Life cycle assessment applied to wastewater treatment: state of the art

Recovery Strategies of Contaminated Marine Sediments: A Life Cycle Assessment

This study performed a Life Cycle Assessment (LCA) on recovery strategies of dredged contaminated marine sediments in a large Mediterranean port located in central Italy (Tuscany) in order to find the most environmentally sound solution. The study considered marine sediments polluted by potentially toxic elements (PTEs) and/or organic compounds, two different sediment particle sizes and the combined use of three soil remediation technologies: soil washing, electrokinetic treatment and enhanced landfarming. The analyzed scenarios depended on the sediment properties and characteristics of the treatment technologies investigated, and were compared with the corresponding reference scenarios, consisting of the landfilling of dredged contaminated sediments. The LCA results show that scenarios associated with sediment recovery generated potential environmental impacts lower than the corresponding reference scenarios. Almost all the impact categories considered in the CML-IA baseline method showed an environmental convenience in the recovery of contaminated sediments, especially for abiotic depletion and global warming. Future studies should focus on optimizing the combined use of multiple technologies and reducing the resource consumptions related to their implementation in order to achieve both environmental and economic benefits.

Assessment of energy use and environmental impacts of wastewater treatment plants in the entire life cycle: A system meta-analysis

Wastewater treatment plants (WWTPs) play a critical role in the sustainable development of water resources due to its outstanding ability of removing pollutants from complex influent wastewater and generating clean and safe effluent. This paper innovatively adopted the meta-analysis method in view of published LCA studies to assess the energy use and environmental impacts of WWTPs during their life cycle. The search and screening process determined a useful data source with 54 LCA literatures covering 109 relevant case studies. The meta-analysis results revealed that, compared with other regions, the WWTPs in China have the higher intensity in terms of energy use, global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), photochemical oxidation (PHO), freshwater ecotoxicity potential (FETP) and terrestrial ecotoxicity potential (TETP) categories, implying that the energy conservation and emission reduction strategies are necessary to wastewater treatment industry in China. Moreover, compared with A/A/O and CASS processes, the A/O process consumes less energy and results in lower GWP and AP intensity, but affects adversely the natural water-body protection due to undesirable treatment efficiency. Furthermore, the treatment capacities of medium and large scales (i.e. 5-20 × 10⁴ m³/d) are most reasonable sizes for WWTPs since their intensity of energy use, GWP, EP and AP are under a relatively low level. Finally, a strict effluent discharge standard is highly recommended from the perspective of protecting aquatic environment, although it leads to a higher energy consumption. The findings of this study could provide valuable references for promoting healthy and sustainable wastewater treatment industry.

Environmental tradeoffs in municipal wastewater treatment plant upgrade: a life cycle perspective

Municipal wastewater treatment plants (WWTPs) play an indispensable role in improving environmental water quality in urban areas. Existing WWTPs, however, are an important source of greenhouse gas (GHG) emissions and may not be able to treat increasingly complicated wastewater or meet stringent environmental standards. These WWTPs can be updated to address these challenges, and different technologies are available but with potentially different environmental implications. Life cycle assessment (LCA) is a widely used approach to identify alternatives with lower environmental footprint. In this study, LCA was applied to an actual urban WWTP, considering four scenarios involving upgrading and energy-resource recovery. The environmental performance with respect to life cycle GHG emissions and eutrophication impact was analyzed. The environmental benefits of reduced water pollution and energy and material displacement associated with energy-resource recovery process were also considered. The results showed tradeoffs among the four scenarios. Although upgrading the studied WWTP would meet discharge standard for total phosphorus and reduce total eutrophication impact by about 19%, it would increase GHG emissions by at least 16%. Besides, the energy-resource recovery mode for existing WWTP (S2) performs the best in terms of GHG emissions. For different biogas utilization methods, combined heat and power (CHP) system is superior to the existing method of delivering biogas to gas grid, in terms of energy recovery or reduction of GHG emissions and eutrophication impact. Our research results may provide a reference for plant managers to select the most environmentally friendly upgrade scheme and energy-resource recovery technique for future upgrade projects.

Assessing METland® Design and Performance Through LCA: Techno-Environmental Study With Multifunctional Unit Perspective

Conventional wastewater treatment technologies are costly and energy demanding; such issues are especially remarkable when small communities have to clean up their pollutants. In response to these requirements, a new variety of nature-based solution, so-called METland®, has been recently develop by using concepts from Microbial Electrochemical Technologies (MET) to outperform classical constructed wetland regarding wastewater treatment. Thus, the current study evaluates two operation modes (aerobic and aerobic-anoxic) of a full-scale METland®, including a Life Cycle Assessment (LCA) conducted under a Net Environmental Balance perspective. Moreover, a combined technical and environmental analysis using a Net Eutrophication Balance (NEuB) focus concluded that the downflow (aerobic) mode achieved the highest removal rates for both organic pollutant and nitrogen, and it was revealed as the most environmentally friendly design. Actually, aerobic configuration outperformed anaero/aero-mixed mode in a fold-range from 9 to 30%. LCA was indeed recalculated under diverse Functional Units (FU) to determine the influence of each FU in the impacts. Furthermore, in comparison with constructed wetland, METland® showed a remarkable increase in wastewater treatment capacity per surface area (0.6 m2/pe) without using external energy. Specifically, these results suggest that aerobic-anoxic configuration could be more environmentally friendly under specific situations where high N removal is required. The removal rates achieved demonstrated a robust adaptation to influent variations, revealing a removal average of 92% of Biology Oxygen Demand (BOD), 90% of Total Suspended Solids (TSS), 40% of total nitrogen (TN), and 30% of total phosphorus (TP). Moreover, regarding the global warming category, the overall impact was 75% lower compared to other conventional treatments like activated sludge. In conclusion, the LCA revealed that METland® appears as ideal solution for rural areas, considering the low energy requirements and high efficiency to remove organic pollutants, nitrogen, and phosphates from urban wastewater.

Life cycle assessment of sewage sludge treatment and disposal based on nutrient and energy recovery: A review

With the acceleration of urbanization, the production of urban sludge is increasing rapidly. To minimize resource input and waste output, it is crucial to execute analyses of environmental impact and assessments of sustainability on different technical strategies involving sludge disposal based on Life Cycle Assessment (LCA), which is a great potential mean of environmental management adopted internationally in the 21st century. This review aims to compare the environmental sustainability of existing sludge management schemes with a purpose of nutrient recovery and energy saving, respectively, and also to include the substitution benefits of alternative sludge products. Simultaneously, LCA research regarding the emerging sludge management technologies and sludge recycling (cement, adsorbent, bricks) is analyzed. Additionally, the key aspects of the LCA process are worth noting in the context of the current limitations reviewed here. It is worth emphasizing that no technical remediation method can reduce all environmental damage simultaneously, and these schemes are typically more applicable to the assumed local conditions. Future LCA research should pay more attention to the toxic effects of different sludge treatment methods, evaluate the technical ways of adding pretreatment technology to the 'front end' of the sludge treatment process, and further explore how to markedly reduce environmental damage in order to maximize energy and nutrient recovery from the LCA perspective.

Improving Life Cycle Economic and Environmental Sustainability of Animal Manure Management in Marginalized Farming Communities Through Resource Recovery

A growing world population with increasing levels of food consumption will lead to more dairy and swine production and increasing amount of manure that requires treatment. Discharge of excessive nutrients and carbon in untreated animal manure can lead to greenhouse gas emissions and eutrophication concerns, and treatment efforts can be expensive for small scale farmers in marginalized communities. The overall goal of this study was to determine the environmental and economic sustainability of four animal manure management scenarios in Costa Rica: (1) no treatment, (2) biodigesters, (3) biodigesters and struvite precipitation, and (4) biodigesters, struvite precipitation, and lagoons. Life cycle assessment was used to assess the carbon footprint and eutrophication potential, whereas life cycle cost analysis was used to evaluate the equivalent uniform annual worth over the construction and operation and maintenance life stages. Recovery of biogas as a cooking fuel and recovery of nutrients from the struvite reactor reduced the carbon footprint, leading to carbon offsets of up to 2,500 kg CO₂ eq/year. Offsets were primarily due to avoiding methane emissions during energy recovery. Eutrophication potential decreased as resource recovery processes were integrated, primarily due to improved removal of phosphorus in effluent waters. Resource recovery efforts led to equivalent uniform annual benefits of $825 to $1,056/year, which could provide a helpful revenue source for lower-income farmers. This research can provide clarity on how small-scale farmers in marginalized settings can utilize resource recovery technologies to better manage animal manure, while improving economic and environmental sustainability outcomes.

Combining Process Modelling and LCA to Assess the Environmental Impacts of Wastewater Treatment Innovations

Alternative wastewater treatment (WWT) technologies with lower environmental impacts seem to be the way forward in the pursuit of sustainable wastewater treatment plants (WWTPs). Process modelling of material and energy flows together with life-cycle assessment (LCA) can help to better understand these impacts and show the right direction for their development. Here, we apply this combined approach to three scenarios: conventional WWT; conventional WWT + chemically enhanced primary treatment (CEPT); conventional WWT + CEPT + side stream partial nitritation/anammox (PN/A). For each scenario, equations were developed to calculate chemical oxygen demand and nitrogen flow (solid and dissolved form) through the WWTP and to estimate the energy demands of its unit operations. LCA showed that the main environmental impact categories for all scenarios were global warming potential (GWP), eutrophication potential (EP) and marine aquatic eco-toxicity potential (MAETP). Compared with conventional WWT, CEPT and CEPT combined with PN/A resulted in a higher sum of normalized and weighed environmental indicators, by 19.5% and 16.4%, respectively (20.0% and 18.3% including biogenic carbon). Interestingly, the environmentally positive features of the alternative scenarios were often traded-off against other increased negative impacts. This suggests that further development is needed to consider these technologies a sustainable alternative.

A bibliometric analysis of industrial wastewater treatments from 1998 to 2019

For the foreseeable future, industrial water demand will grow much faster than agriculture. The demand together with the urgency of wastewater treatment, will pose big challenges for most developing countries. We applied the bibliometric analysis combined with social network analysis and S-curve technique to quantitatively analyze 9413 publications related to industrial wastewater treatment in the Scientific Citation Index (SCI) and Social Sciences Citation Index (SSCI) databases from 1998 to 2019. The results showed that: (1) Publications on industrial wastewater treatment have increased from 120 in 1998 to 895 in 2019 with a steady annual increment rate, and researchers have focused more on the application and optimization of existing technologies. (2) China had the highest number of publications (n = 1651, 19.66% of global output) and was a core country in the international cooperation network, whereas the United States and European countries produced higher quality papers. (3) By analyzing the co-occurrence and clusters of keywords and comparing three wastewater treatment categories (physical, chemical, biological), adsorption (n = 1277), oxidation (n = 1085) and activated sludge process (n = 1288) were the top three techniques. Researchers have shifted their focus to treatment technologies for specific wastewater type, such as textile wastewater, pulp and paper wastewater, and pharmaceutical wastewater. The S-curve from articles indicates that physical and chemical treatment technologies are attached with great potential in the near future, especially adsorption and advanced oxidation, while the biological treatment technologies are approaching to the saturation stage. Different pattern is observed for the S-curve derived from patents, which stressed the limited achievement until now and further exploration in the field application for the three treatment categories. Our analysis provides information of technology development landscape and future opportunities, which is useful for decision makers and researchers who are interested in this area.

Oxygen vacancies and Lewis sites activating O3/H2O2 at wide pH range via surface electron transfer over CeOx@SiO2 for nitrobenzene mineralization

The low efficiency of peroxone (O₃/H₂O₂) at acidic and neutral pH restrained its application in water purification. To overcome this shortcoming, CeO_X@SiO₂ with large surface area, abundant surface oxygen vacancies (V_o), Lewis sites (L sites) and high Ce(III)/Ce(IV) ratio were synthesized to change the traditional electron transfer pathway between O₃ and H₂O₂. V_o was facile in absorbing H₂O₂ to form V_o-H₂O₂ and L sites were capable of absorbing O₃ to form L-O₃. The electron at V_o could be donated to V_o-H₂O₂ and generate V_o-HO₂^-, which then effectively triggered the decomposition of L-O₃ at CeO_X@SiO₂'s interface and O₃ in bulk solution. The electron transfer at the solid-liquid interface with the help of Ce³⁺/Ce⁴⁺ redox cycle and V_o was pH independent and different from the traditional electron transfer of peroxone reaction. Nitrobenzene (NB) mineralization was promoted to 92.5% in CeO_X@SiO₂-peroxone, but only 63.8% TOC was removed in tradition peroxone process. Moreover, CeO_X@SiO₂-peroxone had a wide pH application range. NB's degradation in CeO_X@SiO₂-peroxone process followed the co-oxidation mechanism of superoxide free (•O₂^-) and hydroxyl radical (•OH). The finding of this study could broaden the popularization of peroxone in water treatment and provided a strategy for catalyst design.

Assessment of sludge management strategies in wastewater treatment systems using a plant-wide approach

The objective of this paper is to use plant-wide modeling to assess the net impacts of varying sludge management strategies. Special emphasis is placed on effluent quality, operational cost and potential resource recovery (energy, nutrients). The study is particularly focused on a centralized bio-solids beneficiation facility (BBF), which enables larger, more capital intensive sludge management strategies. Potential barriers include the ability to process reject streams from multiple donor plants in the host plant. Cape Flats (CF) wastewater treatment works (WWTW) (Cape Town, South Africa) was used as a relevant test case since it is currently assessing to process sludge cake from three nearby facilities (Athlone, Mitchells Plain and Wildevoelvlei). A plant-wide model based on the Benchmark Simulation Model no 2 (BSM2) extended with phosphorus transformations was adapted to the CF design / operational conditions. Flow diagram and model parameters were adjusted to reproduce the influent, effluent and process characteristics. Historical data between January 2014 and December 2019 was used to compare full-scale measurements and predictions. Next, different process intensification / mitigation technologies were evaluated using multiple criteria. Simulation values for COD, TSS, VSS/TSS ratio, TN, TP, NH₄⁺/NH₃, H_xPO4^3-x, NO_x alkalinity and pH fall within the interquartile ranges of measured data. The effects of the 2017 severe drought on influent variations and biological phosphorus removal are successfully reproduced for the entire period with dynamic simulations. Indeed, 80% of all dynamically simulated values are included within the plant measurement uncertainty ranges. Sludge management analysis reveals that flow diagrams with thermal hydrolysis pre-treatment (THP) result in a better energy balance in spite of having higher heat demands. The flow diagram with THP is able to i) increase biodegradability/solubility, ii) handle higher sludge loads, iii) change methanogenic microbial population and iv) generate lower solids volumes to dispose by improving sludge dewaterability. The study also reveals the importance of including struvite precipitation and harvesting (SPH) technology, and the effect that pH in the AD and the use of chemicals (NaOH, MgO) may have on phosphorus recovery. Model-based results indicate that the current aerobic volume in the water line (if properly aerated) would be able to handle the returns from the sludge line and the contribution of a granular partial nitritation/Anammox (PN/ANX) reactor on the overall nitrogen removal would be marginal. However autotrophic N denitrification generates a much lower sludge production and therefore increases AD treatment capacity. The study shows for the very first time in Africa how the use of a (calibrated) plant-wide model could assist water utilities to decide between competing plant layouts when upgrading a WWTW.

Life cycle assessment of urban wastewater treatment plants: a critical analysis and guideline proposal

In its 30 years of existence, there are still many improvement possibilities in studies performing the life cycle assessment (LCA) of wastewater treatment plants (WWTPs). Hence, this paper aims to start a guideline development for LCA of urban WWTPs based on the information available in the scientific literature on the topic. The authors used the ProKnow-C systematic review methodology for paper selection and 111 studies were analyzed. The most significant points that can be improved are caused by missing essential information (e.g. functional unity and input data). Other important methodological aspects are covered: allocation process, functional unit choice, sensitivity analysis, and important fluxes to be considered. Many opportunities within the LCA of WWTPs were identified, such as optimization of WWTP operational aspects and resource recovery. Furthermore, LCA should be combined with other methodologies such as big data, data envelopment analysis, life cycle cost assessment, and social life cycle assessment. To achieve this potential, it is clear that the scientific and technical community needs to converge on a new protocol to ensure that LCA application becomes more reliable and transparent.

Process Design and Sustainable Development—A European Perspective

This paper describes the state of the art and future opportunities for process design and sustainable development. In the Introduction, the main global megatrends and the European Union’s response to two of them, the European Green Deal, are presented. The organization of professionals in the field, their conferences, and their publications support the two topics. A brief analysis of the published documents in the two most popular databases shows that the environmental dimension predominates, followed by the economic one, while the social pillar of sustainable development is undervalued. The main design tools for sustainability are described. As an important practical case, the European chemical and process industries are analyzed, and their achievements in sustainable development are highlighted; in particular, their strategies are presented in more detail. The conclusions cover the most urgent future development areas of (i) process industries and carbon capture with utilization or storage; (ii) process analysis, simulation, synthesis, and optimization tools, and (iii) zero waste, circular economy, and resource efficiency. While these developments are essential, more profound changes will be needed in the coming decades, such as shifting away from growth with changes in habits, lifestyles, and business models. Lifelong education for sustainable development will play a very important role in the growth of democracy and happiness instead of consumerism and neoliberalism.

Life Cycle Assessment of Municipal Wastewater Treatment Processes Regarding Energy Production from the Sludge Line

The efficient and timely removal of organic matter and nutrients from water used in normal municipal functions is considered to be the main task of wastewater treatment plants (WWTPs). Therefore, these facilities are considered to be essential units that are required to avoid pollution of the water environment and decrease the possibility of triggering eutrophication. Even though these benefits are undeniable, they remain at odds with the high energy demand of wastewater treatment and sludge processes. As a consequence, WWTPs have various environmental impacts, which can be estimated and categorized using Life Cycle Assessment (LCA) analysis. In this study, a municipal WWTP based in Poznań, Poland, was examined using the method defined in ISO 14040. ReCiPe Endpoint and Midpoint (v1.11), in a hierarchical approach, were used to evaluate the environmental impacts regarding 18 different categories. All calculations were conducted using a detailed database from 2019, which describes each chosen facility. It was found that the energy component, related to the wastewater treatment process demand and electricity production, is the main determinant of the sum of the environmental impact indicators in light of the modelled energy mix. Therefore, it determines the entire process as an environmentally friendly activity.

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.

Making wastewater obsolete: Selective separations to enable circular water treatment

By 2050, the societal needs and innovation drivers of the 21st century will be in full swing: mitigating climate change, minimizing anthropogenic effects on natural ecosystems, navigating scarcity of natural resources, and ensuring equitable access to quality of life will have matured from future needs to exigent realities. Water is one such natural resource, and will need to be treated and transported to maximize resource efficiency. In particular, wastewater will be mined for the valuable product precursors it contains, which will require highly selective separation processes capable of capturing specific target compounds from complex solutions. As a case study, we focus on the nitrogen cycle because it plays a central role in both natural and engineered systems. Nitrogen occurs as several species, including ammonia, a fertilizer and precursor to many nitrogen products, and nitrate, a fertilizer and component of explosives. We describe two applications of selective separations: selective materials and electrochemical processes. Ultimately, this perspective outlines the next thirty years of modular, selective, resource-efficient separations that will play a major role in enabling element-specific circular economies and redefining wastewater as a resource.

A new approach of ecologically based life cycle assessment for biological wastewater treatments focused on energy recovery goals

The energy potential of high-organic loaded agro-industrial effluents receiving biological treatment is often neglected, particularly in emergent regions, because of different technical and regulatory drawbacks. In addition, small alternative bioenergy sources are forced to compete disadvantageously with conventional energy supply, hindering their more extended exploitation. Thus, smart strategies to prove the environmental/economic potential of biogas and sludge produced in biological wastewater treatment systems (Bio-WWTs) are required to promote them as truly sustainable energy sources. In this view, the present study depicts a refined methodological framework for a more appropriate appraisal of Bio-WWTs promoting bioenergy recovery. Life cycle assessment (LCA) and emergy analysis (EmA) methods were merged around the statement of some identified and stated Principle-Criteria of Sustainability (PCS) for this kind of "water-energy nexus." As a result, a novel set of four single sustainability development indicators (SDIs) and one aggregated SDI were obtained to address sustainable conditions for valorization of bio-energy from agro-industrial Bio-WWTs. These indicators were made up of an environmental term coming from an LCA based on a system expansion approach as well as a second or "eco-economic" term obtained by means of EmA. This work introduces and shapes the "additionality" notion as an expression of overall sustainability and uses novel sustainability charts to interpret the obtained SDIs and their shifting or changes for different Bio-WWTs' life cycle scenarios. The "proof of concept" of this methodology is discussed along the obtained results for two case studies in Colombia.

Quantifying urban wastewater treatment sector's greenhouse gas emissions using a hybrid life cycle analysis method - An application on Shenzhen city in China

Substantial amounts of greenhouse gas (GHG) emissions generated at urban wastewater treatment plants (WWTP) are gaining increasing appreciation. Improving upon the commonly used Process-Based Life-Cycle Analysis (PLCA) and Environmentally-Extended Life-Cycle Analysis (EIO-LCA) models, we construct a Hybrid Life Cycle Analysis (HLCA) model and quantify both direct and indirect GHG emissions at the operational stage of WWTPs in Shenzhen, one of the fastest urbanizing cities in the world. Data are collected from 26 wastewater treatment plants in Shenzhen, out of all 32, covering 5 commonly used wastewater treatment technologies in China, i.e. Sequencing Batch Reactor, Oxidation Ditch, Biological Filter, AAO-MBR and AAO. The results show that WWTPs using AAO-MBR technology have the highest GHG emission intensity, averaging 0.79 tons per m³, primarily due to its large electricity intensity required. WWTPs using other technologies emit 0.27 to 0.39 tons of GHGs per m³ of wastewater treated. GHG emissions associated with electricity use occupy the largest share, ranging from 65 to 75%. Therefore, transforming the energy structure of the electric power sector to low-carbon sources can reduce WWTPs operational GHG emissions. In total, GHG emissions from Shenzhen's urban wastewater sector have increased from below 0.5 million tons in 2012 to over 0.6 million tons in 2017. Inter-model comparison shows that EIO-LCA substantially underestimates the urban wastewater sector's GHG emissions using the water sector's average parameters while PLCA also results in minor underestimations due the omission of indirect emissions in the production stage of chemicals and other material inputs.

Wastewater Treatment Plant Assessment by Quantifying the Carbon and Water Footprint

In the context of efficient and sustainable management of the elements of the urban water cycle as an aim of the Water Framework Directive (WFD), the evaluation of indicators such as the water footprint (WF) and the carbon footprint (CF) in a wastewater treatment plant (WWTP) provides a quantification of the environmental impact, both negative and positive, which implies its exploitation. In this study, in addition to WF and CF quantification, a joint evaluation of both indicators was conducted. Consumption is indicated by the blue water footprint (WFBlue) and emissions by CF. Both are related to the operational grey water footprint (∆WFG,mef) in two ratios, WFR and CFR. In this way, the water consumed and gases emitted are measured according to the reduction range of the pollutant load of the discharge. The results for four WWTPs show operational scenarios for better management in accordance with the WFD.

Contribution of the construction phase to environmental impacts of the wastewater treatment plant

This study aims to investigate the environmental issues regarding the construction phase of the wastewater treatment plant (WWTP) and explore the roles of different materials through their environmental impacts. Detailed inventories of the two WWTPs were conducted by involving materials and transportation for civil works undertaken. EPD 2018 and ReCiPe life cycle impact assessment methods were employed to measure all the impact categories. Five treatment processes - (1) pumping, (2) primary treatment, (3) secondary treatment, (4) sludge line, and (5) building landscape - were considered for the assessment. It was found that concrete and reinforcing steel played similarly vital roles in most of the EPD 2018 impacts. The significant score of reinforcing steel was found on human cancer toxicity, which contributed more than 90% of the impacts. The contribution of diesel on ozone formation was 5% higher than that of reinforcing steel. Glassfiber was responsible for 70% of the burdens on ozone depletion, showing much higher than the total share of concrete and reinforcing steel. Primary treatment units only contributed 9.5% of the construction impacts in the Girona WWTP but up to 43.8% in Mill Creek WWTP mainly because of the proportion of consumed materials. In short, the comprehensive data inventories were necessary when evaluating the total environmental impacts of the WWTP.

Life Cycle Assessment of the Mesophilic, Thermophilic, and Temperature-Phased Anaerobic Digestion of Sewage Sludge

In this study the environmental impact of the anaerobic digestion (AD) of sewage sludge within an activated sludge wastewater treatment plant (WWTP) was investigated. Three alternative AD systems (mesophilic, thermophilic, and temperature-phased anaerobic digestion (TPAD)) were compared to determine which system may have the best environmental performance. Two life cycle assessments (LCA) were performed considering: (i) the whole WWTP (for a functional unit (FU) of 1 m3 of treated wastewater), and (ii) the sludge line (SL) alone (for FU of 1 m3 of produced methane). The data for the LCA were obtained from previous laboratory experimental work in combination with full-scale WWTP and literature. According to the results, the WWTP with TPAD outperforms those with mesophilic and thermophilic AD in most analyzed impact categories (i.e., Human toxicity, Ionizing radiation, Metal and Fossil depletion, Agricultural land occupation, Terrestrial acidification, Freshwater eutrophication, and Ozone depletion), except for Climate change where the WWTP with mesophilic AD performed better than with TPAD by 7%. In the case of the SL alone, the production of heat and electricity (here accounted for as avoided environmental impacts) led to credits in most of the analyzed impact categories except for Human toxicity where credits did not balance out the impacts caused by the wastewater treatment system. The best AD alternative was thermophilic concerning all environmental impact categories, besides Climate change and Human toxicity. Differences between both LCA results may be attributed to the FU.

The application of life cycle assessment (LCA) to wastewater treatment: A best practice guide and critical review

Life cycle assessment (LCA) has been widely applied in the wastewater industry, but inconsistencies in assumptions and methods have made it difficult for researchers and practitioners to synthesize results from across studies. This paper presents a critical review of published LCAs related to municipal wastewater management with a focus on developing systematic guidance for researchers and practitioners to conduct LCA studies to inform planning, design, and optimization of wastewater management and infrastructure (wastewater treatment plants, WWTPs; collection and reuse systems; related treatment technologies and policies), and to support the development of new technologies to advance treatment objectives and the sustainability of wastewater management. The paper guides the reader step by step through LCA methodology to make informed decisions on i) the definition of the goal and scope, ii) the selection of the functional unit and system boundaries, iii) the selection of variables to include and their sources to obtain inventories, iv) the selection of impact assessment methods, and v) the selection of an effective approach for data interpretation and communication to decision-makers.

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.

Potential for co-disposal and treatment of food waste with sewage: A plant-wide steady-state model evaluation

The water, food and energy nexus is a vital subject to achieve sustainable development goals worldwide. Wastewater (WW) and food waste (FW) from municipal sources are the primary contributors of organic waste from cities. Along with the loss of these valuable natural resources, their treatment systems also consume a considerable amount of abiotic energy and resource input and make a perceptible contribution to global warming. Hence, the global paradigm has evolved from simple pollution mitigation to resource recovery systems. In this study, the prospects of FW co-disposal into the sewer system and treatment with municipal sewage were quantitatively investigated for Hong Kong's largest biological WW treatment plant (WWTP) by integrated plant-wide steady-state modelling (PWSSM) and lifecycle assessment (LCA) approaches. The investigation assessed the impacts on the design and operational capacity of the WWTP, effluent quality, sludge output, and its net energy and carbon footprint. The results revealed that even at a higher than normal FW to sewage ratio, the WWTP's organic load capacity and performance in terms of organics and nitrogen removal was not significantly degraded, in fact the denitrification efficiency was improved by the FW organics with low N/C ratio. The net energy balance was improved by 80-400%, the net carbon footprint was lowered by 37-63% (without biogenic emissions), while the sludge production was increased by ∼33%. The results are very sensitive and improved with greater influent FW concentration and solids capture in the primary settling unit of the WWTP. The differences in the results have to be seen in relation to uncontrolled methane emission and a faster filling rate if the FW were disposed to landfill. The study provides valuable insights and policy guidelines for the decision makers locally and a generic methodological template.

Extracting the characteristics of life cycle assessments via data mining

Life cycle assessments (LCAs) follow the ISO 14040 standard and consist of the following steps: 1) goal and scope definition, 2) life cycle inventory analysis, 3) life cycle impact assessment, and 4) interpretation. Prior literature reviews of wastewater treatment and water reuse LCAs have evaluated the methods implemented within these assessments. In lieu of manually tabulating the characteristic features of LCAs, Data Mining LCAs provides a method to facilitate the extraction of key characteristics. The process consists of the following:•

Each journal article is converted to a text file and read in Python.

•

Search terms are defined for each characteristic of the LCA to be extracted.

•

By employing Python's regular expressions operations and the natural language toolkit (NLTK), the functional unit, life cycle impact characterization method, and the location of each case study are identified.

A composite indicator approach to assess the sustainability and resilience of wastewater management alternatives

Evaluating the sustainability of wastewater management alternatives is a challenging task. This paper proposes an innovative methodology to assess and compare the sustainability of four wastewater management alternatives: a) centralised water resource recovery facility (WRRF) based on activated sludge (AS); b) centralised WRRF with membrane bioreactors (MBR); c) decentralised WRRFs with upflow anaerobic sludge blanket reactors and trickling filters; d) centralised-decentralised hybrid system. In doing so, a composite indicator embracing total annual equivalent costs, carbon emission intensity, eutrophication and resilience (based on robustness and rapidity metrics) was developed using the analytic hierarchy process (AHP) method. The results show that decentralised and hybrid systems contribute less to carbon emission and eutrophication because of energy and fertilizer harvest and with a trade-off of higher costs of 7-17% than the ones of AS and MBR. In addition, decentralised and hybrid systems are more resilient, contributing to lower environmental impacts facing natural disasters. Based on the weights obtained by AHP, the decentralised alternative appears to be the most sustainable option due to its best performance in terms of carbon emission intensity and resilience. By contrast, the MBR alternative appeared the least sustainable evaluated wastewater management alternative. However, this alternative is sustainable option when the eutrophication criterion is heavily prioritized. The proposed approach contributes to the selection of the most sustainable wastewater management alternative from a holistic perspective.

Environmental and cost benefits of co-digesting food waste at wastewater treatment facilities

The wastewater industry is undergoing a paradigm shift from focusing solely on treatment to incorporating concepts aimed at mitigating environmental impacts such as energy and nutrient recovery and water reuse. This study uses life cycle assessment and life cycle cost analysis to investigate the effect of expanding anaerobic digestion (AD) capacity and adding combined heat and power on environmental and cost indicators at a mid-sized wastewater treatment facility (WWTF) in Massachusetts, USA. Since 2014, Massachusetts has banned the disposal of organic waste from commercial organizations producing more than one ton of material per week. The WWTF's additional digester capacity allows the co-digestion of municipal solids with a food-based engineered bioslurry due to this ban. Study data were compiled for several AD feedstock quantity and performance scenarios, and compared to a baseline scenario representative of historic plant operations prior to co-digestion. Reductions in environmental impact are demonstrated for six of eight environmental impacts, including global climate change potential and cumulative energy demand. Eutrophication potential increases by 10 percent and 24 percent across assessed scenarios. Water use remains relatively constant across scenarios. Facility energy production increases dramatically with co-digestion, satisfying 100 percent of the WWTF's thermal energy requirement and producing surplus electricity assuming full AD capacity utilization.

A critical review on life cycle assessment and plant-wide models towards emission control strategies for greenhouse gas from wastewater treatment plants

For decades, there has been a strong interest in mitigating greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs). Numerous models were developed to measure the emissions and propose the quantification. Existing studies looked at the relationship between GHG emissions and operational cost (OCI), which is one of the most important indicators for decision-makers. Other parameters that can influence the control strategies include the effluent quality (EQI) and total environmental impacts. Plant-wide models are reliable methods to examine the OCI, EQI and GHG emissions while Life cycle assessment (LCA) works to assess the potential environmental impacts. A combined LCA and plant-wide model proved to be a valuable tool evaluating and comparing strategies for the best performance of WWTPs. For this study involving a WWTP, the benchmark model is used while LCA is the decision tool to find the most suitable treatment strategy. LCA adds extra criteria that complement the existing criteria provided by such models. Complementing the cost/performance criteria is proposed for plant-wide models, including environmental evaluation, based on LCA, which provides an overall better assessment of WWTPs. It can capture both the dynamic effects and potential environmental impacts. This study provides an overview of the integration between plant-wide models and LCA.

Resource recovery and waste-to-energy from wastewater sludge via thermochemical conversion technologies in support of circular economy: a comprehensive review

With the rapid rise in global population over the past decades, there has been a corresponding surge in demand for resources such as food and energy. As a consequence, the rate of waste generation and resultant pollution levels have risen drastically. Currently, most organic solid wastes are either land applied or sent to landfills, with the remaining fraction incinerated or anaerobically digested. However, with the current emphasis on the reduction of emissions, nutrient recovery, clean energy production and circular economy, it is important to revisit some of the conventional methods of treating these wastes and tap into their largely unrealized potential in terms of environmental and economic benefits. Wastewater sludge, with its high organic content and fairly constant supply, provides a great opportunity to implement some of these strategies using thermochemical conversion technologies, which are considered as one of the alternatives for upcycling such waste streams. This paper summarizes the results of prominent studies for valorizing wastewater sludge through thermochemical conversion technologies while drawing inferences and identifying relationships between different technical and operating parameters involved. This is followed by sections emphasizing the environmental and economic implications of these technologies, and their corresponding products in context of the broader fields of waste-to-energy, nutrient recycling and the progress towards a circular economy.

Assessing the life-cycle sustainability of algae and bacteria-based wastewater treatment systems: High-rate algae pond and sequencing batch reactor

High Rate Algae Ponds (HRAPs) are a promising technology for the treatment of municipal wastewater in locations with sufficient space and solar radiation. Algae-based processes do not require aeration, and thus have the potential to be less energy-intensive than activated sludge processes. We used a combination of LCA and LCCA analysis to evaluate the sustainability of HRAP systems, using data from the construction and operation of two demonstration-scale systems in Almería and Cádiz, Spain. As a reference for comparison, we used data from an activated sludge-based Sequencing Batch Reactor (SBR) treatment system in operation in Leppersdorf, Germany, which has comparable removal rates for a similar inflow. We focused solely on the actual wastewater treatment aspect of these technologies, excluding sludge treatment from this analysis. Based on our analysis, the current HRAP technology is more energy-efficient than activated sludge-based SBRs and requires only 22% of its electricity consumption. In addition, HRAP is more advantageous both economically (0.18 €/m³ versus 0.26 €/m³) and environmentally, with both lower global warming and eutrophication potentials (146.27 vs. 458.27 × 10^-3 kg CO₂ equiv./m³; 126.14 vs. 158.01 × 10^-6 kg PO₄ equiv./m³). However, the Net Environmental Benefit of SBR was slightly more favorable than of HRAP because of the higher removal rate for nutrients of SBR.

The SPPD-WRF Framework: A Novel and Holistic Methodology for Strategical Planning and Process Design of Water Resource Factories

This paper guides decision making in more sustainable urban water management practices that feed into a circular economy by presenting a novel framework for conceptually designing and strategically planning wastewater treatment processes from a resource recovery perspective. Municipal wastewater cannot any longer be perceived as waste stream because a great variety of technologies are available to recover water, energy, fertilizer, and other valuable products from it. Despite the vast technological recovery possibilities, only a few processes have yet been implemented that deserve the name water resource factory instead of wastewater treatment plant. This transition relies on process designs that are not only technically feasible but also overcome various non-technical bottlenecks. A multidimensional and multidisciplinary approach is needed to design water resource factories (WRFs) in the future that are technically feasible, cost effective, show low environmental impacts, and successfully market recovered resources. To achieve that, the wastewater treatment plant (WWTP) design space needs to be opened up for a variety of expertise that complements the traditional wastewater engineering domain. Implementable WRF processes can only be designed if the current design perspective, which is dominated by the fulfilment of legal effluent qualities and process costs, is extended to include resource recovery as an assessable design objective from an early stage on. Therefore, the framework combines insights and methodologies from different fields and disciplines beyond WWTP design like, e.g., circular economy, industrial process engineering, project management, value chain development, and environmental impact assessment. It supports the transfer of the end-of-waste concept into the wastewater sector as it structures possible resource recovery activities according to clear criteria. This makes recovered resources more likely to fulfil the conditions of the end-of-waste concept and allows the change in their definition from wastes to full-fledged products.

Life Cycle Assessment of Community-Based Sewer Mining: Integrated Heat Recovery and Fit-For-Purpose Water Reuse

Municipal sewage contains significant embedded resources in the form of chemical and thermal energy. Recent developments in sustainable technology have pushed for the integration of resource recovery from household wastewater to achieve net zero energy consumption and carbon-neutral communities. Sewage heat recovery and fit-for-purpose water reuse are options to optimize the resource recovery potential of municipal wastewater. This study presents a comparative life cycle assessment (LCA) focused on global warming potential (GWP), eutrophication potential (EUP), and human health carcinogenic potential (HHCP) of an integrated sewage heat recovery and water reuse system for a hypothetical community of 30,000 people. Conventional space and water heating components generally demonstrated the highest GWP contribution between the different system components evaluated. Sewage-heat-recovery-based district heating offered better environmental performance overall. Lower impact contributions were demonstrated by scenarios with a membrane bioreactor (MBR) and chlorination prior to water reuse applications compared to scenarios that use more traditional water and wastewater treatment technologies and discharge. The LCA findings show that integrating MBR wastewater treatment and water reuse into a district heating schema could provide additional environmental savings at a community scale.

Assessing environmental impacts of large centralized wastewater treatment plants with combined or separate sewer systems in dry/wet seasons by using LCA

Rainfall can affect influent flow rate and compositions of wastewater, and thus further affect wastewater treatment performance and the effluent quality. This study aims to study the influence of rainfall on the environmental impacts of centralized wastewater treatment plants. The correlations between rainfall, and influent flow rate and compositions of wastewater in wet and dry seasons with two sewer systems, i.e. combined and separate sewer systems, were primarily established. Environmental impacts were assessed with life cycle assessment (LCA) to understand the temporal environmental burdens in wet and dry seasons. Functional units as per m3 treated wastewater (FU1) and as per kg PO43-eq. removed (FU2), respectively, were used to evaluate impacts of wastewater treatment to the environment. Strong correlation between rainfall and the influent flow rate was found in the wastewater treatment plants with either a combined sewer system (with Pearson correlation coefficient r at 0.66) or a separate sewer system (with r at 0.84), where r represents the strength of the association between two variables. The rainfall effect is more obvious on the eutrophication potential and global warming potential than on other environmental indicators while sewer system, i.e. combined or separate, seems not important in the two cases studied. Both wastewater treatment plants (WWTPs) show a lower environmental burden in the wet season than in the dry season partially due to the dilution of wastewater by using FU1. The WWTP receiving high strength wastewater, however, demonstrates higher environmental impacts in the wet season by using FU2 than FU1, due to the less efficient treatment caused by heavy rainfall. Meanwhile, it is found that environmental impacts from the WWTP receiving low strength wastewater have no difference when using either FU1 or FU2. The results indicate that the environmental burdens particularly eutrophication and global warming caused by WWTPs are dependent on the correlations of rainfall intensity with wastewater quantity and quality instead of combined or separate sewer system. This could be used to guide a stricter control of eutrophication in a more sensitive season in more vulnerable receiving waters.

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.

Designing a robust index for WWTP energy efficiency: The ENERWATER water treatment energy index

The development and use of composite indexes has exploded in the last 15 years as a tool to summarise the large amount of information available nowadays. To ensure that composite indicators reflect faithfully the purpose of evaluation and are widely accepted and used, the users must understand the relationship between individual sub-indicators and the result (transparency) and the evaluation should not depend on weights, lack of information, etc. (robustness). It is proposed here for the first time a composite index to measure energy efficiency in a wastewater treatment plant, from the definition of the individual sub-indicators to the assignation of an energy label, easy to communicate to a broad public. Using as a demonstration real data from 44 wastewater treatment plants, the index robustness is tested and improved by uncertainty and sensitivity analysis results, finally achieving a robust algorithm which can be used by the large majority of wastewater treatment plants.

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.

Model of Carbon Footprint Assessment for the Life Cycle of the System of Wastewater Collection, Transport and Treatment

This article presents a model of the environmental assessment of the system of wastewater collection, transport and treatment. The model was developed based on an original environmental assessment method of a system consisting of four elements: septic tanks, household wastewater treatment plants, a sewerage system and a central wastewater treatment plant. To conduct the environmental assessment, the Life Cycle Assessment technique was applied. The Intergovernmental Panel on Climate Change (IPCC) method was also applied, which enabled the determination of the carbon footprint of the analysed wastewater management system. This article presents the outline of an original method applied to create a model and an inventory of the data necessary for environmental assessment and the application of the model for the environmental assessment of a system of wastewater collection, transport and treatment in a city with over 50.000 inhabitants. Three feasible variants (from a functional, technical, organizational and financial point of view) of the system’s development were analysed. The variants were subjected to comparative analysis using the solution. The obtained results, together with the assessment method can be used as a practical tool to assess whether the European Commission’s guidelines are met, as well as the challenges facing wastewater management in the circular economy are overcome.

Evaluation of environmental impacts for future influent scenarios using a model-based approach

Changes in dilution of wastewater to a treatment plant due to infiltration or surface runoff can have a great impact on treatment process performance. This paper presents a model-based approach in which realistic influent scenarios are generated and used as inputs to a dynamic plant-wide process model of the wastewater treatment plant. The simulated operation is subsequently evaluated using life-cycle assessment (LCA) to quantify the environmental impacts of the future influent scenarios. The results show that increased infiltration led to higher environmental impact per kg nitrogen removed. The increase in surface runoff had a minor impact.

Hybrid life cycle assessment of agro-industrial wastewater valorisation

Wastewater from food processing facilities can have high nutrient valorisation potential. Valorising sugar-rich agro-industrial wastewater may have significant impacts on sustainability of wastewater treatment plant (WWTP). The objective of this study is to evaluate the environmental, economic and social impacts of a novel wastewater valorisation technology. This technology is designed to produce single cell protein (SCP) from wastewater of a fruit juice processing facility. To evaluate the comprehensive sustainability impacts on WWTP and overall background economy, a hybrid life cycle assessment model was developed by combining the multi-regional input-output database (Exiobase) with process-based life cycle inventories of conventional and AgroCycle WWTP. The results indicated the upstream impacts of wastewater could have significant influence on sustainability of WWTP with nutrient valorisation. Therefore the 'zero burden assumption' should not be adopted for upstream wastewater. For the sustainability performance, valorising nutrients from WWTP with AgroCycle technology can improve the environmental performance of WWTP. However, the positive social-economic impacts were directly associated with WWTP system, not the whole background economy. The production of SCP could reduce the Gross Value Added (GVA) and employment in the 'oil seeds sector'. In order to improve the social-economic impacts and promote a circular bioeconomy model in the fruit juice sector, further development is required to improve valorisation productivity and create a better value chain for valorised products.

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.

Comparative assessment of sewage sludge disposal alternatives in Mashhad: a life cycle perspective

Municipal wastewater treatment facilities produce a lot of sludge which is concentrated with different pollutants. The sustainable design of the sludge disposal alternatives is of crucial importance for touristic cities like Mashhad in Iran. Increasing sludge generation and its accumulation in the city and more stringent legislations highlight the challenge of sludge disposal, recently. This study compares different alternatives to reach maximum possible environmental benefits as well as the most cost-effective technologies. In this study, life cycle analysis (LCA) assesses different scenarios for disposal of sewage sludge which is aerobically treated and dewatered for two real case studies. Alteymore and KhinArab are wastewater treatment units in the city. The scenarios include incineration, composting, and landfilling alternatives. The incineration and landfill scenarios are the least interesting solutions according to different life cycle impact categories. The heavy metals' emission to the soil worsens their impacts. Also, lifecycle cost analysis reveals that composting scenario is more cost-saving than others. However, main disadvantage of the composting scenario is its contribution in freshwater eutrophication. To move towards sustainability, the composting scenario is here determined as the best scenario for sludge disposal in Mashhad.

Life cycle assessment of decentralized greywater treatment systems with reuse at different scales in cold regions

Decentralized source-separated wastewater treatment systems offer an attractive alternative to conventional centralized wastewater treatment systems in various regions, yet few system analyses specifically address decentralized greywater treatment over different scales. Here we present a comparative life cycle assessment (LCA) and focus on global warming potential (GWP), eutrophication potential (EUP) and human health - carcinogenic potential (HHCP) of decentralized greywater management systems at different scales for a hypothetical community in a cold (winter) region. To provide a comparison between nature-based and engineered greywater treatment solutions, constructed wetlands (CW) and membrane bioreactors (MBR), respectively, were investigated at three different scales; community (3500 person equivalent [PE]), neighborhood (350 PE) and household (a single household [up to 5 PE]). Conventional centralized wastewater treatment was also included as a business-as-usual (BAU) scenario. In the MBR scenarios, greywater reuse was also considered for multiple non-potable applications due to its high-quality effluent and subsurface garden irrigation was considered for reuse in the CW scenarios. For scenarios with the same treatment technology, larger scales reduced GWP, EUP and HHCP up to 57 kg CO₂-eq.PE^-1.y^-1, 0.2 kg N-eq.PE^-1.y^-1 and 5.3E-6 CTUh.PE^-1.y^-1, respectively, despite the need for more extensive wastewater networks. The CW scenarios at community and neighborhood scales outperformed the MBR and BAU scenarios for greywater treatment, while the community-scale MBR scenario may be environmentally preferable when large amount of greywater can be reused. The scale of decentralized systems, quantity of water reused and mix of electricity technologies all played important roles in determining GWP, EUP and HHCP values.

Environmental impacts of an advanced oxidation process as tertiary treatment in a wastewater treatment plant

Due to global water scarcity, the use of reclaimed wastewater for crop irrigation is required; however, if the wastewater treatment is inadequate, it can be a source of environmental pollution. In order to improve wastewater reclamation, advanced oxidation processes (AOPs) have been tested. At full scale, ozonation is one such process that effectively removes micropollutants, despite its high-energy consumption. At pilot scale, other technologies such as the solar photo-Fenton process are being developed. This process is under consideration as a sustainable technology because it uses sunlight as a source of radiation. However, there is little information available on its environmental performance. In this work, we perform a comparative analysis between the ozonation and the photo-Fenton process as tertiary wastewater treatment processes used to reclaim wastewater for agricultural irrigation. We apply the Life Cycle Assessment (LCA) methodology for quantifying environmental impacts with ReCiPe and USEtox as life cycle impact assessment (LCIA) methods. The results show that both tertiary treatment options reduce water stress locally. Ozonation has a better overall environmental performance compared to the photo-Fenton process because the environmental impact of the required ozone is smaller than of the reactants involved in the solar photo-Fenton. Moreover, the first can be operated both day and night, and therefore needs no additional storage for collecting the nightly secondary effluent, and thus has lower infrastructure related impacts. Additionally, when the solar photo-Fenton process operates at an acidic pH, there are environmental drawbacks related to the pH adjustment, which consumes a large amount of acid thus liberating CO₂. Finally, the environmental impacts associated with the discharge of micropollutants to soil through the use of reclaimed water are very small compared to the other impacts generated by the treatment. However, due to the current LCIA method limitations of micropollutant impact assessment, these are subject to major uncertainty.

Evaluation of potential environmental benefits from seawater toilet flushing

Water scarcity has become a global issue that has forced many communities to seek alternative water resources. The majority of water on the earth's surface comes from the sea. Seawater has the potential to mitigate water stress after proper treatment. In Hong Kong, seawater has been used directly for toilet flushing for more than 50 years and the seawater toilet flushing (SWTF) system serves 80% of the residents. However, its environmental feasibility remains unknown. This study is a pioneer evaluating the environmental performances of the SWTF system by comparing SWTF with other alternative water resources including desalinated seawater, desalinated wastewater effluent, centralized wastewater reclamation and on-site greywater reclamation systems, while the conventional long-distance imported water scenario is set as the baseline for comparison. This evaluation is first conducted in the Southern District and North New Territory in Hong Kong, demonstrating SWTF is significantly more environmentally-friendly than other alternative water resources, which is the only alternative water resource application approach with environmental impacts comparable with the conventional long-distance imported water scenario. On the contrary, other alternative water resources application approaches would result in additional environmental impacts. Seaside distances and effective population density are two major geographical impact factors effecting the environmental impacts of different water systems in these two districts. The benefits obtained from SWTF in fourteen cities in South China are further investigated. It is confirmed that SWTF can significantly relieve water stress with the lowest environmental impacts comparing with other alternative options in these cities if alternative water resources must be applied for domestic usage. However, the assessment from different aspects should be further conducted to compare these alternative water resources.

Bioaugmentation of atrazine removal in constructed wetland: Performance, microbial dynamics, and environmental impacts

Constructed wetland (CW) is an efficient technology to treat urban storm water runoff. However, the CW has limited capacity to degrade atrazine, a frequently detected herbicide in runoff. Bioaugmentation provides a feasible enhanced alternative; nevertheless, incorporating bioaugmentation into CW is likely to perpetuate the environmental consequences and incur complex trade-offs between environmental improvement and burdens. Since few efforts were made to improve above situation, the present work proposed the application of bioaugmentation, and tested the feasibility from both efficiency and sustainability dimensions. Results showed that bioaugmentation markedly enhanced atrazine degradation from 5 mg/L to below the threshold value within 43 day by increasing functional atrazine-degrading bacteria. Pseudomonas and Arthrobacter significantly proliferated among atrazine-degrading bacterial genera, indicating high adaptability and atrazine-degrading contribution. With life cycle assessment, enhancing 1 kg of atrazine degradation could decrease environmental burdens with 27.60 kg 1,4-DCB-Eq of freshwater-ecotoxicity reduction, and achieve shorter payback period compared to non-bioaugmented CW.

Decision support systems (DSS) for wastewater treatment plants - A review of the state of the art

The use of decision support systems (DSS) allows integrating all the issues related with sustainable development in view of providing a useful support to solve multi-scenario problems. In this work an extensive review on the DSSs applied to wastewater treatment plants (WWTPs) is presented. The main aim of the work is to provide an updated compendium on DSSs in view of supporting researchers and engineers on the selection of the most suitable method to address their management/operation/design problems. Results showed that DSSs were mostly used as a comprehensive tool that is capable of integrating several data and a multi-criteria perspective in order to provide more reliable results. Only one energy-focused DSS was found in literature, while DSSs based on quality and operational issues are very often applied to site-specific conditions. Finally, it would be important to encourage the development of more user-friendly DSSs to increase general interest and usability.

Sanitation for Low-Income Regions: A Cross-Disciplinary Review

Sanitation research focuses primarily on containing human waste and preventing disease; thus, it has traditionally been dominated by the fields of environmental engineering and public health. Over the past 20 years, however, the field has grown broader in scope and deeper in complexity, spanning diverse disciplinary perspectives. In this article, we review the current literature in the range of disciplines engaged with sanitation research in low- and middle-income countries (LMICs). We find that perspectives on what sanitation is, and what sanitation policy should prioritize, vary widely. We show how these diverse perspectives augment the conventional sanitation service chain, a framework describing the flow of waste from capture to disposal. We review how these perspectives can inform progress toward equitable sanitation for all [i.e., Sustainable Development Goal (SDG) 6]. Our key message is that both material and nonmaterial flows-and both technological and social functions-make up a sanitation "system." The components of the sanitation service chain are embedded within the flows of finance, decision making, and labor that make material flows of waste possible. The functions of capture, storage, transport, treatment, reuse, and disposal are interlinked with those of ensuring equity and affordability. We find that a multilayered understanding of sanitation, with contributions from multiple disciplines, is necessary to facilitate inclusive and robust research toward the goal of sanitation for all.

Environmental impacts of resource recovery from wastewater treatment plants

Conventional wastewater treatment plants (WWTPs) clean wastewater and minimize water pollution; but, while doing so, they also contribute to air pollution and need energy/material input with associated emissions. However, energy recovery (e.g. anaerobic digestion) and resource recovery (e.g. water reuse) allow us to offset the adverse environmental impacts of wastewater treatment. Life cycle assessments (LCA) have been used more and more to evaluate the environmental impacts of WWTPs and to suggest improvement options. There is a need to search for resource recovery applications that genuinely realize a net-zero impact on the total environment of WWTPs. In this work, a scheme with highly efficient energy and resource recovery (especially for thermal energy) is proposed and evaluated. The environmental impact of a conventional WWTP in comparison with the scheme proposed here, with energy/resource recovery included, was calculated, and discussed with reference to LCA methodology. In the process of using LCA, it was necessary to choose a regional situation to focus on. In this case, a Chinese situation was focused as a reference, but the qualitative information gained is of worldwide relevance. The results clearly revealed that conventional WWTP does not benefit the total environment as a whole while the new scheme benefited the total environment via resource/energy recovery-based processes. Among others, thermal energy recovery played a significant role towards a net-zero LCA analysis (contributing around 40%) which suggests that more attention and research should be focused on it.

Evaluation of the Environmental and Economic Impacts on the Life Cycle of Different Solutions for Toilet Flush Systems

The use of plumbing fixtures to promote water saving in the built environment is a common practice in water conservation programs. However, the environmental implications of fixtures replacement should be taken into consideration. This paper analyzes three different scenarios for the provision of water in toilets installed in a university campus. In scenarios 1 and 2, single flush and dual flush devices were installed in the toilets, respectively. In scenario 3, in addition to the installation of dual flush devices, a greywater reuse system from the lavatories was analyzed. The objective is to evaluate, through the Life Cycle Assessment, the environmental aspects related to these scenarios. The economic analysis of the three scenarios was also carried out. Measurements were taken on all plumbing fixtures installed in a building of a university campus in Southern Brazil. The research was conducted using smart meters in two periods: with single flush and dual flush devices installed in toilets. Considering the environmental impacts analyzed, scenario 3 presented lower water and energy consumption in the life cycle. Scenario 2, however, presented lower global warming potential. The net present value results were R$ 23,575.71, R$ 19,091.41, and R$ 22,500.55 for scenarios 1, 2 and 3, respectively.

Performance evaluation of a decentralized wastewater treatment system in India

A Decentralized Wastewater Treatment System (DEWATS) provides an economically feasible and efficient wastewater treatment solution especially in developing countries. It has an enormous potential for developing a sustainable environmental sanitation system. In this study, the treatment efficiency of eight DEWATS plants was evaluated in the state of Maharashtra, India, for their performance in terms of selected physico-chemical parameters of the wastewater. Although the efficiency of some of the plants was lower than that reported in literature, the effluent quality of all the plants was within the permissible discharge limits of the Central Pollution Control Board for all the parameters. Comprehensive assessment of Plant I was carried in terms of its technical and socio-economic aspects. Moreover, LCA tool has been utilized to evaluate the environmental impacts of the operation stage of DEWATS. The midpoint, CML 2001 (April 2015) methodology was adopted, in which 11 impact categories were considered. From the life cycle impact assessment and interpretation, the main impacts are identified as releases of COD, P-PO₄^3-, and N-NH₄⁺ to water bodies and disposal of sludge. Due to negligible energy consumption, the operation stage was found to be less damaging to the environment. It was concluded that DEWATS can be a good alternative for treating wastewater with negligible energy and chemical consumption.