Anthropogenic phosphorus flows under different scenarios for the city of Stockholm, Sweden

Scenario Analysis of Food Phosphorus Footprint in Kisumu, a Lakeside East African City in Lake Victoria (Kenya)

Increased food production and consumption patterns have resulted in higher urban food phosphorus footprints, leading to a series of resource and environmental problems worldwide. We quantified the food phosphorus footprint of the African city of Kisumu using substance flow analysis. Our aim was to develop Kisumu's sustainable phosphorus management framework so that the city would reduce phosphorus losses into the food system. Our results show that in the year 2023, the import and export of food phosphorus in the Kisumu food system was 2730.26 ± 2.7% t P yr-1 and 3297.05 ± 2.4% t P yr-1, respectively. There was -566.79 ± -18% t P yr-1 food phosphorus deficit in the Kisumu food system. Crop planting subsystem runoff/leaching/erosion loss, household consumption subsystem waste loss, and pit latrine subsystem blackwater loss are the major pathways of phosphorus losses into the environment and the main contributors to the food phosphorus footprint in the city. The 2030 scenario analysis shows that implementing a comprehensive scenario scheme throughout the entire lifecycle process from phosphorus input to waste disposal is the best choice for reducing phosphorus losses and suppressing the growth of food phosphorus footprint in the future. Our study shows that the food phosphorus footprint in the Kisumu food system was 0.67 kg P cap-1yr-1 in 2023, which is still at a low level but may enter a continuous upward trend with the improvement of socio-economic development of the city. In our framework, we have proposed a few essential measures that include urine separation, installation of septic tank, adjustment of dietary structure, flexible layout of sanitary disposal facilities, and separation of organic waste streams to reduce food phosphorus footprints in Kisumu. Given the similarity of cities along the shores of Lake Victoria, our calculation methods and management strategies can be applied to other cities in the region.

Scenario analysis of phosphorus flow in food production and consumption system in the Mwanza region, Tanzania

Since the mineral, phosphorus (P), has dual properties of being limited resources for use, and being a pollutant for studying sustainable management of anthropogenic P flows in wetlands and soils, currently P receives the highest interests among researchers around the world. This study has successfully mapped P flows for a reference year (2017) and a future year (2030) using different scenarios of food production and consumption system (hereafter 'system') in the Mwanza region (Tanzania). The results showed that the total P input and output for 2017 alone were 9770 t and 7989 t, respectively. However, as high as 1781 tP accumulated in the system and the potentially recyclable P found, is yet to be recovered due to economic reasons and the lack of market. The main anthropogenic P input to the system occurred via imported feed, fertilizer, and crop food, accounting for about 99.72 % of the total input flow. The output was comprised of animal products exported with 3428 tP, and various P-contained wastes which were lost to water bodies with 4561tP. Analysis of the 2030 scenario showed that setting P management objectives from different perspectives such as the total P budget balance, potential recyclable P, and P emission, can help develop differentially preferred management strategies and measures in the Mwanza region. The combination of diet change, precision feeding, and integrated waste management practices presents the best prospects for decreasing P budget and losses, and the amount of P that can be potentially recovered from the system. We propose a package of integrated P management measures for the Mwanza region. Given the similarity of regional socio-economic development background around the Lake Victoria basin, the model can be used to guide the study of anthropogenic P flow analysis in other areas along the shore of Lake Victoria (Africa).

International trade reduces global phosphorus demand but intensifies the imbalance in local consumption

International trade has led to increasing levels of economic development; however, its role in altering the global phosphorus (P) demand and local P footprint (PF) is unclear. Here, through a multi-regional input-output (MRIO) analysis, we quantified the PF associated with the global consumption of agricultural products for 159 countries and 169 crops over the period of 1995-2015. The results suggested that the international network of P flows was highly connected and the flow distribution was overridingly driven by developed economies (e.g., USA and Germany) and large emerging economies (e.g., China and India). A decoupling between the PF and economic growth was observed in most countries. The high PF per capita in developed economies was mainly driven by imports from developing countries rather than domestic P applications. Our results also highlighted that international trade had two impacts on global P management. Firstly, it reduced the total global P demand from agricultural production by 16%; secondly, it intensified the imbalance of local P consumption. Therefore, the future sustainable management of P requires consideration of the original suppliers and final consumers along the global supply chains and the associated consequences on P management from both local and global perspectives.

Phosphorus flow analysis in the maize based food-feed-energy systems in China

Phosphorus (P) is an essential and limiting nutrient for agricultural systems, where the demand for agricultural products such as food, feed, and bio-fuel are the major drivers of the intensification of agricultural production systems. Globally, maize is one of three main cereal crops, a main feedstock for animal production and a substrate for the production of bio-ethanol. This study investigated P flows through the multiple utilization systems of maize (as represented by the subsystems of food, feed and energy production) at a crop level of 2016 as reference year and made future predictions of P flows for the year 2030 based on different scenarios for food-feed-energy systems in China. For 2016, the subsystem of animal production resulted in the highest waste of P due to inappropriate manure management, but the subsystem of value-added products (Bio-fuel production, distillers dried grains with solubles (DDGS), maize-oil) showed the lowest P use efficiency (39%). From the value-added subsystem, 17% of P from the process flow to the subsystem of animal production as DDGS, and 61% of P is wasted associated with wastewater and sludge. Future scenarios of structural adjustments in the maize consumption system predict that the supply of maize for animal feed will be threatened if the policy of the Biofuel National Promotion before 2020 is fully implemented in China, as current maize production will not meet the future demand of food, feed and energy simultaneously. The results emphasized the use of P waste resources and better sludge management from a systems perspective. This also implied the importance of exploring coordinated development and integrated strategies for sustainable P flow management in multiple utilization systems.

Consumers' Acceptance of Agricultural Fertilizers Derived from Diverted and Recycled Human Urine

Nitrogen and phosphorus are essential ingredients in fertilizers used to produce food. Novel methods are emerging for more efficiently sourcing these nutrients, one of which is to recover them from recycled human urine; once recovered, N and P can be redirected to fertilizer production. While the technology for creating human urine-derived fertilizer (HUDF) exists, implementing it at scale will depend on public acceptance. Thus, this study examined U.S. consumers' acceptance of HUDF across a range of applications and, in comparison, to other fertilizer types. Data were collected from a representative national sample, and analyses of variance with post-hoc comparisons were conducted to compare across fertilizer applications and types. A hierarchical regression was conducted to assess if demographics, psychological variables, and value orientations predict HUDF acceptance. Results suggest that HUDF and biosolid-based fertilizers are equally preferred and more strongly preferred than synthetic fertilizers. HUDF is not preferred as strongly as organic fertilizers. HUDF was deemed most acceptable when used on nonedible plants and least acceptable when used on crops for human consumption. Regression analysis revealed that judgments about risks and benefits were the strongest predictors of acceptance of UDF use. These results are promising for sanitation practitioners and regulators among others.

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

The availability of carbon (C) from high levels of atmospheric carbon dioxide (CO2 ) and anthropogenic release of nitrogen (N) is increasing, but these increases are not paralleled by increases in levels of phosphorus (P). The current unstoppable changes in the stoichiometries of C and N relative to P have no historical precedent. We describe changes in P and N fluxes over the last five decades that have led to asymmetrical increases in P and N inputs to the biosphere. We identified widespread and rapid changes in N:P ratios in air, soil, water, and organisms and important consequences to the structure, function, and biodiversity of ecosystems. A mass-balance approach found that the combined limited availability of P and N was likely to reduce C storage by natural ecosystems during the remainder of the 21st Century, and projected crop yields of the Millennium Ecosystem Assessment indicated an increase in nutrient deficiency in developing regions if access to P fertilizer is limited. Imbalances of the N:P ratio would likely negatively affect human health, food security, and global economic and geopolitical stability, with feedbacks and synergistic effects on drivers of global environmental change, such as increasing levels of CO2 , climatic warming, and increasing pollution. We summarize potential solutions for avoiding the negative impacts of global imbalances of N:P ratios on the environment, biodiversity, climate change, food security, and human health.

Unexpected Favorable Role of Ca2+ in Phosphate Removal by Using Nanosized Ferric Oxides Confined in Porous Polystyrene Beads

Polystyrene-based nanoferric oxide composite is a representative nanomaterial successfully applied in scale-up water decontamination for arsenic and phosphorus. However, little is available on the effect of solution chemistry (for instance, the coexisting Ca²⁺) on the long-term performance of the nanocomposite. In this study, we carried out 20 cyclic runs of phosphate adsorption-desorption on a polymer-supported ferric nanocomposite HFO@201. Unexpectedly, an enhanced phosphate removal was observed in the presence of Ca²⁺, which is quite different from its adverse effect on phosphate capture by granular ferric oxide. Further mechanistic studies revealed that enhanced phosphate removal was mainly realized via the Ca-P coprecipitation inside the networking pores of HFO@201 as well as the possible formation of the multiple Fe-P-Ca-P complex. The complex formation led to a distinct increase in P adsorption, and the coprecipitation, driven by the accumulated OH^- in confined pores during phosphate adsorption and alkaline regeneration, favored P removal via the formation of amorphous calcium phosphate (ACP) and hydroxyapatite inside. TEM-EDS spectra indicated that coprecipitation did not occur on the surface of loaded nano-HFO, greatly mitigating its adverse effect on P adsorption on the surface of nano-HFO. Fixed-bed column study showed that the presence of Ca²⁺ increased the effective treatable volume of HFO@201 toward P-containing influents by ∼70%. This study is believed to shed new insights into the effect of solution chemistry on similar nanocomposites for advanced water treatment.

Electrochemical Induced Calcium Phosphate Precipitation: Importance of Local pH

Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.

Phosphorus in recycling fertilizers - analytical challenges

The importance of secondary raw materials for phosphorus (P) fertilizer production is expected to increase in the future due to resource depletion, supply risks, and heavy metal contamination of fossil phosphate resources. Municipal wastewater is a promising source for P recovery. In Germany for instance, it contains almost 50% of the total amount of P that is currently applied as mineral fertilizer. Several procedures have been developed to recover and re-use P resulting in a growing number of recycling fertilizers that are currently not regulated in terms of fertilizer efficiency. We tested various materials and matrices for their total P content, solubility of P in neutral ammonium citrate (P_nac) and water, and performed robustness tests to check if existing analytical methods are suitable for those new materials. Digestion with inverse aqua regia was best suited to determine the total P content. P_nac sample preparation and analyses were feasible for all matrices. However, we found significant time and temperature dependencies, especially for materials containing organic matter. Furthermore, several materials didn't reach equilibrium during the extractions. Thus, strict compliance of the test conditions is strongly recommended to achieve comparable results.

Insight into chemical phosphate recovery from municipal wastewater

Phosphate plays an irreplaceable role in the production of fertilizers. However, its finite availability may not be enough to satisfy increasing demands for the fertilizer production worldwide. In this scenario, phosphate recovery can effectively alleviate this problem. Municipal wastewater has received high priority to recover phosphate because its quantity is considerable. Therefore, phosphate recovery from municipal wastewater can bring many benefits such as relieving the burden of increasing production of fertilizers and reduction in occurrence of eutrophication caused by the excessive concentration of phosphate in the released effluent. The chemical processes are the most widely applied in phosphate recovery in municipal wastewater treatment because they are highly stable and efficient, and simple to operate. This paper compares chemical technologies for phosphate recovery from municipal wastewater. As phosphate in the influent is transferred to the liquid and sludge phases, a technical overview of chemical phosphate recovery in both phases is presented with reference to mechanism, efficiency and the main governing parameters. Moreover, an analysis on their applications at plant-scale is also presented. The properties of recovered phosphate and its impact on crops and plants are also assessed with a discussion on the economic feasibility of the technologies.