Gaseous ammonia (NH3) recovered from residual waters may be used as a fuel in solid oxide fuel cells (SOFCs) to generate electricity without emission of undesirable oxidised nitrogen species. NH3 can be directly recovered from water as a gas by vacuum membrane stripping (VMS), which also results in the evaporation of water (H2O), leading to the recovery of NH3-H2O mixtures. However, in currently available literature, information is lacking on the NH3 concentrations in NH3-H2O mixtures that may be used as a fuel for an oxygen-conducting SOFC (SOFC-O). In this study, we assessed the effect of feed water temperature and the NH3 feed water concentration on the NH3 concentrations in gaseous VMS permeate. Besides, we assessed the feasibility to use NH3-H2O mixtures in the concentration range between 5 and 25 wt% for the generation of electricity in an SOFC-O. The results show that increasing the NH3 feed water concentration from 1 to 10 g∙L−1 increased the NH3 concentration in the gaseous VMS permeate from 1 wt% to up to 11 wt%. Increasing the feed water temperature from 25 to 35 °C also results in an increase in the NH3 concentration in the gaseous permeate, whereas increasing the feed water temperature from 35 °C to 55 °C leads to dilution of the VMS permeate. Furthermore, electricity was generated at an electrical efficiency of 43% in an SOFC-O when the NH3 concentration in the NH3-H2O fuel was only 5 wt%. Hence, according results on the obtained NH3 concentrations in the gaseous VMS permeate and the generation of electricity using dilute NH3-H2O mixtures as a fuel, VMS and SOFC-O can be combined for the generation of electricity from NH3 recovered from water. Moreover, the electrical energy generation of the SOFC-O, which reached values of 9 MJ∙kg-N−1, was higher than the electrical energy consumption for VMS, for which values of 7 MJ∙kg-N−1 were calculated.@en

Recovery of ammonia (NH₃) from residual waters offers various reuse opportunities, such as the production of fertilisers and the generation of electricity and heat. However, simultaneous evaporation of water (H₂O) during NH₃ stripping under vacuum results in diluted recovered NH₃ gas with high H₂O contents. Whereas porous gas-permeable membranes are already used for vacuum NH₃ stripping, the use of non-porous silica-based pervaporation (PV) membranes showed promising results in recent literature, with respect to more selective transfer of NH₃ compared to H₂O. In this study, we assessed the selectivity of NH₃ over H₂O transfer (S_NH3/H2O) for different types of membranes, under various hydraulic conditions and feed water compositions. The three following membranes were tested: a porous gas-permeable polytetrafluoroethylene (PTFE) membrane, a hydrophilic (Hybrid Silica PV) membrane and a hydrophobic polydimethylsiloxane PV (PDMS PV) membrane. For the PTFE and the Hybrid Silica PV membrane, S_NH3/H2O ranged between 0.1 and 0.4, indicating that the transfer of NH₃ was consistently less preferred compared to the transfer of H₂O. The preference for H₂O over NH₃ transfer through the membranes at various hydraulic conditions and feed water compositions can be assigned to the similarity in polarity and kinetic diameter of NH₃ and H₂O and the low relative concentration of NH₃ in the used feed waters (approximately 0.1–1.0 wt%). The PDMS PV membrane showed negligible NH₃ transfer and deteriorated rapidly during the NH₃ stripping experiments. The S_NH3/H2O of both gas-permeable and PV membranes was higher for unsteady than for steady hydraulic conditions. Furthermore, the S_NH3/H2O of the both PTFE and the Hybrid Silica decreased when the ionic strength of the feed water increased from 0.0 to 0.8 mol∙L⁻¹ and when the NH₃ feed water concentration increased from 1 to 10 g∙L⁻¹. According to the results, the used PV membranes did not show selectivity of NH₃ over H₂O transfer. In fact, the used PV membranes consistently had a lower S_NH3/H2O than the PTFE membrane. Hence, the dense silica-based PV membranes did not allow for the recovery of gaseous NH₃ from water, with lower H₂O content in the recovered gas, compared to porous PTFE membranes.

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Traditionally, industrial processes produce wastes that, even though often containing useful materials, are discarded, contributing to environmental pollution and depletion of natural resources. An example of such wastes are brines, flows of concentrated salts, produced in water treatment processes, which are now routinely discharged into receiving water bodies. Brines however can also be considered as flows of reusable materials which should be recovered, and the Zero Brine cooperation project aims to develop processes for that purpose. For a demineralized water production plant in the port of Rotterdam (the Netherlands), a closed water processing cycle was proposed to treat the large volume of spent Ion Exchange (IEX) regenerant brine which, apart from recovering demineralized water, is also intended to produce magnesium (Mg2+) and calcium (Ca2+) salts, with the highest purity possible, from the otherwise discharged brine. The process scheme includes nanofiltration (NF) for separating mono- and multivalent ions, followed by sequential chemical precipitation of Mg2+ and Ca2+ ions from the NF concentrate, and production of demineralized water by evaporation of the NF permeate. The concentrate of monovalent ions produced in the evaporator, essentially a concentrated sodium chloride solution, in its turn might be reused for IEX regeneration. Part of the supernatant of the sequential precipitation may be fed to the evaporator as well, but bleeding the other part of this supernatant is essential in order to maintain process stability, avoid accumulation of minor pollutants, and reduce scaling. In this study, various scenarios to operate the process were modeled, using PHREEQC and Excel. According to the simulation results, recovery of ≈97% of Mg2+ and Ca2+ is possible, the latter with a higher purity than the former. The main factors affecting the results are the concentration of carbonate present in the spent IEX regenerant, as well as characteristics of the NF membrane and the dosing of sodium hydroxide in the sequential precipitation steps. The results of the simulations were used for the design and operation of a pilot plant, comprising all mentioned process steps.

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Ammonia (NH3) is one of world’s most-produced chemicals and is mostly used as a raw resource for fertilisers. From the used NH3-based fertilisers, almost half of the NH3 ends up in receiving water bodies, leading to eutrophication, eventually resulting in species diversity loss in the aquatic environment. To minimise environmental damage, total ammoniacal nitrogen (TAN) should be removed from residual waters before discharge. Currently, the treatment of residual waters with high TAN concentrations (hereafter nitrogen (N)-loaded residual waters) by biological processes, such as partial nitritation in combined with anammox (reaching TAN removal efficiencies up to 90%), is challenged by the undesired emission of oxidised nitrogen species. In addition, current methods to recover TAN from N-loaded residual waters for reuse purposes require large amounts of energy and chemicals. Interestingly, NH3 was recently acknowledged as a carbon-free carrier of energy, having an energy content of 21 MJ∙kg-N-1. The fact that NH3 carries energy, opens possibilities to remove TAN from N-loaded residual waters and subsequently recover NH3 for the generation of electricity, potentially leading to energy-positive methods to remove TAN from N-loaded residual streams. The objective of this thesis was to assess the feasibility to achieve competitive (approximately 90%) TAN removal from N-loaded residual waters and to use the recovered NH3 for electricity generation purposes, using a combination of technologies without using chemicals. The used technologies in this thesis are electrodialysis (ED), bipolar membrane electrodialysis (BPMED), vacuum membrane stripping (VMS) and a solid oxide fuel cell (SOFC). To determine the suitability of the combination of technologies, the research conducted in this thesis focused on the mass transfer and achievable concentrations of the various TAN species (ammonium (NH4 +), dissolved NH3 and gaseous NH3), as well as the electrical energy aspects (consumption and generation) for the various technologies… @en

Total ammoniacal nitrogen (TAN) is considered to be a pollutant, but is also a versatile resource. This review presents an overview of the TAN recovery potentials from nitrogen (N)-loaded residual streams by discussing the sources, recovery technologies and potential applications. The first section of the review addresses the fate of TAN after its production. The second section describes the identification and categorisation of N-loaded (≥0.5 g L⁻¹ of reduced N) residual streams based on total suspended solids (TSS), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), TAN, and TAN/TKN ratio. Category 1 represents streams with a low TAN/TKN ratio (<0.5) that need conversion of organic-N to TAN prior to TAN recovery, for example by anaerobic digestion (AD). Category 2 represents streams with a high TAN/TKN ratio (≥0.5) and high TSS (>1 g L⁻¹) that require a decrease of the TSS prior to TAN recovery, whereas category 3 represents streams with a high TAN/TKN ratio (≥0.5) and low TSS (≤1 g L⁻¹) that are suitable for direct TAN recovery. The third section focuses on the key processes and limitations of AD, which is identified as a suitable technology to increase the TAN/TKN ratio by converting organic-N to TAN. In the fourth section, TAN recovery technologies are evaluated in terms of the feed composition tolerance, the required inputs (energy, chemicals, etc.) and obtained outputs of TAN (chemical form, concentration, etc.). Finally, in the fifth section, the use of recovered TAN for three major potential applications (fertilizer, fuel, and resource for chemical and biochemical processes) is discussed. This review presents an overview of possible TAN recovery strategies based on the available technologies, but the choice of the recovery strategy shall ultimately depend on the product characteristics required by the application. The major challenges identified in this review are the lack of information on enhancing the conversion of organic-N into TAN by AD, the difficulties in comparing the performance and required input of the recovery technologies, and the deficiency of information on the required concentration and quality of the final TAN products for reuse.

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This study investigates the feasibility of electricity production in a solid oxide fuel cell using methane recovered from groundwater as the fuel. Methane must be removed from groundwater for the production of drinking water to, amongst others, avoid bacterial regrowth. Instead of releasing methane to the atmosphere or converting it to carbon dioxide by flaring, methane can also be recovered by vacuum stripping and served as a fuel. However, the electrical efficiency of currently used combustion-based technologies fuelled with methane-rich gas is limited to 35% due to the low heating value of the recovered gas (70 mol. % methane) and power derating due to the presence of carbon dioxide (25 mol.%). We propose to use a solid oxide fuel cell to use the methane-rich gas as fuel. Solid Oxide Fuel Cells are fuel-flexible and potentially attain higher electrical efficiencies up to 60%. To this end, specific gas processing, including cleaning and methane reforming, is required to allow for durable operation in a solid oxide fuel cell. We assessed whether electricity could be generated by a solid oxide fuel cell using methane recovered from a full-scale drinking water treatment plant as a fuel. The groundwater had a methane concentration of 45 mg∙L^-1, and the recovered gas by vacuum towers contained 70 mol% methane. We used a gas cleaning reactor with impregnated activated carbon to remove hydrogen sulfide traces from the methane-rich gas. Thermodynamic calculations showed that additional steam is required to achieve a high methane reforming. The added steam and the carbon dioxide content in the recovered gas simultaneously contribute to the methane reforming to prevent carbon deposition. The measured open circuit potential corresponded with the theoretical Nernst voltage, implying high methane reforming in the solid oxide fuel cell. The achieved power density of the cell fuelled with the methane-rich gas (mixed with steam) was 27% less than the hydrogen-fuelled cell. Ultimately, 51.2% of the power demand of the plant can be covered by replacing the gas engine in a drinking water treatment with a 915 kW solid oxide fuel cell system fuelled by the methane recovered from the groundwater, while the greenhouse gas emission can be reduced by 17.6%.

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Removal of ammoniacal nitrogen from residual waters traditionally relies on energy-consuming biochemical processes, while more novel alternative strategies focus on the recovery of total ammoniacal nitrogen for the production of fertilisers or the generation of energy. The recovery of total ammoniacal nitrogen as gaseous ammonia is more effective at high ammonia concentrations in the liquid feed. Typically, chemicals are added to increase the solution pH, while

bipolar membrane electrodialysis can be used to convert salt solutions to acid and base solutions by using only electricity. In this study, we used bipolar membrane electrodialysis to remove ammonium from water and to simultaneously produce concentrated dissolved ammonia, without using chemicals. The energy consumption and current efficiency to transport ammonium from the diluate (the feed water) were assessed throughout sequencing batch experiments.

The total ammoniacal nitrogen removal efficiency for bipolar membrane electrodialysis ranged between 85 and 91% and the energy consumption was stable at 19 MJ·kg-N−1, taking both electrochemical and pumping energy into account. The base pH increased from 7.8 to 9.8 and thetotal ammoniacal nitrogen concentration increased from 1.5 to 7.3 g L−1, corresponding to a final ammonia concentration of 4.5 g L−1 in the base. Leakage of hydroxide, diffusion of dissolved ammonia and ionic species from the base to the diluate all contributed to a loss in current efficiency. Due to the increase in operational run time and concentration gradients throughout the sequencing batch experiments, the current efficiency decreased from 69 to 54%. We showed that

bipolar membrane electrodialysis can effectively be used to simultaneously remove ammonium from water and produce concentrated dissolved ammonia while avoiding the use of chemicals. Moreover, the energy consumption was competitive with that of the combination of electrodialysis and the addition of chemicals (22 MJ·kg-N−1).@en

The application of zero liquid discharge (ZLD) results in the generation of solid residual streams, which are often not fit for reuse. In this study, we assessed the separation of natural organic matter (NOM) and sodium chloride (NaCl) by nanofiltration (NF), electrodialysis (ED) and ion exchange (IEX) in reverse osmosis brine (RO-brine) and by the extraction of impurities from salt (SALEX) in the generated mixed solids of a full-scale ZLD water treatment plant. The NaCl recovery by NF, ED and IEX ranged 69-99% and the rejection of NOM ranged 18–19%, 43–65% and 53–76%, respectively. The recovery of NaCl by SALEX ranged 52–99%, while the rejection of NOM ranged 59–92%. The results show that NOM and NaCl can be sepa-rated both in RO-brine and mixed solids, opening opportunities for recovery of reusable salt from brines in ZLD. @en