Evaluation of new alternatives in wastewater treatment plants based on dynamic modelling and life cycle assessment (DM-LCA)

Life cycle environmental impacts of urban water systems in China

Urban water systems in China are facing multiple challenges, including rapid urbanisation, climate change and infrastructure ageing. It is crucial to evaluate their environmental performance from a holistic perspective in planning and management processes. To the best of our knowledge, there is a lack of nationwide life cycle assessment (LCA) studies on China's urban water systems that cover all system stages. Therefore, this study aims to present a comprehensive and nationwide LCA analysis that pinpoints the environmental hotspots and their major sources across China. This study was conducted based on water utility databases at the province level, covering water abstraction and treatment, waterwork sludge treatment, water distribution, sewage collection, stormwater drainage, wastewater treatment and sewage sludge treatment. Nine environmental impact categories were calculated and analysed. The results reveal the inequity of environmental impacts across provinces, with overall impacts geographically higher in the east and south, lower in the west and north. However, at the functional unit level, the impacts in the northern and northeastern provinces are higher than other regions. Most environmental categories are dominated by multiple water system stages. The analyses of underlying drivers found that purchased electricity is the primary source of several environmental impacts. This study provides a holistic understanding of the environmental performance of China's urban water systems, offers some insights for comprehensive decision-making support on sustainable water system management, and can also serve as a benchmark for future scenario analysis to explore options for reducing environmental impact.

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.

Impact of urbanism on source separation systems: A life cycle assessment

This study aims to assess the effect of different urban configuration regarding the choice of wastewater management of the district with source separation systems. Understanding this link can guide researchers, and also urban actors, in order to choose the best source separation solution to implement in a specific urban configuration. For this purpose, an integrated modelling approach was used to model the district with different types of urban planning, the water resources recovery facility (WRRF) and create a life cycle inventory to carry out a life cycle assessment (LCA). Six different urban configurations were tested with three different source separation scenarios and compared with an advanced WRRF with high level of nutrients and organic matter recovery. This study concludes that urine source separation is beneficial compared to advanced WWRF for all the urban configurations. Sewer construction was identified as the main contributor to environmental impact for the low-density configuration (pavilions), limiting the benefits of source separation in this urban settlement. Blackwater separation with a decentralised treatment is only beneficial for high densely populated area. Treatment of blackwater and greywater for reuse, has greater impact than reference scenario, in all urban configurations, due to high energy consumption for greywater treatment. Future research should therefore explore technical solutions for limiting the energy consumption.

A comprehensive framework for eco-environmental impact evaluation of wastewater treatment plants: Integrating carbon footprint, energy footprint, toxicity, and economic assessments

The need for clear and straightforward guidelines for carbon footprint (CFP) and energy footprint (EFP) evaluations is critical due to the non-transparent and misleading results that have been reported. This study aims to address this gap by integrating CFP, EFP, toxicity, and economic assessments to evaluate the eco-environmental impacts of wastewater treatment plants (WWTPs). The results indicate that the total CFP was below 0.6 kg CO2/kg COD removed, which is attributed to CO2 offset and biogas recovery. However, site-specific EFP varied considerably from 482.7 to 2294 kgCO2/kWh due to design differences of WWTPs and their aeration and mixing energy demand (46.96-66.1%). The use of crude oil and natural gas for electricity generation significantly increased EFP, CFP, and carcinogenic human toxicity. In contrast, a combined heat and power (CHP) installation enabled energy recovery ranging from 12.09% to 65.65%. Construction costs dominated the highest share of total costs (85.43%), with indirect construction costs (42.9%) and operation labor costs (61.4%) being the primary elements in the total net costs. It is worth noting that site-specific CO2 emission factors were used in the calculations to decrease model uncertainty. However, to improve modeling reliability, we recommend modifying the regional CO2 emission factor and focusing on emerging technologies to recover energy and biogas.

Continuous Systems Bioremediation of Wastewaters Loaded with Heavy Metals Using Microorganisms

Heavy metal pollution is a serious concern of the modern era due to its widespread negative effects on human health and to the environment. Conventional technologies applied for the uptake of this category of persistent pollutants are complex, often expensive, and inefficient at low metal concentrations. In the last few years, non-conventional alternatives have been studied in search of better solutions in terms of costs and sustainability. Microbial adsorbents are one of the biomass-based sorbents that have extensively demonstrated excellent heavy metals removal capacity even at low concentrations. However, most of the carried-out research regarding their application in wastewater treatment has been performed in discontinuous systems. The use of microorganisms for the uptake of metal ions in continuous systems could be an important step for the upscale of the remediation processes since it facilitates a faster remediation of higher quantities of wastewaters loaded with heavy metals, in comparison with batch systems removal. Thus, the current research aims to analyze the available studies focusing on the removal of metal ions from wastewaters using microorganisms, in continuous systems, with a focus on obtained performances, optimized experimental conditions, and the sustainability of the bioremoval process. The present work found that microbial-based remediation processes have demonstrated very good performances in continuous systems. Further sustainability analyses are required in order to apply the bioremediation technology in an optimized environmentally friendly way in large-scale facilities.

Modelling the benefits of urine source separation scenarios on wastewater treatment plants within an urban water basin

Stringent discharge regulations are encouraging researchers to create innovative and sustainable wastewater treatment solutions. Urine source separation (USS) is among the potent approaches that may reduce nutrient peak loads in the influent wastewater and improve nutrient recovery. A phenomenological model was used to simulate dynamic influent properties and predict the advantages gained from implementing USS in an urban water basin. Several scenarios were investigated assuming different levels of deployment: at the entire city, or specifically in office buildings for men's urine only, or for both men and women employees. The results confirmed that all scenarios of urine source separation offered benefits at the treatment plant in terms of reducing nitrogen influent load. The economic benefits in terms of reducing energy consumption for nitrification and decreasing methanol addition for denitrification were quantified, and results confirmed environmental advantages gained from different USS scenarios. Despite larger advantages gained from a global USS rate in an entire city, implementation of a specific USS in office buildings would remain more feasible from a logistical perspective. A significant benefit in terms of reducing greenhouse gas emissions is demonstrated and this was especially due to the high level of N₂O emissions avoided in nitrifying biological aerated filter.

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.

Adaptive pressure-driven multi-criteria spatial decision-making for a targeted placement of green and grey runoff control infrastructures

Traditional runoff control measures ignore the spatial imbalance of regional pressures, thereby failing to achieve a site-specific placement for green and grey infrastructure simultaneously. A multi-criterion decision-making framework for runoff control infrastructure spatial planning was therefore developed in this study. The pressure-state-response framework was applied to creatively match the pressure induced adjustment demands with the infrastructure effectiveness. The pressures were quantified from the perspective of environment, economy, and ecology on a grid scale. States were considered as the relative priority of regional pressure adjustment demand in multiple perspectives. Responses were presented as state-targeted green and grey infrastructure placement. Multi-perspective effectiveness of different green and grey infrastructure was simultaneously evaluated at an effective scale of controlling 1 m³/s runoff for comparison. Methods such as data mining, hydrological model simulation, and remote sensing inversion were combined to quantify the regional pressures. The capital investment and ecological impact of infrastructures were quantified from a life cycle perspective. A case study was carried out in Wuhan, China. The study area was clustered by gridded pressure into three regions. In region Ⅰ, ecological and environmental pressure were of higher weight. In region Ⅱ, the environmental pressure was dominant. In region Ⅲ, the ecological pressure took precedence over the environmental and economic constraints. The area ratios of the region Ⅰ, Ⅱ, and Ⅲ were 43%, 36%, and 21% respectively. The result indicated a synergy and spatial heterogeneity of multi-perspective pressures, and further demonstrating that expert experience tends to fail to weigh the multi-function of green and grey infrastructures for coping with the pressures. Results also stated that green infrastructures were more acceptable in areas that aspire to achieve simultaneous runoff control and ecological improvement. The decision-making framework developed in this study can maximize the overall performance by providing targeted infrastructure placement solutions.

Fertiliser recovery from source-separated urine via membrane bioreactor and heat localized solar evaporation

Urine with its abundant macronutrients (N-P-K) is an ideal resource for the production of fertiliser. However, the odor and pathogens in the raw urine must be removed to meet the public acceptance of urine collection systems and to enable its safe reuse as a fertiliser. In this work, real urine was collected and treated through a pilot-scale gravity-driven membrane bioreactor (GDMBR) to remove the malodorous organics and to nitrify almost 50% of the ammonia into nitrate. The stablised urine was subsequently distilled via low-cost heat localized solar evaporation (HLSE) to produce a non-odorous solid fertiliser. The developed HLSE with a small footprint can attract bulk solution into a vertical insulated space and quickly heat it up to 68 °C within 1 h. The HLSE process had vapour flux at 1.3 kg m^-2 h^-1 as well as high solar to vapour conversion efficiency at 87%. Based on the EDX mapping and XRD analysis, the generated crystals are mainly NaNO₃, NH₄Cl, NaCl, NH₄H₂PO₄ and K₂HPO₄, which are ideal nutrients for vegetation. In this study, the produced urine-derived fertilisers have a better performance on the growth of the leafy basil than the all-purpose commercial fertilisers. Generally, the GDMBR-HLSE is a promising cost-effective and green technology for nutrients recovery from urine.

Integrating dairy manure for enhanced resource recovery at a WRRF: Environmental life cycle and pilot-scale analyses

The Twin Falls, Idaho wastewater treatment plant (WWTP), currently operates solely to achieve regulatory permit compliance. Research was conducted to evaluate conversion of the WWTP to a water resource recovery facility (WRRF) and to assess the WRRF environmental sustainability; process configurations were evaluated to produce five resources-reclaimed water, biosolids, struvite, biogas, and bioplastics (polyhydroxyalkanoates, PHA). PHA production occurred using fermented dairy manure. State-of-the-art biokinetic modeling, performed using Dynamita's SUMO process model, was coupled with environmental life cycle assessment to quantify environmental sustainability. Results indicate that electricity production via combined heat and power (CHP) was most important in achieving environmental sustainability; energy offset ranged from 43% to 60%, thereby reducing demand for external fossil fuel-based energy. While struvite production helps maintain a resilient enhanced biological phosphorus removal (EBPR) process, MgO₂ production exhibits negative environmental impacts; integration with CHP negates the adverse consequences. Integrating dairy manure to produce bioplastics diversifies the resource recovery portfolio while maintaining WRRF environmental sustainability; pilot-scale evaluations demonstrated that WRRF effluent quality was not affected by the addition of effluent from PHA production. Collectively, results show that a WRRF integrating dairy manure can yield a diverse portfolio of products while operating in an environmentally sustainable manner. PRACTITIONER POINTS: Wastewater carbon recovery via anaerobic digestion with combined heat/power production significantly reduces water resource recovery facility (WRRF) environmental emissions. Wastewater phosphorus recovery is of value; however, struvite production exhibits negative environmental impacts due to MgO₂ production emissions. Bioplastics production on imported organic-rich agri-food waste can diversify the WRRF portfolio. Dairy manure can be successfully integrated into a WRRF for bioplastics production without compromising WRRF performance. Diversifying the WRRF products portfolio is a strategy to maximize resource recovery from wastewater while concurrently achieving environmental sustainability.

Greenhouse gases emission control in WWTS via potential operational strategies: A critical review

Greenhouse gases (GHGs; particularly, CO₂, CH₄, and N₂O) emission from wastewater treatment systems (WWTS) is one of the inevitable concerns for sustainable development. This indicator is directly linked with the carbon footprint and potential impacts of WWTS on climate change. In this view, various modeling, design, and operational tools have been introduced to mitigate the WWTS associated GHGs, at regional and global scales. In this study, authors have critically reviewed the selected potential operational control strategies for GHGs emission, particularly emitted from the operational stages of biological WWTS. The investigated operational control strategies and/or treatment configurations included intermittent aeration, varying dissolved oxygen, enhanced sludge retention time, coupled aerobic-anoxic nitrous decomposition operation, and microalgae integrated treatment process. Based on this analysis and considering the trade-off between treatment performance of WWTS and GHGs control, an integrated framework is also proposed for existing and upcoming WWTS. The findings of this study and proposed framework will play an instrumental role in mitigating the GHGs at various operational stages of WWTS. Future research works in this direction can lead to a better understanding of investigated operational GHGs emission control strategies in WWTS.

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.

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.

Addressing temporal considerations in life cycle assessment

In life cycle assessment (LCA), temporal considerations are usually lost during the life cycle inventory calculation, resulting in an aggregated "snapshot" of potential impacts. Disregarding such temporal considerations has previously been underlined as an important source of uncertainty, but a growing number of approaches have been developed to tackle this issue. Nevertheless, their adoption by LCA practitioners is still uncommon, which raises concerns about the representativeness of current LCA results. Furthermore, a lack of consistency can be observed in the used terms for discussions on temporal considerations. The purpose of this review is thus to search for common ground and to identify the current implementation challenges while also proposing development pathways. This paper introduces a glossary of the most frequently used terms related to temporal considerations in LCA to build a common understanding of key concepts and to facilitate discussions. A review is also performed on current solutions for temporal considerations in different LCA phases (goal and scope definition, life cycle inventory analysis and life cycle impact assessment), analysing each temporal consideration for its relevant conceptual developments in LCA and its level of operationalisation. We then present a potential stepwise approach and development pathways to address the current challenges of implementation for dynamic LCA (DLCA). Three key focal areas for integrating temporal considerations within the LCA framework are discussed: i) define the temporal scope over which temporal distributions of emissions are occurring, ii) use calendar-specific information to model systems and associated impacts, and iii) select the appropriate level of temporal resolution to describe the variations of flows and characterisation factors. Addressing more temporal considerations within a DLCA framework is expected to reduce uncertainties and increase the representativeness of results, but possible trade-offs between additional data collection efforts and the increased value of results from DLCAs should be kept in mind.

Toward Energy Savings in Campus Buildings under a Life Cycle Thinking Approach

Recent studies have identified that buildings all over the world are great contributors to energy consumption and greenhouse gas emissions. The relationship between the building industry and environmental pollution is continuously discussed. The building industry includes many phases: extraction of raw materials, manufacturing, construction, use, and demolition. Each phase consumes a large amount of energy, and subsequent emissions are released. The life cycle energy assessment (LCEA) is a simplified version of the life cycle assessment (LCA) that focuses only on the evaluation of energy inputs for different phases of the life cycle. Operational energy is the energy required for day-to-day operation processes of buildings, such as heating, cooling and ventilation systems, lighting, as well as appliances. This use phase accounts for the largest portion of energy consumption of the life cycle of conventional buildings. In addition, energy performance certification of buildings is an obligation under current European legislation, which promotes efficient energy use, so it is necessary to ensure that the energy performance of the building is upgraded to meet minimum requirements. For this purpose, this work proposes the consideration of the energy impacts and material resources used in the operation phase of a building to calculate the contribution of these energy impacts as new variables for the energy performance certification. The application of this new approach to the evaluation of university buildings has been selected as a case study. From a methodological point of view, the approach relied on the energy consumption records obtained from energy and materials audit exercises with the aid of LCA databases. Taking into practice the proposed methodology, the primary energy impact and the related emissions were assessed to simplify the decision-making process for the energy certification of buildings. From the results obtained, it was concluded that the consumption of water and other consumable items (paper) are important from energy and environmental perspectives.

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.

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.

Plant diversity improves the effluent quality and stability of floating constructed wetlands under increased ammonium/nitrate ratio in influent

The major targets of constructed wetlands (CWs) during wastewater treatment include achieving high-quality effluent and maintaining stable effluent quality. Plant species diversity can increase nitrogen (N) removal efficiency and improve effluent quality by decreasing the effluent N concentrations, including nitrate (NO₃^--N), ammonium (NH₄⁺-N) and total inorganic nitrogen (TIN) concentrations in CWs. However, the effect of plant diversity on the stability of effluent quality in response to perturbation in the form of an increased NH₄⁺/NO₃^- ratio in influent has not been studied. This study conducted a microcosm experiment and assembled four plant species richness levels (1, 2, 3 and 4) and 15 species compositions by using 90 simulated CW microcosms to investigate the effect of plant diversity on the effluent N concentrations and their stability with an increase in the influent NH₄⁺/NO₃^- ratio from 0:100 to 33:67 in the later stage of the experiment. The results showed that (1) plant species richness maintained a positive effect on effluent quality under an increased influent NH₄⁺/NO₃^- ratio; (2) high species richness enhanced the stability of effluent water quality; (3) the presence of Phragmites australis in the community decreased the effluent TIN concentration and improved its stability under perturbation; and (4) the presence of Typha latifolia had a positive effect on N removal efficiency under perturbation. The establishment of communities with high plant species richness and proper species (such as P. australis) could simultaneously improve the effluent quality and stability in CWs for treating wastewater with increased NH₄⁺/NO₃^- ratio.

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.

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.

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.

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.

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.

A Standardized Stoichiometric Life-Cycle Inventory for Enhanced Specificity in Environmental Assessment of Sewage Treatment

In recent years, many life-cycle assessments (LCAs) have been applied to the field of sewage treatment (ST). However, most LCAs lack systematic data collection (DC) and processing methods for inventories of conventional ST (CST), much less for recently developed technologies. In addition, the use of site-generic databases results in LCAs that lack the representativeness and understanding of the regional environmental impacts and trade-offs between different impact categories, especially nutrient enrichment and toxicity-related categories. These shortcomings make comparative evaluation and implementation more challenging. In order to assist in the decision-making process, a novel stoichiometric life-cycle inventory (S-LCI) for ST was developed. In the S-LCI, biochemical pathways derived from elemental analyses combined with process-engineering calculations enable steady-state comparison of the water, air, and soil emissions of any sewage and sludge sample treated through the ST configurations analyzed herein. The DC required for the estimation of the foreground data for a CST is summarized in a 41-item checklist. Moreover, the S-LCI was validated for CST by comparing the S-LCI with actual ST plant operations performed in Hong Kong. A novel energy-derived ST inventory is developed and compared here with the CST. The resulting inventories are ready to be integrated into the SimaPro software for life cycle impact assessment as illustrated by the case study. Using the S-LCI not only helps to standardize the DC and processing, but it also enhances the level of specificity by using sample characterization and site-specific data. The EcoInvent database, which contains a single sample characterization per Swiss and global average ST plant class could be expanded by using the S-LCI.

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.

Influences of water quality and climate on the water-energy nexus: A spatial comparison of two water systems

As drinking water supply systems plan for sustainable management practices, impacts from future water quality and climate changes are a major concern. This study aims to understand the intraannual changes of energy consumption for water treatment, investigate the relative importance of water quality and climate indicators on energy consumption for water treatment, and predict the effects of climate change on the embodied energy of treated, potable water at two municipal drinking water systems located in the northeast and southeast US. To achieve this goal, a life cycle assessment was first performed to quantify the monthly energy consumption in the two drinking water systems. Regression and relative importance analyses were then performed between climate indicators, raw water quality indicators, and chemical and energy usages in the treatment processes to determine their correlations. These relationships were then used to project changes in embodied energy associated with the plants' processes, and the results were compared between the two regions. The projections of the southeastern US water plant were for an increase in energy demand resulted from an increase of treatment chemical usages. The northeastern US plant was projected to decrease its energy demand due to a reduced demand for heating the plant's infrastructure. The findings indicate that geographic location and treatment process may determine the way climate change affects drinking water systems.

Sensitivity analysis of temporal parameters in a dynamic LCA framework

Including the temporal dimension in the Life Cycle Assessment (LCA) method is a very recent research subject. A complete framework including dynamic Life Cycle Inventory (LCI) and dynamic Life Cycle Impact Assessment (LCIA) was proposed with the possibility to calculate temporal deployment of climate change and ecotoxicity/toxicity indicators. However, the influence of different temporal parameters involved in the new dynamic method was not still evaluated. In the new framework, LCI and LCIA results are obtained as discrete values in function of time (vectors and matrices). The objective of this study is to evaluate the influence of the temporal profile of the dynamic LCI and calculation time span (or time horizon in conventional LCA) on the final LCA results. Additionally, the influence of the time step used for the impact dynamic model resolution was analysed. The range of variation of the different time steps was from 0.5day to 1year. The graphical representation of the dynamic LCA results shown important features such as the period in time and the intensity of the worst or relevant impact values. The use of a fixed time horizon as in conventional LCA does not allow the proper consideration of essential information especially for time periods encompassing the life time of the studied system. Regarding the different time step sizes used for the dynamic LCI definition, they did not have important influence on the dynamic climate change results. At the contrary, the dynamic ecotoxicity and human toxicity impacts were strongly affected by this parameter. Similarly, the time step for impact dynamic model resolution had no influence on climate change calculation (step size up to 1year was supported), while the toxicity model resolution requires adaptive time step definition with maximum size of 0.5day.

Assessment of environmental impacts and operational costs of the implementation of an innovative source-separated urine treatment

Innovative treatment technologies and management methods are necessary to valorise the constituents of wastewater, in particular nutrients from urine (highly concentrated and can have significant impacts related to artificial fertilizer production). The FP7 project, ValuefromUrine, proposed a new two-step process (called VFU) based on struvite precipitation and microbial electrolysis cell (MEC) to recover ammonia, which is further transformed into ammonium sulphate. The environmental and economic impacts of its prospective implementation in the Netherlands were evaluated based on life cycle assessment (LCA) methodology and operational costs. In order to tackle the lack of stable data from the pilot plant and the complex effects on wastewater treatment plant (WWTP), process simulation was coupled with LCA and costs assessment using the Python programming language. Additionally, particular attention was given to the propagation and analysis of inputs uncertainties. Five scenarios of VFU implementation were compared to the conventional treatment of 1 m³ of wastewater. Inventory data were obtained from SUMO software for the WWTP operation. LCA was based on Brightway2 software (using ecoinvent database and ReCiPe method). The results, based on 500 iterations sampled from inputs distributions (foreground parameters, ecoinvent background data and market prices), showed a significant advantage of VFU technology, both at a small and decentralized scale and at a large and centralized scale (95% confidence intervals not including zero values). The benefits mainly concern the production of fertilizers, the decreased efforts at the WWTP, the water savings from toilets flushing, as well as the lower infrastructure volumes if the WWTP is redesigned (in case of significant reduction of nutrients load in wastewater). The modelling approach, which could be applied to other case studies, improves the representativeness and the interpretation of results (e.g. complex relationships, global sensitivity analysis) but requires additional efforts (computing and engineering knowledge, longer calculation time). Finally, the sustainability assessment should be refined in the future with the development of the technology at larger scale to update these preliminary conclusions before its commercialization.

A Multiobjective Optimization Including Results of Life Cycle Assessment in Developing Biorenewables-Based Processes

A decision support tool has been developed that uses global multiobjective optimization based on 1) the environmental impacts, evaluated within the framework of full life cycle assessment; and 2) process costs, evaluated by using rigorous process models. This approach is particularly useful in developing biorenewable-based energy solutions and chemicals manufacturing, for which multiple criteria must be evaluated and optimization-based decision-making processes are particularly attractive. The framework is demonstrated by using a case study of the conversion of terpenes derived from biowaste feedstocks into reactive intermediates. A two-step chemical conversion/separation sequence was implemented as a rigorous process model and combined with a life cycle model. A life cycle inventory for crude sulfate turpentine was developed, as well as a conceptual process of its separation into pure terpene feedstocks. The performed single- and multiobjective optimizations demonstrate the functionality of the optimization-based process development and illustrate the approach. The most significant advance is the ability to perform multiobjective global optimization, resulting in identification of a region of Pareto-optimal solutions.

Quantitative assessment of energy and resource recovery in wastewater treatment plants based on plant-wide simulations

The growing development of technologies and processes for resource treatment and recovery is offering endless possibilities for creating new plant-wide configurations or modifying existing ones. However, the configurations' complexity, the interrelation between technologies and the influent characteristics turn decision-making into a complex or unobvious process. In this frame, the Plant-Wide Modelling (PWM) library presented in this paper allows a thorough, comprehensive and refined analysis of different plant configurations that are basic aspects in decision-making from an energy and resource recovery perspective. In order to demonstrate the potential of the library and the need to run simulation analyses, this paper carries out a comparative analysis of WWTPs, from a techno-economic point of view. The selected layouts were (1) a conventional WWTP based on a modified version of the Benchmark Simulation Model No. 2, (2) an upgraded or retrofitted WWTP, and (3) a new Wastewater Resource Recovery Facilities (WRRF) concept denominated as C/N/P decoupling WWTP. The study was based on a preliminary analysis of the organic matter and nutrient energy use and recovery options, a comprehensive mass and energy flux distribution analysis in each configuration in order to compare and identify areas for improvement, and a cost analysis of each plant for different influent COD/TN/TP ratios. Analysing the plants from a standpoint of resources and energy utilization, a low utilization of the energy content of the components could be observed in all configurations. In the conventional plant, the COD used to produce biogas was around 29%, the upgraded plant was around 36%, and 34% in the C/N/P decoupling WWTP. With regard to the self-sufficiency of plants, achieving self-sufficiency was not possible in the conventional plant, in the upgraded plant it depended on the influent C/N ratio, and in the C/N/P decoupling WWTP layout self-sufficiency was feasible for almost all influents, especially at high COD concentrations. The plant layouts proposed in this paper are just a sample of the possibilities offered by current technologies. Even so, the library presented here is generic and can be used to construct any other plant layout, provided that a model is available.

Assessing Location and Scale of Urban Nonpotable Water Reuse Systems for Life-Cycle Energy Consumption and Greenhouse Gas Emissions

Nonpotable water reuse (NPR) is one option for conserving valuable freshwater resources. Decentralization can improve distribution system efficiency by locating treatment closer to the consumer; however, small treatment systems may have higher unit energy and greenhouse-gas (GHG) emissions. This research explored the trade-off between residential NPR systems using a life-cycle approach to analyze the energy use and GHG emissions. Decentralized and centralized NPR options are compared to identify where decentralized systems achieve environmental advantages over centralized reuse alternatives, and vice versa, over a range of scales and spatial and demographic conditions. For high-elevation areas far from the centralized treatment plant, decentralized NPR could lower energy use by 29% and GHG emissions by 28%, but in low-elevation areas close to the centralized treatment plant, decentralized reuse could be higher by up to 85% (energy) and 49% (GHG emissions) for the scales assessed (20-2000 m³/day). Direct GHG emissions from the treatment processes were found to be highly uncertain and variable and were not included in the analysis. The framework presented can be used as a planning support tool to reveal the environmental impacts of integrating decentralized NPR with existing centralized wastewater infrastructure and can be adapted to evaluate different treatment technology scales for reuse.

Cost versus life cycle assessment-based environmental impact optimization of drinking water production plants

Empowering decision makers with cost-effective solutions for reducing industrial processes environmental burden, at both design and operation stages, is nowadays a major worldwide concern. The paper addresses this issue for the sector of drinking water production plants (DWPPs), seeking for optimal solutions trading-off operation cost and life cycle assessment (LCA)-based environmental impact while satisfying outlet water quality criteria. This leads to a challenging bi-objective constrained optimization problem, which relies on a computationally expensive intricate process-modelling simulator of the DWPP and has to be solved with limited computational budget. Since mathematical programming methods are unusable in this case, the paper examines the performances in tackling these challenges of six off-the-shelf state-of-the-art global meta-heuristic optimization algorithms, suitable for such simulation-based optimization, namely Strength Pareto Evolutionary Algorithm (SPEA2), Non-dominated Sorting Genetic Algorithm (NSGA-II), Indicator-based Evolutionary Algorithm (IBEA), Multi-Objective Evolutionary Algorithm based on Decomposition (MOEA/D), Differential Evolution (DE), and Particle Swarm Optimization (PSO). The results of optimization reveal that good reduction in both operating cost and environmental impact of the DWPP can be obtained. Furthermore, NSGA-II outperforms the other competing algorithms while MOEA/D and DE perform unexpectedly poorly.

Greenhouse gases from wastewater treatment - A review of modelling tools

Nitrous oxide, carbon dioxide and methane are greenhouse gases (GHG) emitted from wastewater treatment that contribute to its carbon footprint. As a result of the increasing awareness of GHG emissions from wastewater treatment plants (WWTPs), new modelling, design, and operational tools have been developed to address and reduce GHG emissions at the plant-wide scale and beyond. This paper reviews the state-of-the-art and the recently developed tools used to understand and manage GHG emissions from WWTPs, and discusses open problems and research gaps. The literature review reveals that knowledge on the processes related to N2O formation, especially due to autotrophic biomass, is still incomplete. The literature review shows also that a plant-wide modelling approach that includes GHG is the best option for the understanding how to reduce the carbon footprint of WWTPs. Indeed, several studies have confirmed that a wide vision of the WWPTs has to be considered in order to make them more sustainable as possible. Mechanistic dynamic models were demonstrated as the most comprehensive and reliable tools for GHG assessment. Very few plant-wide GHG modelling studies have been applied to real WWTPs due to the huge difficulties related to data availability and the model complexity. For further improvement in GHG plant-wide modelling and to favour its use at large real scale, knowledge of the mechanisms involved in GHG formation and release, and data acquisition must be enhanced.

Greenhouse Gases Emissions from Wastewater Treatment Plants: Minimization, Treatment, and Prevention

The operation of wastewater treatment plants results in direct emissions, from the biological processes, of greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), as well as indirect emissions resulting from energy generation. In this study, three possible ways to reduce these emissions are discussed and analyzed:(1)minimization through the change of operational conditions,(2)treatment of the gaseous streams, and(3)prevention by applying new configurations and processes to remove both organic matter and pollutants. In current WWTPs, to modify the operational conditions of existing units reveals itself as possibly the most economical way to decrease N2O and CO2emissions without deterioration of effluent quality. Nowadays the treatment of the gaseous streams containing the GHG seems to be a not suitable option due to the high capital costs of systems involved to capture and clean them. The change of WWTP configuration by using microalgae or partial nitritation-Anammox processes to remove ammonia from wastewater, instead of conventional nitrification-denitrification processes, can significantly reduce the GHG emissions and the energy consumed. However, the area required in the case of microalgae systems and the current lack of information about stability of partial nitritation-Anammox processes operating in the main stream of the WWTP are factors to be considered.