Producing green hydrogen can be done using alkaline water electrolysis. Recycling water might help to fulfil the large water demand of hydrogen production facilities. In fertiliser production, steam condensate could be a recyclable water source for hydrogen production. This condensate is relatively clean as its main contaminant is a small concentration of ammonia. This report researches the effect of adding ammonia to the electrolyte of an alkaline water electrolysis cell.

When steam condensate is used instead of ultra-pure water, it is important to find out what happens to the added ammonia and if it affects the production rate and the production efficiency, or if it degrades the equipment. The experiments in this report used three different ammonia concentrations and the electrolyte was made using potassium hydroxide. The electrolysis cell used nickel mesh electrodes and a Selemion™ anion exchange membrane. Each of the experiments were carried out at 2.15 Volts for a duration of 50 minutes.

It was found that adding 1 mmol/L ammonia to the electrolyte decreased the current density of the cell. Doubling the ammonia concentration led to an even larger decrease in current density of up to 19%. A significant effect on the Faraday efficiency was not measured. During the experiments, the ammonia was partially stripped from the electrolyte due to its high alkalinity. Another part was oxidised to produce nitrogen gas and nitrate. Some of the ammonia had not reacted after the 50-minute experiment and could be measured in the spent electrolyte. After all the experiments were carried out, the cell was disassembled. The cathode showed significant signs of degradation. However, the many starts and stops between experiments could be the primary reason for this degradation. The ammonia could have accelerated the degradation, but this was not proven.

Overall, the benefits of using steam condensate do not seem to outweigh the drawbacks. The ammonia caused a significant decrease in current density. On the long term, ammonia might cause electrode poisoning which would further lower the current density. The experiments also found nitrate in the spent electrolyte. Having additional pollutants in both the spent electrolyte and the produced gasses might introduce additional disadvantages to using an ammonia containing electrolyte. If steam condensate is used as a water source, a treatment step is advised. Aeration could be used to strip the ammonia from the electrolyte. To get a more accurate insight into the effects of ammonia on alkaline water electrolysis, additional research is necessary. In future research, the effects of ammonia should be measured more accurately, and the long-term effects should be researched.

Fine sieved fraction (FSF) is a solid waste generated from wastewater treatment plants (WWTPs). Cellulose fiber is the most important component of FSF, which can be fermented into volatile fatty acids (VFAs) and then be used as carbon sources in biological nutrient removal (BNR). This thesis measured and evaluated the aerobic & anaerobic biodegradability of solids in fermented FSF (fFSF) and the BNR performance of FSF-derived VFAs. In addition, this research tested the feasibility of using secondary sieving as a potential downstream processing technology. The products of secondary sieving (liquid: secondary filtrate, solid: secondary FSF) were compared with fFSF in terms of biodegradability and BNR performance. The aerobic biodegradability of raw FSF, fFSF and secondary
filtratewere 52.3 ± 1.4, 60.4 ± 4.7 and 72.1 ± 6.4 %, respectively. The anaerobic biodegradability of raw FSF, fFSF and secondary FSF are 56.8 ± 8.4, 68.2 ± 6.4, 51.5 ± 7.8 %, respectively. The results of biodegradability revealed that secondary sieving increased the proportion of readily biodegradable solids and reduced the overall organic load of activated sludge systems. The residual solids after secondary sieving could be converted into biogas or recovered as building materials. FSF-derived VFAs could substantially increase denitrification rates and phosphate release rates. fFSF and secondary filtrate could increase the denitrification rate by 40 - 50%and increase the phosphate release rate by around 200 % compared to blank. Theoretically, the effluent nitrogen load could be reduced by up to 53.7%if FSF-derived carbon sources are fully used for denitrification atWWTP Aarle-Rixtel. If used for phosphorus removal, the capacity provided by FSF-derived VFAs could nearly remove all phosphate from the effluent. To sum up, FSF-derived VFAs could effectively increase BNR rates
and significantly reduce the effluent nitrogen and phosphorus load. The main advantages of FSFderived VFAs over conventional carbon sources are sustainability and waste-reduction. Secondary sieving could reduce the solid load of activated sludge tank and achieve a combined recycling of VFAs and fibers, but the total COD available for BNR will be reduced as a compensation. The results in this thesis can facilitate the application of fFSF in WWTPs and the improvement of FSF-derived VFAs production.

The aim of this research was to evaluate the feasibility of direct hollow fiber nanofiltration membranes for drinking water purposes. The experiments were performed on the dNF40 pilot provided by NXF. The fouling potential and the ion retention of the dNF40 pilot were determined by continuous filtration experiments using raw IJssellake water under different operational conditions. The performances (ion retention and fouling potential) of the dNF40 on raw IJssellake water were compared with the dNF40 performances on pre-treated water from Waterwinstation Prinses Juliana (WPJ) (previously done at PWNT). The WPJ pre-treated water has undergone extensive pre-treatment consisting of drum screens, flocculation, sedimentation, rapid sand filtration (RSF) and granular activated carbon (GAC). The OMP retention of the dNF40 pilot was determined by full recirculation experiments using WPJ pre-treated water under two different operational conditions with elevated concentrations 'spiked solution'.
Limited to no fouling impact was observed on the membrane performance when feeding the pilot with raw IJssellake water. The membrane performance parameters (mass transfer coefficient (MTC), trans membrane pressure (TMP) and normalized pressure drop (NPD)) were stable over time. In addition, limited to no fouling impact was observed on the membrane when feeding the pilot with WPJ pre-treated water. However, membrane performance (i.e. MTC) was better for raw IJssellake water (1 year old membrane) compared to WPJ pre-treated water (virgin membrane). This implies that the active outer layer of the membrane has undergone a change in properties leading to these higher MTC values.
An increase in recovery, flux and crossflow velocity resulted in a decrease in ion retention. However, a decrease in ion retention with elevated crossflow velocity is unusual. Higher crossflow velocities should actually lead to an increase in ion retention due to reduced ion build-up next to the membrane surface (i.e. lower concentration polarization effect). However, the lower ion retention can be attributed to the elevated MTC during experiments. The removal of natural organic matter (NOM) was consistently above 90% and was not influenced by a change in operational condition. Ion retention was higher for WPJ pre-treated water (virgin membrane) compared to raw IJssellake water (1 year old membrane). This can be attributed to the increase in MTC of 1.5 LMH/bar in raw IJssellake water (compared to WPJ pre-treated water) potentially caused by a change in the properties of the active outer layer.
For determining the OMP retention of the dNF40 membrane, a spiked solution containing per- and polyfluoroalkyl substances (PFAS) and pharmaceutical compounds was analyzed. The PFAS compounds of the spiked solution were retained very well (above 80%). As expected, the retention increased with increasing MW. The adsorption percentage of PFAS was between 40%-90%. The pharmaceutical retention was around 30%, although all pharmaceuticals analyzed had a MW below the MWCO of the membrane.
A 5-stage full-scale dNF40 plant was designed based on a permeate flow of 15 M m3/year, a total hardness concentration in the permeate stream below 1.4 mmol/L and a recovery percentage of 85%. Based on the 5-stage full-scale dNF40 plant an economical analysis was performed and compared to the full-scale UF-RO in Heemskerk. The total cost (OPEX and CAPEX) were cheapest for the full-scale dNF40 plant fed with raw IJssellake water (12 ct/m3), followed by the dNF40 plant fed with WPJ pre-treated water (32 ct/m3) and most expensive for the UF-RO plant (35 ct/m3). The major factors in the OPEX was the membrane replacement cost for the dNF40 plant and the energy and chemical cost for the UF-RO plant.

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 the context of steering product formation in anaerobic digestion systems, the present thesis work elaborates on the potential role of elevated CO2 partial pressures as an environmental driver that may influence end-product selectivity from methane towards compounds from the carboxylic platform. As an emerging field of research, organic acid production via mixed culture fermentation is currently in an exploratory phase and the understanding of basic functional principles driving each of the biochemical conversions of interest is of vital importance.The present investigation forms part of a series of studies conjunctively aimed at elucidating the effect of elevated CO2 partial pressures on glucose fermentation, which consists of a complex network of several metabolic routes. Specifically, this thesis work focuses on the effects of CO2 partial pressure on the degradation of two key metabolites that are central and/or highly relevant to the glucose conversion pathways, namely pyruvate and butyrate.

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.

The increase in greenhouse gas emissions change the precipitation behaviour causing either extreme wet- or dry weather. This impacts the fresh water supply for clean water production. Evides B.V., one of the Dutch water companies, anticipates to these changes with the sewer mining concept called ‘RINEW’ (Rotterdam Innovative Nutrients and Energy Watermanagement). RINEW studies various ways to recover valuable substances in direct decentralized sewage treatment. The treatment scheme involves the pre-treatment microscreen, coagulation and ceramic Microfiltration (cMF) for the water purification step Reverse Osmosis (RO). Since the application of cMF for sewage treatment is a novel concept, the objective of present thesis is to gain insight into technical aspects of cMF (a cMF fouling indicator and effect of oxygen on RO biofouling) and potential financial feasibility of the RINEW concept in the Netherlands.
To study the potential of a fouling indicator for the cMF, irreversible fouling rates and feed water quality results are obtained over a two month period. The feed water quality is digitally monitored and characterized on COD, NTU and EC. The parameter ‘COD’ (chemical oxygen demand) is considered the most suitable as fouling indicator due to the relative large particle size of organic matter and sticky properties of biopolymers. Relating the fouling rates to the feed water quality results in a linear trend where higher irreversible fouling rates occur at higher COD concentrations. Yet, the trend result is scattered significantly since the operational flux was highly instable over time. The feed pump is originally designed for a Nanofiltration (NF) application which may explain the deviant cMF operation.
The effect of oxygen in cMF permeate is studied on the (bio)fouling development on spiral wound Reverse Osmosis (RO). The study is done in duplicate each time using two parallel Membrane Fouling Simulator (MFS) which are fed by cMF permeate. In one MFS setup the water is depleted from oxygen by adding Sodium Bisulfite (NaHSO3). The pressure drop results in the MFS fed by aerobic water indicate a significant unstable fouling rate. The fouling rates obtained from the MFS fed by oxygen depleted water compare to similar studies done with NF permeate and tap water. This suggest a significant stable RO biofouling can be obtained if Sodium Bisulfite treatment is applied to RO feed water.
The potential financial feasibility is studied via a concept study. Concept 1 is the RINEW concept providing high quality water (e.g. demi water) to an industry. Since it is a sewer mining concept the water transport costs are neglected. In concept 2 an equal high quality water flow is produced from secondary effluent by a MF/UF+RO combination at a central Sewage Treatment Plant (SWTP). The water transport from the central SWTP to the industry is taken into account in concept 2. The difference in specific costs [EURm-3] between the two concepts is estimated which is recalculated into a breakeven the high quality water transport distance of approximately 20 km. In other words, if an industry demands high quality water and sewage is the only water source, concept 2 is more financial feasible within a range of 20 km from a SWTP. In relation to the Netherlands the SWTP density is discussed as too high for the RINEW concept to be financial feasible. Similar realized treatment plants in the Netherlands show higher importance to aspects like water source, current expertise and existing facilities in the decision-making of treatment plant.