Resources

AffiliationsSchool of the Environment, Washington State University, Vancouver, WA, USAJitendra Singh & Deepti SinghComputational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN, USAMoetasim AshfaqDepartment of Environmental, Earth and Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA, USAChristopher B. SkinnerInternational Research Institute for Climate and Society, Columbia University, Palisades, NY, USAWeston B. AndersonCivil Engineering, Indian Institute of Technology (IIT) Gandhinagar, Gandhinagar, IndiaVimal MishraEarth Sciences, Indian Institute of Technology (IIT) Gandhinagar, Gandhinagar, IndiaVimal MishraAuthorsJitendra SinghMoetasim AshfaqChristopher B. SkinnerWeston B. AndersonVimal MishraDeepti SinghCorresponding authorCorrespondence to
Jitendra Singh. More

Characterization of self-doped BM-TNA and BP-TNA electrodesFigure 1(a) and (b) show the horizontal and cross-sectional FE-SEM images of the growth shape of the self-doped BM-TNA after annealing on a Ti mesh at 600 °C. The structure of the open TiO2 nanotube array exhibited approximate outer and inner diameters of 138.0 and 75.3 nm, respectively, and a length of 9.7 μm. Similarly, Fig. 1(c) and (d) show the FE-SEM images of the self-doped BP-TNA annealed at 600 °C on a Ti plate. The results suggested that the anodization potential and annealing temperature were the key parameters in determining the crystallographic structure of the TiO2 surface during the synthesis of BM-TNA and BP-TNA. In addition, the XPS results shown in Fig. 1(e) indicate Ti2p and O1s peaks with high binding energy. According to the visualization, the peaks for Ti2p and O1s were equally identified at 459.5 eV and 530.75 eV, respectively, for both the BP-TNA and BM-TNA electrodes. Figure 1(f) shows that the anatase and rutile peaks as the crystal structure were annealed in the order of XRD. This structural aspect was described in a previous study40, and anatase peaks formed at 300 and 450 °C. In addition, mixed peaks (i.e., anatase and rutile) were observed at 600 °C. The behaviors of the self-doped BM-TNA, BP-TNA were confirmed through the applied cathodic reduction followed by the anatase peak at 450 °C, and the anatase and rutile peaks at 600 °C for the TiO2 surface structure according to the change in annealing of the catalyst. These self-doped materials had excellent photochemical efficiency at peaks consisting of anatase and rutile peaks, which hindered reconversion.Fig. 1: Characterization of the BM- and BP-TNA electrodes via SEM, XPS, and XRD analyses.SEM images of a, b BM-TNA and c, d BP-TNA; e XPS signals and f XRD intensities. The length of the scale bars are as follows: a, c 500 µm; b, d 5 µm.Full size imageEffect of the novel catalyst and photoelectrochemical activity via UV-lights sourceTo explore the potential of the catalyst, we evaluated the oxygen evolution reaction (OER) properties by comparing the activities of the BM-TNA and BP-TNA catalysts, as shown in the electrochemical impedance spectroscopy (EIS) results (Fig. 2(a)). EIS analysis confirmed the occurrence of charge transfer, which was evaluated under an open circuit potential with an amplitude of 10.0 mV over a scan frequency of 100.0–10.0 kHz in brackish water (i.e., 3000 mg L−1). The BM-TNA exhibited a much higher transfer resistance than the BP-TNA catalysts, indicating the rapidly induced electron transfer efficiency of the BM-TNA.Fig. 2: Nyquist plot, and degradation of benzoic acid using BM- and BP-TNA electrodes under UV.a Nyquist plot (BM-TNA/BP-TNA) and b, c benzoic acid degradation by BM-TNA and BP-TNA photoelectrochemical processes under different forms of UV light ([NaCl]0 = 3000 ppm; scan rate = 50 mV s−1 for LSV/CV; scan frequency = 100 kHz–10 mHz with 10 mV rms sinusoidal modulation versus open circuit potential for EIS; [Benzoic acid]0 = 0.1 mM; constant voltage = 1 A; pHi = 7.0).Full size imageTo further evaluate the capacity of the two catalysts, degradation performance of BA as a model substrate within the PEC system under UV-A, B, and C lamps with and without the BM-TNA and BP-TNA catalysts was investigated as shown in Fig. 2(b) and (c). When the organic substance was irradiated with only the UV lamps, BA was hardly decomposed under UVA/B, while degradation slightly increased under the UVC light (Fig. 2(a)). However, in Fig. 2(b) and (c), it was confirmed that the morphology of the anodic catalyst (i.e., BM-TNA, BP-TNA) accelerated the decay of BA, and efficiency was much more significant for BM-TNA with its large specific surface area.In the combined operation with the BM-TNA electrode annealed at 600 °C, degradation rate was significant with the reaction rate of the PEC system as follows: (k (UVC-PEC) 0.0444 ± 0.0017 min−1)  > (k (UVB-PEC) 0.0269 ± 0.001 min−1)  > (k (UVA-PEC) 0.0108 ± 0.0004 min−1). In contrast, degradation using the BP-TNA electrode equally annealed at 600 °C showed much lower results with the following reaction rates: (k (UVC-PEC) 0.0145 ± 0.0004 min−1)  > (k (UVB-PEC) 0.0119 ± 0.0004 min−1)  > (k (UVA-PEC) 0.0053 ± 0.0001 min−1). Significance of the novel BM-TNA catalyst was further confirmed through comparison with a similar BM-TNA electrode prepared at 450 °C (Supplementary Fig. 2). The novel electrode annealed at 600 °C exhibited greater mineralization efficiency, and the enhancement was distinguishable under all UV-A, B, and C lights. The measured energy consumption under UV-A, B, and C with a reaction time of 120 min was 0.035, 0.056, and 0.074 kWh, respectively.The quenching effect of the BM-TNA catalyst in the presence of saltwater was also confirmed, as shown in Supplementary Fig. 3(a). When excess methanol and tert-butanol were applied, a dynamic delay in BPA degradation by the BM-TNA was observed. The main oxidant tended to degrade under the influence of hydroxyl radicals during electrolysis, and tert-butanol is effective for eliminating •OH k (•OH + tert-BuoH = 6.0 × 108 M−1S−1). However, in the PEC system without a scavenger, the decomposition of BPA was monitored, indicating that reaction with UV-A light induced the formation of hydroxyl radicals as a powerful oxidizing agent due to the nature of the OER catalyst. Concurrently, the decomposition efficiency was monitored with BA as the target compound to identify the strong ROS generated in the PEC system (Supplementary Fig. 3(b)). When BA was decomposed, the formation of by-product as 4-HBA was confirmed, and an excellent reduction in TOC was observed.Removal of organic compounds and catalytic stability of the PEC systemThe removal efficiencies of various organic pollutants in the PEC system were represented by pseudo-first-order rate constants, as shown in Fig. 3(a). Representative organic contaminants in brackish water were selected for investigation (i.e., BPA, 4CP, CMT, BA, PH, NIB, AMP, and SMX). The reaction rates of the organic pollutants in the system were as follows: (k (4CP) = 0.0447 ± 0.0019 min−1)  > (k (PH) = 0.0381 ± 0.0028 min−1)  > (k (CMT) = 0.0361 ± 0.0012 min−1)  > (k (BPA) = 0.0291 ± 0.001 min−1)  > (k (AMP) = 0.0270 ± 0.003 min−1)  > (k (BA) = 0.0181 ± 0.0012 min−1)  > (k (SMX) = 0.0173 ± 0.0002 min−1)  > (k (NIB) = 0.0127 ± 0.0032 min−1). The PEC oxidation efficiencies, including aromatic compounds (such as electron-donating group (EDG) and electron-withdrawing group (EWG)) for BM-TNA catalysts exhibit different substrate specificities41,42. For instance, the phenolic compounds of EDG more easily released protons into the solution under •OH- induced oxidation, and were more susceptible to PEC anodization43,44. Specifically, the positive redox potential of 4CP exhibited faster degradation than PH (+0.86 VNHE for PH versus +0.8 VNHE for 4CP), which may contribute to the significant resistance against the oxidation45,46. In contrast, the EWG (i.e., BA and NIB) dynamically hindered the degradation of BA and NIB via benzene ring substitution24.Fig. 3: Organic degradation via BM-TNA electrode, and evaluation of electrode stability.a Organic compound removal efficiency of BM-TNA under the photoelectrochemical system ([bisphenol-A]0, [4-chlorophenol]0, [sulfamethoxazole]0, [cimetidine]0, [benzoic acid]0, [acetaminophen]0, [nitrobenzene]0, [phenol]0 = 0.1 mM, [NaCl]0 = 3000 ppm; pHi = 7.0), and b repetition test of bisphenol-A decay ([bisphenol-A]0 = 10 µM, [NaCl]0 = 3000 ppm; pHi = 7.0).Full size imageThe stability and durability of the BM-TNA catalyst system were evaluated via 20 repeated BPA degradation cycles in the PEC cell (Fig. 3(b)). The results indicate the long-term stability of the catalyst through the similar decomposition efficiency to the initial value of BPA when operating continuously at an initial pH of 7 for 20 h. In addition, the catalysts annealed at 600 °C maintained the initial color (i.e., blue) of the photocatalyst activity electrode. This result is linked to Supplementary Fig. 4, in which the BPA removal efficiency of the PEC system was evaluated as a function of pH (pH 3–9). The efficacy of BPA at pH 3, 5, 7, and 9 were 99.3%, 94.4%, 93.9%, and 87.3%, respectively. This result suggests that the kinetic retardation and inhibition of radical formation of the PEC cell under alkaline conditions (above pH 9) increased the OH- content of the aquatic system.Evaluation of the FCDI process operation via deionization and SECThe performance of the FCDI operation was evaluated under three carbon mass loadings (5, 10, and 15 wt%) and three applied voltages (0.5, 0.8, and 1.1 V), and was optimized based on the SEC. In FCDI, activated carbon plays the role of ion adsorption owing to its exceptional surface area, electrical conductance, and ideal adsorption isotherm47. Accordingly, a higher carbon mass loading in the flow-electrode solution increases the surface area available for ion adsorption. In addition, activated carbon particles act as a bridge for charge transportation. In an ideal homogeneous solution, in which the distribution of the activated carbon particles is even throughout the flow-electrode solution, charge transportation is also uniform with no fluctuation in the charge efficiency. However, flow-electrode solutions are heterogeneous and dynamic in nature, thus raising the issue of charge percolation. The deformation in the electrode material distribution during flow causes a decrease in the particle and charge connectivity48. Similarly, increasing the carbon mass loading allows the formation of strongly defined charge-percolation pathways, thereby improving the solution conductivity and accelerating charge transportation49,50. This relationship was confirmed to be consistent with previous studies that reported a positive correlation between the mass loading and conductivity of the flow-electrode solution48.Correspondingly, the ion removal efficiency of the system was enhanced as the mass loading and applied voltage increased, as shown in Fig. 4(a). Under an applied voltage of 0.5 V, the efficiency was, on average, seven-fold and eleven-fold higher when the carbon mass loading increased to 10 and 15 wt%, respectively. For 0.8 and 1.1 V, the efficiencies increased by approximately eightfold and thirteen-fold, and twofold and threefold, under 10 and 15 wt%, respectively. The obtained results were consistent with those of previous studies. One previous study reported a sharp increase in the desalting performance when the carbon mass loading was increased from 0 to 10 wt%51, while another reported a similar trend in process performance as the mass loading increased from 20 to 25 wt%52. Ion removal was quantified in detail as shown in Supplementary Figs. 5–7, with (a) and (b) for the three figures representing the sodium and chloride ion concentrations in the permeate solution, respectively. A comparable reduction can be observed, with the slope of the concentration gradient becoming sharper as mass loading increased. (c) and (d) represent the ionic concentrations within the flow-electrode (slurry) solution, which were confirmed to increase as the ions within the feed stream adsorbed to the flow-electrode solution. The influences of the mass loading and applied voltage were further assessed via solution conductivity, SAC, and SAR, as shown in Supplementary Figs. 8–10. Regarding conductivity, a mass loading of 5 wt% resulted in nominal removal under all applied voltage conditions, with the maximum deionization reaching only ~20%. However, higher mass loadings of 10 and 15 wt% resulted in considerable enhancements. Quantitatively, the deionization performance under a mass loading of 10 wt% increased by 1.3-, 1.6-, and 1.8-fold under applied voltages of 0.5-, 0.8-, and 1.1 V, respectively, and by 1.4-, 1.8-, and 2.0-fold under a mass loading of 15 wt%. Similarly, increasing the two operational parameters enhanced the SAC, and the linear trend in SAR demonstrated the consistent performance of the FCDI system.Fig. 4: Deionization performance and relative energy consumption of the FCDI system.a Ion removal efficiency, and b specific energy consumption of the flow-electrode capacitive deionization system (activated carbon mass loading = 5, 10, 15 wt%, applied voltage = 0.5, 0.8, 1.1 V, flow-electrode electrolyte = 1 M).Full size imageHowever, the parallel increase in viscosity and the decrease in solution fluidity are common major obstacles associated with increasing mass loading. Owing to the trade-off relationship, the loading in FCDI systems is commonly restricted to within 20 wt%53,54,55 when no additional surface modification methods are followed for electrode material synthesis. Consistently, the mass loading condition in this study was limited to 15 wt%, and solution viscosity and clogging in the flow channel were not observed. As shown in Fig. 4(b), the validity of the mass loading and applied voltage was further assessed via SEC and quantified based on the total amount of ions removed during operation. The SEC followed a similar trend under all conditions, with the value increasing under higher loading rates. The change in the applied voltage followed comparable trends under mass loadings of 10 and 15 wt%. Despite the improvement in the deionization performance as the mass loading increased, as shown in Fig. 4(a), the reason for the higher SEC was the concurrent enhancement in the charge percolation of the system52. The strengthened electrical conductance and synchronous reduction in cell resistance led to the enhancement of current efficiency56,57, resulting in a higher projected SEC. Specifically, the SEC values under a mass loading of 10 wt% were highly similar to those under 5 wt%. The changes in the values were below twofold for all applied voltage conditions, with the maximum being 1.6-fold. However, increasing the mass loading to 15 wt% increased the SEC values by 1.7, 2.4, and 2.5-fold under applied voltages of 0.5, 0.8, and 1.1 V, respectively. As the initial objective of the study was to obtain permeate within the suggested TDS range of potable water set by the World Health Organization or domestic water58, the sequential two-adsorption operation was deemed sufficient to satisfy the standards based on the ion removal efficiency, as shown in Fig. 4(a). Therefore, a carbon mass loading and applied voltage of 10 wt% and 0.8 V were determined to be the optimal operational parameters, respectively. Comparably, a higher applied voltage (1.1 V) resulted in nominal changes in ion removal, with a much larger SEC. Similarly, a carbon mass loading of 15 wt% resulted in a higher deionization efficiency, which was also within a nominal range of ~1.2-fold with a much higher SEC.Evaluation on the performance of PEC-FCDI dual processThe feasibility of the PEC-FCDI dual system was investigated by treating brackish water to produce organic contaminant-free permeate that meets the freshwater TDS standards. To investigate the efficacy of the system more accurately, the brackish water was prepared as a complex solution including multiple monovalent and divalent salts to reflect the composition of real brackish water as detailed in Supplementary Table 1. As shown in Fig. 5, the organic mineralization of BPA was evaluated at the PEC stage by measuring the TOC level. During the 60 min operation, an extremely sharp decrease in the TOC to 20% of the initial concentration was observed in the first 20 min. Subsequently, a three-log removal of BPA was monitored, with the final, complete degradation of the target pollutant occurring within 40 min of operation. No further formation of oxidation by-products was detected during the PEC process.Fig. 5: Operation of the PEC-FCDI dual system.PEC-FCDI dual system (PEC: [bisphenol-A]0 = 0.1 mM, pHi = 7.0; operation time = 60 min) (FCDI: [NaCl]0 = 1947 ppm, [MgCl2]0 = 428 ppm, [Na2SO4]0 = 278 ppm, pHi = 7.0; activated carbon mass loading = 10 wt%, applied voltage = 0.8/−0.8 V, flow-electrode electrolyte = 1 M; first-adsorption time = 40 min, desorption time = 30 min, second-adsorption time = 20 min).Full size imageA subsequent FCDI stage was conducted for the purpose of deionization, and performance was evaluated based on the quantification of the removal of individual ions. During the first adsorption phase, a rapid decrease in the ion concentration generally occurred within 20 min. Specifically, the contents of sodium, magnesium, chloride and sulfate ions were reduced by 71, 72, 75.6 and 75.2%, respectively, indicating similar deionization efficiencies for both cations and anions. The adsorption rate eventually decelerated and reached a plateau as the pores of the activated carbon electrode became fully saturated with ions transported from the feed solution; thus, a desorption phase was required for the pores and charge balance of the system to recover to the initial state38. The desorption phase was conducted by reversing the applied voltage, and was operated for 30 min. The ions adsorbed in the micro-/ macropores of the electrode particles were discharged via electrostatic repulsion and transported across the ion exchange membranes to the feed stream. The ionic concentration of the flow-electrode slurry solution gradually decreased during the 30 min discharge operation, and all the ions adsorbed during the adsorption phase were discharged from the solution. After 30 min, the slurry solution was fully recovered for the operation of the second-adsorption phase. The final adsorption phase was conducted for 20 min with the permeate from the first adsorption phase as the feedwater solution. Under the low initial ion concentration, a similar rapid decline was observed, with almost two-log removal within minutes of operation, and complete deionization of the feedwater was ultimately achieved. Lastly, the energy consumption of the FCDI system was monitored, and the total combined SEC of the two-adsorption phases was 0.031 kWh g−1 ion removal, which was lower than that evaluated during the process optimization (Fig. 4), thereby further strengthening the feasibility of the technology for real water applications.The treatment of brackish water for drinking or domestic use has mostly been conducted using brackish water RO or NF processes. However, critical drawbacks due to the low removal of trace organic pollutants, membrane surface fouling by the attachment of organics, and high energy consumption due to the pressure-driven nature of the technology indicate the limitations of the processes. In contrast, oxidation via the PEC system can achieve complete mineralization of trace organic compounds, while the subsequent deionization sequence of FCDI can attain ion desalination within the brackish water source under low energy consumption.The novel self-doped BP-TNA and BM-TNA electrodes prepared by annealing at 600 °C revealed excellent charge transfer efficiencies, and effective degradation of eight model organic pollutants, with the BP-TNA showing superior performance. Organic mineralization was stably maintained at high levels throughout a wide pH range of 3–9, and a continuous experiment of seven repetitive cycles with uniform performance demonstrated the stability of the electrode. In addition, solution desalination was observed during the subsequent FCDI stage, and particularly, the increase in carbon mass loading improved charge-percolation pathways, which led to superior solution conductivity and charge transportation efficiency of the system.The use of the hybrid PEC-FCDI system is expected to be a superior alternative to conventional processes. Owing to its exceptional performance and low energy consumption levels, the system is promising for practical application in the field of brackish water treatment for both potable or domestic use. More

To simultaneously consider the complexity of hydrology (that is, the impact of rainfall intensity and local topography, which influence flooding) and water quality, urban runoff storage and treatment processes should be more common, especially for densely populated cities where natural landscape is insufficiently available to process, infiltrate and treat stormwater. New and strategically geolocalized infiltration areas, collection systems and/or modular treatment processes that provide certain flexibility for expansion can help mitigate floods and the load of contaminants during peak rainfall or snowmelt events. Large-scale viable and sustainable solutions are needed to store and passively treat urban runoff and deal with intense rainfall events that cannot be hydraulically supported by existing wastewater treatment plants designed to treat lower flow rates. Examples of such existing solutions, as well as more sustainable solutions to be adapted for runoff treatment, include retention ponds, bioretention cells or raingardens (~95% particle removal), coarse sand filters, bio-assisted aggregation and filtration systems, aerated ponds, underground tanks in dense urban areas, adsorption via functionalized media in a granular filter, passive aggregation and settling tanks and passive O2/ultraviolet (photo)oxidation. Such retention processes could act as onsite surge tanks while also removing several contaminants from runoff, combined sewer overflow, or cross-connected sewers before discharge into natural waters.Examples of existing and new promising solutions are presented in Fig. 2 and include hydraulic buffers (solutions 2, 4, 5, 7, 8, 9 and 10), physicochemical filtration and adsorption systems (solution 6, for soluble and particulate matters), bioretention and biodegradation processes (solutions 4, 7, 9 and 10), underground separation units based on centripetal or gravitational force (solutions 3 and 5, for particulates), and (bio)flocculant-assisted bioretention and settling tank (solution 2; partially buried, for soluble and particulate matters). Simple process units can be implemented directly in stormwater sewers or manholes; for instance, vortex separators (solution 3) to remove denser particles from water, screens to trap larger debris ( >10 mm), modular biofilters to remove nutrients, heavy metals and oils, and porous granular filters to trap smaller particles ( More

Mora, C. et al. Broad threat to humanity from cumulative climate hazards intensified by greenhouse gas emissions. Nat. Clim. Change 8, 1062–1071 (2018).CAS 
Article 

Google Scholar 
AghaKouchak, A. et al. How do natural hazards cascade to cause disasters? Nature 561, 458–460 (2018).CAS 
Article 

Google Scholar 
Brammer, H. Agriculture and food production in polder areas. Water Int. 8, 74–81 (1983).Article 

Google Scholar 
Flood Action Plan 4 (FAP 4). Southwest Area Water Resources Management Project, Final Report (People’s Republic of Bangladesh, Ministry of Irrigation, Water Development and Flood Control, 1993).Afroz, S., Cramb, R. & Grünbühel, C. Exclusion and counter-exclusion: the struggle over shrimp farming in a coastal village in Bangladesh. Dev. Change 48, 692–720 (2017).Article 

Google Scholar 
Adnan, S. in Water, Sovereignty and Borders: Fresh and Salt in Asia and Oceania (eds Ghosh, D. et al.) 104–124 (Routledge, 2009).Paprocki, K. & Cons, J. Life in a shrimp zone: aqua- and other cultures of Bangladesh’s coastal landscape. J. Peasant Stud. 41, 1109–1130 (2014).Article 

Google Scholar 
Nowreen, S., Jalal, M. R. & Shah Alam Khan, M. Historical analysis of rationalizing south west coastal polders of Bangladesh. Water Policy 16, 264–279 (2013).Article 

Google Scholar 
Swapan, M. S. H. & Gavin, M. A desert in the delta: participatory assessment of changing livelihoods induced by commercial shrimp farming in Southwest Bangladesh. Ocean Coast. Manage. 54, 45–54 (2011).Article 

Google Scholar 
Grey, D. & Sadoff, C. W. Sink or swim? Water security for growth and development. Water Policy 9, 545–571 (2007).Article 

Google Scholar 
Dadson, S. et al. Water security, risk, and economic growth: insights from a dynamical systems model. Water Resour. Res. 53, 6425–6438 (2017).Article 

Google Scholar 
Hall, J. W. et al. Coping with the curse of freshwater variability. Science 346, 429–430 (2014).CAS 
Article 

Google Scholar 
Di Baldassarre, G. et al. Water shortages worsened by reservoir effects. Nat. Sustain. 1, 617–622 (2018).Article 

Google Scholar 
Palmer, M. A., Liu, J., Matthews, J. H., Mumba, M. & D’Odorico, P. Manage water in a green way. Science 349, 584–585 (2015).CAS 
Article 

Google Scholar 
Tortajada, C. Water infrastructure as an essential element for human development. Int. J. Water Resour. Dev. 30, 8–19 (2014).Article 

Google Scholar 
Zeitoun, M. et al. Reductionist and integrative research approaches to complex water security policy challenges. Glob. Environ. Change 39, 143–154 (2016).Article 

Google Scholar 
Howe, C. et al. Paradoxical infrastructures: ruins, retrofit, and risk. Sci. Technol. Human Values 41, 547–565 (2016).Article 

Google Scholar 
Gleick, P. H. Global freshwater resources: soft-path solutions for the 21st century. Science 302, 1524–1528 (2003).CAS 
Article 

Google Scholar 
Eriksen, S. et al. Adaptation interventions and their effect on vulnerability in developing countries: help, hindrance or irrelevance? World Dev. 141, 105383 (2021).Article 

Google Scholar 
Anand, N., Gupta, A. & Appel, H. The Promise of Infrastructure (Duke Univ. Press, 2018).Thacker, S. et al. Infrastructure for sustainable development. Nat. Sustain. 2, 324–331 (2019).Article 

Google Scholar 
Poff, N. L. et al. Sustainable water management under future uncertainty with eco-engineering decision scaling. Nat. Clim. Change 6, 25–34 (2016).Article 

Google Scholar 
Winemiller, K. O. et al. Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong. Science 351, 128–129 (2016).CAS 
Article 

Google Scholar 
Loftus, A. Water (in)security: securing the right to water. Geographical J. 181, 350–356 (2015).Article 

Google Scholar 
Haasnoot, M. et al. Investments under non-stationarity: economic evaluation of adaptation pathways. Climatic Change https://doi.org/10.1007/s10584-019-02409-6 (2019).Hino, M. & Hall, J. W. Real options analysis of adaptation to changing flood risk: structural and nonstructural measures. ASCE ASME J. Risk Uncertain. Eng. Syst. A 3, 04017005 (2017).
Google Scholar 
Borgomeo, E., Hall, J. W. & Salehin, M. Avoiding the water-poverty trap: insights from a conceptual human–water dynamical model for coastal Bangladesh. Int. J. Water Resour. Dev. 34, 900–922 (2018).Article 

Google Scholar 
Verschuur, J., Koks, E. E., Haque, A. & Hall, J. W. Prioritising resilience policies to reduce welfare losses from natural disasters: a case study for coastal Bangladesh. Glob. Environ. Change 65, 102179 (2020).Article 

Google Scholar 
Lázár, A. N. et al. Agricultural livelihoods in coastal Bangladesh under climate and environmental change—a model framework. Environ. Sci. Process. Impacts 17, 1018–1031 (2015).Article 

Google Scholar 
Paprocki, K. Threatening dystopias: development and adaptation regimes in Bangladesh. Ann. Am. Assoc. Geogr. 108, 955–973 (2018).
Google Scholar 
Yearbook of Agricultural Statistics-2016 (Bangladesh Bureau of Statistics, Statistics and Information Division, Ministry of Planning, Government of the People’s Republic of Bangladesh, 2017).Haque, A., Kay, S. & Nicholls, R. J. in Ecosystem Services for Well-Being in Deltas: Integrated Assessment for Policy Analysis (eds Nicholls, R. J. et al.) 293–314 (Springer, 2018).Adnan, M. S. G., Haque, A. & Hall, J. W. Have coastal embankments reduced flooding in Bangladesh? Sci. Total Environ. 682, 405–416 (2019).CAS 
Article 

Google Scholar 
National Water Resources Database (NWRD) (Bangladesh Water Resources Planning Organization, 2018).Census of Agriculture 2008 (Bangladesh Bureau of Statistics, Planning Division, Ministry of Planning, Government of the People’s Republic of Bangladesh, 2011).Dasgupta, S., Hossain, M. M., Huq, M. & Wheeler, D. Climate change and soil salinity: the case of coastal Bangladesh. Ambio 44, 815–826 (2015).Article 

Google Scholar 
Salehin, M. et al. in Ecosystem Services for Well-Being in Deltas: Integrated Assessment for Policy Analysis (eds Nicholls, R. J. et al.) 333–347 (Springer, 2018).Rabbani, G., Rahman, A. & Mainuddin, K. Salinity-induced loss and damage to farming households in coastal Bangladesh. Int. J. Glob. Warm. 5, 400–415 (2013).Article 

Google Scholar 
Saline Soils of Bangladesh (Soil Resource Development Institute, SRMAF Project, Ministry of Agriculture, 2010).Alam, M. S., Sasaki, N. & Datta, A. Waterlogging, crop damage and adaptation interventions in the coastal region of Bangladesh: a perception analysis of local people. Environ. Dev. 23, 22–32 (2017).Article 

Google Scholar 
Farr, T. G. et al. The shuttle radar topography mission. Rev. Geophys. https://doi.org/10.1029/2005rg000183 (2007).Poverty in Bangladesh: Building on Progress (World Bank and Asian Development Bank, 2002).Hall, J. W., Brown, S., Nicholls, R. J., Pidgeon, N. F. & Watson, R. T. Proportionate adaptation. Nat. Clim. Change 2, 833–834 (2012).Article 

Google Scholar 
Development Project Proforma/Proposal (DPP) for Blue Gold Program (BWDB Component) (Government of the People’s Republic of Bangladesh, Ministry of Water Resources, Bangladesh Water Development Board, 2013).del Ninno, C., Dorosh, P., Smith, L. & Roy, D. The 1998 Floods in Bangladesh Disaster Impacts, Household Coping Strategies, and Response Research Report (International Food Policy Research Institute, 2001).van Staveren, M. F., Warner, J. F. & Shah Alam Khan, M. Bringing in the tides. From closing down to opening up delta polders via tidal river management in the southwest delta of Bangladesh. Water Policy 19, 147–164 (2016).Article 

Google Scholar 
Adnan, M. S. G., Talchabhadel, R., Nakagawa, H. & Hall, J. W. The potential of tidal river management for flood alleviation in south western Bangladesh. Sci. Total Environ. 731, 138747 (2020).CAS 
Article 

Google Scholar 
Auerbach, L. W. et al. Flood risk of natural and embanked landscapes on the Ganges–Brahmaputra tidal delta plain. Nat. Clim. Change 5, 153–157 (2015).Article 

Google Scholar 
Bangladesh Delta Plan 2100 Draft Report (Government of the People’s Republic of Bangladesh, 2017).Brouwer, R., Akter, S., Brander, L. & Haque, E. Socioeconomic vulnerability and adaptation to environmental risk: a case study of climate change and flooding in Bangladesh. Risk Anal. 27, 313–326 (2007).Article 

Google Scholar 
Bangladesh Vision 2021 (Centre for Policy Dialogue, 2007).Project Information Document (PID) Appraisal Stage: Coastal Embankment Improvement Project—Phase 1 (CEIP-1) (World Bank, 2013).Hallegatte, S., Vogt-Schilb, A., Bangalore, M. & Rozenberg, J. Unbreakable: Building the Resilience of the Poor in the Face of Natural Disasters (World Bank, 2017).
Google Scholar 
Di Baldassarre, G. et al. Sociohydrology: scientific challenges in addressing the sustainable development goals. Water Resour. Res. 55, 6327–6355 (2019).Article 

Google Scholar 
Nicholls, R. J. et al. Integrated assessment of social and environmental sustainability dynamics in the Ganges–Brahmaputra–Meghna delta, Bangladesh. Estuar. Coast. Shelf Sci. 183, 370–381 (2016).Article 

Google Scholar 
Payo, A. et al. Modeling daily soil salinity dynamics in response to agricultural and environmental changes in coastal Bangladesh. Earths Future 5, 495–514 (2017).CAS 
Article 

Google Scholar 
Brown, S. & Nicholls, R. J. Subsidence and human influences in mega deltas: the case of the Ganges–Brahmaputra–Meghna. Sci. Total Environ. 527–528, 362–374 (2015).Article 

Google Scholar 
Bangladesh Poverty Maps (Zila Upazila) (World Bank, Bangladesh Bureau of Statistics and World Food Programme, 2010). More

Power, S., Casey, T., Folland, C., Colman, A. & Mehta, V. Interdecadal modulation of the impact of ENSO on Australia. Clim. Dyn. 15, 319–324 (1999).
Google Scholar 
Mantua, N. & Hare, S. The Pacific decadal oscillation. J. Oceanogr. 58, 35–44 (2002).
Google Scholar 
Kiem, A. S., Franks, S. W. & Kuczera, G. Multi-decadal variability of flood risk. Geophys. Res. Lett. 30, 1035 (2003).
Google Scholar 
Kiem, A. S. & Franks, S. W. Multi-decadal variability of drought risk – Eastern Australia. Hydrol. Process. 18, 2039–2050 (2004).
Google Scholar 
Verdon, D. C., Kiem, A. S. & Franks, S. W. Multi-decadal variability of forest fire risk – Eastern Australia. Int. J. Wildland Fire 13, 165–171 (2004).
Google Scholar 
Parker, D. et al. Decadal to multidecadal variability and the climate change background. J. Geophys. Res. Atmos. https://doi.org/10.1029/2007JD008411 (2007).England, M. H. et al. Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nat. Clim. Change https://doi.org/10.1038/NCLIMATE2106 (2014).Dai, A., Fyfe, J. C., Xie, S.-P. & Dai, X. Decadal modulation of global surface temperature by internal climate variability. Nat. Clim. Change 5, 555–559 (2015).
Google Scholar 
Henley, B. J. Pacific decadal variability: indices, patterns and tropical-extratropical interactions. Glob. Planet. Change 155, 42–55 (2017).
Google Scholar 
Magee, A. D. & Verdon-Kidd, D. C. Historical variability of Southwest Pacific tropical cyclone counts since 1855. Geophys. Res. Lett. https://doi.org/10.1029/2019GL082900 (2019).Gray, J. L., Verdon-Kidd, D. C., Callaghan, J. & English, N. B. On the recent hiatus of tropical cyclones landfalling in NSW, Australia. J. South. Hemisph. Earth Syst. Sci. 70, 180–192 (2020).
Google Scholar 
Meehl, G., Arblaster, J., Bitz, C., Chung, C. & Teng, H. Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability. Nat. Geosci. 9, 590–595 (2016).CAS 

Google Scholar 
Clem, K. R. et al. Record warming at the South Pole during the past three decades. Nat. Clim. Change https://doi.org/10.1038/s41558-020-0815-z (2020).Turner, J. et al. Absence of 21st century warming on Antarctic Peninsula consistent with natural variability. Nature 535, 411–415 (2016).CAS 

Google Scholar 
Jones, J. M. et al. Assessing recent trends in high-latitude Southern Hemisphere surface climate. Nat. Clim. Change 6, 917–926 (2016).
Google Scholar 
Newman, M., Compo, G. P. & Alexander, M. A. ENSO-forced variability of the Pacific Decadal Oscillation. J. Clim. 16, 3853–3857 (2003).
Google Scholar 
Liu, Z. Y. Dynamics of interdecadal climate variability: a historical perspective. J. Clim. 25, 1963–1995 (2012).
Google Scholar 
Smith, D. M. et al. Role of volcanic and anthropogenic aerosols in the recent global surface warming slowdown. Nat. Clim. Change 6, 936–941 (2016).CAS 

Google Scholar 
Lou, J., Holbrook, N. J. & O’Kane, T. J. South Pacific decadal climate variability and potential predictability. J. Clim. 32, 6051–6069 (2019).
Google Scholar 
Mann, M. E., Steinman, B. A. & Miller, S. K. Absence of internal multidecadal and interdecadal oscillations in climate model simulations. Nat. Commun. 11, 49 (2020).CAS 

Google Scholar 
Mann, M. E., Steinman, B. A., Brouillette, D. J. & Miller, S. K. Multidecadal climate oscillations during the past millennium driven by volcanic forcing. Science 371, 1014–1019 (2021).CAS 

Google Scholar 
Folland, C. K., Renwick, J. A., Salinger, M. J. & Mullen, A. B. Relative influences of the Interdecadal Pacific Oscillation and ENSO on the South Pacific Convergence Zone. Geophys. Res. Lett. 29, 1643 (2002).
Google Scholar 
D’Arrigo, R. & Wilson, R. On the Asian expression of the PDO. Int. J. Climatol. 26, 1607–1617 (2006).
Google Scholar 
Henley, B. et al. A tripole index for the Interdecadal Pacific Oscillation. Clim. Dyn. 45, 3077–3090 (2015).
Google Scholar 
Bonfils, C. J. W. et al. Human influence on joint changes in temperature, rainfall and continental aridity. Nat. Clim. Change 10, 726–731 (2020).CAS 

Google Scholar 
Zhang, L., Kuczera, G., Kiem, A. S. & Willgoose, G. R. Using paleoclimate reconstructions to analyse hydrological epochs associated with Pacific decadal variability. Hydrol. Earth Syst. Sci. 22, 6399–6414 (2018).
Google Scholar 
Collins, M. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 1029–1136 (Cambridge University Press, 2013).Armstrong, M. S., Kiem, A. S. & Vance, T. R. Comparing instrumental, palaeoclimate and projected rainfall data: Implications for water resources management and hydrological modelling. J. Hydrol. 31, 100728 (2020).
Google Scholar 
Buckley, B. M. et al. Interdecadal Pacific Oscillation reconstructed from trans-Pacific tree rings: 1350–2004 CE. Clim. Dyn. 53, 3181–3196 (2019).
Google Scholar 
Verdon, D. C. & Franks, S. W. Long-term behaviour of ENSO: Interactions with the PDO over the past 400 years inferred from palaeoclimate records. Geophys. Res. Lett. https://doi.org/10.1029/2005GL025052 (2006).Porter, S. E., Mosley-Thompson, E., Thompson, L. G. & Wilson, A. B. Reconstructing a Pacific Interdecadal Oscillation Index from a Pacific basin-wide collection of ice core records. J. Clim. 34, 3839–3852 (2021).
Google Scholar 
Vance, T. R., Roberts, J. L., Plummer, C. T., Kiem, A. S. & van Ommen, T. D. Interdecadal Pacific variability and eastern Australian megadroughts over the last millennium. Geophys. Res. Lett. 42, 129–137 (2015).
Google Scholar 
Roberts, J. et al. A 2000-year annual record of snow accumulation rates for Law Dome, East Antarctica. Clim. Past 11, 697–707 (2015).
Google Scholar 
van Ommen, T. D. & Morgan, V. Snowfall increase in coastal East Antarctica linked with southwest Western Australian drought. Nat. Geosci. 3, 267 (2010).
Google Scholar 
Vance, T. R., Ommen, T. D. V., Curran, M. A. J., Plummer, C. T. & Moy, A. D. A millennial proxy record of ENSO and Eastern Australian rainfall from the Law Dome Ice Core, East Antarctica. J. Clim. 26, 710–725 (2013).
Google Scholar 
Vance, T. R. et al. Optimal site selection for a high-resolution ice core record in East Antarctica. Clim. Past 12, 595–610 (2016).
Google Scholar 
Udy, D. G., Vance, T. R., Kiem, A. S., Holbrook, N. J. & Curran, M. A. J. Links between large-scale modes of climate variability and synoptic weather patterns in the southern Indian Ocean. J. Clim. 34, 883–899 (2021).
Google Scholar 
Crockart, C. K. et al. El Niño-Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South. Clim. Past 17, 1795–1818 (2021).
Google Scholar 
Stevens, H. R. & Kiem, A. S. Developing hazard lines in response to coastal flooding and sea level change. Urban Pol. Res. 32, 341–360 (2014).
Google Scholar 
Magee, A. D., Verdon-Kidd, D. C., Diamond, H. J. & Kiem, A. S. Influence of ENSO, ENSO Modoki, and the IPO on tropical cyclogenesis: a spatial analysis of the southwest Pacific region. Int. J. Climatol. 37, 1118–1137 (2017).
Google Scholar 
McMahon, G. M. & Kiem, A. S. Large floods in South East Queensland, Australia: is it valid to assume they occur randomly? Austral. J. Water Resour. 22, 4–14 (2018).
Google Scholar 
Deb, P. et al. Causes of the Widespread 2019–2020 Australian Bushfire Season. Earth’s Future 8, e2020EF001671 (2020).
Google Scholar 
Magee, A. D. & Kiem, A. S. Using indicators of ENSO, IOD, and SAM to improve lead time and accuracy of tropical cyclone outlooks for Australia. J. Appl. Meteorol. Climatol. https://doi.org/10.1175/jamc-d-20-0131.1 (2020).van Dijk, A. I. J. M. et al. The millennium drought in southeast Australia (2001–2009): natural and human causes and implications for water resources, ecosystems, economy and society. Water Resour. Res. 49, 1–18 (2013).
Google Scholar 
Johnson, F. et al. Natural hazards in Australia: floods. Clim. Change 139, 21–35 (2016).
Google Scholar 
Holgate, C. M., van Dijk, A. I. J. M., Evans, J. P. & Pitman, A. J. Local and remote drivers of southeast Australian drought. Geophys. Res. Lett. https://doi.org/10.1029/2020GL090238 (2020).Chiew, F. S. H. Estimation of rainfall elasticity of streamflow in Australia. Hydrol. Sci. J. 51, 613–625 (2006).
Google Scholar 
Wooldridge, S. A., Franks, S. W. & Kalma, J. D. Hydrological implications of the Southern Oscillation: variability of the rainfall-runoff relationship. Hydrol. Sci. J. 46, 73–88 (2001).
Google Scholar 
Kiem, A. S. & Verdon-Kidd, D. C. Climatic drivers of Victorian streamflow: is ENSO the dominant influence? Austral. J. Water Resour. 13, 17–29 (2009).
Google Scholar 
Flack, A. L., Kiem, A. S., Vance, T. R., Tozer, C. R. & Roberts, J. L. Comparison of published palaeoclimate records suitable for reconstructing annual to sub-decadal hydroclimatic variability in eastern Australia: implications for water resource management and planning. Hydrol. Earth Syst. Sci. 24, 5699–5712 (2020).
Google Scholar 
Barr, C. et al. Holocene El Niño–Southern Oscillation variability reflected in subtropical Australian precipitation. Sci. Rep. 9, 1627 (2019).CAS 

Google Scholar 
Tozer, C. R. et al. Reconstructing pre-instrumental streamflow in Eastern Australia using a water balance approach. J. Hydrol. 558, 632–646 (2018).
Google Scholar 
Etheridge, D. M., Steele, L. P., Lagenfelds, R. L. & Francey, R. J. Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. J. Geophys. Res. 101, 4115–4128 (1996).CAS 

Google Scholar 
Massom, R. A. et al. Precipitation over the Interior East Antarctic Ice Sheet related to midlatitude blocking-high activity. J. Clim. 17, 1914–1928 (2004).
Google Scholar 
Morgan, V. et al. Site information and initial results from deep ice drilling on Law Dome. J. Glaciol. 43, 3–10 (1997).CAS 

Google Scholar 
Plummer, C. T. et al. An independently dated 200-yr volcanic record from Law Dome, East Antarctica, including a new perspective on the dating of the c. 1450s eruption of Kuwae, Vanuatu. Clim. Past 8, 1929–1940 (2012).
Google Scholar 
Curran, M. A. J., van Ommen, T. D., Morgan, V. I., Phillips, K. L. & Palmer, A. S. Ice core evidence for Antarctic sea ice decline since the 1950s. Science 302, 1203–1206 (2003).CAS 

Google Scholar 
Curran, M. A. J. & Palmer, A. S. Suppressed ion chromatography method for the routine determination of ultra low level anions and cations in ice cores. J. Chromatogr. A 919, 107–113 (2001).CAS 

Google Scholar 
van Ommen, T. D. & Morgan, V. Peroxide concentrations in the Dome Summit South ice core, Law Dome, Antarctica. J. Geophys. Res. 101, 15,147–15,152 (1996).
Google Scholar 
van Ommen, T. D. & Morgan, V. Calibrating the ice core paleothermometer using seasonality. J. Geophys. Res. 102, 9351–9357 (1997).
Google Scholar 
Kiem, A. S. et al. Learning from the past – using palaeoclimate data to better understand and manage drought in South East Queensland (SEQ), Australia. J. Hydrol. Reg. Stud. https://doi.org/10.1016/j.ejrh.2020.100686 (2020).Friedman, J. H. Multivariate adaptive regression spines. Ann. Stat. 19, 1–67 (1991).
Google Scholar 
Roberts, J. L. et al. Reconciling unevenly sampled palaeoclimate proxies: a Gaussian kernel correlation multiproxy reconstruction. J. Environ. Inform. https://doi.org/10.3808/jei.201900420 (2019).Mann, M. E. & Lees, J. Robust estimation of background noise and signal detection in climatic time series. Clim. Change 33, 409–455 (1996).
Google Scholar  More

NEWS
15 February 2022

Gran Turismo champion, reimagined urine — the week in infographics

Nature highlights three key graphics from the week in science and research.

Twitter

Facebook

Email

Artificial intelligence overtakes human gamersThis graphic shows one way in which an artificial intelligence (AI) is able to win against the best human players of the video game Gran Turismo. In a paper in Nature, a team of researchers introduce GT Sophy, which learns through a neural-network model. GT Sophy stands out for its performance against human drivers in a head-to-head competition. Far from using a lap-time advantage to outlast opponents, GT Sophy simply outraces them. Through the training process, GT Sophy learnt to take different lines through the corners in response to different conditions. Our graphic shows how, in one case, two human drivers attempted to block the preferred path of two GT Sophy cars, yet the AI succeeded in finding two trajectories that overcame this block and allowed its cars to overtake. You can read more about what it takes to win at racing (both real and simulated) in this News & Views article.

The march of methaneLevels of methane, a potent greenhouse gas, have been growing for decades — but they began a rapid and mysterious uptick around 2007. Last year, methane concentrations in the atmosphere raced past 1,900 parts per billion, nearly triple pre-industrial levels, according to data released in January by the US National Oceanic and Atmospheric Administration. Where is it coming from? Potential explanations range from the expanding exploitation of oil and natural gas, and rising emissions from landfill, to growing livestock herds and increasing activity by microbes in wetlands. The spike has caused many researchers to worry that global warming is creating a feedback mechanism that will cause ever more methane to be released, making it even harder to rein in rising global temperatures.

Source: NOAA

Urine, reimaginedOur final graphic this week illustrates some of the many ways in which human urine could be recycled into useful products. Scientists say that urine diversion would have huge environmental and public-health benefits if deployed on a large scale. That’s in part because urine is rich in nutrients that could help to fertilize crops or feed into industrial processes; furthermore, not flushing urine down the drain could save vast amounts of water.But urine diversion and reuse would require “drastic reimagining of how we do human sanitation”, as a Feature reports. It would involve wide-scale use of special urine-diverting toilets, and even processing devices in your building’s basement.

doi: https://doi.org/10.1038/d41586-022-00458-z

Related Articles

Neural networks overtake humans in Gran Turismo racing game

Scientists raise alarm over ‘dangerously fast’ growth in atmospheric methane

The urine revolution: how recycling pee could help to save the world

Subjects

Machine learning

Water resources

Climate change

Latest on:

Machine learning

Neural networks overtake humans in Gran Turismo racing game
News & Views 09 FEB 22

Early prediction of preeclampsia in pregnancy with cell-free RNA
Article 09 FEB 22

DeepMind AI tackles one of chemistry’s most valuable techniques
News 10 DEC 21

Water resources

The urine revolution: how recycling pee could help to save the world
News Feature 09 FEB 22

‘Sky river’ brought Iran deadly floods — but also welcome water
Research Highlight 08 DEC 21

Brazil is in water crisis — it needs a drought plan
Comment 08 DEC 21

Climate change

Scientists raise alarm over ‘dangerously fast’ growth in atmospheric methane
News 08 FEB 22

Climate pledges from top companies crumble under scrutiny
News 07 FEB 22

Emissions cuts take political and social innovation too
Correspondence 01 FEB 22

Jobs

Flow cytometrist – Sorter Operator (m/f/div)

Max Planck Institute for Biology of Ageing (MPIAGE)
Köln, Germany

Physicist, Engineer Electrical Engineering and/or photonics or similar (f/m/x) – Doctoral Fellowship – Optical technologies for space navigation

German Aerospace Center (DLR)
Oberpfaffenhofen, Germany

Doctoral Researcher (f/m/d) 75 % for the project C2 Seismic imaging by full waveform inversion

Karlsruhe Institute of Technology (KIT)
Karlsruhe, Germany

Research associate / PhD candidate (f/m/d) Embedded Electronic Systems

Karlsruhe Institute of Technology (KIT)
Karlsruhe, Germany More

Mankin, J. S. et al. NOAA Drought Task Force Report on the 2020–2021 Southwestern U.S. Drought (NOAA Drought Task Force, MAPP and NIDIS, 2021); https://www.drought.gov/sites/default/files/2021-09/NOAA-Drought-Task-Force-IV-Southwest-Drought-Report-9-23-21.pdfH.R.2030—Colorado River Drought Contingency Plan Authorization Act (US House of Representatives, 2019); https://www.congress.gov/bill/116th-congress/house-bill/2030Svoboda, M. et al. The Drought Monitor. Bull. Am. Meteorol. Soc. 83, 1181–1190 (2002).Article 

Google Scholar 
Cook, E. R. et al. Megadroughts in North America: placing IPCC projections of hydroclimatic change in a long-term palaeoclimate context. J. Quat. Sci. 25, 48–61 (2010).Article 

Google Scholar 
Williams, A. P. et al. Large contribution from anthropogenic warming to a developing North American megadrought. Science 368, 314–318 (2020).CAS 
Article 

Google Scholar 
Cook, B. I. et al. North American megadroughts in the Common Era: reconstructions and simulations. WIREs Clim. Change 7, 411–432 (2016).Article 

Google Scholar 
Woodhouse, C. A. & Overpeck, J. T. 2000 years of drought variability in the central United States. Bull. Am. Meteorol. Soc. 79, 2693–2714 (1998).Article 

Google Scholar 
Breshears, D. D. et al. Regional vegetation die-off in response to global-change-type drought. Proc. Natl Acad. Sci. USA 102, 15144–15148 (2005).CAS 
Article 

Google Scholar 
Williams, A. P. et al. Temperature as a potent driver of regional forest drought stress and tree mortality. Nat. Clim. Change 3, 292–297 (2013).Article 

Google Scholar 
Eyring, V. et al. Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev. 9, 1937–1958 (2016).Barnett, T. P., Adam, J. C. & Lettenmaier, D. P. Potential impacts of a warming climate on water availability in snow-dominated regions. Nature 438, 303–309 (2005).CAS 
Article 

Google Scholar 
Das, T., Pierce, D. W., Cayan, D. R., Vano, J. A. & Lettenmaier, D. P. The importance of warm season warming to western US streamflow changes. Geophys. Res. Lett. 38, L23403 (2011).Article 

Google Scholar 
Milly, P. C. D. & Dunne, K. A. Colorado River flow dwindles as warming-driven loss of reflective snow energizes evaporation. Science 367, 1252–1255 (2020).CAS 
Article 

Google Scholar 
Pascolini-Campbell, M., Reager, J. T., Chandanpurkar, H. A. & Rodell, M. A 10 per cent increase in global land evapotranspiration from 2003 to 2019. Nature 593, 543–547 (2021).CAS 
Article 

Google Scholar 
Udall, B. & Overpeck, J. The twenty‐first century Colorado River hot drought and implications for the future. Water Resour. Res. 53, 2404–2418 (2017).Article 

Google Scholar 
Cook, B. I. et al. Uncertainties, limits, and benefits of climate change mitigation for soil moisture drought in southwestern North America. Earth’s Future 9, e2021EF002014 (2021).Article 

Google Scholar 
Ault, T. R., Mankin, J. S., Cook, B. I. & Smerdon, J. E. Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest. Sci. Adv. 2, e1600873 (2016).Article 

Google Scholar 
Woodhouse, C. A., Meko, D. M., MacDonald, G. M. & Stahle, D. W. A 1,200-year perspective of 21st century drought in southwestern North America. Proc. Natl Acad. Sci. USA 107, 21283–21288 (2010).CAS 
Article 

Google Scholar 
Lepley, K. et al. A multi-century Sierra Nevada snowpack reconstruction modeled using upper-elevation coniferous tree rings (California, USA). Holocene 30, 1266–1278 (2020).Article 

Google Scholar 
Williams, A. P. et al. Tree rings and observations suggest no stable cycles in Sierra Nevada cool-season precipitation. Water Resour. Res. 57, e2020WR028599 (2021).Article 

Google Scholar  More

NEWS FEATURE
09 February 2022

The urine revolution: how recycling pee could help to save the world

Separating urine from the rest of sewage could mitigate some difficult environmental problems, but there are big obstacles to radically re-engineering one of the most basic aspects of life.

Chelsea Wald

0

Chelsea Wald

Chelsea Wald is a freelance reporter in The Hague, the Netherlands, and the author of Pipe Dreams: The Urgent Global Quest to Transform the Toilet.

View author publications

You can also search for this author in PubMed
 Google Scholar

Twitter

Facebook

Email

Download PDF

Specialized toilet systems recover nitrogen and other nutrients from urine for use as fertilizers and other products.Credit: MAK/Georg Mayer/EOOS NEXT

On Gotland, the largest island in Sweden, fresh water is scarce. At the same time, residents are battling dangerous amounts of pollution from agriculture and sewer systems that causes harmful algal blooms in the surrounding Baltic Sea. These can kill fish and make people ill.To help solve this set of environmental challenges, the island is pinning its hopes on a single, unlikely substance that connects them: human urine.Starting in 2021, a team of researchers began collaborating with a local company that rents out portable toilets. The goal is to collect more than 70,000 litres of urine over 3 years from waterless urinals and specialized toilets at several locations during the booming summer tourist season. The team is from the Swedish University of Agricultural Sciences (SLU) in Uppsala, which has spun off a company called Sanitation360. Using a process that the researchers developed, they are drying the urine into concrete-like chunks that they hammer into a powder and press into fertilizer pellets that fit into standard farming equipment. A local farmer uses the fertilizer to grow barley that will go to a brewery to make ale — which, after consumption, could enter the cycle all over again.The researchers aim to take urine reuse “beyond concept and into practice” on a large scale, says Prithvi Simha, a chemical-process engineer at the SLU and Sanitation360’s chief technology officer. The aim is to provide a model that regions around the world could follow. “The ambition is that everyone, everywhere, does this practice.”

The Gotland experiment compared barley fertilized with urine (right) to plants grown without fertilizer (middle) and ones with mineral fertilizer (left).Credit: Jenna Senecal

The Gotland project is part of a wave of similar efforts worldwide to separate urine from the rest of sewage and to recycle it into products such as fertilizer. That practice, known as urine diversion, is being studied by groups in the United States, Australia, Switzerland, Ethiopia and South Africa, among other places. The efforts reach far beyond the confines of university labs. Waterless urinals connect to basement treatment systems in offices in Oregon and the Netherlands. In Paris, there are plans to install urine-diverting toilets in a 1,000-resident eco-quarter being built in the 14th district of the city. The European Space Agency is to put 80 urine-diverting toilets into its Paris headquarters, which will begin operating later this year. According to proponents of urine diversion, it could see uses in sites from temporary military outposts to refugee encampments, rich urban centres and sprawling slums.Scientists say that urine diversion would have huge environmental and public-health benefits if deployed on a large scale around the world. That’s in part because urine is rich in nutrients that, instead of polluting water bodies, could go towards fertilizing crops or feed into industrial processes. According to Simha’s estimates, humans produce enough urine to replace about one-quarter of current nitrogen and phosphorus fertilizers worldwide; it also contains potassium and many micronutrients (see ‘What’s in urine’). On top of that, not flushing urine down the drain could save vast amounts of water and reduce some of the strain on ageing and overloaded sewer systems.

Source: M. Qadir et al. Nat. Resour. Forum 44, 40–51 (2020)

Thanks to advances in toilets and urine-treatment strategies, many components of urine diversion could soon be ready for widespread roll-out, according to experts in the field. But there are also big obstacles to radically re-engineering one of the most basic aspects of life. Researchers and companies need to solve a number of problems, from improving the design of urine-diverting toilets to making it easier to treat urine and turn it into valuable products. This could involve chemical-treatment systems connected to individual toilets or basement devices that serve entire buildings, with pick-up and maintenance services for the resulting concentrated or solidified product (see ‘From pee to products’). Then there are broader questions of social change and acceptance, related both to varying levels of cultural taboos around human waste and to deeply entrenched conventions about industrial sewage and food systems.Urine diversion and reuse is the type of “drastic reimagining of how we do human sanitation” that will become increasingly crucial as societies battle shortages in energy, water and raw materials for agriculture and industry, says biologist Lynn Broaddus, a sustainability consultant in Minneapolis, Minnesota, who is former president of the Water Environment Federation in Alexandria, Virginia, an association of water-quality professionals worldwide. “The fact of the matter is, it’s valuable stuff.”

Mixed wasteUrine used to be a valuable commodity. In the past, some societies used it for fertilizing crops, tanning leather, washing clothes and producing gunpowder. Then, in the late nineteenth and early twentieth century, the modern model of centralized sewage management arose in England and spread worldwide, ultimately leading to what has been called urine blindness.In this model, flush toilets use water to quickly send urine, faeces and toilet paper into sewers, where it mixes with other liquids from households, industrial sources and sometimes storm run-off. At centralized treatment plants, an energy-intensive process uses microbes to clean the sewage.Depending on local regulations and a treatment plant’s condition, the wastewater discharged from the process can still contain a lot of nitrogen and other nutrients, as well as some other contaminants. And 57% of the world’s population isn’t connected to centralized sewer systems at all (see ‘Human sewage’).

Source: C. Tuholske et al. PLoS ONE 16, e0258898 (2021).

Scientists are working on ways to make centralized systems more sustainable and less polluting, but, beginning in Sweden in the 1990s, some researchers began pushing for more fundamental change. The end-of-pipe advances are “just, you know, another evolution of the same damn thing”, says Nancy Love, an environmental engineer at the University of Michigan in Ann Arbor. Urine diversion would be “transformative”, she says. In a study1 that modelled wastewater-management systems in three US states, she and her colleagues compared conventional wastewater systems with hypothetical ones that divert urine and use the recovered nutrients to replace synthetic fertilizers. They projected that communities with urine diversion could lower their overall greenhouse-gas emissions by up to 47%, energy consumption by up to 41%, freshwater use by about half, and nutrient pollution from the wastewater by up to 64%, depending on the technologies used.Still, the concept has remained niche, mostly limited to off-grid locales such as northern European eco-villages, rural outhouses and development projects in low-income settings.A lot of the lag is a result of the toilets themselves, says Tove Larsen, a chemical engineer at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) in Dübendorf. First sold in the 1990s and 2000s, most urine-diverting toilets have a small basin at the front to capture the liquid — a set-up that requires careful aim. Other designs have incorporated foot-powered conveyor belts that let urine drain away while transporting the faeces to a composting vault, or sensors that operate valves to direct the urine to separate outlets.

A prototype toilet that separates urine and dries it into a powder is being tested at the head office of VA SYD, the Swedish public water and wastewater utility, in Malmö.Credit: Lotte Kristoferitsch

But in European pilot and demonstration projects, people failed to embrace their use, Larsen says, complaining that they were too unwieldy, smelly and unreliable. “We have really been stalled by this topic of toilets.”These concerns plagued the first large-scale use of urine-diversion toilets — a project in the 2000s in South Africa’s eThekwini municipality. After apartheid, the municipality’s boundaries suddenly expanded, causing authorities to take over responsibility for some poor rural areas where there was no toilet infrastructure and little water service, says Anthony Odili, who researches sanitation governance at the University of KwaZulu-Natal in Durban.After a cholera outbreak there in August 2000, the authorities quickly rolled out several types of sanitation that met financial and practical constraints, including about 80,000 urine-diversion dry toilets, most of which are still in use today. The urine drains below the toilet into the soil and the faeces falls into a vault, which, since 2016, the municipality has emptied every five years.
The secret history of ancient toilets
The project was successful at establishing safer sanitation in the region, Odili says. Social-science research, however, has revealed many problems with the programme. Although people felt that the toilets were better than nothing, Odili says, studies — including some he was involved in2 — later found that users generally disliked them. Many had been constructed with poor materials and were awkward to use. Although such toilets should prevent bad odours in theory, urine in the eThekwini ones often entered the vaults with the faeces, causing a terrible stink. People were “not able to breathe properly”, Odili says. What’s more, the urine remains largely unused.Ultimately, the decision to go with urine-diversion dry toilets, driven largely by public-health concerns, was top-down, and failed to take people’s preferences into account, Odili says. A 2017 study3 found that more than 95% of respondents in eThekwini aspired to the convenient, odourless flush toilets that wealthier white people use in the city — and that many have intentions to install them when their circumstances allow. In South Africa, toilets have long served as a symbol of racial disparity.A new design, however, could represent a breakthrough for urine diversion. Led by designer Harald Gründl and in collaboration with Larsen and others, in 2017, the Austrian design firm EOOS (which has since spun off the company EOOS Next) unveiled the Urine Trap. This removes the need for users to aim, and the urine-diverting function is almost invisible (see ‘A new kind of toilet’).

Source: EOOS

It takes advantage of water’s tendency to cling to surfaces (known as the teapot effect because it’s like an inconveniently dribbling teapot) to direct urine down the front inner side of the toilet into a separate hole (see ‘How to recycle pee’). Developed with funding from the Bill & Melinda Gates Foundation in Seattle, Washington, which has supported a broad swathe of research into toilet innovation for low-income settings, the Urine Trap can be incorporated into everything from high-end ceramic pedestal models to plastic squat pans. LAUFEN, a manufacturer headquartered in Switzerland, is already producing one for the European market, called save!, although it is too costly for many consumers.The University of KwaZulu-Natal and the eThekwini municipality have also been testing versions of Urine Trap toilets that divert the urine and flush the solids. This time, the research is more focused on the user. Odili is optimistic that people will prefer the new urine-diversion toilets because they smell better and are easier to use, but he points out that men would have to sit down to urinate, which is a big cultural shift. But if the toilet is “also adopted and accepted in high-income areas — people from different racial groups here — it really will help in the roll-out”, he says. “We must always put on that racial lens,” he adds, to ensure that they’re not developing something that will be seen as ‘just for Black people’ or ‘just for poor people’.Uses for urineSeparating urine is just the first step in transforming sanitation. The next part is working out what to do with it. In rural areas, people could store it in vats to kill any pathogens and then apply it to fields. The World Health Organization provides guidelines for this practice.But urban settings are trickier — and that’s where most urine is produced. It’s not practical to add a separate set of sewer pipes throughout a city to move urine to a central location. And because urine is about 95% water, it is too expensive to store and transport. So researchers are focusing on drying, concentrating or otherwise extracting nutrients from urine at the toilet or building level, leaving the water behind.This isn’t easy, says Larsen. From an engineering perspective, “urine is a nasty solution”, she says. Aside from water, the largest portion is urea, a nitrogen-rich compound that bodies produce as a by-product of metabolizing proteins. Urea by itself is useful: a synthetic version is a common nitrogen fertilizer (see ‘Nitrogen demand’). But it’s also tricky: when combined with water, the urea transforms into ammonia gas, which helps to give urine its characteristic scent. If not contained, the ammonia stinks, pollutes the air and carries valuable nitrogen away. Catalysed by the widespread enzyme urease, this reaction, called urea hydrolysis, can take microseconds, making urease one of the most efficient enzymes known4.

Source: FAO

Some approaches allow the hydrolysis to go ahead. Researchers at Eawag have developed an advanced process for turning hydrolysed urine into a concentrated nutrient solution. First, in a tank, microorganisms transform the volatile ammonia into non-volatile ammonium nitrate, which is a common fertilizer. Then a distiller concentrates the liquid. A spin-off company called Vuna, also in Dübendorf, is working to commercialize both the system for use in buildings and the product, called Aurin, which has been approved in Switzerland for use on edible plants — a world first.Others try to stop the hydrolysis reaction by quickly raising or lowering the pH of the urine, which is usually neutral when it comes out of the body. On campus at the University of Michigan, a collaboration between Love and the non-profit Rich Earth Institute in Brattleboro, Vermont, is developing a system for buildings that squirts liquid citric acid down the pipes of a urine-diverting toilet and a waterless urinal. It then concentrates the urine through repeated freezing and thawing5.
The new economy of excrement
The SLU team doing the project on Gotland island, led by environmental engineer Björn Vinnerås, has worked out how to dry urine into a solid urea mixed with the other nutrients. The team is evaluating its latest prototype, a self-contained toilet including a built-in dryer, at the head office of the Swedish public water and wastewater utility VA SYD in Malmö.Other methods target individual nutrients from urine. These could more easily slot into existing supply chains for fertilizers and industrial chemicals, says chemical engineer William Tarpeh, a former postdoc of Love’s who is now at Stanford University in California.One well-established way of recovering phosphorus from hydrolysed urine is to add magnesium, which causes the precipitation of a fertilizer called struvite. And Tarpeh is experimenting with beads of adsorption materials that selectively pluck out nitrogen in the form of ammonia6 or phosphorus in the form of phosphate. His system uses another liquid, called a regenerant, to flow over the beads after they are spent. The regenerant carries off the nutrients and renews the beads for another round. It’s a low-tech, passive method, but the commercial regenerants are environmentally damaging. His team is now trying to make ones that are cheaper and more environmentally friendly (see ‘Future pollution’).

Source: P. J. T. M. van Puijenbroek et al. J. Environ. Mgmt 231, 446–456 (2019)

Other researchers are developing ways to produce electricity by putting urine into microbial fuel cells. In Cape Town, South Africa, another team has developed a method for making an unconventional construction brick by combining urine, sand and urease-producing bacteria in a mould; these calcify into any shape without the need for firing. And the European Space Agency is eyeing astronaut urine as a resource for building habitats on the Moon.“When I think about the big future of urine recovery and wastewater recovery, we want to be able to make as many products as possible,” Tarpeh says.As researchers pursue a slew of ideas to turn urine into commodities, they know it’s an uphill battle, particularly with entrenched industries. Fertilizer and food companies, farmers, toilet manufacturers and regulators are slow to make big changes to their practices. “There’s quite a lot of inertia,” says Simha.At the University of California, Berkeley, for example, a research and education installation of the LAUFEN save! toilet, including a drainpipe to a storage tank on the floor below, has unexpectedly taken nearly three years and cost more than US$50,000. That includes fees for architects, construction and complying with municipal codes, says environmental engineer Kevin Orner, now at West Virginia University in Morgantown — and it’s still not done. The lack of existing codes and regulations has caused troubles with facilities management, he says, which is why he is on a panel that is developing new codes.Some of the inertia might be due to concerns over customer resistance, but a 2021 survey of people in 16 countries7 indicated that willingness to consume urine-fertilized food approached 80% in places such as France, China and Uganda (see ‘Will people eat it?’).

Source: Ref. 7

Pam Elardo, who leads the Bureau of Wastewater Treatment as a deputy commissioner in the New York City Department of Environmental Protection, says she supports innovations such as urine diversion, because further reducing pollution and recovering resources are key goals for her utility. The most practical and cost-effective approach to urine diversion for a city such as New York, she foresees, would be off-grid systems for renovated or new buildings, supported by maintenance and collection operations. If innovators can work that out, she says, “they should go for it”.Given the advances, Larsen predicts that mass production and automation of urine-diversion technologies could be around the corner. And that would improve the business cases for this transformation in dealing with waste. Urine diversion “is the right technology”, she says. “It’s the only technology which can solve the problem of nutrients from households in a reasonable time. But people have to dare.”

Nature 602, 202-206 (2022)
doi: https://doi.org/10.1038/d41586-022-00338-6

References1.Hilton, S. P., Keoleian, G. A., Daigger, G. T., Zhou, B. & Love, N. G. Environ. Sci. Technol. 55, 593–603 (2021).PubMed 
Article 

Google Scholar 
2.Sutherland, C. et al. Perceptions on Emptying of Urine Diverting Dehydration Toilets. Phase 2: Post eThekwini Municipality UDDT Emptying Programme (Univ. KwaZulu-Natal, 2018).
Google Scholar 
3.Mkhize, N., Taylor, M., Udert, K. M., Gounden, T. G. & Buckley, C. A. J. Water Sanit. Hyg. Dev. 7, 111–120 (2017).PubMed 
Article 

Google Scholar 
4.Mazzei, L., Cianci, M., Benini, S. & Ciurli, S. Angew. Chem. Int. Edn Engl. 58, 7415–7419 (2019).Article 

Google Scholar 
5.Noe-Hays, A., Homeyer, R. J., Davis, A. P. & Love, N. G. ACS EST Engg. https://doi.org/10.1021/acsestengg.1c00271 (2021).Article 

Google Scholar 
6.Clark, B. & Tarpeh, W. A. Chem. Eur. J. 26, 10099–10112 (2020).PubMed 
Article 

Google Scholar 
7.Simha, P. et al. Sci. Total Environ. 765, 144438 (2021).PubMed 
Article 

Google Scholar 
Download references

Related Articles

Toilets – what will it take to fix them?

The secret history of ancient toilets

The new economy of excrement

Subjects

Chemistry

Developing world

Water resources

Latest on:

Chemistry

Nuclear-fusion reactor smashes energy record
News 09 FEB 22

Automated iterative Csp3-C bond formation
Article 08 FEB 22

Structure of a B12-dependent radical SAM enzyme in carbapenem biosynthesis
Article 02 FEB 22

Developing world

The wise counsel that can drive public-health research in Kenya
Career Feature 09 FEB 22

Africa is bringing vaccine manufacturing home
Editorial 09 FEB 22

Female scientists can advance by saying: ‘Yes, I’ll do it’
Career Feature 08 FEB 22

Water resources

‘Sky river’ brought Iran deadly floods — but also welcome water
Research Highlight 08 DEC 21

Brazil is in water crisis — it needs a drought plan
Comment 08 DEC 21

Global potential for harvesting drinking water from air using solar energy
Article 27 OCT 21

Jobs

postdoctoral fellow

Ghent University (UGent)
Ghent, Belgium

Open Rank, Term Tenure Track

The University of Texas MD Anderson Cancer Center
Houston, TX, United States

R464 Project Research Scientist, Cancer Metabolism

Francis Crick Institute
London, United Kingdom

Postdoctoral Training Fellow

Francis Crick Institute
London, United Kingdom More