised by but is not limited to one or more of discs, pellets, beads, and nets, where a suitable carrier may be selected depending on the type of reactor chosen. Various such carriers are as such known in the art and can be suitable selected by the skilled person, depending on the scale of the system and other operating conditions. In some embodiments of the invention, the microorganism bio culture serves at its own carrier, i.e. aggregate to form granules. Such granular bio culture comprising the microorganisms of the bioreactor are also within the scope of the invention. In such embodiments granulation enhancers or starter cultures may be added to initiate and/or facilitate granulation of the microorganisms.

As understood from above, the nitrifier microorganisms are preferably grown to form a biofilm on the selected carrier of the system. The nitrifier organisms are selected so as to provide efficient conversion to nitrate, in a well-defined optimised pure medium. In some embodiments the nitrifiers are selected from one or more species from ammonia oxidizing bacteria, ammonia oxidizing archaea, nitrite oxidizing bacteria, and comammox bacteria. In some embodiments the nitrifiers comprise one or more species from Nitrosomonas spp., Nitrospira spp, Nitrosospira spp., Nitrososphaera spp., Nitrosotalea spp., Nitrosoarchaeum spp., Nitrobacter spp., Nitrosococcus spp. Nitrospina spp. , and Nitrococcus spp. Thus, in some embodiments the nitrifiers comprise one or more species of Nitrosomonas europaea, Nitrosococcus halophilus, Nitrosomonas mobilis, Nitrosococcus watsonii, and Nitrospira inopinata. The nitrifier microorganisms are preferably environmentally enriched, by cultivating seed inoculum in optimized well defined growth medium, such as is further described herein. In such embodiments initial inoculum may be initially grown in starter medium, e.g. with lower content of salt or nitrate in particular, and then the medium is slowly adapted to higher concentrations, to enrich for the microorganisms in the system that thrive at such conditions. The system and process of the invention make use of halophilic nitrifier microorganisms. The terms halophilic and halophile as used herein refer to microorganisms that thrive in saline conditions and may include slight halophiles (herein referred to as those that thrive at a salt concentration in the range of about 1 ,7%-4,7% NaCI (corresponding to about 2, 9-8,1% KN03 salinity on an equimolar basis), moderate halophiles (typically meaning those that thrive at a salt concentration in the range of about 4,7-20% NaCI (corresponding to ~8, 1 -35% KNO3 salinity on an equimolar basis). Thus, in some embodiments moderate halophilic nitrifier microorganism are used whereas in some embodiments slight halophiles are used or a mixture of slight halophiles and moderate halophiles. In the prior art, the above definition of halophiles typically refers to concentration of sodium chloride or salt such as in seawater, which is 90% NaCI; in the present case the use of halophilic microorganisms in the invention does not indicate a high content of NaCI, in fact as described below the invention preferably is based on medium with relative low concentration of NaCI but high concentration of other salts, in particular one or more nitrate salts. Such suitable organisms can be selected and are preferably enriched for under the selected suitable conditions, in accordance with the invention. In halophilic embodiments, high salt concentration (high salinity) medium is used, which is suitable for the halophilic nitrifiers used, and at the same time such medium minimizes biofouling (growth of unwanted microorganisms). The high salt concentration is in useful embodiments obtained by a high concentration of nitrate salt, such as one or more of potassium nitrate, calcium nitrate, ammonium nitrate and sodium nitrate or a combination of two or more of those. Thus, typically the desired high salt concentration is provided in the initial medium when starting a system of the invention, the system is then fed with ammonia and water, and product effluent (nitrate solution) drained off the system while maintaining an equilibrium nitrate concentration in the reactor. A solution of base is fed to the system to maintain an optimal pH and will determine the main counter ion of the nitrate salt. The influent ammonia is in some embodiments provided as ammonia solution, also referred to as ammonia water or ammonium hydroxide, denoted as NH3(aq) or NH₄0H(aq). In other embodiments the ammonia is provided as gas fed directly to the reactor tank, where the gas is dissolved. Also, in some embodiments ammonia gas may be fed into a separate tank where it is dissolved in water or medium, which is then fed into the reactor tank. As understood from above, the product nitrate in the reactor tank preferably serves as well as the main salt component of the medium, providing the high salinity. Accordingly, in some embodiments the medium comprises a nitrate content of about 2% or higher (calculated as w/v of NO3), such as about 2% or 2,5%, and preferably of about 3% or higher and more preferably or of about 4% or higher, and more preferably of about 5% or higher, such as about 6% or higher, such as about 7% or higher, such as about 8% or higher, such as about 9% or higher, such as about 10%, or even higher. The nitrate can advantageously be provided by but is not limited one of potassium nitrate, calcium nitrate, ammonium nitrate or a combination of two or more nitrate salts. The nitrate concentration can advantageously be indicated as an equivalent concentration of KNO3 though the nitrate may be provided by one or more other salt or a combination of KNO3 and another salt. Thus, in some embodiments the reactor medium will comprise an equilibrium concentration of nitrate corresponding to at least 2,9% KNO3 and preferably the medium has an equilibrium nitrate concentration corresponding to at least 4% KNO3, more preferably corresponding to at least 5% KNO3, yet more preferably corresponding to at least 6% KNO3, even more preferably corresponding to at least 7% KNO3. Total amount of the respective nitrate salt(s) is decided so as to provide the desired concentration of nitrate as recited above. The ratio between the anion (nitrate) and respective cation(s) (e.g. potassium, calcium or ammonium) does not need to correspond to ratio of forming a neutral salt in the solution from those ions, i.e. one nitrate ion against one potassium ion, two nitrate ions against one calcium ion, or one nitrate ion against one ammonium ion, etc. In some embodiments there may be imbalance of any size between the nitrate anion and specified cations in the solution. Also, the mentioned common nitrate salts are readily soluble in water and will thus interact ionically with any cation source in the medium. As can be understood from herein, in typical embodiments, the output effluent has the same nitrate concentration as the medium.

A chosen desired reactor medium salinity may depend on several factors, such as a balance between obtaining a high conversion rate and obtaining a high product concentration.

It is an advantage of the invention that the reactor medium is a well-defined pure aqueous medium, optimized for efficient conversion of ammonia to nitrate. The medium preferably comprises minerals essential for the nitrifier organisms, such as one or more of CO2 (which may be provided as carbonate CO3²), N, P, K, Na, B, Ca, Fe, Cu, Mg, Mn, Mo, and Zn. And preferably the medium includes all of these elements. As mentioned, the medium can have a high salinity, such as a w/v content of salt of 4% or higher, in particular such as recited above. Such high salinity medium may however contain a relatively low content of other salts than the preferred selected nitrate salt(s), thus, the medium may contain less than 1% NaCI (w/v), or less than 0,5% NaCI, or less than 0,2% NaCI or even less.

A system according to the invention can be batch-operated, batch-fed, semi-continuous or continuous. The system preferably comprises a PLC control system for monitoring and maintaining system conditions, this would in particular be useful as part of a continuous operation system. A control system preferably comprises sensors including a pH sensor, dissolved oxygen sensor, and preferably as well one or more of a temperature sensor and chemical sensors, such as for monitoring ammonia, nitrate, and optionally further sensors for other chemical entities. The control system is preferably also connected to a compressor or blower for feeding the aerator of the system. The control system may also be connected to controllable valves for controlling inflow of reactant, medium and/or medium components, and pH adjusting component (e.g. alkaline solution such as KOH).

The system is in some embodiments temperature controlled, e.g. comprising a heating element and thermostat, in such embodiments the temperature can be maintained for example in the range of about 15-30°C. In other embodiments the system is operated at ambient temperature that may fluctuate but is preferably above at least 10°C and more preferably above about 15°C and yet more preferably above about 20°C. In some embodiments the system is arranged in an indoor facility, which allows for control of the ambient temperature, which in some embodiments is maintained at a range of about 15 to about 35°C, such as within a range of about 15 to 30°C or 20 to 30°C, such as in the range of about 20 to 25°C.

Another aspect of the invention provides a process for production of nitrate from ammonia. The process comprises feeding ammonia into a bioreactor that comprises a carrier with immobilized nitrifier microorganisms that carry out conversion of ammonia to nitrate and an aqueous reactor medium, aerating said medium, feeding the reactor with ammonia and feeding product effluent from said bioreactor to obtain a nitrate product solution. The reactor is preferably a reactor as described above and the reactor medium, nitrifier microorganisms and conditions preferably also as described above.

FIGURES

Figure 1 shows a schematic illustration of a bioreactor of the invention, showing nitrifier carrier and illustrating heat distribution and liquid flow direction.

Figure 2 illustration of continuous-flow bioreactor system.

Figure 3 shows KNO3 concentration in three reactor runs over a 100-day period (see Example 2), showing maintained stable salinity in the range 3-3,5%.

Figure 4 shows ammonia input in the same runs as shown in Figure 3, measured for the same 100- day period.

Figure 5 Figure 5 shows measured nitrate output for the same runs from Example 2 shown in Figures 3 and 4.

EXAMPLES

Example 1 : Bioreactor setup

Eight 25 L reactors were constructed to generate nitrate from aqueous ammonia from a microbial enrichment for the purpose of hydroponic plant cultivation. A working volume of 20 L in each reactor was used to cultivate and enrich nitrifying microorganisms from an inoculum source under different growth conditions.

A schematic of the reactors is shown in Figure 1. Each reactor consists of a 25 L plastic container (A) with a sealable lid, equipped with a waterproof heating element (G) with temperature control (F) (Trixie Aquarium Heater, 50 W) to provide a consistent temperature of approximately 28°C, and an external air pump continuously pumping air (pressure: >0,025 MPa; output: 5,5 L/min) through a feed line (B) into the reactor through an aerator (H) (air stone), which may be contained inside a small plastic basket/suspension container (C) within the reactor. Different carriers (D) were tested to serve as substrates for biofilm attachment, including ceramic tubes (750 g ceramic tubes per bioreactor; ZooBest ceramic aquarium filter tubes) and 3D-printed polylactic acid (PLA) carriers (white PLA filament) with a spherical gyroid geometry. Carriers were placed in the basket where the air stream is introduced. Each reactor has a removable lid allowing access for chemical adjustments and monitoring. In this setup the containers were not hermetically sealed. The right-hand panel of Figure 1 shows heat distribution and liquid flow direction with aeration visualized in the bioreactor. The reactor pH was controlled between 6,5 and 8,5 by addition of base, either potassium hydroxide or calcium hydroxide, and acid (phosphoric acid, H3PO4) as needed. Reactors were operated as fed-batch systems, where ammonia was fed at regular intervals and the nitrate product was allowed to accumulate in the reactor. Different tests were performed with the reactors to compare the nitrification activity of the enriched cultures in different medium, and to compare the effect of different carriers. The different media tested included a complete nutrient medium containing all trace nutrients (CO2, N, P, K, Na, B, Ca, Fe, Cu, Mg, Mn, Mo, and Zn; see Table 1) known to be required for the growth of common ammonia oxidizing and nitrite oxidizing microorganisms, which was formulated to also be compatible with the needs and sensitivities of the plants that would be grown with the effluent from the bioreactors as fertilizer. Tap water alone or supplemented with select nutrients was also tested as a medium.

Table 1 : Nutrient medium recipe

These elements are provided by calcium carbonate, magnesium sulfate, and two commercial fertilizer products from Yara: Yara Tera Super FK30, and Yara Tera Rexolin (micronutrient mix). Suitable nutrient mix can be further adapted or different commercial fertilizers can be used or combined fit for application.

Spent mushroom compost from mushroom producer Flijdasveppir, Iceland (brand name: “Lifraenn massi”) was tested as inoculum source out of an interest in utilizing locally-sourced nitrifiers. To begin the enrichment of nitrifiers from this source, the compost was first moistened with tap water then mixed with 750 g ceramic tubes and sealed in a dark container for one week, near a radiator within a climate chamber to increase microbial activity. After the incubation period, organic debris was removed from the tubes before they were introduced to the reactors. Enrichments in both nutrient medium and water were able to demonstrate 95% nitrate production efficiency and reached 1% potassium nitrate salt. Example 2: Halophilic bioreactor

The enrichment cultures from Example 1 were adapted to increasing concentration of potassium nitrate in a batch system, specifically a fed-batch system, and then transitioned to a continuous system.

The batch system in this Example uses the same hardware as in Example 1 , with the addition of automated pH control, new carriers (Mutag biochip, Multi Umwelttechnologie AG), elimination of the basket/suspension container, and continuous ammonia feeding. For continuous operation it was further adapted for continuous media input, and effluent removal. Carriers were filled to 10% of the working volume, but this can be increased up to 60%. Ammonia feeding rates are started very low and increased stepwise as the nitrifying activity increases. No acid is dosed in this system, and base such as KOH or Ca(OH)2 is added to control the pH. Salt concentration (potassium nitrate or calcium nitrate) increases as nitrate is produced by the nitrifiers. Minimal nutrient medium (see above) is used as the basic medium, potassium carbonate is added as needed as a carbon source to support biomass growth.

This enrichment was adapted to 2,4% NO3- (or 3,9% KN03), a similar growth rate as observed at lower salt concentrations was maintained, and with 90% nitrate production efficiency.

This system is used to adapt this or new inocula to higher salt concentrations. In this example, the initial inoculum was taken from a non-saline environment, and slowly adapted to higher salt concentrations. Another approach is to take inocula from high salinity environments, e.g., sea water, salt lakes, salterns, aquaculture facilities, certain food production facilities, or other hypersaline environments. Different species of bacteria and archaea are likely to be enriched due to the differences in environments, and suitable bacteria can be selected based on efficiency measurements.

Besides environmental enrichment, pure cultures of specific known halophilic nitrifiers can be used in the system.

In case an inoculum or culture is requiring a certain threshold of salt to survive, the growth system is initiated at such salt concentration by addition of nitrate salts to the medium at startup.

The system can be operated for fertilizer production, where part of the reactor content is drained (such that sufficient liquid remains to cover the biocarriers) for use between batches, then nutrient feed and ammonia feed are dosed stepwise to avoid dilution of the medium below a certain minimum salt threshold that is safe for the halophilic biomass.

Higher % NC were then also tested under continuous operation. Three replicate tests maintained 3- 3,5% salinity over 100 days, with confirmed activity and stable output. The replicability between the three reactors was good. Figure 3 shows KNO3 concentration in the three reactor runs over a 100 day period, showing maintained stable salinity in the range 3-3,5%.

Figure 4 shows ammonia input to the reactors, measured for the same 100-day period. Figure 5 shows measured nitrate output. Substantially steady output rates were achieved, with efficiency near 100% (+/- measurement error). The efficiency can be seen because nitrate output and ammonia input in Figures 4 and 5 are shown in the same units, showing substantially similar values and approx. 100% efficiency, integrated overtime.

A number of enrichments (enriched halophilic bacteria) sourced from various environments have been demonstrated to carry out nitrification at higher salinity, in the range of about 5-7% (w/v KNO3) in multiple fed batch tests over a period of 1 to 3 months. Specific ammonia oxidation and nitrite oxidation rates have been determined for at least one of these enrichments over a range of 1-7% KNO3.

Example 3: Continuous-flow bioreactor

The continuous flow reactor has additional input flow control of water and nutrient solution, a level control system for effluent withdrawal, and a baffle to retain the carriers in the reactor tank. Aeration, pH control, and automated ammonia feed is part of the system. The flow rate is based on the residence time required for the system to maintain steady production of nitrate at a specific rate. The specific rate depends on the specific activity of the nitrifiers and volume of carriers used.

The effluent is stored in a separate tank and can be used directly as fertilizer, or if higher concentrations are needed a secondary filtration system (e.g., reverse osmosis, electrodialysis) can be coupled to the nitrification system. For use in hydroponic systems, a secondary filtration or UV treatment system can be coupled to reduce biomass carry-over.

A schematic illustration of the system is shown in Figure 2. Bioreactor tank (1) includes biofilm carriers (2) with nitrifier microorganisms. An aerator unit (3) is coupled to a compressor/blower (not shown). Effluent with product is transmitted via effluent line (5) to product tank (4). A PLC (6) controls the system and is coupled to a pH sensor (14), temperature sensor (13) and chemical sensors (15-18). The PLC is connected to valves (11 , 12, 20) for controlling input dosing of ammonium gas or ammonium hydrate (8), a base (9) and nutrient solution (10). A vent (15) releases excess air and water is fed via a valve (23) and line (7). The chemical sensors shown measure dissolved oxygen (“DO”) (15), NO3^· (16), NO₂ ^· (17), and NH₄ ⁺ (18).

The high salt concentration of the effluent however provides enhanced stability to the effluent, but for longer storage, alternative or additional methods may be used for enhancing shelf-life. Further concentration can solve this, or acidification. Nitrate production rates can be further increased by addition of carriers, up to 60% (v/v).

As used herein, including in the claims, singular forms of terms are to be construed as also including the plural form and vice versa, unless the context indicates otherwise. Thus, it should be noted that as used herein, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.

Throughout the description and claims, the terms “comprise”, “including”, “having”, and “contain” and their variations should be understood as meaning “including but not limited to”, and are not intended to exclude other components. The present invention also covers the exact terms, features, values and ranges etc. in case these terms, features, values and ranges etc. are used in conjunction with terms such as about, around, generally, substantially, essentially, at least etc. (i.e. , "about 3" shall also cover exactly 3 or "substantially constant" shall also cover exactly constant). The term “at least one” should be understood as meaning “one or more”, and therefore includes both embodiments that include one or multiple components. Furthermore, dependent claims that refer to independent claims that describe features with “at least one” have the same meaning, both when the feature is referred to as “the” and “the at least one”.

It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention can be made while still falling within scope of the invention. Features disclosed in the specification, unless stated otherwise, can be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed represents one example of a generic series of equivalent or similar features.

Use of exemplary language, such as “for instance”, “such as”, “for example” and the like, is merely intended to better illustrate the invention and does not indicate a limitation on the scope of the invention unless so claimed. Any steps described in the specification may be performed in any order or simultaneously, unless the context clearly indicates otherwise.

All of the features and/or steps disclosed in the specification can be combined in any combination, except for combinations where at least some of the features and/or steps are mutually exclusive. In particular, preferred features of the invention are applicable to all aspects of the invention and may be used in any combination.

Claims

1. A system for producing nitrate fertilizer from ammonia, comprising at least one bioreactor comprising carrier with immobilized nitrifier microorganisms which include halophilic bacteria and/or archaea, for carrying out conversion of ammonia to nitrate, chemically pure and defined aqueous reactor medium that comprises an equilibrium nitrate concentration corresponding to at least 2,9% KNO3 and one or more aerator.

2. The system of claim 1 , wherein said medium has an equilibrium nitrate concentration corresponding to at least 4% KNO3, and preferably at least 5% KNO3, more preferably corresponding to at least 6% KNO3, yet more preferably at least 7% KNO3.

3. The system of any of the preceding claims wherein said chemically pure and defined aqueous reactor medium further comprises one or more substance or element selected from CO2, P, K, Na, B, Ca, Fe, Cu, Mg, Mn, Mo, S, and Zn.

4. The system of any of claim 1 to 3, wherein said nitrifier microorganisms comprise one or more species selected from ammonia oxidizing bacteria, ammonia oxidizing archaea, nitrite oxidizing bacteria, and comammox bacteria, such as one or more of Nitrosomonas spp., Nitrospira spp, Nitrosospira spp., Nitrososphaera spp., Nitrosotalea spp., Nitrosoarchaeum spp., Nitrobacter spp., Nitrosococcus spp. Nitrospina spp., and Nitrococcus spp.

5. The system of any of the preceding claims, wherein said carrier comprises a plurality of carrier units selected from discs, pellets, beads, flakes and grids.

6. The system of the preceding claim wherein said carrier units comprise a porous structure or pattern to increase surface area for biofilm immobilization.

7. The system of any of the preceding claims, comprising a pH sensor.

8. The system of any of the preceding claims comprising a control unit that comprises a computer, sensors coupled to said computer and arranged to transmit signals to said computer, and valves operable by said computer.

9. The system of the preceding two claims, wherein said control unit is connected to said pH sensor, and connected to one or more valve for controlling inflow from one or more compartment of one or more pH adjusting agent(s), based on signals from the said pH sensor.

10. The system according to any of the preceding claims wherein the system is selected from a batch-operated system, a batch-fed system, a continuous-flow system and a semi-continuous system.

11. The system according to the preceding claims, providing as output a nitrate solution with at least 2% nitrate (w/v).

12. The system according to any of the preceding claims, providing as output a nitrate solution with at least 3% nitrate (w/v), and more preferably at least 4% or at least 5% or at least 6% or at least 7% or at least 8% or at least 9% or at least 10% nitrate.

13. The system according to any of the preceding claims, which is integrated with an electrolysis unit providing ammonia electrolytically produced from N2.

14. A process for producing nitrate from ammonia comprising feeding ammonia into a bioreactor that comprises a carrier with immobilized nitrifier microorganisms which include halophilic bacteria and/or archaea, which carry out conversion of ammonia to nitrate and a chemically pure and defined aqueous medium that comprises a nitrate concentration corresponding to at least 2,9% KNO3, aerating said medium, feeding product effluent from said bioreactor to obtain a nitrate solution.

15. The process of the preceding claim wherein said nitrifier microorganisms comprise one or more species selected from Nitrosomonas spp., Nitrospira spp, Nitrosospira spp., Nitrososphaera spp., Nitrosotalea spp., Nitrosoarchaeum spp., Nitrobacter spp., Nitrosococcus spp. Nitrospina spp., and Nitrococcus spp.

16. The process of any of the preceding two claims, wherein said conversion of ammonia to nitrate is carried out in said medium with an equilibrium nitrate concentration corresponding to at least 2,9% KNO3 and preferably at least 4% KNO3, more preferably at least 5% KNO3, yet more preferably corresponding to at least 6% KNO3, even more preferably corresponding to at least 7% KNO3.

17. The process of any of the preceding three claims, wherein said chemically pure and defined aqueous reactor medium further comprises one or more substance or element selected from CO2, P, K, Na, B, Ca, Fe, Cu, Mg, Mn, Mo, S, and Zn.

18. The process of any of the preceding three claims, which is continuous flow process, and wherein a control system monitors and controls system conditions including pH and nitrate concentration in said reactor medium.