Brine producing industries progressively become the centre of attentionas they carry greater environmental consequences. Despite the extensiveliterature that can be found on desalination, limited information is availableabout the practical comparison of the technologies with regards to the brineconcentration performance and associated energy consumption. This thesis studyaims to contribute to bridging this knowledge gap by comparing reverse osmosis(RO), electrodialysis (ED) and vacuum membrane distillation (VMD). RO wasstudied by simulations using WAVE software, while ED and VMD were studied byperforming lab-scale experiments. Feed NaCl concentrationsbetween 20 and 80 g/L were considered in this study. The achievedconcentration factor (CF) for RO was greatly influenced by the feedconcentration. It was found that applying higher netdriving pressures resulted in higher recoveries, but recoveries are limited by feed concentration. In the VMDstudy, the correlation between operating temperatures and permeate flux wasfound to be positive. A decrease in permeate flux wasobserved with increasing solute content, which is related to the vapourpressure lowering phenomena. It was found that the effect of operatingtemperature on permeate flux is greater than the effect of the feedconcentration. Condensation contributed to the highest energy consumption(81%), followed by the vacuum pump (18.9%). Efficient heating andcooling pumps result in a significant energy consumption decrease. In the ED study it was found that applying different current density (CD) did not influence the CF, so it ismore advantageous to apply lower CD to achieve the same desalination from anenergy saving point of view. Furthermore, the CF decreased with increasing feedconcentration and thistrend intensifies with larger volume ratios. The effectof absolute water transport became more significant at higher feedconcentrations and resulted in overall dilution of the concentrate stream. Thedistribution of mass transport was similar for different volume ratios, meaningthat higher CF can be achieved by larger volume ratios. Higher energy consumptionwas related to higher feed concentration and higher volume ratios resulted in higherenergy consumption due to smaller concentrate volume.RO, VMD and ED proved to be suitabletechnologies for concentrating different NaCl solutions. RO and ED showed verysimilar concentration performance and energy consumption. The concentration limit for RO was 118g/L, while for ED it was 140 g/L. RO was able to achieve higher CF with lowerenergy consumption at concentrations < 60 g/L, compared to ED. EDoutperforms RO at concentrations > 60 g/L. Theenergy consumption of ED and RO can be reduced by applying a multi-stageconfiguration. The VMD results showed that the energy consumptionto achieve a similar CF as RO and ED, increased by a factor of 61. VMD is moreadvantageous at higher feed concentrations and even more so with waste heat. VMD and RO are suitable for cases that require high qualitypermeate whereas ED is not. The technologies could also be applied togetherto minimize waste production, whilst prioritizing concentration.

This thesis constitutes a part of the "IMPRESS" project which is aiming at the production of bio-plastics by utilizing hemicellulosic hydrolysates. The hydrolysate stream, after following the steps of acid hydrolysis and neutralization, consists of monosaccharides (C5/C6 sugars), salt and sugar degradation products. The C5/C6 sugars need to be concentrated by a factor of 10 to be purified afterwards in downstream processes. Evaporation has been the most dominant technology in the sugar treatment sector, however the current study aimed to investigate tubular nanofiltration (NF) and vacuum membrane distillation (VMD) units for concentrating the C5/C6 sugars, as more sustainable alternatives. Synthetic solutions with C5/C6 sugars and salt were used to assess the performance of the NF and MD membranes in terms of sugar and salt rejection before the experiments with the real hydrolysate solution. Among the different NF and MD membranes, the one that met the C5/C6 sugar rejection requirements (>90 %) during the synthetic solution experiments was tested for concentrating the C5/C6 sugars. The most suitable technology for concentrating the C5/C6 sugars was also assessed for its energy consumption. Additionally, single filtration tests were conducted to characterize the NF membranes, while surface tension and contact angle measurements were performed to predict the membrane wetting phenomena during the VMD operation. Based on the C5/C6 sugar rejection values (range of 22-81 %) obtained with ceramic and polymeric NF membranes, it was deduced that the tubular NF membranes were not capable of meeting the C5/C6 sugar concentration goals. The polymeric membranes performed better than the ceramic ones in terms of C5/C6 sugar rejection, with a maximum sugar rejection of 81 %. However, the polymeric membranes were found to be more prone to fouling, showing a maximum decrease of 34 % in the water permeability after 4 hours of operation with the hydrolysate solution. Additionally, the characterization of the NF membranes based on the Donnan Steric Pore Model (DSPM) revealed membrane pore sizes larger than those provided by the manufacturer. On the contrary, the 0.2 μm MD membrane showed >99 % of C5/C6 sugar rejection and was used for the sugar concentration tests. The maximum C5/C6 sugar concentration factor (CF) achieved with the VMD was 8 with a negligible sugar loss (<1 %) in the permeate, indicating that concentrating the C5/C6 sugars by a factor of 10 is feasible with this technology. Surface tension and contact angle measurements disclosed inconsistencies in the hydrophobicity of the MD membrane, which can be linked to the membrane wetting phenomena occurred during the VMD operation. The fouling of the MD membrane (50 % of flux decrease after 39 hours of operation) was found to be reversible with complete flux recovery after chemical cleaning and drying of the membrane. The energy assessment of the VMD technology showed that the main energy consumer was the cooler, contributing to 96 % of the total consumed energy. Based on the cooler's efficiency, the energy consumption of the VMD unit was calculated to be in the range of 207-736 KWh/m³ of distillate. When compared with multi-effect evaporators with up to three effects, the VMD was found to be more energy efficient. Investigating less energy-intensive alternatives for concentrating the C5/C6 sugars, experiments with electrodialysis (ED) showed 90 % removal of both acid and salt from the raw and neutralized hydrolysate water, respectively, making it feasible for reverse osmosis (RO) membranes to be further tested for concentrating the C5/C6 sugars. Therefore, a treatment scheme of ED and tubular RO membranes is proposed for further research on concentrating the C5/C6 sugars. Overall, a pre-treatment step with the most permeable ceramic NF membrane is suggested, as evinced by the high color removal achieved (elimination of big foulants) and the high permeation of the C5/C6 sugars and salt.

Nitrogen (N) removal is one of the key tasks for every wastewater treatment plant under the growing pressure of environmental protection. Prevailing applied N treatment technologies are mostly energy-intensive. This dilemma triggers a rethinking of the way to approach N management. “N2kWh-From pollutant to power” is a project that aims at creating an energy-positive 푁 treatment system by exploiting the energy potential stored in reduced N compounds. Both thermal and electrical energy needed in this scheme will be provided by Solid Oxide Fuel Cell (SOFC) using the ammonia recovered from wastewater. To guarantee a proper function of the SOFC a minimum of 5 wt% of ammonia in the gas mixture is a prerequisite, whereas, the reject water of anaerobic digester only typically contains 0.15 wt%. Therefore, selectively stripping NH₃ in waste streams is the main technical bottleneck of this project.This study aims at contributing to the understanding of selective transport of NH₃ by pervaporation. A comprehensive literature study indicates silica-based ceramic membrane is able to perform this selective transport. Therefore, the task of this research was to test the feasibility of selective transport of NH₃ by commercially available silica-based pervaporation membranes (hydrophobic PDMS and hydrophilic Hybrid Si AR). The objective was to find the optimum operating condition for maximizing the selective transport of NH₃ by silica-based ceramic pervaporation membrane. To this end, the impact of flow regime (laminar and turbulent flow), temperature (35 ^oC and 45 ^oC), presence of additional salt (NaCl and Na₂CO₃) and TAN concentrations (total ammonium nitrogen; 1.5, 12.0 and 20.0 g TAN·L^-1, respectively) was assessed through a series of systematic experiments.It was found that the PDMS membrane was unable to selectively transport NH₃ from liquid solution because both H₂O and NH₃ are polar molecules while the hydrophobic PDMS was nonpolar. Besides, the PDMS membrane tested was not stable under solutions used in this study.The results of Hybrid Si pervaporation membrane showed that the optimum operating conditions for selective transport of NH₃ was 35 ^oC, Re=2,400, 20.0 g TAN·L^-1 ammonium bicarbonate solution (pH adjusted to 10). For these conditions, the highest perm-selectivity (ratio of mass transfer coefficients of NH₃ and H₂O) was 0.5 indicting NH₃ was less selectively transported than H₂O.The impact of flow regime on selective transport of NH₃ was related to polarization effects and depended on TAN concentration in feed solution. In the tested temperature and TAN concentration range, perm-selectivity was independent on both parameters. In addition, the effect of both temperature and TAN concentration on the ammonia was mainly due to the driving force, so their influence on the perm-selectivity was limited. Presence of salt seemed to have a positive impact on the perm-selectivity. Although salt has little impact on the mass transfer coefficient of NH₃, it decreased the mass transfer of H₂O resulting in a better selective transport of NH₃.As for energy consumption, it was inversely related to TAN content. At the optimum operating condition 7 MJ·kg^-1 - N was consumed by pervaporation in this study. Compared with the energy consumption of air stripping, pervaporation is a promising technology for NH₃ recovery.

Municipal and industrial wastewater contains a significant amount of dissolved nitrogen. This is the results of the organic protein degradation and of the large employment of nitrogen (N), usually in the form of ammonia (NH₃), in the industry. Currently, nitrogen is removed in wastewater treatment plant (WWTP) by means of biological treatments. Globally, the most applied treatment consists in the combination of nitrification and denitrification. This technique is characterized by a high energy demand (44.3 MJ per Kg_NH4⁺ removed)  which accounts for 70% of the total energy consumption in the WWTP. A less energetically intensive alternative treatment is the Anammox process. However, this also presents significant limitations, especially when dealing with extremely polluted stream and in the flexibility of operation.
An alternative to reduce the energy cost of nitrogen removal by valorizing the content of residual streams is explored by the N2kWh project. The novel concept underlying the N2kWh project aims to use NH₃ from waste streams as a fuel source for a solid oxide fuel cell (SOFC). In this way, the energy cost for biological N-removal processes is cut, and, ideally, energy can be even produced. WWTP digested reject water was recognized as potential N-source for energy recovery as a result of its relatively high total ammonia nitrogen (TAN) concentrations (up to 1.5 g − N ⋅ L^-1). A (selective) concentration step and pH regulation are needed in order to convert the TAN in the reject water, mostly present in form of ammonium bicarbonate (NH₄HCO₃), into NH₃ gas which can be stripped and directly fed in theSOFC. Previous studies proved electrodialysis (ED) to be the most energetically efficient technology for the removal and concentration of ammonium bicarbonate. However, due to the high alkalinity in the obtained concentrate, a large amount of chemicals is required for the pH regulation. An interesting opportunity to avoid this chemical addition is the employment of a bipolar membrane electrodialysis (BPMED). Through this unique technology, it is possible to simultaneously achieve the concentration of TAN, as well as the regulation of pH without chemicals.
The main objective of this work was to evaluate the potential of BPMED for the recovery of NH₃ in the boundaries of the N2kWh project. The energy performance of BPMED was compared with the alternative use of conventional ED plus sodium hydroxide for pH control. In order to obtain valuable information on the operation, three setups were employed: regular ED, BPMED and BPMED coupled with two membrane vacuum stripping devices (VMS). For this purpose, a synthetic solution obtained by dissolving 6.6 g ⋅ L^-1 NH₄HCO₃ salt in demiwater was used to simulate the digested reject water. Experiments were designed to characterize the BPMED operation and clarify which processes influence the performance.
Experimental laboratory results showed that, in terms of energy consumption for the NH₄⁺ removal, the BPMED used more energy compared to the ED. The removal of 90% of the initial NH₄⁺ is achieved by using an average of 13.2±0.1 MJ ⋅ Kg_NH4^-1. This value was 3.3 times higher than that achieved with regular ED. This discrepancy was explained by the extra-elements in the stack and the water dissociation process, responsible for the higher voltage measured during BPMED operation. The energy consumption was proven to be higher also as a consequence of the lower current efficiency for salt transport (73% compared to 95% of conventional ED). This was due to the more severe undesired diffusion processes, mainly gas diffusion and hydroxide leakage from the alkaline stream to the diluate, taking place within the BPMED stack. However, the energy consumption for ammonium removal in BPMED was still more than three times lower than the energy consumed by nitrification-denitrification and comparable to what used by anammox. 
The implementation of the membrane vacuum stripping modules, in series with the BPMED, only slightly increased the overall current efficiency (up to 3.4 % current efficiency gain). The benefit in current efficiency was less significant for higher concentrations and pH in the alkaline stream. Besides that, the tested technology tandem (BPMED+VMSs) was capable of stripping NH₃ and, consequently, reduce the gas diffusion over the stack. The energy consumed for the production of NH₃ and for the ED operation to reach a pre-defined pH and TAN concentration was estimated to be equal to 82.55 Wℎ per L of concentrate. This value was substantially higher than what consumed by BPMED (48.7 Wℎ) to achieve the same result in the alkaline stream.
To conclude, the studied BPMED system was demonstrated to be superior in terms of energy consumption for the recovery of NH₃ gas when compared to the combination of ED and chemical addition. BPMED showed also crucial advantages for the environment, design and safety of the treatment facility. The energy consumption for the removal of nitrogen with BPMED was proven to be lower than what used in the competitive biological technology. Finally, neither the technology nor the operation methods employed were specifically designed/optimized for this application. This made the use of BPMED for the N2kWh purpose even more interesting and promising.

In today’s industry ammonia is produced on a large scale, and is used in the production of fertilisers, cleaning products and much more. Eventually the ammonia enters our wastewater, either directly or through urine. This is then removed with conventional nitrifying-denitrifying treatment or with Anammox. That process consumes energy and does not recover the ammonia.
Therefore, the goal of the ‘From Pollutant to Power’ project, of which this thesis is a part, is to achieve a paradigm shift for ammonia to become an energy resource instead of a wastewater pollutant. The objective of the project is to recover ammonia and use it in a solid oxide fuel cell (SOFC) to produce energy. To do this, a vapour with at least a mass percentage of ammonia (m%NH3) of 5% is needed. The energy produced with the SOFC can then be used to cover the energy need for the extraction of ammonia. The SOFC can produce 4.2MJ·kg-N-1 of thermal energy and 8.4 MJ·kg-N-1 of electrical energy.
This study examines the use of vacuum membrane stripping (VMS) to strip ammonia from wastewater. The research objective is to go from using VMS to recover ammonia from synthetic wastewater to strip ammonia from real wastewater, in order to produce ammonia fuel for a SOFC. To accomplish this, some knowledge gaps need to be filled. First, methods need to be found that concentrate the permeate more than previously possible with the VMS to reach the desired m%NH3 in the permeate. Therefore, the effect of the cross-flow of the feed side was investigated and how to concentrate the permeate vapour with the help of condensation. Next, the effect of contaminants on the VMS process was examined by looking at the effect of salts in the wastewater and testing with real industrial ammonia-rich wastewater from amide production, which contains some organics. The final issue to consider was whether this process would be feasible in terms of energy; therefore, an energy balance was made.
Multiple experimental tests were conducted with VMS to investigate the knowledge gaps mentioned above. The selected test conditions were a minimum pH of 10 to exclude CO2 gas transfer, and to ensure the total ammonia nitrogen (TAN) in the water was in the form of ammonia and not ammonium. For the experiments, feed solutions of ammonium hydroxide and ammonium bicarbonate were selected with a concentration of 1.5, 12 and 20 gTAN·L-1 with a temperature of 35°C. For the cross-flow experiments, the initial test was carried out with the Reynolds numbers 200, 300, 400, 500 and 600. From this initial test it was concluded that a Reynolds number of 200 is laminar and 500 is turbulent, and those values were used in the rest of the experiments. For the experiments with condensation, a condensation tube with cooling water of 5-10°C, 15-20°C and 25-30°C was added to the setup. Next, the composition of the industrial wastewater was investigated. In the end, the results from the different experiments were used to make an energy balance.
The results of the experiments with VMS show that turbulent flow is preferred above laminar flow, due to the increased ammonia flux and the ammonia selectivity of the membrane, which both provide a higher concentration of ammonia and more permeate. Salt (high ionic strength) will lower the ammonia flux through the membrane and the selectivity of the membrane. The condensation experiment was successful and adding a subsequent condensation step will concentrate the ammonia in the permeate vapour. Moreover, this condensation step will make it possible to recover some of the energy lost in the VMS. The experiment with the real wastewater was however not successful. The membrane fouled badly due to the organics in the water, where organics acted as surfactants and decreased the hydrophobicity of the membranes. The energy balance shows that the system would be energetically beneficial in terms of electrical energy with a concentration above 12 gTAN·L-1 in the solution for both ammonium hydroxide and ammonium bicarbonate, and that a concentration around 100 gTAN·L-1 from ammonium hydroxide is needed to make it energy efficient in terms of thermal energy.
More investigation is needed to be able to use real wastewater in a VMS module. For the wastewater tested in this study, stripping with VMS is not an alternative. This does not mean that other wastewater cannot be used in the VMS, therefore, other industrial wastewaters, reject water and urine should be investigated. Another possibility could be to review other stripping methods for wastewaters with relatively high contents of organics.

Ammonia in aqueous environments leads to eutrophication and toxicity of the receiving water body (Metcalf & Eddy, 2003). In order to prevent environmental pollution, ammonia needs to be removed from residual water streams, before the water can be discharged to the aqueous environment (Song et al., 2012). Waste water treatment plants (WWTPs) reduce the ammonia-nitrogen concentration by applying biological treatment technologies. However, the oxidation of ammonia by bacteria requires high amounts of oxygen and consequently has a high energy consumption. The nitrification and denitrification of wastewater requires 15.83 kWh per kg-N (Magrí et al., 2013). Moreover, the reject water from the digested sludge contains high amounts of nitrogen, which is fed back to the biological treatment, and can contribute 15-20% of the nitrogen load (Fux et al., 2002). Concentrating ammonium fluxes lead to the production of a concentrated ammonium stream, used as potential energy source in the N2kWh project, and a sweet stream.

The influence of feed temperature and total ammonia nitrogen concentration on permeate quantity and quality in a vacuum membrane distillation process has been researched in order to determine the suitability of membrane distillation in an energy producing system including a solid oxide fuel cell.