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Singapore is a city-island-state in the transition towards a circular economy. The country has already implemented policies and adopted several approaches that contribute to closing loops for e-waste, packaging waste, and food waste. However, other areas that also contribute to a circular economy have not been fully explored in Singapore. One of these areas is resource recovery from wastewater streams. In this report, we review state-of-the-art technologies to recover valuable components from domestic wastewater and sludge. These technologies are analyzed based on technological maturity and applicability for the recovery of phosphate, and organic compounds such as volatile fatty acids, bioplastics, and biomass. The report covers the current status of the recovery of these compounds in the Singaporean context and identifies factors that can promote or prevent the application of the recovery processes.

In dit themanummer over Green Deals staan de volgende artikelen: 1) Green Deals: Code oranje, blauwe oplossing. 2) Op zoek naar de gemene deler: agrarisch waterbeheer in de praktijk. 3) Kraamkamer van innovatie. 4) Modern aanbesteden is kennis delen: marktvisie waterschappen. 5) De politicus Liesbeth van Tongeren: Niet langer in discussie met klimaatsceptici. 6) Er valt iets te kiezen: waterschappen integreren duurzame energieproductie succesvol in hun kerntaken. 7) Slimmer investeren: Strategisch asset management. 8) Creativiteit op het snijvlak van orde en chaos: Waterschap De Dommel flirt met paradoxen. 9) Open overheid, ook voor waterschappen. 10) Werken aan morgen is gisteren al begonnen: hoe ziet werken voor een waterschap er in 2026 uit?

Recovery of phosphorus from wastewater as calcium phosphate could diminish the need for mining of scarce phosphate rock resources. This study introduces a novel approach to phosphorus recovery by precipitation of calcium phosphate granules in anaerobic treatment of black water. The granules formed in the Upflow Anaerobic Sludge Blanket (UASB) reactor at lab- and demonstration-scale were analyzed for chemical composition and mineralogy by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES), Electron microprobe (EMP), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and micro X-ray Diffraction (XRD). The granules had a diameter of 1–2 mm, organic content of 33 wt%, and phosphorus content of 11–13 wt%. Three calcium phosphate phases were identified in the granules: hydroxyapatite, calcium phosphate hydrate and carbonated hydroxyapatite. Without any addition of chemicals, 7 gP/person/year can be recovered with the calcium phosphate granules, representing 2% of the incoming phosphorus in the UASB reactor. As the heavy metal content was lower compared to other phosphorus recovery products, phosphate rock and phosphorus fertilizer, the calcium phosphate granules could be considered as a new phosphorus product.

Separation of different domestic wastewater streams and targeted on-site treatment for resource recovery has been recognized as one of the most promising sanitation concepts to re-establish the balance in carbon, nutrient and water cycles. In this study a model was developed based on literature data to compare energy and water balance, nutrient recovery, chemical use, effluent quality and land area requirement in four different sanitation concepts: (1) centralized; (2) centralized with source-separation of urine; (3) source-separation of black water, kitchen refuse and grey water; and (4) source-separation of urine, feces, kitchen refuse and grey water. The highest primary energy consumption of 914 MJ/capita(cap)/year was attained within the centralized sanitation concept, and the lowest primary energy consumption of 437 MJ/cap/year was attained within source-separation of urine, feces, kitchen refuse and grey water. Grey water bio-flocculation and subsequent grey water sludge co-digestion decreased the primary energy consumption, but was not energetically favorable to couple with grey water effluent reuse. Source-separation of urine improved the energy balance, nutrient recovery and effluent quality, but required larger land area and higher chemical use in the centralized concept.

Dit artikel gaat nader in op de terugwinning van nutriënten uit het zwarte (toilet) water. Tegelijkertijd moet hierbij rekening worden gehouden met de twee andere doelen van sanitatie: de bescherming van de publieke gezondheid en het milieu. Bescherming van het milieu betekent in Nederland in principe dat voldaan moet worden aan de lozingseisen voor stikstof van 10 mg N l(-1) en fosfaat van 1 mg P l(-1)

Separate treatment of black (toilet) water offers the possibility to recover energy and nutrients. In this study three combinations of biological treatment and membrane filtration were compared for their biological and membrane performance and nutrient conservation: a UASB followed by effluent membrane filtration, an anaerobic MBR and an aerobic MBR. Methane production in the anaerobic systems was lower than expected. Sludge production was highest in the aerobic MBR, followed by the anaerobic MBR and the UASB-membrane system. The level of nutrient conservation in the effluent was high in all three treatment systems, which is beneficial for their recovery from the effluent. Membrane treatment guaranteed an effluent which is free of suspended and colloidal matter. However, the concentration of soluble COD in the effluent still was relatively high and this may seriously hamper subsequent nutrient recovery by physical-chemical processes. The membrane filtration behaviour of the three systems was very different, and seemed to be dominated by the concentration of colloidals in the membrane feed. In general, membrane fouling was the lowest in the aerobic MBR, followed by the membranes used for UASB effluent filtration and the anaerobic MBR.

Decades of developments and implementations in the field of high-rate anaerobic wastewater treatment have put the technology at a competitive level. With respect to sustainability and cost-effectiveness, anaerobic treatment has a much better score than many alternatives. Particularly, the energy conservation aspect, i.e. avoiding the loss of energy for destruction of organic matter, while energy is reclaimed from the organic waste constituents in the form of biogas, was an important driver in the development of such systems. Invoked by the present greenhouse alert, the energy involved is nowadays translated into carbon credits, providing another incentive to further implement anaerobic technology. Anaerobic conversion processes, however, offer much more than cost-effective treatment systems. Selective recovery of metals, effective desulphurization, recovery of nutrients, reductive detoxification, and anaerobic oxidation of specific compounds are examples of the potentials of anaerobic treatment. This paper presents a survey on the state of the art of full-scale anaerobic high-rate treatment of industrial wastewaters and highlights current trends in anaerobic developments.

In dit themanummer over Green Deals staan de volgende artikelen: 1) Green Deals: Code oranje, blauwe oplossing. 2) Op zoek naar de gemene deler: agrarisch waterbeheer in de praktijk. 3) Kraamkamer van innovatie. 4) Modern aanbesteden is kennis delen: marktvisie waterschappen. 5) De politicus Liesbeth van Tongeren: Niet langer in discussie met klimaatsceptici. 6) Er valt iets te kiezen: waterschappen integreren duurzame energieproductie succesvol in hun kerntaken. 7) Slimmer investeren: Strategisch asset management. 8) Creativiteit op het snijvlak van orde en chaos: Waterschap De Dommel flirt met paradoxen. 9) Open overheid, ook voor waterschappen. 10) Werken aan morgen is gisteren al begonnen: hoe ziet werken voor een waterschap er in 2026 uit?

At present, conventional activated sludge (CAS) systems are widely applied to treat municipal wastewater. The main advantages of CAS systems are that they are robust and generally produce an effluent quality that meets the discharge guidelines. However, CAS systems cannot be considered sustainable because they consume large amounts of energy (mainly for aeration and sludge treatment), have a high CO2 emission and do no recover a potential resource of water, energy and nutrients nitrogen (N) and phosphorus (P). Therefore, in this thesis new municipal wastewater treatment concepts that combine treatment with recovery of valuable resources and can save considerable amounts of energy were investigated by modelling and experiments.Quantitative numerical results showed that the feasibility of two novel wastewater treatment configurations, including combined bioflocculation and anaerobic digestion but with different nutrient removal technologies, i.e. (cold) partial nitritation/Anammox or microalgae treatment, is location dependent. Using Dutch municipal wastewater and climate conditions, the configuration with cold partial nitritation/Anammox is the most promising wastewater treatment concept, because it can: 1) treat wastewater year round; 2) produce an effluent at a quality that meets the discharge guidelines; 3) reduce CO2 emission by 35% compared to the CAS system; 4) achieve a net energy yield up to 0.24 kWh per m3 of wastewater compared to a negative net energy yield of -0.08 kWh per m3 of wastewater for the CAS system; and 5) recover 80% of the sewage P. Additionally, the feasibility of the two configurations was investigated for 16 locations around the globe. The results quantitatively support the pre-assumption that the configuration with (cold) partial nitritation/Anammox is applicable in tropical regions and some locations in temperate regions. The configuration with microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. The results also showed that the configuration employing microalgae treatment has an advantage over the configuration employing partial nitritation/Anammox with respect to consumption of aeration energy and recovery of nutrients, but not with respect to area requirements. For a tropical climate country like Thailand, the net energy yield of both configurations is at least a factor 10 higher than the CAS system, while CO2 emission is at least 22% lower.In CAS systems energy recovery from wastewater is accomplished by anaerobic digestion of the organic solids in primary and secondary sludge into methane. However, volatile fatty acids (VFA), which are intermediate digestion products, may be preferred over methane, because VFA can be used as starting compounds for a wide range of higher value products. In this thesis the experimental results showed that a combined process with bioflocculation, using a high-loaded membrane bioreactor (HL-MBR) to concentrate sewage organic matter, and anaerobic fermentation, using a sequencing batch reactor to produce VFA is technologically feasible. An HL-MBR operated at a hydraulic retention time (HRT) of 1 hour and a sludge retention time (SRT) of 1 day resulted in very good performance, because as high as 75.5% of the sewage COD (chemical oxygen demand) was diverted to the concentrate and only 7.5% was mineralized into CO2. It was also found that 90% of the sewage NH4-N and PO4-P were conserved in the HL-MBR permeate, which can be reused as irrigation water as it is free from solids and pathogens.During anaerobic fermentation of the HL-MBR concentrate at an SRT of 5 days, 35°C and without pH control, methane production was inhibited, but incomplete solids degradation mainly limited the VFA production as only 15% of the sewage COD was converted to VFA. Thus, the VFA yield needed to be increased. It was hypothesized that high pH (pH 8–10) fermentation combined with a long SRT, allowing for sufficient solubilization of solids and colloidal COD, can improve the VFA yield. In the current study, it was found that application of a pH shock of 9 in the first 3.5 hours of a sequencing batch cycle followed by a pH uncontrolled phase for 7 days gave the highest VFA yield of 440 mg VFA-COD/g VSS and this was equivalent to 26% of the sewage COD. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shock fermentation could be explained by: 1) a reduction of methanogenic activity; or 2) a high degree of solids degradation; or 3) an enhanced protein hydrolysis and fermentation. This study also demonstrated that the VFA yield can still be further optimized by fine-tuning pH levels and longer operation, possibly with fermentative microorganisms adapted to a high pH that are commonly found in nature. This would further increase VFA yield to 33% of the sewage COD.

Sanitation planning in developing countries: Added value of resource recovery Worldwide 2.5 billion people lack access to sanitation. This impacts human live, the environment and represents a loss of valuable resources that can be regained from wastewater. This study shows that resource recovery can be a potential driver to accelerate sanitation. A new sanitation decision framework for policy makers was created and tested in Indonesia. The variety of advantages and disadvantages of sanitation interventions complicates the sanitation planning process. Conventional sanitation systems consume energy, chemicals and land or produce a sludge that requires disposal, whereas a range of opportunities exists that enables valorization of resources from our “waste”. To support policy makers in planning sanitation that considers sustainability dimensions (social, environment and economy), a new sanitation framework was developed. This framework resolves trade-offs of sanitation alternatives across spatial and temporal scales in three steps. First, it identifies feasible wastewater and solid waste systems in relation to the type of residential area. Secondly, the anticipated population development, current access and formulated targets are an input to generate the number of required systems, their location and associated implementation costs. The required systems are visualized in geographical maps, while budgets are allocated to responsible implementing institutions. Thirdly, the potential demand from “back-end users” of sanitation products, such as agriculture for compost and phosphorus, aquaculture for produced duckweed and industries for recovered plastic and paper, to substitute conventionally produced materials is determined. These three steps are then combined to quantitatively evaluate the (1) environmental impact, (2) operational costs and benefits, and (3) the potential of selected sanitation alternatives to close material cycles. A case study of the Citarum River was performed in which (monetized) benefits such as health, welfare and revenues from the sale of recovered resources were compared with the costs of different (conventional and resource recovery) sanitation systems. The study showed that the economic Benefit to Cost Ratio (BCR) of resource recovery technologies is bigger than BCR of conventional (low cost) technologies, while improving the water quality. It thus shows that resource recovery is a potential driver to accelerate sanitation development. The framework was illustrated using Indonesia as an example, but its application can benefit the quality of millions of lives worldwide.

At present, conventional activated sludge (CAS) systems are widely applied to treat municipal wastewater. The main advantages of CAS systems are that they are robust and generally produce an effluent quality that meets the discharge guidelines. However, CAS systems cannot be considered sustainable because they consume large amounts of energy (mainly for aeration and sludge treatment), have a high CO2 emission and do no recover a potential resource of water, energy and nutrients nitrogen (N) and phosphorus (P). Therefore, in this thesis new municipal wastewater treatment concepts that combine treatment with recovery of valuable resources and can save considerable amounts of energy were investigated by modelling and experiments.Quantitative numerical results showed that the feasibility of two novel wastewater treatment configurations, including combined bioflocculation and anaerobic digestion but with different nutrient removal technologies, i.e. (cold) partial nitritation/Anammox or microalgae treatment, is location dependent. Using Dutch municipal wastewater and climate conditions, the configuration with cold partial nitritation/Anammox is the most promising wastewater treatment concept, because it can: 1) treat wastewater year round; 2) produce an effluent at a quality that meets the discharge guidelines; 3) reduce CO2 emission by 35% compared to the CAS system; 4) achieve a net energy yield up to 0.24 kWh per m3 of wastewater compared to a negative net energy yield of -0.08 kWh per m3 of wastewater for the CAS system; and 5) recover 80% of the sewage P. Additionally, the feasibility of the two configurations was investigated for 16 locations around the globe. The results quantitatively support the pre-assumption that the configuration with (cold) partial nitritation/Anammox is applicable in tropical regions and some locations in temperate regions. The configuration with microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. The results also showed that the configuration employing microalgae treatment has an advantage over the configuration employing partial nitritation/Anammox with respect to consumption of aeration energy and recovery of nutrients, but not with respect to area requirements. For a tropical climate country like Thailand, the net energy yield of both configurations is at least a factor 10 higher than the CAS system, while CO2 emission is at least 22% lower.In CAS systems energy recovery from wastewater is accomplished by anaerobic digestion of the organic solids in primary and secondary sludge into methane. However, volatile fatty acids (VFA), which are intermediate digestion products, may be preferred over methane, because VFA can be used as starting compounds for a wide range of higher value products. In this thesis the experimental results showed that a combined process with bioflocculation, using a high-loaded membrane bioreactor (HL-MBR) to concentrate sewage organic matter, and anaerobic fermentation, using a sequencing batch reactor to produce VFA is technologically feasible. An HL-MBR operated at a hydraulic retention time (HRT) of 1 hour and a sludge retention time (SRT) of 1 day resulted in very good performance, because as high as 75.5% of the sewage COD (chemical oxygen demand) was diverted to the concentrate and only 7.5% was mineralized into CO2. It was also found that 90% of the sewage NH4-N and PO4-P were conserved in the HL-MBR permeate, which can be reused as irrigation water as it is free from solids and pathogens.During anaerobic fermentation of the HL-MBR concentrate at an SRT of 5 days, 35°C and without pH control, methane production was inhibited, but incomplete solids degradation mainly limited the VFA production as only 15% of the sewage COD was converted to VFA. Thus, the VFA yield needed to be increased. It was hypothesized that high pH (pH 8–10) fermentation combined with a long SRT, allowing for sufficient solubilization of solids and colloidal COD, can improve the VFA yield. In the current study, it was found that application of a pH shock of 9 in the first 3.5 hours of a sequencing batch cycle followed by a pH uncontrolled phase for 7 days gave the highest VFA yield of 440 mg VFA-COD/g VSS and this was equivalent to 26% of the sewage COD. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shock fermentation could be explained by: 1) a reduction of methanogenic activity; or 2) a high degree of solids degradation; or 3) an enhanced protein hydrolysis and fermentation. This study also demonstrated that the VFA yield can still be further optimized by fine-tuning pH levels and longer operation, possibly with fermentative microorganisms adapted to a high pH that are commonly found in nature. This would further increase VFA yield to 33% of the sewage COD.

Sanitation planning in developing countries: Added value of resource recovery Worldwide 2.5 billion people lack access to sanitation. This impacts human live, the environment and represents a loss of valuable resources that can be regained from wastewater. This study shows that resource recovery can be a potential driver to accelerate sanitation. A new sanitation decision framework for policy makers was created and tested in Indonesia. The variety of advantages and disadvantages of sanitation interventions complicates the sanitation planning process. Conventional sanitation systems consume energy, chemicals and land or produce a sludge that requires disposal, whereas a range of opportunities exists that enables valorization of resources from our “waste”. To support policy makers in planning sanitation that considers sustainability dimensions (social, environment and economy), a new sanitation framework was developed. This framework resolves trade-offs of sanitation alternatives across spatial and temporal scales in three steps. First, it identifies feasible wastewater and solid waste systems in relation to the type of residential area. Secondly, the anticipated population development, current access and formulated targets are an input to generate the number of required systems, their location and associated implementation costs. The required systems are visualized in geographical maps, while budgets are allocated to responsible implementing institutions. Thirdly, the potential demand from “back-end users” of sanitation products, such as agriculture for compost and phosphorus, aquaculture for produced duckweed and industries for recovered plastic and paper, to substitute conventionally produced materials is determined. These three steps are then combined to quantitatively evaluate the (1) environmental impact, (2) operational costs and benefits, and (3) the potential of selected sanitation alternatives to close material cycles. A case study of the Citarum River was performed in which (monetized) benefits such as health, welfare and revenues from the sale of recovered resources were compared with the costs of different (conventional and resource recovery) sanitation systems. The study showed that the economic Benefit to Cost Ratio (BCR) of resource recovery technologies is bigger than BCR of conventional (low cost) technologies, while improving the water quality. It thus shows that resource recovery is a potential driver to accelerate sanitation development. The framework was illustrated using Indonesia as an example, but its application can benefit the quality of millions of lives worldwide.

In dit themanummer over Green Deals staan de volgende artikelen: 1) Green Deals: Code oranje, blauwe oplossing. 2) Op zoek naar de gemene deler: agrarisch waterbeheer in de praktijk. 3) Kraamkamer van innovatie. 4) Modern aanbesteden is kennis delen: marktvisie waterschappen. 5) De politicus Liesbeth van Tongeren: Niet langer in discussie met klimaatsceptici. 6) Er valt iets te kiezen: waterschappen integreren duurzame energieproductie succesvol in hun kerntaken. 7) Slimmer investeren: Strategisch asset management. 8) Creativiteit op het snijvlak van orde en chaos: Waterschap De Dommel flirt met paradoxen. 9) Open overheid, ook voor waterschappen. 10) Werken aan morgen is gisteren al begonnen: hoe ziet werken voor een waterschap er in 2026 uit?

The applicability of in situ metal precipitation (ISMP) based on bacterial sulfate reduction (BSR) with molasses as carbon source was tested for the immobilization of a zinc plume in an aquifer with highly unsuitable initial conditions (high Eh, low pH, low organic matter content, and low sulfate concentrations), using deep wells for substrate injectionThe applicability of in situ metal precipitation (ISMP) based on bacterial sulfate reduction (BSR) with molasses as carbon source was tested for the immobilization of a zinc plume in an aquifer with highly unsuitable initial conditions (high E-h, low pH, low organic matter content, and low sulfate concentrations), using deep wells for substrate injection. Batch experiments revealed an optimal molasses concentration range of 1-5 g/L and demonstrated the necessity of adding a specific growth medium to the groundwater. Without this growth medium, even sulfate, nitrogen, phosphorus, and potassium addition combined with pH optimization could not trigger biological sulfate reduction. In column experiments, precipitation of ZnS(s) was induced biologically as well as chemically (by adding Na2S). In both systems, zinc concentrations dropped from about 30 mg/L to below 0.02 mg/L. After termination of substrate addition the biological system showed continuation of BSR for at least 2 months, suggesting the insensitivity of the sulfate reducing system for short stagnations of nutrient supply, whereas in the chemical system an immediate increase of Zn concentrations was observed. A pilot experiment conducted in situ at the zinc-contaminated site showed a reduction of zinc concentrations from around 40 mg/L to below 0.01 mg/L. Termination of substrate supply did not result in an immediate stagnation of the BSR process, but continuation of BSR was observed for at least 5 weeks.

Technieken om dierlijke mest en andere biomassa stromen te verwerken om de waardevolle componenten te benutten krijgen steeds meer de aandacht nu makkelijk winbare ertsen en energiebronnen van fossiele herkomst gelimiteerd raken en er meer en meer aandacht gegeven wordt aan terugdringen van uitstoot van CO2 van fossiele bronnen. Producten van dierlijke mest ressorteren onder diverse stelsels van regels van de Europese Unie. Deze stelsels zijn complex en bevorderen daardoor niet altijd een hergebruik. Dit rapport beschrijft kort welke technologieën er zijn om dierlijke mest te verwerken en welke producten daaruit resulteren. Vervolgens worden Europese wettelijke bepalingen beschreven die op deze producten van toepassing zijn. Deze bepalingen vragen aanpassing aan de nieuwe technologieën voor verwerking van dierlijke mest. Het rapport geeft daarvoor aanbevelingen.

Selenium in the form of selenate or selenite in wastewater needs to be removed due to its potential toxicity in the environment. Also, selenium is a valuable element that is used in several industries and current selenium resources are likely to be exhausted in less than 50 years. Waste streams containing selenium can therefore be used as a source of selenium. This requires conversion of the selenium in wastewater into a form that can be recovered. Biologically induced selenate reduction to recoverable selenium has the advantage that it uses the selective reduction capacities of biomass and a renewable electron donor. To improve the recoverability of selenium the conversion of selenate to selenite was seen as an interesting opportunity. Selenite is more reactive than selenate and can be removed in a second step. As described in Chapter 2, it proved possible to convert selenate to mainly selenite at a low electron donor concentration. Another method which is reviewed in this thesis is direct biological reduction of selenate to elemental selenium. After reduction the solids can be removed by a liquid solid separation process. Previously amorphous selenium particles were produced, which hampered recovery. In this research it is demonstrated that at a higher temperature, around 40 - 50°C, and at a higher pH, around pH 8 - 9, a more hexagonal selenium structure can be produced (Chapter 3). Crystalline acicular selenium particles of different sizes were thus obtained. This implies that selenium particles formation can be controlled and that selenium particles can grow. Large selenium particles make the separation process economic. To grow larger selenium particles, a long-term experiment was performed at 50°C (Chapter 4). The reduction rate was poor, but selenium acicular particles were produced. These particles were also detected as clusters. These clusters open up new recovery opportunities. With Eerbeek sludge the optimal conditions for selenate conversion are around pH=7 and 30°C. To enlarge the selenium particles it is strongly recommended to use a different sludge since the optimal conditions with Eerbeek sludge do not match the conditions needed for acicular particle formation. When selenate is converted to selenite, the selenite can be precipitated by sulphide to form selenium sulphide. Emmtec sludge was used to reduce the sulphur compounds to sulphide, leaving selenium as the sole remaining element. This process was performed at T=30°C and a pH between 6 and 7. The selenium thus recovered had a crystalline hexagonal structure (revealed by x-ray diffraction) and the particles were as large as 125µm3. Future research on the two routes that are explored in this thesis can give insights into selenium reduction mechanisms and the formation of large selenium particles. The recoverability of biological selenium particles has also been improved (as discussed in this thesis). In conclusion, this thesis has resulted in a new, bio-selective, renewable selenium recovery method via selenium sulphide.

Nieuwe, brongerichte sanitatieconcepten krijgen meer en meer aandacht en laten een groot potentieel zien voor het terugwinnen van nutriënten, organische stof en water, en voor de productie van energie. Verschillende van deze nieuwe sanitatieconcepten zijn geïmplementeerd in landen zoals Nederland, Duitsland, Zweden en China. Van de beschikbare terugwinningstechnieken voor urine is er geen één die zowel stikstof als fosfor kan terugwinnen. Dat is wel mogelijk door algen te kweken op urine, vanwege de hoge N:P ratio in de algen biomassa. Tot nu toe zijn er maar een beperkt aantal studies uitgevoerd gericht op het gebruik van urine voor het kweken van microalgen. Microalgenkweek heeft een groot potentieel voor de behandeling van urine in vergelijking met de meeste andere technieken die op dit moment al commercieel beschikbaar zijn. Een model system voor Nederlandse omstandigheden werd geëvalueerd, gebruik makend van parameterwaarden uit de experimenten beschreven in dit proefschrift als wel uit de literatuur. Dit heeft aangetoond dat in Nederland microalgenkweek mogelijk is van de late lente tot laat in de zomer.

Het doel van deze studie was te inventariseren welke waardevolle stoffen uit mest gewonnen kunnen worden en wat de potentie is in technologie en markt om deze te verwaarden. De inhoud van mest kan onderverdeeld worden in de volgende hoofdcategorieën: organische stof, mineralen, zware metalen, aminozuren, vluchtige vetzuren, antibiotica, hormonen. Via literatuuronderzoek is de samenstelling van elke categorie uiteen gesplitst in de verschillende stoffen met daarbij het gemiddelde gehalte van de betreffende stof in mest. Voor elke stof is de range in marktprijs nagegaan en aan de hand van het gehalte en marktprijs is de intrinsieke waarde van elke stof in de mest bepaald. Per hoofdcategorie van stoffen valt aan de hand van de waarde van de componenten te voorspellen of het mogelijk is om een sluitende business case te maken.

Nieuwe, brongerichte sanitatieconcepten krijgen meer en meer aandacht en laten een groot potentieel zien voor het terugwinnen van nutriënten, organische stof en water, en voor de productie van energie. Verschillende van deze nieuwe sanitatieconcepten zijn geïmplementeerd in landen zoals Nederland, Duitsland, Zweden en China. Van de beschikbare terugwinningstechnieken voor urine is er geen één die zowel stikstof als fosfor kan terugwinnen. Dat is wel mogelijk door algen te kweken op urine, vanwege de hoge N:P ratio in de algen biomassa. Tot nu toe zijn er maar een beperkt aantal studies uitgevoerd gericht op het gebruik van urine voor het kweken van microalgen. Microalgenkweek heeft een groot potentieel voor de behandeling van urine in vergelijking met de meeste andere technieken die op dit moment al commercieel beschikbaar zijn. Een model system voor Nederlandse omstandigheden werd geëvalueerd, gebruik makend van parameterwaarden uit de experimenten beschreven in dit proefschrift als wel uit de literatuur. Dit heeft aangetoond dat in Nederland microalgenkweek mogelijk is van de late lente tot laat in de zomer.

Het doel van deze studie was te inventariseren welke waardevolle stoffen uit mest gewonnen kunnen worden en wat de potentie is in technologie en markt om deze te verwaarden. De inhoud van mest kan onderverdeeld worden in de volgende hoofdcategorieën: organische stof, mineralen, zware metalen, aminozuren, vluchtige vetzuren, antibiotica, hormonen. Via literatuuronderzoek is de samenstelling van elke categorie uiteen gesplitst in de verschillende stoffen met daarbij het gemiddelde gehalte van de betreffende stof in mest. Voor elke stof is de range in marktprijs nagegaan en aan de hand van het gehalte en marktprijs is de intrinsieke waarde van elke stof in de mest bepaald. Per hoofdcategorie van stoffen valt aan de hand van de waarde van de componenten te voorspellen of het mogelijk is om een sluitende business case te maken.

Het gezamenlijk verwerken van dierlijke en humane uitwerpselen (rioolwater) op een rioolwaterzuiveringsinstallatie kan synergievoordelen bieden. Financieel kansrijk is de behandeling van het permeaat, dat ontstaat bij de verwerking van mest tot mineralenconcentraat. Deze reststroom bevat relatief weinig vervuiling. Gezamenlijke verwerking van dikkere, meer vervuilde mestfracties blijkt financieel (nog) niet aantrekkelijk. Stowa, Productschap Vee en Vlees en Waterschapsbedrijf Limburg hebben via een haalbaarheidsstudie de synergievoordelen laten onderzoeken bij mestverwerking op een rioolwaterzuivering.

Due to limited water resources available in the world and the ever growing world population, there is an increasing need for water recycling, recovery and multi-sourcing strategies. One of the new physical process technologies being investigated for water purification and/or constituent recycling is ultrasonic particle separation. This technology is especially interesting for harvesting particles with an almost neutral buoyancy. An ultrasonic particle filter does not use a filter medium, like sand or a membrane, but filters on a basis of acoustic forces in ultrasonic standing waves, which are able to immobilise particles in flowing water. The objective of this study was to develop an ultrasonic separation device for particle recovery and water purification. This separator should be fit for industrial applications treating cubic meters of water per hour. In order to reach this objective, a combined numerical-experimental approach was proposed to develop a model-based design of an ultrasonic separator. Each individual component of this separator was modelled using a finite element (FE) approach. The numerical simulations were continuously cross-checked with experiments in order to find the best solution possible. In this thesis, the source of the acoustic wave is a piezoelectric transducer attached to a glass matching layer of the acoustic cavity, which couples the transducer to the fluid inside the cavity, forming an acoustic resonator/separator. In order to obtain a valid FE transducer model, a limited set of material parameters for the piezoelectric transducer were obtained from the manufacturer, thus preserving prior physical knowledge to a large extent. The remaining unknown parameters were estimated from impedance (admittance) analysis combined with a numerical optimisation routine using 2D and 3D FE models. Thus, a full set of physically interpretable material parameters was obtained. The approach provided adequate accuracy of the estimates of the material parameters, near 1%. A similar approach as used for the transducer was applied to an existing ultrasonic separator, again preserving known physical parameters and estimating the remaining unknown or less certain parameters. The results showed that the approach led to a fully calibrated 2D model of the emptyseparator, which was subsequently validated with experiments on a filledseparator chamber. The large sensitivity of the separator to small variations indicated that either such system should be made and operated within tight specifications to obtain the required performance. Alternatively, the operation of the system should be adaptable to cope with a slightly off-spec system, requiring a feedback controller. Starting from a fully characterised existing separator with all material parameters found so far, the subsequent step was the actual design of, or extrapolation to, a new separator. A basic design for an industrial scale acoustic separator was obtained based on simulated flow characteristics inside the separation chamber, on acoustic analysis within the chamber and simulated particle trajectories combining these two analyses. Results showed that positioning the piezoelectric transducer surfaces perpendicular to the flow direction and introducing chamber partitioning with multiple flow lanes to enforce laminar flow, resulted in high particle retention. The average particle displacement was found to be related to acoustic pressure in the fluid, showing large retention at peak pressures above 1 MPa or average pressures above 0.5 MPa for small (10 µm), near buoyant (1100 kg/m3) particles at a flow speed of 3.5 cm/s, thus providing comprehensible criteria for subsequent optimisation. This basic ultrasonic standing wave separator design was optimised with respect to separation efficiency, throughput and energy consumption. The methodology, using a design of experiments (DOE) approach, showed that it was possible to improve system performance based on acoustic pressure profiles, separation efficiency and flow robustness. Compromising the energy consumption and aiming for maximum separation efficiency with a laminar stable flow up to 5 ml/s resulted in a separator with inner dimensions of 70 mm length, 20 mm width and 28.5 mm height using two transducers perpendicular to the direction of flow and three parallel flow lanes with 9.5 mm height each. The lowest power consumption (with an average of 30 W) with adequate pressure to trap the particles was obtained when it was not operated at the main eigenfrequency. Finally, this new ultrasonic particle filter was built and evaluated experimentally. The particle filter was a three channel device, manufactured from glass with four in/outlet ports made of ABS. It was operated in sequenced batch mode and the separation efficiency was determined at three flow rates ranging from 1 to 3 ml/s, using a stock suspension of insoluble potato starch of 1 g/l (1000 ppm). Concentrations of stock, filtrate and concentrate were measured using a turbidity meter and significant effects of acoustic particle concentration were measured at both outlets of the process. The maximum filtration efficiency and concentration efficiency were 54% and 76%, respectively. The performance found was lower than the 100% that was expected for 10 µm particles from the model based design study. The deviation in performance is mainly a result of (i) the pulsation of the feed pump, (ii) differences between the model and the actual prototype, (iii) the limited power supply of only 10 W used and (iv) (too) small particles, below 10 µm, occurring in the starch suspension. The best dimensions for an acoustic separator were obtained, but thus far operational characteristics were not yet studied. Operational characterisation and optimisation is the last step in the process of obtaining the best possible solution for operation. With the aim to achieve a high separation efficiency with minimal energy consumption, a model-based open-loop switching control strategy was designed for the commercially available BioSep, using a numerical-experimental approach. Firstly, a dynamic BioSep model structure was derived from mass balances and its system properties were studied. Then, the unknown system parameters were estimated from steady state and dynamic experimental data and subsequently, the switching times of the control input were determined. The model with switching control outputs was then validated by experiments. Finally, the control strategy was implemented in an experimental setup and tested using suspended potato starch. Results showed that the optimal control strategy reached a mass separation efficiency of 96%, which was an improvement of 4% with respect to the initial settings, while using less energy. Concluding, a stepwise numerical-experimental approach to acoustic separator design was presented in this study. The minimum power required was estimated to be 22-34 W, resulting in an average electric energy consumption of 1-1.5 kWh/m3. The practical concentration efficiency obtained was 76% at a flow rate of 2 ml/s and a filtration efficiency of 54% at 1 ml/s with a real power input of 8.8 W. An optimal open loop control strategy showed that it is possible to operate an acoustic separator with high separation efficiency using the least power possible. Parallelisation, instead of enlarging the separator, is recommended to scale this system up to larger, industrial flows.

Here, we report on laboratory experiments with the aim to explore cheap and innovative techniques. The main focus of the experiments was to lower the P-content in pig slurry with 25%. In that case, in principle all manure produced in the Netherlands can be applied on agricultural land in The Netherlands itself, including the organic matter and other nutrients in the manure. The results show that with physical and chemical treatment techniques 25% of the phosphate can rather easily be recovered from the solid or liquid fractions of the pig slurry. The costs of chemicals depend highly on the buffer capacity of the studied (n=3) pig slurries, and are less than 5 € per ton pig slurry.

Here, we report on laboratory experiments with the aim to explore cheap and innovative techniques. The main focus of the experiments was to lower the P-content in pig slurry with 25%. In that case, in principle all manure produced in the Netherlands can be applied on agricultural land in The Netherlands itself, including the organic matter and other nutrients in the manure. The results show that with physical and chemical treatment techniques 25% of the phosphate can rather easily be recovered from the solid or liquid fractions of the pig slurry. The costs of chemicals depend highly on the buffer capacity of the studied (n=3) pig slurries, and are less than 5 € per ton pig slurry.

In this thesis the integration of treatment systems for black and grey water was investigated to improve resource recovery within source-separated sanitation concepts. Special focus was set on phosphate and organic fertilizer recovery from vacuum collected black water. Currently, the soil application of black water sludge is prohibited in the Netherlands due to elevated heavy metal concentrations.

This thesis seeks to analyse whether and in what way institutional reconstruction meets the needs, and fits the context, of the population they are meant to serve. Often we talk about post-conflict societies as ‘being in transition’ or ‘moving out of crisis’, and this thesis basically asks the question: ‘transition to whatand movement to where’? The thesis is based predominantly on ethnographic work undertaken in Pader district, northern Uganda between 2010 and 2012 where stimulation of the agricultural sector has been pursued as a way to consolidate peace and promote recovery after years of displacement. The thesis finds that the processes and dynamics of transition in northern Uganda involve: (1) Messy transitions between humanitarian services and state-led market ‘modernisation’(2) an attempt to bridge policy and practice mismatches – a process through which institutional relations or new institutions evolve out of the process of recovery and reconstruction (3) that the transition and recovery in northern Uganda relates to the linking of Relief Rehabilitation and Destitution, rather than linking to Development. Assets erode to such an extent that development is not an achievable goal for many of those formerly displaced. Many people see their ‘normality’ becoming a state of ‘Destitution’ instead of ‘Development’.

SUMMARY Surfactants are produced and used in the formulation of many different commercial products. After use, these compounds end up in wastewater treatment plants (WWTPs) or in the environment. Although many surfactants can be degraded in aerobic conditions, anaerobic conditions are also common in Nature and in WWTPs. For achieving nutrients removal from wastewater, biological removal of nitrogen and phosphorus can be performed in a WWTP using the anaerobic-anoxic-aerobic (A2/O) concept. Using the A2/O process sequence, surfactants can be degraded anaerobically before reaching the aerobic compartment. In the anoxic compartment, facultative anaerobic bacteria can degrade surfactants by using nitrate/nitrite as electron acceptor. However, not much is known about surfactant-degrading denitrifying bacteria. In this thesis, Pseudomonas stutzeri strain SN1 and Pseudomonas nitroreducens strain SN2 were isolated from activated sludge of a WWTP with the A2/O process, using the anionic surfactant sodium dodecyl sulfate (SDS) as sole carbon and energy source. Both strains were able to completely degrade SDS coupled to nitrate reduction to dinitrogen gas (Chapter II). In the A2/O process, the diversity of bacterial communities involved in the degradation of surfactants may differ between anoxic and oxic compartments, where two different electron acceptors are involved. Surfactants can directly affect the biological activity of microorganisms present in WWTPs and disturb the treatment efficiency. In this way, increased concentrations of surfactants may give rise to a different bacterial diversity selection in anaerobic, anoxic and oxic conditions. The degradation of the anionic surfactant sodium lauryl ether sulfate (SLES) in aerobic conditions is known, but not in denitrifying conditions. In this thesis, the bacterial diversity of enrichments cultures able to degrade different concentrations of SLES in anoxic and aerobic conditions was determined. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8 and Pseudomonas nitroreducens strain S11 were isolated from anoxic enrichments. Comamonas testosteroni strain S13 and Acinetobacter sp. S15 were isolated from aerobic enrichments (Chapter III). SLES initial degradation steps by pure bacterial cultures were previously investigated, but much is still unknown about how the cleavage of ether bonds from chemical compounds is catalyzed by bacterial enzymes. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8 and Pseudomonas nitroreducens strain S11 are able to use SLES in anoxic conditions coupled to nitrate reduction (Chapter III). SLES degradation in anoxic conditions was compared between the three strains. P. nitroreducens strain S11 was found to be the best SLES degrader in anoxic conditions and also to be an excellent aerobic SLES degrader (Chapter IV). Sulfatases and ether cleaving enzymes were probably used by P. nitroreducens strain S11 in both conditions, although differences between SLES degradation in aerobic and anoxic conditions indicated that ether cleavage and following SLES complete degradation is faster under aerobic conditions. Although surfactants can be toxic to microorganisms, surfactant-degrading bacteria are known to be resistant to high surfactants concentration, in aerobic conditions. This was not previously investigated using surfactant-degrading denitrifying bacteria. Surfactant-resistant bacteria, with the ability to couple surfactant degradation to nitrate reduction, can be very useful for degrading the surfactants arriving to the anoxic compartments of a WWTP at high concentration. In this thesis, high concentrations of SDS and SLES were used to investigate the effect of these on SDS/SLES-degrading bacteria (P. stutzeri strain SN1, P. nitroreducens strain SN2, P. stutzeri strain S8 and P. nitroreducens strain S11), under anoxic conditions (Chapter V). P. stutzeri strain SN1 was inhibited by increasing SDS and SLES concentrations, after degrading a certain amount of the surfactants. Overall, P. nitroreducens strains showed to be more resistant to high surfactant concentrations compared to P. stutzeri strains. Nevertheless, high concentrations of SDS and SLES did not inhibit growth and nitrate reduction ability of any of the tested Pseudomonas sp.. Protein domains represent the evolutionary conserved autonomously folding functional building blocks of the proteins. Prediction of protein domains from genomes can be used for species classification and validation of known physiological abilities. P. nitroreducens are facultative anaerobic bacteria from the P. aeruginosa group, which can degrade complex compounds. P. nitroreducens DSM 14399T shares with P. nitroreducens strain SN2 the ability for SDS degradation in anoxic conditions. For increasing the insight into P. nitroreducens DSM 14399T phylogenetic classification and physiological properties (e.g. SDS degradation) its genome was sequenced, annotated and compared to other Pseudomonas spp. genomes. This was performed by comparing functional profiles, based on protein domains presence or absence, with physiological data (Chapter VI). Functional profile comparison confirmed P. nitroreducens classification. Protein domain analysis and genes annotation validated SDS degradation by P. nitroreducens DSM 14399T. This study showed that protein domains prediction and functional profiles comparison can be used for studying and comparing different Pseudomonas species at the physiological level.

Due to limited water resources available in the world and the ever growing world population, there is an increasing need for water recycling, recovery and multi-sourcing strategies. One of the new physical process technologies being investigated for water purification and/or constituent recycling is ultrasonic particle separation. This technology is especially interesting for harvesting particles with an almost neutral buoyancy. An ultrasonic particle filter does not use a filter medium, like sand or a membrane, but filters on a basis of acoustic forces in ultrasonic standing waves, which are able to immobilise particles in flowing water. The objective of this study was to develop an ultrasonic separation device for particle recovery and water purification. This separator should be fit for industrial applications treating cubic meters of water per hour. In order to reach this objective, a combined numerical-experimental approach was proposed to develop a model-based design of an ultrasonic separator. Each individual component of this separator was modelled using a finite element (FE) approach. The numerical simulations were continuously cross-checked with experiments in order to find the best solution possible. In this thesis, the source of the acoustic wave is a piezoelectric transducer attached to a glass matching layer of the acoustic cavity, which couples the transducer to the fluid inside the cavity, forming an acoustic resonator/separator. In order to obtain a valid FE transducer model, a limited set of material parameters for the piezoelectric transducer were obtained from the manufacturer, thus preserving prior physical knowledge to a large extent. The remaining unknown parameters were estimated from impedance (admittance) analysis combined with a numerical optimisation routine using 2D and 3D FE models. Thus, a full set of physically interpretable material parameters was obtained. The approach provided adequate accuracy of the estimates of the material parameters, near 1%. A similar approach as used for the transducer was applied to an existing ultrasonic separator, again preserving known physical parameters and estimating the remaining unknown or less certain parameters. The results showed that the approach led to a fully calibrated 2D model of the emptyseparator, which was subsequently validated with experiments on a filledseparator chamber. The large sensitivity of the separator to small variations indicated that either such system should be made and operated within tight specifications to obtain the required performance. Alternatively, the operation of the system should be adaptable to cope with a slightly off-spec system, requiring a feedback controller. Starting from a fully characterised existing separator with all material parameters found so far, the subsequent step was the actual design of, or extrapolation to, a new separator. A basic design for an industrial scale acoustic separator was obtained based on simulated flow characteristics inside the separation chamber, on acoustic analysis within the chamber and simulated particle trajectories combining these two analyses. Results showed that positioning the piezoelectric transducer surfaces perpendicular to the flow direction and introducing chamber partitioning with multiple flow lanes to enforce laminar flow, resulted in high particle retention. The average particle displacement was found to be related to acoustic pressure in the fluid, showing large retention at peak pressures above 1 MPa or average pressures above 0.5 MPa for small (10 µm), near buoyant (1100 kg/m3) particles at a flow speed of 3.5 cm/s, thus providing comprehensible criteria for subsequent optimisation. This basic ultrasonic standing wave separator design was optimised with respect to separation efficiency, throughput and energy consumption. The methodology, using a design of experiments (DOE) approach, showed that it was possible to improve system performance based on acoustic pressure profiles, separation efficiency and flow robustness. Compromising the energy consumption and aiming for maximum separation efficiency with a laminar stable flow up to 5 ml/s resulted in a separator with inner dimensions of 70 mm length, 20 mm width and 28.5 mm height using two transducers perpendicular to the direction of flow and three parallel flow lanes with 9.5 mm height each. The lowest power consumption (with an average of 30 W) with adequate pressure to trap the particles was obtained when it was not operated at the main eigenfrequency. Finally, this new ultrasonic particle filter was built and evaluated experimentally. The particle filter was a three channel device, manufactured from glass with four in/outlet ports made of ABS. It was operated in sequenced batch mode and the separation efficiency was determined at three flow rates ranging from 1 to 3 ml/s, using a stock suspension of insoluble potato starch of 1 g/l (1000 ppm). Concentrations of stock, filtrate and concentrate were measured using a turbidity meter and significant effects of acoustic particle concentration were measured at both outlets of the process. The maximum filtration efficiency and concentration efficiency were 54% and 76%, respectively. The performance found was lower than the 100% that was expected for 10 µm particles from the model based design study. The deviation in performance is mainly a result of (i) the pulsation of the feed pump, (ii) differences between the model and the actual prototype, (iii) the limited power supply of only 10 W used and (iv) (too) small particles, below 10 µm, occurring in the starch suspension. The best dimensions for an acoustic separator were obtained, but thus far operational characteristics were not yet studied. Operational characterisation and optimisation is the last step in the process of obtaining the best possible solution for operation. With the aim to achieve a high separation efficiency with minimal energy consumption, a model-based open-loop switching control strategy was designed for the commercially available BioSep, using a numerical-experimental approach. Firstly, a dynamic BioSep model structure was derived from mass balances and its system properties were studied. Then, the unknown system parameters were estimated from steady state and dynamic experimental data and subsequently, the switching times of the control input were determined. The model with switching control outputs was then validated by experiments. Finally, the control strategy was implemented in an experimental setup and tested using suspended potato starch. Results showed that the optimal control strategy reached a mass separation efficiency of 96%, which was an improvement of 4% with respect to the initial settings, while using less energy. Concluding, a stepwise numerical-experimental approach to acoustic separator design was presented in this study. The minimum power required was estimated to be 22-34 W, resulting in an average electric energy consumption of 1-1.5 kWh/m3. The practical concentration efficiency obtained was 76% at a flow rate of 2 ml/s and a filtration efficiency of 54% at 1 ml/s with a real power input of 8.8 W. An optimal open loop control strategy showed that it is possible to operate an acoustic separator with high separation efficiency using the least power possible. Parallelisation, instead of enlarging the separator, is recommended to scale this system up to larger, industrial flows.

This thesis seeks to analyse whether and in what way institutional reconstruction meets the needs, and fits the context, of the population they are meant to serve. Often we talk about post-conflict societies as ‘being in transition’ or ‘moving out of crisis’, and this thesis basically asks the question: ‘transition to whatand movement to where’? The thesis is based predominantly on ethnographic work undertaken in Pader district, northern Uganda between 2010 and 2012 where stimulation of the agricultural sector has been pursued as a way to consolidate peace and promote recovery after years of displacement. The thesis finds that the processes and dynamics of transition in northern Uganda involve: (1) Messy transitions between humanitarian services and state-led market ‘modernisation’(2) an attempt to bridge policy and practice mismatches – a process through which institutional relations or new institutions evolve out of the process of recovery and reconstruction (3) that the transition and recovery in northern Uganda relates to the linking of Relief Rehabilitation and Destitution, rather than linking to Development. Assets erode to such an extent that development is not an achievable goal for many of those formerly displaced. Many people see their ‘normality’ becoming a state of ‘Destitution’ instead of ‘Development’.

SUMMARY Surfactants are produced and used in the formulation of many different commercial products. After use, these compounds end up in wastewater treatment plants (WWTPs) or in the environment. Although many surfactants can be degraded in aerobic conditions, anaerobic conditions are also common in Nature and in WWTPs. For achieving nutrients removal from wastewater, biological removal of nitrogen and phosphorus can be performed in a WWTP using the anaerobic-anoxic-aerobic (A2/O) concept. Using the A2/O process sequence, surfactants can be degraded anaerobically before reaching the aerobic compartment. In the anoxic compartment, facultative anaerobic bacteria can degrade surfactants by using nitrate/nitrite as electron acceptor. However, not much is known about surfactant-degrading denitrifying bacteria. In this thesis, Pseudomonas stutzeri strain SN1 and Pseudomonas nitroreducens strain SN2 were isolated from activated sludge of a WWTP with the A2/O process, using the anionic surfactant sodium dodecyl sulfate (SDS) as sole carbon and energy source. Both strains were able to completely degrade SDS coupled to nitrate reduction to dinitrogen gas (Chapter II). In the A2/O process, the diversity of bacterial communities involved in the degradation of surfactants may differ between anoxic and oxic compartments, where two different electron acceptors are involved. Surfactants can directly affect the biological activity of microorganisms present in WWTPs and disturb the treatment efficiency. In this way, increased concentrations of surfactants may give rise to a different bacterial diversity selection in anaerobic, anoxic and oxic conditions. The degradation of the anionic surfactant sodium lauryl ether sulfate (SLES) in aerobic conditions is known, but not in denitrifying conditions. In this thesis, the bacterial diversity of enrichments cultures able to degrade different concentrations of SLES in anoxic and aerobic conditions was determined. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8 and Pseudomonas nitroreducens strain S11 were isolated from anoxic enrichments. Comamonas testosteroni strain S13 and Acinetobacter sp. S15 were isolated from aerobic enrichments (Chapter III). SLES initial degradation steps by pure bacterial cultures were previously investigated, but much is still unknown about how the cleavage of ether bonds from chemical compounds is catalyzed by bacterial enzymes. Aeromonas hydrophila strain S7, Pseudomonas stutzeri strain S8 and Pseudomonas nitroreducens strain S11 are able to use SLES in anoxic conditions coupled to nitrate reduction (Chapter III). SLES degradation in anoxic conditions was compared between the three strains. P. nitroreducens strain S11 was found to be the best SLES degrader in anoxic conditions and also to be an excellent aerobic SLES degrader (Chapter IV). Sulfatases and ether cleaving enzymes were probably used by P. nitroreducens strain S11 in both conditions, although differences between SLES degradation in aerobic and anoxic conditions indicated that ether cleavage and following SLES complete degradation is faster under aerobic conditions. Although surfactants can be toxic to microorganisms, surfactant-degrading bacteria are known to be resistant to high surfactants concentration, in aerobic conditions. This was not previously investigated using surfactant-degrading denitrifying bacteria. Surfactant-resistant bacteria, with the ability to couple surfactant degradation to nitrate reduction, can be very useful for degrading the surfactants arriving to the anoxic compartments of a WWTP at high concentration. In this thesis, high concentrations of SDS and SLES were used to investigate the effect of these on SDS/SLES-degrading bacteria (P. stutzeri strain SN1, P. nitroreducens strain SN2, P. stutzeri strain S8 and P. nitroreducens strain S11), under anoxic conditions (Chapter V). P. stutzeri strain SN1 was inhibited by increasing SDS and SLES concentrations, after degrading a certain amount of the surfactants. Overall, P. nitroreducens strains showed to be more resistant to high surfactant concentrations compared to P. stutzeri strains. Nevertheless, high concentrations of SDS and SLES did not inhibit growth and nitrate reduction ability of any of the tested Pseudomonas sp.. Protein domains represent the evolutionary conserved autonomously folding functional building blocks of the proteins. Prediction of protein domains from genomes can be used for species classification and validation of known physiological abilities. P. nitroreducens are facultative anaerobic bacteria from the P. aeruginosa group, which can degrade complex compounds. P. nitroreducens DSM 14399T shares with P. nitroreducens strain SN2 the ability for SDS degradation in anoxic conditions. For increasing the insight into P. nitroreducens DSM 14399T phylogenetic classification and physiological properties (e.g. SDS degradation) its genome was sequenced, annotated and compared to other Pseudomonas spp. genomes. This was performed by comparing functional profiles, based on protein domains presence or absence, with physiological data (Chapter VI). Functional profile comparison confirmed P. nitroreducens classification. Protein domain analysis and genes annotation validated SDS degradation by P. nitroreducens DSM 14399T. This study showed that protein domains prediction and functional profiles comparison can be used for studying and comparing different Pseudomonas species at the physiological level.

Due to the high nitrogen and phosphorus content, source-separated urine can serve as a major nutrient source for microalgae production. The aim of this study was to evaluate the nutrient removal rate and the biomass production rate of Chlorella sorokiniana being grown continuously in urine employing a short light-path photobioreactor. The results demonstrated, for the first time, the possibility of continuous microalgae cultivation in human urine. The lowest dilution factor successfully employed was a factor of 2 (50% v/v urine). Microalgae dominated a smaller bacterial population and were responsible for more than 90% of total nitrogen and phosphorus removal. With a light-path of 10 mm, a maximum volumetric biomass productivity as high as 9.3 g L(-1) d(-1) was achieved. The co-existing bacterial population removed up to 70% of organic pollutants from the urine at a rate of 1300 mg COD L(-1) d(-1). Enriching the urine with magnesium, adjusting the N:P molar ratio, and shortening the reactor light-path further increased the volumetric biomass productivity to 14.8 g L(-1) d(-1). The corresponding nitrogen and phosphorus removal rates were 1300 and 150 mg L(-1) d(-1), respectively. The subsequently produced biomass contained 43-53% w/w proteins and 16-25% w/w total fatty acids.

In this thesis the integration of treatment systems for black and grey water was investigated to improve resource recovery within source-separated sanitation concepts. Special focus was set on phosphate and organic fertilizer recovery from vacuum collected black water. Currently, the soil application of black water sludge is prohibited in the Netherlands due to elevated heavy metal concentrations.

Phoslock(®) is a lanthanum (La) modified bentonite clay that is being increasingly used as a geo-engineering tool for the control of legacy phosphorus (P) release from lake bed sediments to overlying waters. This study investigates the potential for negative ecological impacts from elevated La concentrations associated with the use of Phoslock(®) across 16 case study lakes. Impact-recovery trajectories associated with total lanthanum (TLa) and filterable La (FLa) concentrations in surface and bottom waters were quantified over a period of up to 60 months following Phoslock(®) application. Both surface and bottom water TLa and FLa concentrations were0.001 mg L(-1) in all lakes prior to the application of Phoslock(®). The effects of Phoslock(®) application were evident in the post-application maximum TLa and FLa concentrations reported for surface waters between 0.026 mg L(-1)-2.30 mg L(-1) and 0.002 mg L(-1) to 0.14 mg L(-1), respectively. Results of generalised additive modelling indicated that recovery trajectories for TLa and FLa in surface and bottom waters in lakes were represented by 2nd order decay relationships, with time, and that recovery reached an end-point between 3 and 12 months post-application. Recovery in bottom water was slower (11-12 months) than surface waters (3-8 months), most probably as a result of variation in physicochemical conditions of the receiving waters and associated effects on product settling rates and processes relating to the disturbance of bed sediments. CHEAQS PRO modelling was also undertaken on 11 of the treated lakes in order to predict concentrations of La(3+) ions and the potential for negative ecological impacts. This modelling indicated that the concentrations of La(3+) ions will be very low (0.0004 mg L(-1)) in lakes of moderately low to high alkalinity (0.8 mEq L(-1)), but higher (up to 0.12 mg L(-1)) in lakes characterised by very low alkalinity. The effects of elevated La(3+) concentrations following Phoslock(®) applications in lakes of very low alkalinity requires further evaluation. The implications for the use of Phoslock(®) in eutrophication management are discussed.

Membrane capacitive deionization (MCDI) is a water desalination technique based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports the water to be desalinated. In MCDI, ion-exchange membranes are positioned in front of each porous electrode to prevent co-ions from leaving the electrode region during ion adsorption, thereby enhancing the salt adsorption capacity. MCDI can be operated at constant cell voltage (CV), or at a constant electrical current (CC). In this paper, we present both experimental and theoretical results for desalination capacity and rate in MCDI (both in the CV- and the CC-mode) as function of adsorption/desorption time, salt feed concentration, electrical current, and cell voltage. We demonstrate how by varying each parameter individually, it is possible to systematically optimize the parameter settings of a given system to achieve the highest average salt adsorption rate and water recovery.

Bij de verwerking van menselijke en dierlijke mest kunnen meer nutriënten en energie worden teruggewonnen. Waterzuiveraars en mestverwerkers kunnen elkaar versterken door samen in onderzoek en praktijk te werken aan nieuwe verwerkingsmethoden.

Als resultaat van de samenwerking met de Metropoolregio Amsterdam benoemt Wageningen UR in dit document voor vier kringlopen actuele mogelijkheden en bijbehorende maatregelen om de kringlopen zo goed mogelijk te sluiten. In de vorm van factsheets wordt voor elke maatregel uitgewerkt wat deze oplevert voor de dimensies people, planet, profit en proces en wat de kosten, de risico’s en de randvoorwaarden daarbij zijn. De vier kringlopen zijn fosfaat, water, afval en voedsel.

Keywords: urine, urine treatment, nutrient recovery, microbial fuel cells, energy production from urine, membrane capacitive deionization. In conventional wastewater treatment plants large amounts of energy are required for the removal and recovery of nutrients (i.e. nitrogen and phosphorus). Nitrogen (N) compounds are removed as inert nitrogen gas and phosphorus (P) is for example removed as iron phosphate. About 80% of the N and 50% of the P in wastewater originate from urine1, but urine only contributes about 1% to the volume of this wastewater. High nutrient concentrations can be found in urine when it is collected separately from other wastewater streams. In this thesis, the nutrient and energy recovery from urine was investigated. At first, urine samples were analyzed for their composition. This characterization showed that the composition of the organic fraction in these samples was always similar. The differences between the concentrations of specific organic compounds were caused by dilution, due to individual consumption patterns of people. Two alternatives to the state-of-the-art nutrient recovery concepts are evaluated. These alternatives are on the one hand membrane capacitive deionization (MCDI) and on the other hand struvite precipitation combined with a microbial fuel cell (MFC). The evaluation of the MCDI system showed that nutrients can be concentrated from diluted urine. With its relatively low energy demand, MCDI could be an alternative to electrodialysis. The evaluation of the phosphate recovery by struvite precipitation combined with ammonium recovery and energy production by an MFC showed that this concept is most promising. The highest ammonium recovery rate achieved was 9.57 gN m-2 d-1 at a current density of 2.6 A m-2 (0.67 W m-2) using real undiluted urine. The ammonium recovery and energy production by an MFC (-10 kJ gN-1) can be considered a breakthrough, as usually energy is needed to recover (i.e. ammonia stripping 32.5 kJ gN-1)1 or convert (i.e. Sharon-Anammox 16 kJ gN-1)1 ammonium. Predictions show that approximately 5.1 kg struvite and 7.3 kg ammonia-nitrogen can be recovered from one cubic meter of urine, while producing approximately 20 kWh. A comparison to state-of-the-art technology showed that this process can be a good alternative for nutrient recovery from urine. Furthermore, ammonium recovery and energy production by an MFC can possibly be applied to other wastewater streams.

Het Biorenewable Business Platform en Energy Valley hebben LEI Wageningen UR gevraagd een studie uit te voeren voor routes waarlangs fosfaatwinning gestalte kan krijgen. Het onderzoek is gefinancierd door het Inter Provinciaal Overleg (IPO). Namens IPO is de provincie Groningen de opdrachtgever van het onderzoek. In het offertetraject waren in hoofdlijnen de vijf uit te werken routes voor fosfaatterugwinning al vastgelegd. Bij dit onderzoek zijn die vijf routes verder uitgewerkt met daarbij de nadruk op economie en innovativiteit. Belangrijkste uitkomsten: Recycling van fosfaat uit verbrandingsas van zuiveringsslib is praktijkrijp en economisch haalbaar. De economische vooruitzichten voor het recyclen van fosfaat uit varkensmest en organisch industrieel afval zijn heel onzeker. Winning van struviet uit organische afvalstromen is voor fosfaatrecycling economisch niet interessant.

Bij de verwerking van menselijke en dierlijke mest kunnen meer nutriënten en energie worden teruggewonnen. Waterzuiveraars en mestverwerkers kunnen elkaar versterken door samen in onderzoek en praktijk te werken aan nieuwe verwerkingsmethoden.

Het Biorenewable Business Platform en Energy Valley hebben LEI Wageningen UR gevraagd een studie uit te voeren voor routes waarlangs fosfaatwinning gestalte kan krijgen. Het onderzoek is gefinancierd door het Inter Provinciaal Overleg (IPO). Namens IPO is de provincie Groningen de opdrachtgever van het onderzoek. In het offertetraject waren in hoofdlijnen de vijf uit te werken routes voor fosfaatterugwinning al vastgelegd. Bij dit onderzoek zijn die vijf routes verder uitgewerkt met daarbij de nadruk op economie en innovativiteit. Belangrijkste uitkomsten: Recycling van fosfaat uit verbrandingsas van zuiveringsslib is praktijkrijp en economisch haalbaar. De economische vooruitzichten voor het recyclen van fosfaat uit varkensmest en organisch industrieel afval zijn heel onzeker. Winning van struviet uit organische afvalstromen is voor fosfaatrecycling economisch niet interessant.

Bij de verwerking van menselijke en dierlijke mest kunnen meer nutriënten en energie worden teruggewonnen. Waterzuiveraars en mestverwerkers kunnen elkaar versterken door samen in onderzoek en praktijk te werken aan nieuwe verwerkingsmethoden.

Als resultaat van de samenwerking met de Metropoolregio Amsterdam benoemt Wageningen UR in dit document voor vier kringlopen actuele mogelijkheden en bijbehorende maatregelen om de kringlopen zo goed mogelijk te sluiten. In de vorm van factsheets wordt voor elke maatregel uitgewerkt wat deze oplevert voor de dimensies people, planet, profit en proces en wat de kosten, de risico’s en de randvoorwaarden daarbij zijn. De vier kringlopen zijn fosfaat, water, afval en voedsel.

Met het model galvanisch bedrijf zijn computerberekeningen uitgevoerd aan 24 modelbedrijven. Daarbij is met name nagegaan, welke kosten moeten worden gemaakt om welk rendement te verkrijgen bij diverse saneringsvarianten. Het blijkt, dat tegen kosten tussen nul en 300 gulden per verwijderde kilogram zwaar metaal (incl. die uit concentraten) restvrachten van enkele tientallen kg zware metalen kunnen worden bereikt. De combinatie van een procesgeintegreerde aanpak en eindzuivering blijkt voordeliger en levert betere resultaten dan alleen eindzuivering. Kleine bedrijven kunnen veel bereiken met alleen een procesgeintegreerde aanpak.

Met het model galvanisch bedrijf zijn computerberekeningen uitgevoerd aan 24 modelbedrijven. Daarbij is met name nagegaan, welke kosten moeten worden gemaakt om welk rendement te verkrijgen bij diverse saneringsvarianten. Het blijkt, dat tegen kosten tussen nul en 300 gulden per verwijderde kilogram zwaar metaal (incl. die uit concentraten) restvrachten van enkele tientallen kg zware metalen kunnen worden bereikt. De combinatie van een procesgeintegreerde aanpak en eindzuivering blijkt voordeliger en levert betere resultaten dan alleen eindzuivering. Kleine bedrijven kunnen veel bereiken met alleen een procesgeintegreerde aanpak.

This report comprises the results of an explorative study on innovative nitrogen recovery from side streams of wastewater treatment plants (WWTPs) in the Netherlands. The main objective of the study was to identify promising new technologies for recovery of nitrogen which can be subsequently used as an artificial fertilizer. This shortcircuits the global nitrogen cycle and thereby reduces the environmental impact of the nitrogen cycle that has been distorted by human influence (eutrophication, greenhouse gases).

Dit werkpakket gaat over terugwinnen van grondstoffen uit zij- en eindstromen van de Biobased Economy en het veilig en duurzaam hergebruik daarvan bij de productie of verwerking van biomassa, of bij herstellen van de natuurlijke balans van bodem- en watersystemen. De focus van dit werkpakket ligt op water, mineralen en koolstof, en de effecten op biodiversiteit.

This report comprises the results of an explorative study on innovative nitrogen recovery from side streams of wastewater treatment plants (WWTPs) in the Netherlands. The main objective of the study was to identify promising new technologies for recovery of nitrogen which can be subsequently used as an artificial fertilizer. This shortcircuits the global nitrogen cycle and thereby reduces the environmental impact of the nitrogen cycle that has been distorted by human influence (eutrophication, greenhouse gases).

De Nederlandse landbouw heeft een mineralenoverschot in de vorm van dierlijke mest. Verwerking van mest wordt gezien als één van de opties om dit overschot te reduceren. Aan de hand van drie scenario’s is nagegaan welke mogelijkheden er zijn voor de plaatsing van verschillende dunne mestfracties in de akkerbouw als uitgegaan wordt van de gebruiksnormen voor 2013. Ook is nagegaan welke opties er zijn om de mineralen uit deze dunne mestfracties terug te winnen om via een RWZI lozing op het oppervlaktewater mogelijk te maken. Hierbij wordt naar maximale synergie gezocht tussen mestverwerking en de zuiveringstechnieken op de RWZI. De plaatsingsmogelijkheden voor dunne mest in de akkerbouw zijn beperkt aanwezig. Er zijn mogelijkheden om mineralen uit dunne mestfracties terug te winnen en op onderdelen is synergie te bereiken met RWZI’s, echter de praktijkervaringen zijn zeer gering en het verdient aanbeveling om deze nader in de praktijk te verkennen.

De Nederlandse landbouw heeft een mineralenoverschot in de vorm van dierlijke mest. Verwerking van mest wordt gezien als één van de opties om dit overschot te reduceren. Aan de hand van drie scenario’s is nagegaan welke mogelijkheden er zijn voor de plaatsing van verschillende dunne mestfracties in de akkerbouw als uitgegaan wordt van de gebruiksnormen voor 2013. Ook is nagegaan welke opties er zijn om de mineralen uit deze dunne mestfracties terug te winnen om via een RWZI lozing op het oppervlaktewater mogelijk te maken. Hierbij wordt naar maximale synergie gezocht tussen mestverwerking en de zuiveringstechnieken op de RWZI. De plaatsingsmogelijkheden voor dunne mest in de akkerbouw zijn beperkt aanwezig. Er zijn mogelijkheden om mineralen uit dunne mestfracties terug te winnen en op onderdelen is synergie te bereiken met RWZI’s, echter de praktijkervaringen zijn zeer gering en het verdient aanbeveling om deze nader in de praktijk te verkennen.