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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.

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.