Environmental Benefits and Burdens of Phosphorus Recovery from Municipal Wastewater

Digitalization of phosphorous removal process in biological wastewater treatment systems: Challenges, and way forward

Phosphorus in wastewater poses a significant environmental threat, leading to water pollution and eutrophication. However, it plays a crucial role in the water-energy-resource recovery-environment (WERE) nexus. Recovering Phosphorus from wastewater can close the phosphorus loop, supporting circular economy principles by reusing it as fertilizer or in industrial applications. Despite the recognized importance of phosphorus recovery, there is a lack of analysis of the cyber-physical framework concerning the WERE nexus. Advanced methods like automatic control, optimal process technologies, artificial intelligence (AI), and life cycle assessment (LCA) have emerged to enhance wastewater treatment plants (WWTPs) operations focusing on improving effluent quality, energy efficiency, resource recovery, and reducing greenhouse gas (GHG) emissions. Providing insights into implementing modeling and simulation platforms, control, and optimization systems for Phosphorus recovery in WERE (P-WERE) in WWTPs is extremely important in WWTPs. This review highlights the valuable applications of AI algorithms, such as machine learning, deep learning, and explainable AI, for predicting phosphorus (P) dynamics in WWTPs. It emphasizes the importance of using AI to analyze microbial communities and optimize WWTPs for different various objectives. Additionally, it discusses the benefits of integrating mechanistic and data-driven models into plant-wide frameworks, which can enhance GHG simulation and enable simultaneous nitrogen (N) and Phosphorus (P) removal. The review underscores the significance of prioritizing recovery actions to redirect Phosphorus from effluent to reusable products for future considerations.

Compiling life cycle inventories for wastewater-derived products

With the paradigm shift in wastewater management from pollutant removal to resource recovery, more wastewater-derived products are emerging from different recovery pathways. It is becoming increasingly important to understand the potential environmental impacts of these products through life cycle assessment (LCA). This study aims to compile life cycle inventories of wastewater-derived products from the perspective of the product end users (e.g., agricultural sector, packaging industry), and to explore the challenges of their compilation. Using inventories from wastewater resource recovery LCA literature, we compiled an attributional inventory (88 sets) and a consequential inventory (33 sets) of three categories of wastewater-derived products - phosphorus compounds, nitrogen compounds, and biopolymers. The two inventories differ by the choices of system boundary, how foreground systems are being modelled, and how co-products are being handled. We found that while there is a large body of literature related to wastewater resource recovery LCA, very few studies (29 out of 174 for the three categories of products) are suitable for end users to successfully compile inventories of derived products. The inventories were assessed by the technology readiness level assessment, the data quality assessment, and the cumulative energy demand indicator. The inventories can be used directly by end users or served as "screening" inventories for end users to prioritize data collection effort. The identified challenges of inventory compilation include diverse recovery settings, the absence of baseline scenarios, the multifunctional nature of wastewater treatment plants, the lack of inventory transparency and completeness, and low technology readiness level for some recovery pathways. While established or emerging approaches exist to address most of these challenges for end users, wastewater resource recovery LCA practitioners can enhance their assessments to be more end-user-oriented. This can be achieved by including baseline non-recovery scenarios, disclosing detailed life cycle inventory by system components, and assessing a wide variety of operating scenarios. Addressing some of these compilation challenges would enhance the comprehensiveness and quality of wastewater-derived product inventories.

A review of struvite crystallization for nutrient source recovery from wastewater

Nutrient recovery from wastewater not only reduces the nutrient load on water resources but also alleviates the environmental problems in aquatic ecosystems, which is a solution to achieve a sustainable society. Besides, struvite crystallization technology is considered a potential nutrient recovery technology because the precipitate obtained can be reused as a slow-release fertilizer. This review presents the basic properties of struvite and the theory of the basic crystallization process. In addition, the possible influencing variables of the struvite crystallization process on the recovery efficiency and product purity are also examined in detail. Then, the advanced auxiliary technologies for facilitating the struvite crystallization process are systematically discussed. Moreover, the economic and environmental benefits of the struvite crystallization process for nutrient recovery are introduced. Finally, the shortcomings and inadequacies of struvite crystallization technology are presented, and future research prospects are provided. This work serves as the foundation for the future use of struvite crystallization technology to recover nutrients in response to the increasingly serious environmental problems and resource depletion.

Environmental sustainability opportunity and socio-economic cost analyses of phosphorus recovery from sewage sludge

Although phosphorus (P) recovery and management from sewage sludge are practiced in North America and Europe, such practices are not yet to be implemented in China. Here, we evaluated the environmental sustainability opportunity and socio-economic costs of recovering P from sewage sludge by replacing the current-day treatments (CT; sludge treatment and landfill) and P chemical fertilizer application (CF) in China using life cycle assessment and life cycle costing methods. Three potential P recovery scenarios (PR₁‒PR₃: struvite, vivianite, and treated sludge) and corresponding current-day scenarios (CT₁‒CT₃ and CF) were considered. Results indicated that PR₁ and PR₂ have smaller environmental impacts than the current-day scenarios, whereas PR₃ has larger impacts in most categories. PR₃ has the lowest net costs (sum of internal costs and benefits, 39.1-54.7 CNY per kg P), whereas PR₂ has the lowest external costs (366.8 CNY per kg P). Societal costs for production and land use of 1 kg P by P recovery from sewage sludge (e.g., ∼527 CNY for PR₁) are much higher than those of P chemical fertilizers (∼20 CNY for CF). However, considering the costs in the current-day treatments (e.g., ∼524 CNY for CT₁), societal costs of P recovery scenarios are close to or slightly lower than those of current-day scenarios. Among the three P recovery scenarios, we found that recovering struvite as P fertilizer has the highest societal feasibility. This study will provide valuable information for improved sewage sludge management and will help promote the sustainable supply of P in China.

Phosphonium-Based Polyelectrolytes: Preparation, Properties, and Usage in Lithium-Ion Batteries

Phosphorous is an essential element for the life of organisms, and phosphorus-based compounds have many uses in industry, such as flame retardancy reagents, ingredients in fertilizers, pyrotechnics, etc. Ionic liquids are salts with melting points lower than the boiling point of water. The term "polymerized ionic liquids" (PILs) refers to a class of polyelectrolytes that contain an ionic liquid (IL) species in each monomer repeating unit and are connected by a polymeric backbone to form macromolecular structures. PILs provide a new class of polymeric materials by combining some of the distinctive qualities of ILs in the polymer chain. Ionic liquids have been identified as attractive prospects for a variety of applications due to the high stability (thermal, chemical, and electrochemical) and high mobility of their ions, but their practical applicability is constrained because they lack the benefits of both liquids and solids, suffering from both leakage issues and excessive viscosity. PILs are garnering for developing non-volatile and non-flammable solid electrolytes. In this paper, we provide a brief review of phosphonium-based PILs, including their synthesis route, properties, advantages and drawbacks, and the comparison between nitrogen-based and phosphonium-based PILs. As phosphonium PILs can be used as polymer electrolytes in lithium-ion battery (LIB) applications, the conductivity and the thermo-mechanical properties are the most important features for this polymer electrolyte system. The chemical structure of phosphonium-based PILs that was reported in previous literature has been reviewed and summarized in this article. Generally, the phosphonium PILs that have more flexible backbones exhibit better conductivity values compared to the PILs that consist of a rigid backbone. At the end of this section, future directions for research regarding PILs are discussed, including the use of recyclable phosphorus from waste.

Techno-economic and life cycle analysis of circular phosphorus systems in agriculture

Fertilizer runoff is a global nuisance that disrupts biogeochemical cycles of nitrogen and phosphorus. We perform techno-economic and life cycle analyses of selected approaches for enabling a circular economy of phosphorus. We consider four schemes: capturing P with ion-exchange resins followed by precipitation, interception by wetland and recovery in char after biomass pyrolysis, removal by bioreactor and recovery in char after bioreactor substrate pyrolysis, and using legacy phosphorus accumulated in a saturated wetland to grow crops by wetlaculture. For each system, we analyze the mass flow, calculate the degree of circularity, and examine the feasibility by techno-economic and life cycle analyses. We find that although ion exchange outperforms the others, the associated economic and emissions burden are too high. Approaches that rely on wetlands are most economically attractive and can have lower impact. However, without policy interventions, the linear economy of phosphorus is likely to remain economically most attractive.

Effect of corn pre-puffing on the efficiency of MgO-engineered biochar for phosphorus recovery from livestock wastewater: mechanistic investigations and cost benefit analyses

To improve the phosphorus (P) recovery efficiency from livestock wastewater, a novel MgO doped mildewed corn biochar with thermal pre-puffing treatment (Mg-PBC) and without pre-puffing (Mg-BC) was synthesized and tested. The thermal-puffing pretreatment improved the effectiveness of metal soaking and MgO dispersion. P recovery time with Mg-PBC (7 h) was significantly shorter than that with Mg-BC (12 h). Moreover, Mg-PBC showed significantly higher P recovery capacity (241 mg g−1) than Mg-BC (96.6 mg g−1). P recovery capacity of the Mg-PBC fitted to the Thomas model was 90.7 mg g−1, which was 4 times higher than that of Mg-BC (22.9 mg g−1) under column test conditions. The mechanisms involved in P recovery included precipitation, surface complexation, and electrostatic interaction. After adsorption, both Mg-BC and Mg-PBC showed relatively low regeneration abilities. The P loaded Mg-BC (Mg-BC-P) and Mg-PBC (Mg-PBC-P), the later particularly, obviously increased the available P content and promoted plant growth. The release of P increased with time in the Mg-PBC-P treated soil, while it decreased with time in the P fertilizer treated soil. A cost–benefit analysis revealed that thermal-puffing pretreatment greatly increased the profit of MgO doped biochar from −0.66 to 5.90 US$ kg−1. These findings highlight that biomass pre-puffing is a feasible treatment to produce MgO modified biochar and to recover P from livestock wastewater, and that the Mg-PBC-P can be used as a slow-release P fertilizer.

Graphical Abstract

A comparative LCA of three WWTPs in a tourist area: Effects of seasonal loading rate variations

Although the wastewater treatment is a fundamental utility for the protection of human health and the environment, non-evident drawbacks are associated with it. Wastewater treatment plants (WWTPs) located in tourist areas generally suffer from the seasonal increase in wastewater flow-rate and associated pollution loads. In this study, a Life Cycle Assessment (LCA) of three medium-size urban WWTPs, located in a tourist area in central Italy, was carried out. The study compared the environmental impacts generated by 1 m³ of treated wastewater in low season (LS) and high season (HS). All the material and energy flows involved in the operational phase of wastewater treatment were considered within the system boundaries, including the disposal or recovery treatment of the waste streams generated by the WWTPs, namely screenings, waste from grit removal and wastewater sludge. The analysis was conducted using almost only real data from full-scale plants. In each WWTP, the environmental impacts produced in HS were higher than those generated in LS; therefore, the environmental impacts increased as the loading rate increased. Furthermore, a correlation between WWTP size and environmental performance was observed. Indeed, in 8 out of 11 environmental indicators, the percentage increase in pollutant emissions due to wastewater treatment in HS decreased as the WWTP size increased. Results revealed that larger WWTPs suffered less from seasonal loading rate variations, showing greater flexibility. The existence of a scale factor suggests that the centralization of WWTPs in tourist areas can be an option to enable better treatment performance in terms of environmental impacts. A sensitivity analysis was performed, increasing N₂O emission factors from wastewater treatment in LS: considering a 75 % increase, the outcomes found in default LCA were not confirmed. Future research should investigate the operational factors and biological mechanisms that most affect wastewater treatment when significant seasonal variations are present.

Systematic data-driven exploration of Austrian wastewater and sludge treatment - implications for phosphorus governance, costs and environment

Within the new policy framework shaped by the EU Green Deal and the Circular Economy Action Plans, the field of wastewater and sludge treatment in Europe is subject to high expectations and new challenges related to mitigation of greenhouse gas emissions, micropollutant removal and resource recovery. With respect to phosphorus recovery, several technologies and processes have been thoroughly investigated. Nevertheless, a systemic and detailed understanding of the existing infrastructure and of the related environmental and economic implications is missing. Such basis is essential to avoid unwanted consequences in designing new strategies, given the long lifespan of any infrastructural change. This study couples a newly collected and highly detailed database for all wastewater treatment plants in Austria bigger than 2000 population equivalent with a combination of analyses, namely Substance Flow Analysis with focus on nutrient and metal distribution in different environmental and anthropogenic compartments, Energy Flow Analysis, Life Cycle Assessment and cost estimation. The case study of Austria is of special interest, given its highly autonomous administration in federal states and its contrasting traits, ranging from flat metropolitan areas like Vienna to low-populated alpine areas. The significant impact of electricity demand of wastewater treatment on the overall Cumulative Energy Demand (CED) shows the importance of optimization measures. Further, the current system of wastewater and sludge disposal have a low efficiency in recovering nutrients and in directing pollutants as heavy metals into final sinks. Sludge composting with subsequent use in landscaping does not only show an unfavorable environmental balance, but it is the only relevant route leading to additional CED and Global Warming Potential emissions and to the highest transport volume. Altogether, the outcomes of this study provide a sound basis to further develop national strategies for resource recovery aimed to optimize trade-offs between different economic and environmental objectives.

Environmental impacts and optimizing strategies of municipal sludge treatment and disposal routes in China based on life cycle analysis

The management and utilization of sludge in a sustainable approach require a systematic analysis of the environmental impacts generated from diverse sludge treatment and disposal processes. This study systematically assessed 12 common sludge treatment and disposal routes based on the existing operating and construction conditions of representative sludge disposal projects in China. We evaluated their environmental impacts using a life cycle assessment following the International Organization for Standardization (ISO 14040 and ISO 14044), and found that the routes of co-incineration, mono-incineration, and anaerobic digestion with or without thermal hydrolysis may be useful in terms of simultaneously controlling environmental pollution and carbon emissions in China. Therein, the route of co-incineration was recommended as the best one because its human toxicity potential (-152.31 kg dichlorobenzene (1,4-DB) eq/ton dry solid (t DS)), freshwater ecotoxicity potential (FEP, -127.40 kg 1,4-DB eq/t DS), terrestrial ecotoxicity potential (TEP, -0.81 kg 1,4-DB eq/t DS), and global warming potential (-27.26 kg CO2 eq/t DS) were all negative (environmental benefits). Furthermore, the toxicity impacts of the mono-incineration route were also negative, but it still needed to further enhance energy recovery to reduce carbon emissions. Despite the routes of anaerobic digestion and thermal hydrolysis in combination with anaerobic digestion had the excellent negative carbon emission attributes (-572.44 kg CO2 eq/t DS, -474.92 kg CO2 eq/t DS), they showed serious FEP and TEP owing to the heavy metals pollution caused by subsequent land use of anaerobic digested sludge. Overall, this study selected the most suitable sludge treatment and disposal routes to simultaneously satisfy the requirements of carbon emission reduction and pollution control in China and proposed optimizing suggestions for future technical improvement and development.

Life Cycle Environmental Impacts of Wastewater-Derived Phosphorus Products: An Agricultural End-User Perspective

Recovering phosphorus from wastewater in more concentrated forms has potential to sustainably recirculate phosphorus from cities to agriculture. The environmental sustainability of wastewater-based phosphorus recovery processes or wastewater-derived phosphorus products can be evaluated using life cycle assessment (LCA). Many LCA studies used a process perspective to account for the impacts of integrating phosphorus recovery processes at wastewater treatment plants, while some used a product perspective to assess the impacts of producing wastewater-derived phosphorus products. We demonstrated the application of an end-user perspective by assessing life cycle environmental impacts of substituting half of the conventional phosphorus rock-based fertilizers used in three crop production systems with wastewater-derived phosphorus products from six recovery pathways (RPs). The consequential LCA results show that the substitution reduces global warming potential, eutrophication potential, ecotoxicity potential, and acidification potential of the assessed crop production systems in most RPs and scenarios. The end-user perspective introduced in this study can (i) complement with the process perspective and the product perspective to give a more holistic picture of environmental impacts along the "circular economy value chains" of wastewater-based resource recovery, (ii) enable systemwide assessment of wide uptake of wastewater-derived products, and (iii) draw attention to understanding the long-term environmental impacts of using wastewater-derived products.

Life cycle assessment of struvite recovery and wastewater sludge end-use: A Flemish illustration

Phosphate rock (PR) has been designated as a Critical Raw Material in the European Union (EU). This has led to increased emphasis on alternative P recovery (APR) from secondary streams like wastewater sludge (WWS). However, WWS end-use is a contentious topic, and EU member states prefer different end-use pathways (land application/incineration/valorisation in cement kilns). Previous Life Cycle Assessments (LCA) on APRs from WWS reached contrasting conclusions; while most considered WWS as waste and highlighted a net benefit relative to PR mining and beneficiation, others viewed WWS as a resource and highlighted a net burden of the treatment. We used a combined functional unit (that views WWS from a waste as well as a resource perspective) and applied it on a Flemish wastewater treatment plant (WWTP) with struvite recovery as APR technology. Firstly, a retrospective comparison was performed to measure the WWTP performance before and after struvite recovery and the analysis was complemented by uncertainty and global sensitivity analyses. The results showed struvite recovery provides marginal environmental benefits due to improved WWS dewatering and reduced polymer use. Secondly, a prospective LCA approach was performed to reflect policy changes regarding WWS end-use options in Flanders. Results indicated complete mono-incineration of WWS, ash processing to recover P and the subsequent land application appears to be less sustainable in terms of climate change, human toxicity, and terrestrial acidification relative to the status quo, i.e., co-incineration with municipal solid waste and valorisation at cement kilns. Impacts on fossil depletion, however, favour mono-incineration over the status quo.

Nitrogen and phosphorous recycling from human urine by household electrochemical fixed bed in sparsely populated regions

Decentralized treatment of human urine in sparsely populated regions could avoid the problem of sewage collection in traditionally centralized treatment schemes and simultaneously utilize the recovered N/P fertilizer in-situ to nurture gardens. Herein, an integrated electrochemical fixed bed packed with divided magnesite and carbon zones was constructed for the pretreatment of human urine, followed by the recovery of 95.0% NH₄⁺ and 85.8% PO₄^3- via struvite precipitation and NH₃ volatilization as well as the on-site employment of the produced struvite as fertilizer. In the process, the acid/base zones created by electrochemical water splitting dissolved the magnesite filler as the Mg²⁺ source of struvite, further creating an ideal pH environment for struvite precipitation and NH₃ volatilization in the effluent. Without the need to control solution pH by chemical addition, the system can resist impacts from changes in water quality by adjustment of the current density and flow rate, indicating its great potential for automatic operation. Life cycle assessment indicated that the on-site employment of produced struvite avoids the long-distance fertilizer transportation required for fertilization, thus reducing carbon emission by a hundred million tons per year if the household facility is driven by clean electricity.

Pivotal role of municipal wastewater resource recovery facilities in urban agriculture: A review

Urban agriculture provides a promising, comprehensive solution to water, energy, and food scarcity challenges resulting from the population growth, urbanization, and the accelerating effects of anthropogenic climate change. Their close access to consumers, profitable business models, and important roles in educational, social, and physical entertainment benefit both developing and developed nations. In this sense, Urban Water Resource Reclamation Facilities (WRRFs) can play a pivotal role in the sustainable implementation of urban agriculture. Reclaimed water as a recovered resource has less supply variability and in certain cases can be of higher quality than other water sources used in agriculture. Another recovered resource, namely, biosolids, as byproduct from wastewater treatment can be put to beneficial use as fertilizers, soil amendments, and construction material additives. The renewable electricity, heat, CO2, and bioplastics produced from WRRFs can also serve as essential resources in support of urban agriculture operation with enhanced sustainability. In short, this review exhibits a holistic picture of the state-of-the-art of urban agriculture in which WRRFs can potentially play a pivotal role. PRACTITIONER POINTS: Reclaimed water can be of higher quality than other sources used in urban agriculture. Biosolids can be put to beneficial use as fertilizers, soil amendments, and construction material additives. The renewable electricity, heat, CO2, and bioplastics produced can also serve as essential resources in support of urban agriculture.

Analysis of Reject Water Formed in the Mechanical Dewatering Process of Digested Sludge Conditioned by Physical and Chemical Methods

Reject water separated from digested sludge may be a potential source of nutrients due to its high content. However, most often, reject water after sludge dewatering is directed to sewage lines at wastewater treatment plants, negatively affecting their operation, especially in the biological part. The activities related to sludge conditioning before dewatering have a direct impact on the quality of the reject water. The reject water of raw digested sludge is characterized by very high concentrations of ammonium nitrogen, at 1718 mgN-NH4+/dm3; phosphates, at 122.4 mgPO43−/dm3; and chemical oxygen demand (COD), at 2240 mgO2/dm3. The objective of the research was to determine the impact of selected sludge conditioning methods on the quality of reject water obtained after sludge dewatering. The following parameters were analyzed in the reject water: the chemical oxygen demand (COD), phosphates, ammonium nitrogen, and total suspended solids (TSS). It has been observed that the sludge sonification process increases the content of impurities (COD, phosphates) in reject water with an increase in the amplitude of the ultrasonic field. On the other hand, the chemical reagents cause a decrease in the concentration of the pollutants with an increase of the chemical dose. It has been found that the inorganic coagulant PIX 113 gives much better results regarding the reduction of contamination than the polyelectrolyte Zetag 8180.

The Mediating Role of Policy-Related Factors in the Relationship between Practice of Waste Generation and Sustainable Construction Waste Minimisation: PLS-SEM

As the construction industry grows, it produces large volumes of construction waste, which has a tremendous environmental impact and generates public concern in the neighbouring towns. The construction industry generates a significant volume of waste and faces a challenge with poor construction waste minimisation in order to prevent adverse environmental and dumping impacts worldwide. In developing countries, regional waste management systems have increased problems. Environmental pollution (air, water, and soil) and human health issues are caused by waste produced in a country as a result of different cultural, social, and religious activities. Prior studies were reviewed to choose dimensions and items for the data gathering instrument. A pilot test was conducted to identify potential questionnaire adjustments, and hypotheses were tested using structural equation modelling (SEM). A total of 220 Malaysian construction professionals answered the survey, which yielded the results. Five hypotheses have direct correlations based on the findings, three of which have a significant effect. Furthermore, the findings reveal that policy-related factors mediate the relationship between improving factors and sustainable construction waste minimisation. In contrast, they did not mediate the relationship between current practices/generation and sustainable construction waste management. The established framework can help improve construction waste management and help achieve global sustainable development goals. The data reveal that adopting preventive plans to reduce construction waste is one of the most important aspects of enhancing profitability. This study could aid construction industry players in evaluating waste management components during the construction and design stages of a building project.

Growing phosphorus dilemma: The opportunity from aquatic systems' secondary phosphorus retention capacity

The essential cause of phosphorus scarcity and phosphorus-induced risks, i.e. phosphorus dilemma, mainly lies in current low phosphorus flow efficiency (PFE) in agricultural systems. Improving PFE largely depends on secondary phosphorus retention along the phosphorus flow chain from phosphate mining to terrestrial agricultural systems, to aquatic systems, and ultimately to seabed deposition. Our review found that aquatic systems will have the opportunity and growing capacity to retain seaward secondary phosphorus carried by the runoff, due to its location between land and water systems, its ability of converting secondary phosphorus from both land and aquatic systems into aquatic products, and its rapid expansion with low PFE. However, a knowledge gap exists in secondary phosphorus retention in aquatic systems compared to in terrestrial systems. Although the phosphorus retention literature continues to grow in environmental and agricultural & biological sciences, only 8.8% of the documents are related to aquatic systems with few quantification studies. Based on the literature with phosphorus retention quantification since 1979, we divided the reported phosphorus interceptors into abiotic and biotic groups, further into 7 categories and more subcategories. By 2020, eight categories of interceptors had been reported, increased from only one interceptor in 1979. However, most of them focused on wetlands, only a few studies on aquatic organisms which concentrated in 8 countries before 2000. Thus, it is urgent to emphasize aquatic systems' secondary phosphorus retention capacity and its systemic benefits for a sustainable phosphorus use.

Phosphate recovery as vivianite using a flow-electrode capacitive desalination (FCDI) and fluidized bed crystallization (FBC) coupled system

It is critical to both effectively remove and recover phosphate (P) from wastewater given the wide-ranging environmental (i.e., preventing eutrophication and restoring water quality) and economic (i.e., overcoming P resource scarcity) benefits. More recently, considerable academic effort has been devoted towards harvesting P as vivianite, which can be used as a potential slow-release fertilizer and possible reagent for the manufacture of lithium iron phosphate (LiFePO₄), the precursor in fabricating Li-ion secondary batteries. In this study, we propose an innovative P recovery process, in which P is first preconcentrated via a flow-electrode capacitive deionization (FCDI) device followed by immobilization as vivianite crystals in a fluidized bed crystallization (FBC) column. The effects of different operational parameters on FCDI P preconcentration performance and energy consumption are investigated. Results show that 63% of P can be removed and concentrated in the flow-electrode chamber with a reasonable energy requirement under optimal operating conditions. The FBC system resulted in immobilization of ~80% of P as triangular or quadrangular pellets, which were verified to be high-purity vivianite crystals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and extended X-ray absorption fine structure (EXAFS) spectroscopy. This study provides a pathway for efficient recovery of P as a value-added product (i.e., vivianite) from P-rich wastewaters.

Phosphate selective recovery by magnetic iron oxide impregnated carbon flow-electrode capacitive deionization (FCDI)

The recovery of phosphorus (P) from wastewaters is a worthy goal considering the potential environmental and economic benefits. Flow-electrode capacitive deionization (FCDI), which employs flowable carbon electrodes instead of the static electrodes used in conventional CDI, has been demonstrated to be a promising P recovery technology. FCDI outperforms CDI and other competitive technologies in a number of aspects including (i) large salt adsorption capacity and (ii) extremely high water recovery rate. In this study, magnetic (Fe₃O₄ impregnated) activated carbon particles were prepared and applied as FCDI electrodes. The magnetic carbon electrodes were found to have a strong affinity towards P, facilitating the selective adsorption of P to the magnetic particles through a ligand exhange mechanism. Continuous operation of the FCDI system could be achieved with only three minutes required to separate the electrode particles from the brine stream on application of an external magnetic field. A P-rich stream was produced on regeneration of the exhausted magnetic electrodes using alkali solution. We envision that the use of magnetic carbon enhanced flow-electrodes will pave the way for efficient operation of FCDI as well as the preferential recovery of P.

Life Cycle Assessment of Urine Diversion and Conversion to Fertilizer Products at the City Scale

Urine diversion has been proposed as an approach for producing renewable fertilizers and reducing nutrient loads to wastewater treatment plants. Life cycle assessment was used to compare environmental impacts of the operations phase of urine diversion and fertilizer processing systems [via (1) a urine concentration alternative and (2) a struvite precipitation and ion exchange alternative] at a city scale to conventional systems. Scenarios in Vermont, Michigan, and Virginia were modeled, along with additional sensitivity analyses to understand the importance of key parameters, such as the electricity grid and wastewater treatment method. Both urine diversion technologies had better environmental performance than the conventional system and led to reductions of 29-47% in greenhouse gas emissions, 26-41% in energy consumption, approximately half the freshwater use, and 25-64% in eutrophication potential, while acidification potential ranged between a 24% decrease to a 90% increase. In some situations, wastewater treatment chemical requirements were eliminated. The environmental performance improvement was usually dependent on offsetting the production of synthetic fertilizers. This study suggests that urine diversion could be applied broadly as a strategy for both improving wastewater management and decarbonization.

Can wastewater feed cities? Determining the feasibility and environmental burdens of struvite recovery and reuse for urban regions

Phosphorus (P) resources are decreasing at an alarming rate due to global fertilizer use and insufficient nutrient recovery strategies. Currently, more circular approaches are promoted, such as recovering P from wastewater in the form of struvite. This is especially attractive for urban areas, where there is a growing trend of local crop production and large volumes of wastewater are treated in centralized wastewater treatment plants (WWTPs). This research aims to assess the technical and environmental feasibility of applying a struvite recovery and reuse strategy to meet the P requirements to fertilize the agricultural fields of an urban region. To do so, we analyze the potential P recovery and the environmental impacts of integrating three recovery technologies (REM-NUT®, Ostara® and AirPrex®) in the two biggest WWTPs of the Àrea Metropolitana de Barcelona. The results show that all technologies are able to recover between 5 and 30 times the amount of P required to fertilize the agricultural area of the region annually (36.5 t). As can be expected, including P recovery technologies result in additional impacts per m³ of wastewater due to increased electricity consumption and chemicals required for the struvite precipitation. However, struvite recovery results in less eutrophication potential, especially in the REM-NUT® case, with an average reduction of 5.4 times. On the other hand, Ostara®, that recovers P from the digestate, had the lowest impacts (9 kgCO₂eq/kgP), even compared to the production of mineral fertilizer. When we apply our findings to the whole region, we can see that chemical use for struvite precipitation and energy consumption during the wastewater treatment process are the elements with the greatest impact. Thus, choosing the most appropriate technology in the most suitable WWTP is the most efficient strategy to diminish the environmental impacts of the system.

The transformation of phosphorus fractions in high-solid sludge by anaerobic digestion combined with the high temperature thermal hydrolysis process

Transforming inactive phosphorus (P) to active P to recover it from waste activated sludge is important. The transformation of P fractions from high-solid sludge by the anaerobic digestion (AD) and acidification phase of AD (AAD) combined with a high temperature thermal hydrolysis process (HTTHP) was investigated. The results showed that the sequence of P release effects by three processes was HTTHP + AAD > AD + HTTHP > HTTHP + AD. The PO₄^3--P release from high-solid sludge was directly affected by the temperature of HTTHP. At 140 °C, each process had more PO₄^3--P release than that at 160 °C. The total amount of PO₄^3--P release in AD + HTTHP was approximately 6 times that of HTTHP + AD. Based on the experimental results, a new process of mesophilic AD - post HTTHP was recommended, in which, enhancement of P release by sulfide ions was also proposed.

An integral approach to sludge handling in a WWTP operated for EBPR aiming phosphorus recovery: Simulation of alternatives, LCA and LCC analyses

As phosphorus is a non-renewable resource mainly used to produce fertilizers and helps to provide food all over the world, the proper management of its reserves is a global concern since it is expected to become scarcer in the near future. In this work we assessed two different sludge line configurations aiming for P extraction and recovery before anaerobic digestion and compared them with the classical configuration. This study has been performed by simulation with the model BNRM2 integrated in the software package DESASS 7.1. Configuration 1 was based on the production of a PO₄-enriched stream from sludge via elutriation in the primary thickeners, while Configuration 2 was based on the WASSTRIP® process and its PO₄-enriched stream was mechanically obtained with dynamic thickeners. In both alternatives recovery was enhanced by promoting poly-phosphate (poly-P) extraction under anaerobic conditions, for which both configurations were fully evaluated in a full-scale WWTP. Both were also optimized to maximize phosphorus extraction. Their costs and life cycles were also analysed. The novelty of this research lies in the lack of literature about the integral evaluation of pre-anaerobic digestion P recovery from wastewaters. This study included a holistic approach and an optimization study of both alternatives plus their economic and environmental aspects. In Configuration 1, the PO₄-P load in the recovery stream reached 43.1% of the total influent P load and reduced uncontrolled P-precipitation in the sludge line up to 52.9%. In Configuration 2, extraction was 48.2% of the influent P load and it reduced precipitation by up to 60.0%. Despite Configuration 1's lower phosphorus recovery efficiency, it had a 23.0% lower life cycle cost and a 14.2% lower global warming impact per hm³ of treated influent than Configuration 2. Configuration 1 also reduced the TAEC by 17.6% and global warming impact by 2.0% less than Configuration 0.

Beyond Energy Balance: Environmental Trade-Offs of Organics Capture and Low Carbon-to-Nitrogen Ratio Sewage Treatment Systems

Several life-cycle assessments (LCAs) have evaluated the environmental impacts (EIs) of different wastewater treatment (WWT) configurations, attempting resource recovery and energy efficiency. However, a plant-wide LCA considering up-concentration primary treatment and low carbon-to-nitrogen (C/N) ratio sewage at the secondary biological treatment (SBT) has not yet been conducted. This study identifies the environmental trade-offs and hotspots for the chemically enhanced primary treatment (CEPT) and low C/N ratio SBT emerging processes compared to conventional WWT. The life-cycle inventories were calculated using a stoichiometric life-cycle inventory framework that couples stoichiometry and kinetics to obtain site-specific water, air, and soil emissions. The midpoint results of LCA show that CEPT with anaerobic digestion (AD) for sludge treatment achieves energy self-sufficiency, but increases marine eutrophication (MEu) by 1 order of magnitude compared to conventional WWT. A mainstream anaerobic fluidized-bed bioreactor and a partial nitritation-anammox fluidized-bed membrane bioreactor which can reduce all environmental impacts by 17-47%, including MEu, are proposed as the SBT of the low-carbon CEPT settled sewage. Integrating the standardized S-LCI framework resulted in a site-specific LCA that aids decision-makers on choosing between higher reductions in most EIs at the expense of high MEu or less but consistent reductions in all EI categories.

Life cycle assessment of nutrient recycling from wastewater: A critical review

Recovering resources from wastewater systems is increasingly being emphasised. Many technologies exist or are under development for recycling nutrients such as nitrogen and phosphorus from wastewater to agriculture. Planning and design methodologies are needed to identify and deploy the most sustainable solutions in given contexts. For the environmental sustainability dimension, life cycle assessment (LCA) can be used to assess environmental impact potentials of wastewater-based nutrient recycling alternatives, especially nitrogen and phosphorus recycling. This review aims to evaluate how well the LCA methodology has been adapted and applied for assessing opportunities of wastewater-based nutrient recycling in the form of monomineral, multimineral, nutrient solution and organic solid. We reviewed 65 LCA studies that considered nutrient recycling from wastewater for agricultural land application. We synthesised some of their insights and methodological practices, and discussed the future outlook of using LCA for wastewater-based nutrient recycling. In general, more studies suggested positive environmental outcomes from wastewater-based nutrient recycling, especially when chemical inputs are minimised, and source separation of human excreta is achieved. The review shows the need to improve methodological consistency (e.g., multifunctionality, fertiliser offset accounting, contaminant accounting), ensure transparency of inventory and methods, consider uncertainty in comparative LCA context, integrate up-to-date cross-disciplinary knowledge (e.g., agriculture science, soil science) into LCA models, and consider the localised impacts of recycled nutrient products. Many opportunities exist for applying LCA at various scales to support decisions on wastewater-based nutrient recycling - for instance, performing "product perspective" LCA on recycled nutrient products, integrating "process perspective" LCA with other systems approaches for selecting and optimising individual recovery processes, assessing emerging nutrient recovery technologies and integrated resource recovery systems, and conducting systems analysis at city, national and global level.

Mitigation Life Cycle Assessment: Best Practices from LCA of Energy and Water Infrastructure That Incurs Impacts to Mitigate Harm

Climate change will require societal-scale infrastructural changes. Balancing priorities for water, energy, and climate will demand that approaches to water and energy management deviate from historical practice. Infrastructure designed to mitigate environmental harm, particularly related to climate change, is likely to become increasingly prevalent. Understanding the implications of such infrastructure for environmental quality is thus of interest. Environmental life cycle assessment (LCA) is a common sustainability assessment tool that aims to quantify the total, multicriteria environmental impact caused by a functional unit. Notably, however, LCA quantifies impacts in the form of environmental “costs” of delivering the functional unit. In the case of mitigation infrastructures, LCA results can be confusing because they are generally reported as the harmful impacts of performing mitigation rather than as net impacts that incorporate benefits of successful mitigation. This paper argues for defining mitigation LCA as a subtype of LCA to facilitate better understanding of results and consistency across studies. Our recommendations are informed by existing LCA literature on mitigation infrastructure, focused particularly on stormwater and carbon management. We specifically recommend that analysts: (1) use a performance-based functional unit; (2) be attentive to burden shifting; and (3) assess and define uncertainty, especially related to mitigation performance.

Electrochemical removal of phosphate in the presence of calcium at low current density: Precipitation or adsorption？

Phosphorus removal and recovery from waste streams are crucial to prevent eutrophication and sustain fertilizer production. As has been shown in our previous papers, electrochemical treatment has the potential to achieve this goal. However, the adoption of electrochemical approach is limited by its high energy consumption. Here, we investigate the possibility of electrochemical phosphorus removal at extremely low current density using graphite felt as the cathode. We found a current density as low as 0.04 A/m² can enhance the removal of phosphate in our electrochemical system. The removal of phosphate at extremely low current density resulted from electrochemical induced calcium phosphate precipitation and not by electrochemical adsorption. Electrochemical treatment of real domestic wastewater at 0.2 A/m² almost eliminates the precipitation of Mg(OH)₂ and limits the formation of CaCO₃. The recovered precipitates are dominated by calcium phosphate (59%), followed by 35% CaCO₃ and 6% Mg(OH)₂. The specific energy consumption of this newly electrochemical system is between 4.4 and 26.4 kW h/kg P, which is 2 orders of magnitude lower than our previous system (110-2238 kW h/kg P). Key factors for this improvement prove to be enlarged precipitation area and hydroxide flux retardation by graphite felt. Practically, our study offers a potential way to reduce the energy consumption in electrochemical removal of phosphate by using a graphite felt cathode and at a current density below 0.2 A/m². Fundamentally, our study contributes to the understanding of adsorption and precipitation in electrochemical removal of phosphate at an extremely low current density and with carbon-based electrodes.

Environmental performances of production and land application of sludge-based phosphate fertilizers-a life cycle assessment case study

Phosphorus (P) is a non-renewable resource extracted from phosphate rock to produce agricultural fertilizers. Since P is essential for life, it is important to preserve this resource and explore alternative sources of P to reduce its criticality. This study aimed to assess whether fertilizing with sludge-based phosphate fertilizers (SBPF) can be a suitable alternative to doing so with fertilizers produced from phosphate rock. Environmental impacts of production and land application of SBPF from four recovery processes were compared to those of two reference scenarios: triple super phosphate (TSP) and sewage sludge. To avoid bias when comparing scenarios, part of the environmental burden of wastewater treatment is allocated to sludge production. The CML-IA method was used to perform life cycle impact assessment. Results highlighted that production and land application of SBPF had higher environmental impacts than those of TSP due to the large amounts of energy and reactants needed to recover P, especially when sludge had a low P concentration. Certain environmental impacts of production and land application of sewage sludge were similar to those of SBPF. Sensitivity analysis conducted for cropping systems highlighted variability in potential application rates of sewage sludge or SBPF. Finally, because they contain lower contents of heavy metals than sewage sludge or TSP, SBPF are of great interest, but they require more mineral fertilizers to supplement their fertilization than sewage sludge. Thus, SBPF have advantages and disadvantages that need to be considered, since they may influence their use within fertilization practices.

Characterization of implementation limits and identification of optimization strategies for sustainable water resource recovery through life cycle impact analysis

How we manage alternative freshwater resources to close the gap between water supply and demand is pivotal to the future of the environment and human well-being. Increased scarcity of water for agricultural irrigation in semi-arid and arid regions has resulted in a growing interest in water reuse practices. However, insight into the life cycle impacts and potential trade-offs of these emerging practices are still limited by the paucity of systematic evaluations of different water reuse implementations. In this study, a host of environmental and human health impacts at three implementation levels of allowing water reclamation for crop irrigation was comparatively evaluated across the operational landscape via a combination of scenario modelling, life-cycle impact analyses and Monte Carlo simulations. Net harvesting of reclaimed water for irrigation was found to be dependent upon the sophistication of the treatment processes, since multistage and complex configurations can cause greater direct water consumption during processing. Further, the direct benefits of water resource recovery can be essentially offset by indirect adverse impacts, such as mineral depletion, global warming, ozone depletion, ecotoxicity, and human health risks, which are associated with increased usage of energy and chemicals for rigorous removal of contaminants, such as heavy metals and contaminants of emerging concern. Nonetheless, expanded simulations suggest the significance of concurrently implementing energy recovery, nutrient recycling, and/or nature-based, chemical-free water technologies to reduce the magnitude of negative impacts from engineered water reclamation processes.

Nutrient Recovery from Municipal Wastewater for Sustainable Food Production Systems: An Alternative to Traditional Fertilizers

Traditional wastewater management uses end-of-pipe approaches to remove pollutants in wastewater before discharge. Although effective in human health protection for decades, this approach of removal and disposal requires a high investment of energy and materials and overlooks the values of the key nutrients in wastewater such as phosphorus (P). Phosphorus in wastewater comes from the human metabolites of food, resulted from crop uptakes of fertilizer that ultimately derived from phosphate rock (PR). PR, however, could be depleted in this century, which would lead to a global food crisis. To address the question whether nutrient recovery is indeed a more efficient strategy from a system perspective and provides more benefits to society, this research compares fertilizer production from struvite to the traditional commercial fertilizers (e.g., diammonium phosphate, DAP). Emergy defined as the available energy required directly and indirectly through all transformations to make a product, process, or service is the tool used for system analysis in this study. Emergy accounting provides system analysis of total resource use and whole system efficiency. The results show that struvite production uses one order of magnitude less emergy than DAP production to produce one unit of fertilizer, indicating that struvite production is a more efficient process. This research sheds light on alternative nutrient management through nutrient recovery, which may achieve economic and environmental benefits and overall higher system efficiency.

Environmental sustainability of phosphorus recycling from wastewater, manure and solid wastes

Phosphorus (P) is an important critical material essential for crops cultivation and animal husbandry. Effective phosphorous recycling is considered one of the most significant factors in alleviating its criticality. However, despite the importance of phosphorous recycling, its sustainability is not studied extensively. This paper aims to answer the question if recycling of phosphorus is an environmentally sustainable option. To address this problem, two issues are analyzed in this paper: energy consumption and greenhouse gas (GHG) emissions in phosphorous recycling. The analysis was performed by simulating mass and energy flows in the global phosphorus supply chain (from mining to recycling) in order to understand and analyze its environmental impact in 2000-2050. The results of simulation show that around 82% of recycled phosphorous originates from manure. Moreover, the calculations indicate that about 70% of total GHG emissions from phosphorous recycling is caused by wastewater processing. In addition, the results show that phosphorous obtained from recycled wastewater constitutes only 2% of the whole amount recovered in the recycling process. Therefore, the obtained results show a clear need for a detailed analysis of the sustainability of phosphorous recycling processes. Moreover, the analysis of scenarios of phosphorus consumption indicates that GHG emissions increase slowly in the mining phase and grow exponentially in the recycling stage. The main finding of this paper contradicts the general opinion about environmental friendliness of recycling. It shows that phosphorus recycling is not a sustainable solution in a longer perspective.

Impact hotspots of reduced nutrient discharge shift across the globe with population and dietary changes

Reducing nutrient discharge from wastewater is essential to mitigating aquatic eutrophication; however, energy- and chemicals-intensive nutrient removal processes, accompanied with the emissions of airborne contaminants, can create other, unexpected, environmental consequences. Implementing mitigation strategies requires a complete understanding of the effects of nutrient control practices, given spatial and temporal variations. Here we simulate the environmental impacts of reducing nutrient discharge from domestic wastewater in 173 countries during 1990-2050. We find that improvements in wastewater infrastructure achieve a large-scale decline in nutrient input to surface waters, but this is causing detrimental effects on the atmosphere and the broader environment. Population size and dietary protein intake have the most significant effects over all the impacts arising from reduction of wastewater nutrients. Wastewater-related impact hotspots are also shifting from Asia to Africa, suggesting a need for interventions in such countries, mostly with growing populations, rising dietary intake, rapid urbanisation, and inadequate sanitation.

Environmental impacts of phosphorus recovery from a "product" Life Cycle Assessment perspective: Allocating burdens of wastewater treatment in the production of sludge-based phosphate fertilizers

Since phosphorus (P) is a non-renewable element essential for life, it is extremely important to explore any potential supply of P, including that recovered from human excreta and urban wastewater. This study aimed to assess, using Life Cycle Assessment (LCA), whether recovering dissipated P by producing sludge-based phosphate fertilizer can be a suitable method to reduce P depletion. Environmental impacts of four scenarios of production of sludge-based phosphate fertilizers were compared to those of production of triple super phosphate, a mineral phosphate fertilizer used as a reference scenario. The novelty of this study was to estimate environmental impacts of sludge-based phosphate fertilizer production using a "product" LCA perspective instead of a "waste" LCA perspective. Consequently, upstream production of sludge was considered by allocating part of the environmental burdens of wastewater treatment to sludge production. Life Cycle Impact Assessment was performed using the CML-IA characterization method. Results indicated that sludge-based phosphate fertilizers appeared less environmentally friendly than mineral phosphate fertilizers, due to the contribution of the upstream burden of sludge production and P recovery. Finally, although P recovery helps preserve the mineral P resource, the overall assessment remains unfavorable for sludge-based products due to the low yields of P recovery, low P concentration of the sludge and the large amounts of energy and reactants needed to recover the P.

Promoting information technology for the sustainable development of the phosphate fertilizer industry: a case study of Guizhou Province, China

The information technology revolution has brought unprecedented opportunities to the sustainable development of the traditional phosphate fertilizer industry. In this paper, the changes in characteristic indexes during this technological progress and business innovation are investigated at the industrial level and for different stakeholders using scenario simulation analysis based on system dynamics. The results show that information technology will have a significant impact on the traditional fertilizer industry. The popularity of information technology represents a win-win situation for industries, farmers, enterprises and governments. The sustainable development of the phosphate fertilizer industry promoted by information technology means that agrochemical services are a new growth point for the industry, and farmers will be the largest beneficiaries. Enterprises will adjust their product structures to achieve the relevant phosphate reduction goals before 2020. At the government level, the indirect benefits from energy savings, water conservation and reductions in non-point source pollution control treatment also increase significantly. In the new production and sales model, the development of the phosphate fertilizer industry is completely decoupled from resource consumption. In the future, this technological progress will eventually form a sustainable network of industrial innovation patterns. Our finding suggests that the application of information technology in the phosphate fertilizer industry can stimulate the vitality of each entity in the industry and achieve a win-win situation.

Dynamics and Molecular Mechanism of Phosphate Binding to a Biomimetic Hexapeptide

Phosphorus (P) recovery from wastewater is essential for sustainable P management. A biomimetic hexapeptide (SGAGKT) has been demonstrated to bind inorganic P in P-rich environments, however the dynamics and molecular mechanisms of P-binding to the hexapeptide still remain largely unknown. We used dynamic force spectroscopy (DFS) to directly distinguish the P-unbound and P-bound SGAGKT adsorbed to a mica (001) surface by measuring the single-molecule binding free energy (Δ G_b). Using atomic force microscopy (AFM) to determine real-time step retreat velocities of triangular etch pits formed at the nanoscale on the dissolving (010) face of brushite (CaHPO₄·2H₂O) in the presence of SGAGKT, we observed that SGAGKT peptides promoted in situ dissolution through an enhanced P-binding driven by hydrogen bonds in a P-loop being capable of discriminating phosphate over arsenate, concomitantly forming a thermodynamically favored SGAGKT-HPO₄^2- complexation at pH 8.0 and relatively low ionic strength, consistent with the DFS and isothermal titration calorimetry (ITC) determinations. The findings reveal the thermodynamic and kinetic basis for binding of phosphate to SGAGKT and provide direct evidence for phosphate discrimination in phosphate/arsenate-rich environments.

Is There a Precipitation Sequence in Municipal Wastewater Induced by Electrolysis?

Electrochemical wastewater treatment can induce calcium phosphate precipitation on the cathode surface. This provides a simple yet efficient way for extracting phosphorus from municipal wastewater without dosing chemicals. However, the precipitation of amorphous calcium phosphate (ACP) is accompanied by the precipitation of calcite (CaCO₃) and brucite (Mg(OH)₂). To increase the content of ACP in the products, it is essential to understand the precipitation sequence of ACP, calcite, and brucite in electrochemical wastewater treatment. Given the fact that calcium phosphate (i.e., hydroxyapatite) has the lowest thermodynamic solubility product and highest saturation index in the wastewater, it has the potential to precipitate first. However, this is not observed in electrochemical phosphate recovery from raw wastewater, which is probably because of the very high Ca/P molar ratio (7.5) and high bicarbonate concentration in the wastewater resulting in formation of calcite. In the case of decreased Ca/P molar ratio (1.77) by spiking external phosphate, most of the removed Ca in the wastewater was used for ACP formation instead of calcite. The formation of of brucite, however, was only affected when the current density was decreased or the size of cathode was changed. Overall, the removal of Ca and Mg is much more affected by current density than the surface area of cathode, whereas for P removal, the reverse is true. Because of these dependencies, though there is no definite precipitation sequence among ACP, calcite, and brucite, it is still possible to influence the precipitation degree of these species by relatively low current density and high surface area or by targeting phosphorus-rich wastewaters.

Evolving wastewater infrastructure paradigm to enhance harmony with nature

Restoring and improving harmony between human activities and nature are essential to human well-being and survival. The role of wastewater infrastructure is evolving toward resource recovery to address this challenge. Yet, existing design approaches for wastewater systems focus merely on technological aspects of these systems. If system design could take advantage of natural ecological processes, it could ensure infrastructure development within ecological constraints and maximize other benefits. To test this hypothesis, we illustrate a data-driven, systems-level approach that couples natural ecosystems and the services they deliver to explore how sustainability principles could be embedded into the life phases of wastewater systems. We show that our design could produce outcomes vastly superior to those of conventional paradigms that focus on technologies alone, by enabling high-level recovery of both energy and materials and providing substantial benefits to offset a host of unintended environmental effects. This integrative study advances our understanding and suggests approaches for regaining a balance between satisfying human demands and maintaining ecosystems.

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.

Life cycle analysis of pistachio production in Greece

In the present paper, a life cycle assessment (LCA) study regarding pistachio (Pistacia vera L.) cultivation in Aegina island, Greece, was performed to evaluate the energy use footprint and the associated environmental impacts. In this context, a detailed life cycle inventory was created based on site-survey data and used for a holistic cradle-to-farm gate LCA analysis using the GaBi 6.5 software. The main impact categories assessed were acidification potential (AP), eutrophication potential (EP), global warming potential (GWP), ozone depletion potential (ODP), photochemical ozone creation potential (POCP) and cumulative energy demand (CED). In order to reveal the main environmental concerns pertinent to pistachio production and in turn propose measures for the reduction of environmental and energetic impacts, three scenarios were compared, namely the Baseline scenario (BS) that involves current cultivation practices, the Green Energy (GE) scenario that involves the use of biological fertilizers i.e. compost, and the Waste Utilization (WU) scenario that involves the production of biochar from pistachio and other agricultural wastes and its subsequent soil application to promote carbon sequestration and improve soil quality. Based on the results of this study, the use of compost for fertilization (GE scenario), which results in approximately 9% savings in terms of energy consumption and the five environmental impact categories studied compared to BS scenario, is considered a promising alternative cultivation strategy. Slightly higher savings (10% on average) in terms of the five calculated environmental impact categories, compared to the BS scenario, were indicated when the WU scenario was considered. Regarding energy consumption, the WU scenario results in minor increase, 3%, compared to the BS scenario. Results of uncertainty analysis performed using the Monte Carlo technique and contribution analysis showed that GE and WU scenarios offer reliable and significant eco-profile improvements for pistachio production in the study area compared to the current situation.

Sludge management modeling to enhance P-recovery as struvite in wastewater treatment plants

Interest in phosphorus (P) recovery and reuse has increased in recent years as supplies of P are declining. After use, most of the P remains in wastewater, making Wastewater Treatment Plants (WWTPs) a vital part of P recycling. In this work, a new sludge management operation was studied by modeling in order to recover P in the form of struvite and minimize operating problems due to uncontrolled P precipitation in WWTPs. During the study, intensive analytical campaigns were carried out on the water and sludge lines. The results identified the anaerobic digester as a "hot spot" of uncontrolled P precipitation (9.5 gP/kg sludge) and highlighted possible operating problems due to the accumulation of precipitates. A new sludge line management strategy was simulated therefore using DESASS^© software, consisting of the elutriation of the mixed sludge in the mixing chamber, to reduce uncontrolled P precipitation and to obtain a P-rich stream (primary thickener supernatant) to be used in a crystallization process. The key operating parameters were found to be: the elutriation flow from the mixing chamber to the primary thickener, the digestion flow and the sludge blanket height of the primary thickener, with optimized values between 70 and 80 m³/d, 90-100 m³/d and 1.4-1.5 m, respectively. Under these operating conditions, the preliminary results showed that P concentration in the primary thickener overflow significantly increased (from 38 to 100 mg PO₄-P/L), which shows that this stream is suitable for use in a subsequent crystallization reactor to recover P in the form of struvite.

Toward Nucleating the Concept of the Water Resource Recovery Facility (WRRF): Perspective from the Principal Actors

Wastewater resource recovery has been advocated for decades; necessary structural pathways were long-ago articulated, and established and emerging technologies exist. Nevertheless, broad wastewater valorization remains elusive. In considering implementation barriers, the argument is made that decision-makers focus on avoiding permit violations and negative publicity by embracing a conservative/safe approach-seemingly ignoring research on economic/environmental benefits. Conversely positing that economics is a primary barrier, we investigated, characterized, and described nontechnical socio-political barriers to realizing wastewater resource recovery. Principal actors in the Pacific NW region of the U.S. (representing a progressive populace facing stringent water quality regulations) were interviewed. Results revealed that economics were, indeed, the primary barrier to implementation/expansion of the WRRF concept. Consistent throughout interviews was a prevalent sense that the "cost of doing something (different)" was a principal consideration in resource recovery actions/policies. Moreover, "economics drives decisions," and "95% the bottom line is money. Show return on investment, it will get people's attention." Who pays was also a concern: "Government isn't going to pay. The states and Federal government won't give any grants, and we can't raise rates." Applying business case evaluations was seen as a pathway to actualizing resource recovery. Most encouragingly, the consensus was that resource recovery is a necessary future paradigm, and that real barriers are surmountable.

Influence of low pH on continuous anaerobic digestion of waste activated sludge

The influence of low pH on single stage continuous anaerobic digestion was evaluated, with the goal of increasing soluble phosphorus (P) concentration to mitigate in-reactor P precipitation. This was performed at pH 5.0, 5.5, 6.0, 6.5 and 7.0 using 1 L stirred-tank mesophilic reactors fed with sewage waste activated sludge. Low pH (5.5) caused a significant (p < 0.01) increase in soluble P concentration up to 79% of the total P, while methane yield was reduced by 50%. Total volatile fatty acids and soluble chemical oxygen demand concentrations increased from 40 to 504 mg L^-1 and 600 to 2017 mg L^-1 respectively, as the pH was reduced from 7.0 to 5.5. Higher concentrations of propionic acid (370-430 mg L^-1) were found at low pH (5.5). The reduction in methane yield was associated with a shift in microbial community and decreased destruction of particulate organics. Acidogens dominated at low pH (< 6.0), while methanogens decreased by 88% at pH 5.5 compared to neutral pH. Apart from the loss in methanogenic and hydrolytic capacity, chemical needs for acid dosing to maintain low pH conditions, and other negative impacts of chemical dosing were identified as key limitations.

Energy use and carbon footprints differ dramatically for diverse wastewater-derived carbonaceous substrates: An integrated exploration of biokinetics and life-cycle assessment

Energy neutrality and reduction of carbon emissions are significant challenges to the enhanced sustainability of wastewater treatment plants (WWTPs). Harvesting energy from wastewater carbonaceous substrates can offset energy demands and enable net power generation; yet, there is limited research about how carbonaceous substrates influence energy and carbon implications of WWTPs with integrated energy recovery at systems-level. Consequently, this research uses biokinetics modelling and life cycle assessment philology to explore this notion, by tracing and assessing the quantitative flows of energy embodied or captured, and by exploring the carbon footprint throughout an energy-intensive activated sludge process with integrated energy recovery facilities. The results indicate that energy use and carbon footprint per cubic meter of wastewater treated, varies markedly with the carbon substrate. Compared with systems driven with proteins, carbohydrates or other short-chain fatty acids, systems fed with acetic acid realized energy neutrality with maximal net gain of power from methane combustion (0.198 kWh) and incineration of residual biosolids (0.153 kWh); and also achieved a negative carbon footprint (72.6 g CO₂). The findings from this work help us to better understand and develop new technical schemes for improving the energy efficiency of WWTPs by repurposing the stream of carbon substrates across systems.