Sustainability analysis of primary wastewater treatment by willow plantations in Québec

Wastewater treatment is a necessary step to avoid environmental impacts of water consumption and usage. Traditional approaches are expensive and are limited to developed countries. Phytofiltration using fast-growing trees and shrubs like willows potentially offer an alternative. This paper aims to determine if wastewater treatment using phytofiltration can provide complementary environmental and economic benefits for rural communities in a Nordic climate such as the province of Québec, Canada. It looks at different perspectives of the wastewater treatment solution in a local and rural context. Based on life cycle analysis (LCA) and life cycle cost analysis (LCC), we found that, for an exemplar Québec municipality, the conventional wastewater treatment scenario impacted more on climate change, ecosystem quality and human health than the two phytofiltration of wastewater scenarios studied, where impact is highly dependant on the biomass valorization. The net present cost of the phytofiltration scenarios were lower than typical conventional treatment in Québec. For a biomass producer, conventional biomass production had the highest environmental impact on ecosystem quality, while biomass production from phytofiltration had the highest environmental impact on climate change, human health, and resources. We demonstrate that the phytofiltration is a viable and multifunctional technology that could provide good incentives for a local biomass value chain. it allows to both alleviate wastewater treatment burden and provide affordable biomass for bioenergy development for rural communities. Mobilizing local stakeholders will be key to make phytofiltration an alternative solution for both environmental burden alleviation and rural economic development.


Introduction
Wastewater treatment is a major issue around the world, with 2.4 billion people lacking access to wastewater facilities, particularly in developing countries.Even among developed nations, only 70% treat their own wastewater [1].In 2009, The Canadian Council of Ministers of the Environment implemented a pancanadian strategy [2] to address the 6,074 million m 3 of wastewater discharged into the environment each year.As much as 4.4 % of that wastewater is still discharged with no treatment.In the province of Québec, Canada 2,027 million m 3 of wastewater is discharged annually, with 2.7 % untreated, mostly in small rural municipalities that do not have the necessary infrastructures [3,4].The environmental burden on ecosystems and human health needs to be addressed by developing new solutions for wastewater treatment adapted to this context.Québec has passed regulations in order to comply with the Canadian strategy, first establishing guidelines for municipal wastewater treatment practices, the 'Règlement sur les ouvrages municipaux d'assainisssment des eaux usées' (hereafter ROMEAU) [5,6] in 2013, and then a water treatment strategy, in 2018 [7], the 'Plan d'assainissement des eaux du Québec'.The ROMEAU imposes more constraints on wastewater treatment by municipalities, and represents substantial expenditures for each level of governments [5].Both federal and provincial governments aim to ensure that all municipalities provide at least secondary wastewater treatment, and in order to achieve this, solutions need to be identified [8].
Phytotechnologies such as phytofiltration can be an effective way to treat wastewater [9].Phytofiltration is a process that uses willow plantations first and foremost for primary wastewater treatment.Willow plantations are most efficient at removing pollutant compounds from wastewater, while producing biomass as an important secondary function [10].That biomass can be used for different applications, including heating, biofuels or bioproducts.These can represent a real opportunity for bioindustrial spin-offs while remediating an environmental burden [11].This environmental burden is a collective one that every municipality must address [6] ideally in the most cost-efficient way, and the different technologies currently available can have different economic impacts [5].In recent years, biomass valorization has been seen as an avenue to help rural areas in Québec transition away from fossil fuel use by increasing investments and structuring the value chain.New value chain development includes identifying new sources of biomass supply, as well as developing technologies to ensure fossil fuel replacement in applications such as heating systems and bioethanol for biofuel [12].
Because phytofiltration is an efficient solution to both treat wastewater and produce biomass [9], it is important to determine the conditions under which it can have a positive economic and environmental impact.Using phytofiltration to produce biomass has secondary economic and environmental advantages for local economic development, but they are highly dependent on the way the biomass is valorized.The economic and environmental drivers for a sustainable supply of biomass are the main constraints on stakeholders in integrating this new type of biomass [13][14][15].Each small municipality charged with managing wastewater treatment and each biomass producer has a specific set of objectives and mission.For municipalities, especially small ones with about 500 inhabitants, the objective is to determine the most environmentally-friendly and costeffective way to efficiently treat wastewater.For the biomass producer, the objective is to obtain a good price for the biomass produced with no greater impact on the environment than conventional cultivation methods.To be able to connect these two different stakeholder perspectives, this study proposes a life-cycle and a technoeconomic analysis for each stakeholder, according to their principal goal, to assess the economic and environmental relevance of using phytofiltration.These results should determine if integrating wastewater treatment using phytofiltration and biomass production can provide complementary environmental and economic benefits for rural communities.

Methods
Life cycle analysis (LCA) An attributional process-based LCA [16,17] was performed on wastewater treatment following ISO 14041 guidelines [3].For the Life Cycle Impact Assessment (LCIA), the Impact 2002+ methodology was used [18,19], which includes four damage categories and fourteen midpoint categories.The four major categories included climate change, ecosystem quality, human health, and resources.Climate change is both an endpoint category and a single midpoint category.Ecosystem quality is composed of six different midpoint categories: aquatic ecotoxicity, terrestrial ecotoxicity, aquatic acidification, aquatic eutrophication, terrestrial acidification or nitrification and land occupation.Human health is composed of five midpoint categories: human toxicity, respiratory effects, ionizing radiation, ozone layer depletion and photochemical oxidation.Resources is composed of two midpoint categories: non-renewable energy and mineral extraction.

Life cycle cost (LCC)
The LCC is ex-ante in the form of data derived from a demonstration site and not established infrastructure.The environmental analysis was performed using the Net Present Cost (NPC) calculation for analysis from a wastewater treatment perspective, and the Net Present Value (NPV) calculation for analysis from a biomass production perspective.

Goal and scope: wastewater treatment perspective
The objective was to determine the most environmentally friendly and more cost-effective way to efficiently treat wastewater at a municipal scale within a Québec municipality.To accurately evaluate the wastewater treatment, a functional unit of 1 m 3 of wastewater treated to comply with Québec effluent standards was used.Three different wastewater treatment scenarios were assessed: a conventional process (CONVENTIONAL), a phytofiltration process including bioenergy for heat valorization (PHYTOFILTRATION + HEAT), and a phytofiltration process including cellulosic ethanol valorization (PHYTOFILTRATION + BIOPRODUCT) (figure 1).CONVENTIONAL is a conventional process based on data from the Ecoinvent database version 3.5 [20], adapted to the Québec electricity grid and incineration of biosolids.PHYTOFILTRATION + HEAT is based on three different processes: primary wastewater treatment, willow cultivation and substitution of oil by willow biomass for heat production.PHYTOFILTRATION + BIOPRODUCT is based on three different processes: primary wastewater treatment, willow cultivation and substitution of ethanol from maize with cellulosic ethanol from willow biomass.
Municipal wastewater treatment is publicly funded in Québec, based on the average cost (CAD$/m 3 ) of wastewater treatment and municipality size.The NPC of the phytofiltration was therefore calculated for wastewater treatment within a standard Québec municipality of 500 inhabitants, allowing comparison of median municipal authority costs between the three scenarios tested [21].

Goal and scope: biomass production perspective
The objective was to compare the value and environmental impact of biomass production from conventional cultivation (BIOMASS + CONVENTIONAL) and phytofiltration (BIOMASS + PHYTOFILTRATION) (figure 2).The functional unit was the production of 1 Kg of willow biomass in southern Québec.BIOMASS + CONVENTIONAL, conventional willow , was based on data from the Ecoinvent database version 3.5 [20], adapted to the Québec electricity grid and southern Québec fertilization good practices, and three processes: fertilization, cultivation and harvesting.BIOMASS + PHYTOFILTRATION is willow biomass production using phytofiltration and is based on three processes: primary wastewater treatment, cultivation and harvesting.
The scope of biomass production analysis is based on biomass producer revenues from biomass derived from phytofiltration.These include the revenues from biomass sales and the effect of municipal incentives and the Canadian carbon tax system on revenues from willow cultivation as part of a wastewater facility servicing a municipality with 500 inhabitants where fallow lands are available for plantation.

Inventory analysis
Wastewater treatment sustainability analysis Environmental analysis Analysis of the phytofiltration process is based on onsite data from a demonstration field trial which successfully treated primary effluent wastewater to achieve Québec standards for release of effluent into surface waters [10,11,22].The background processes, consisting of willow cultivation, primary wastewater treatment and valorization of the biomass through substitution, are based on values from the Ecoinvent database version 3.5 [20].Analysis of the data for conventional wastewater treatment processes is based on activated sludge treatment within Québec from the Ecoinvent database.All processes are adapted to the Québec electrical grid, which predominantly uses hydroelectricity.
The land use change (LUC) is assumed to be transformation from cropland fallow to forest, intensive, shortcycle (table 1), as fallow land and a lack of wastewater treatment infrastructure are common in Québec's rural areas [7].
The number of trees, volume of wastewater treated, willow life expectancy, biomass yield and ethanol production yield assumptions for phytofiltration were based on the demonstration phytofiltration field trial and biomass valorization from the site [10,11,22] (table 2), while more general parameters, such as aerial and belowground carbon sequestration, are based on literature [23][24][25][26][27]. Construction and operational inputs for the anaerobic pond were used for primary wastewater treatment prior to plantation irrigation within phytofiltration (figure 1) and were adapted for seasonal operation from landfill infrastructure values within the Ecoinvent database [20].

Economic analysis
The net present cost of wastewater treatment from phytofiltration scenarios PHYTOFILTRATION + HEAT and PHYTOFILTRATION + BIOPRODUCT was calculated for a 30-year term (life expectancy of a conventional wastewater plant) and previous economic assessment from the demonstration phytofiltration field trial [22], adapted to cost analysis in 2021 in a rural context using the EcoWillow 2.0 tool [28] (table 3) at a 4% discount rate based on cost analysis of climate change effects on Québec infrastructure [29].

Environmental analysis
The BIOMASS + CONVENTIONAL scenario is based on conventional biomass production used in Québec [30] and the Ecoinvent database for the background processes.The BIOMASS + PHYTOFILTRATION scenario for biomass production from phytofiltration is based on onsite data from a demonstration project that was carried out between 2015 and 2018 [10,11,22].The background processes of willow cultivation, primary wastewater treatment, fertilization and harvesting are based on values from the Ecoinvent database version 3.5 [20].All processes are adapted to the Québec electrical grid, which predominantly relies on hydroelectricity.The land use change (LUC) is assumed to be transformation from cropland fallow to forest, intensive, shortcycle (table 1), as fallow land and a lack of wastewater treatment infrastructure are common in Québec's rural areas [7].
In order to compare conventional (BIOMASS + CONVENTIONAL) and phytofiltration (BIOMASS + PHYTOFILTRATION) processes for willow biomass production, the common parameters were the number of trees and willow life expectancy (table 4).More global parameters, such as aerial and belowground CO 2 sequestration, were based on literature [23][24][25][26][27].For BIOMASS + PHYTOFILTRATION, the biomass yield, volume of wastewater treated and ethanol yields were based on onsite project data [10,11].

Economic analysis
The NPV of biomass production from BIOMASS + PHYTOFILTRATION was calculated over a 25-year period (life expectancy of a willow plantation) and previous economic assessment from the demonstration phytofiltration field trial [22], adapted to cost analysis in 2021 in a rural context using the EcoWillow 2.0 tool [28] at a 4% discount rate based on cost analysis of climate change effects on Québec infrastructure [29] (table 3).The NPV of the project used the same infrastructure and operational costs as those in the previous section for the net present cost of wastewater treatment with phytofiltration.Six different revenue scenarios were assessed: revenues from municipal incentives, revenues from municipal incentives and a biomass price at gate of $100.t −1 and revenues from municipal incentives and a biomass price at gate of 150 $.t −1 with or without revenues from carbon tax incentives.A common price for wood chips in local biomass-to-bioenergy projects in rural parts of Québec is $150.t−1 , whereas 100 $.t −1 is a more conservative price and closer to the minimum selling price mentioned in the literature [31].The municipal incentives were set at a reference net present cost of 0.141 $.m 3 and 2% inflation rate based on Bank of Canada stability objectives [32].Canadian government projections were used to estimate the impact of the Canadian carbon tax incentives on willow phytofiltration biomass producers [33].

Wastewater treatment Environmental results -damage categories
The damage categories climate change, ecosystem quality and human health were more impacted by the conventional wastewater treatment scenario than by the two phytofiltration of wastewater scenarios.PHYTOFILTRATION + BIOPRODUCT had the highest impact on the climate change damage category, in contrast to PHYTOFILTRATION + HEAT, which had 7% of that negative impact (figure 3).Substitution of heating (PHYTOFILTRATION + HEAT) or ethanol production (PHYTOFILTRATION + BIOPRODUCT) was the main contributor to the environmental impact of the phytofiltration scenarios (figure 4).This highlights that valorization of willow biomass is a sensitive factor in the environmental impact of phytofiltration.The choice of whether to valorize biomass through bioenergy versus bioethanol production affects the entire system.

Environmental resultsmidpoint categories
For ecosystem quality midpoint categories, the main differences between conventional and phytofiltration processes were in terms of aquatic ecotoxicity, terrestrial ecotoxicity and land occupation.Conventional treatment caused the greatest damage to aquatic ecotoxicology and terrestrial ecotoxicology, while phytofiltration had the greatest impact on land occupation (figure 3).For terrestrial acidification and nitrification, the two phytofiltration scenarios differed greatly, PHYTOFILTRATION + HEAT had the most impact and PHYTOFILTRATION + BIOPRODUCT had a −74% impact.Substitution was the greatest contributor (63 % for PHYTOFILTRATION + HEAT and 72% for PHYTOFILTRATION + BIOPRODUCT), the sensitivity of biomass valorization for both phytofiltration scenarios had a great impact on terrestrial acidification and nitrification, and the substitution of ethanol for maize had a negative impact, thus, reducing the damage (figure 5).
For human health midpoint categories, conventional treatment (CONVENTIONAL) had a greater impact on human toxicity than phytofiltration scenarios (PHYTOFILTRATION + HEAT+PHYTOFILTRATION + BIOPRODUCT), which had a greater impact on photochemical oxidation (figure 3).For the midpoint categories ionizing radiation, ozone depletion and respiratory effects, there was no clear difference between phytofiltration and conventional processes.Substitution of heating (PHYTOFILTRATION + HEAT) or ethanol production (PHYTOFILTRATION + BIOPRODUCT) was the main contributor to environmental impact in the phytofiltration scenarios, such that the sensitivity of the biomass valorization was notable for these midpoint categories as well (figure 5).
For resources midpoint categories, mineral extraction and non-renewable energy, PHYTOFILTRATION + HEAT had the greatest impact on mineral extraction, whereas PHYTOFILTRATION + BIOPRODUCT had the greatest impact on non-renewable energy (figure 3).PHYTOFILTRATION + HEAT was the second most impacting on both midpoint categories, such that there was no clear difference between the conventional (CONVENTIONAL) and the phytofiltration processes (PHYTOFILTRATION + HEAT + PHYTOFILTRATION + BIOPRODUCT).
For midpoint categories, the conventional treatment had a lower impact than phytofiltration on land occupation and photochemical oxidation (figure 3).Otherwise, phytofiltration had a lower environmental impact on climate change, aquatic ecotoxicity, terrestrial ecotoxicity, human toxicity and ozone depletion.The contribution analysis shows that phytofiltration can have a lesser impact than conventional wastewater treatment on aquatic acidification and nitrification, ionizing radiation, ozone depletion, respiratory effects, mineral extraction, and non-renewable energy depending on the substitution process (figure 5).
Conventional wastewater treatment had a lesser environmental impact on land occupation than both phytofiltration scenarios.This difference is driven by the non-aerated pond, anticipated as necessary for these phytofiltration scenarios.When land occupation is dependent on the primary wastewater treatment contribution, the remaining impacts of the midpoints of other categories are dependent on the substitution process (figure 5).

LCC -net present cost
The present cost of phytofiltration (PHYTOFILTRATION + HEAT and PHYTOFILTRATION + BIOPRODUCT scenarios) was $1.01 m 3 of wastewater treated.The allocation for the primary wastewater treatment was $0.91 m 3 and the allocation for willow cultivation was $0.10 m 3 , accounting for 90.1 % and 9.9 % of the project cost, respectively (table 6).The average net present cost for conventional wastewater treatment in Québec for municipalities of around 500 inhabitants is $1.76 m 3 [21].The net present cost of a phytofiltration plantation, common to both PHYTOFILTRATION + HEAT and PHYTOFILTRATION + BIOPRODUCT scenarios, was calculated as $1.03 m 3 (table 6).Most of this cost (89.21%) is associated with the construction of an anaerobic pond for primary wastewater treatment.

Biomass production
Environmental resultsdamage categories Conventional biomass production (BIOMASS + CONVENTIONAL) had the highest environmental impact on ecosystem quality, while biomass production from phytofiltration (BIOMASS + PHYTOFILTRATION) had the highest environmental impact on climate change, human health and resources (figure 6).Across all damage categories, harvesting was the major contributor to environmental impact for conventional biomass production, whereas primary wastewater treatment was the major contributor for biomass production from phytofiltration (figure 7).In addition to highlighting the environmental importance of harvesting in the context of conventional biomass production, these findings illustrate how primary wastewater treatment as part of phytofiltration results in greater environmental impact than fertilizer production and application of conventional biomass.
The impact analysis conducted shows no substantial difference in terms of impact between the two biomass production scenarios (BIOMASS + CONVENTIONAL and BIOMASS + PHYTOFILTRATION), either at damage points or midpoint.The type of contribution was substantially different, however.As the impact of harvesting is calculated based on the surface area harvested and is independent of the biomass weight or volume harvested, the difference in biomass yield between conventional production (12 t −1 ha −1 yr −1 ) and phytofiltration (34 t −1 ha −1 yr −1 ) has a substantial impact.This means that a higher biomass yield can reduce the environmental impact of harvesting.
Environmental resultsmidpoint categories Phytofiltration has a higher impact for all midpoint categories except two: terrestrial ecotoxicity and mineral extraction.The midpoint categories most impacted by BIOMASS + PHYTOFILTRATION were land occupation (with an impact of only 3% for BIOMASS + CONVENTIONAL), ozone layer depletion (with an impact of only 14% for BIOMASS + CONVENTIONAL) and non-renewable energies (with an impact of only 16% for BIOMASS + CONVENTIONAL) (figure 6).These categories also show the three greatest contributions from primary wastewater treatment in the BIOMASS + PHYTOFILTRATION scenario, with contributions of respectively 99%, 95% and 95% (figure 8).On the other hand, the two categories with a higher impact in the conventional scenario (terrestrial ecotoxicity and mineral extraction) are those for which the contribution of primary wastewater treatment is the lowest.

Economic analysis LCC -Net present value
The NPV for Biomass + Phytofiltration was $3,662 when the revenues were municipal incentives (tables 4 and 5).This increases to $200,926 when biomass valued at $100 t −1 was also included, and to $299,558 when biomass was valued at $150 t −1 .If both municipal incentives and the Canadian carbon tax would be included as revenues without biomass value, the phytofiltration plantation NPV was $57,815.This increases to 255 080 $ with biomass valued at $100 t −1 and to $353,712 with biomass valued at $150 t −1 (table 6).
In regard to the chronological evaluation of the NPV, the phytofiltration scenario (BIOMASS + PHYTOFILTRATION) with only municipal incentives as revenues reaches a positive NPV in year 23, the scenario with municipal incentives and biomass at $100 t −1 reaches a positive NPV in year 6, the scenario with municipal incentives and biomass at $150 t −1 reaches a positive NPV in year 6, the scenario with municipal incentives and the Canadian carbon tax incentive reaches a positive NPV in year 14, the scenario with municipal incentives, biomass at $100 t −1 and the Canadian carbon tax incentive reaches a positive NPV in year 6 and the scenario with municipal incentives, biomass at $100 t 1 and the Canadian carbon tax incentive reaches a positive NPV in year 5 (figure 9).To explore the influence of biomass price, municipal incentives, and carbon tax incentives on the net present value (NPV) for biomass production on a phytofiltration plantation, six revenue scenarios were compared, all of which resulted in a positive NPV (table 7).Willow biomass production using phytofiltration shows a positive NPV after 6 years where the mandate to treat wastewater is for a 25-year time frame and a biomass price is $100 t −1 , which is low for the Québec wood chip market (common selling price for biomass is over $90 [31,34]) (figure 9).
Municipal incentives are an important driver of phytofiltration development, as the economic viability of the project would then be less dependent on the biomass selling price.Although municipal incentives alone can make biomass production from phytofiltration economically viable, the addition of biomass revenues (at $100 or $150 per t −1 ) substantially increases the NPV and makes the option more appealing for investors.If tax carbon revenues are added, NPV is increased by $54 153 (table 7).Such an approach could provide additional incentives along the whole biomass value chain.

Discussion
Phytofiltration has a better environmental impact than conventional wastewater treatment The first objective of the environmental and economic analysis presented above was to evaluate the impacts of three different treatment approaches on 1 m 3 of wastewater.We have shown that phytofiltration can reduce the environmental impact compared to conventional wastewater treatment, which had less environment impact in terms of land occupation.Aquatic ecotoxicity, terrestrial ecotoxicity, aquatic acidification, aquatic eutrophication and terrestrial acidification and nitrification and land occupation [16,17,35] are important midpoint categories according to which wastewater treatment technology options can be evaluated.Phytofiltration is the best option for all five midpoint categories except in terms of land occupation.Improvement of primary wastewater treatment efficiency, by reducing the area dedicated to the anaerobic pond, can lower the impact in terms of land occupation.

Phytofiltration is cost effective
The NPC evaluation also proved that phytofiltration technology is a viable option for municipalities with around 500 inhabitants.Construction costs of non-aerated ponds can be highly dependent on existing and accessible infrastructure [36] and therefore could substantially influence the uncertainty of the net present costs of phytofiltration.Some more research need to be conducted in order to limit the downsides associated with cold climate.It creates challenges because it implies using storage infrastructure for wastewater during wintertime [22].Adapted solutions need to be created according to local community's capacities.Despite this uncertainty and these challenges, the 41.6 % reduction in net present cost from phytofiltration does suggest that this technology can be economically feasible for municipalities of this scale in Québec.Phytofiltration can thus represent an environmentally and economically efficient option in areas where there is low pressure on the land.

Phytofiltration impact on environment is sensitive to biomass valorization options
We also highlighted that valorization of willow biomass is a sensitive factor to consider in analyzing the environmental impact of phytofiltration.Since willow biomass has strong potential as a substitute for both heating oil or conventional biomass supply such as wood in rural communities [28,[37][38][39], the local context of energy providers and users will have the strongest influence on the real environmental impact of the system.Heating with a bioenergy source rather than nonrenewable fuel can represent a good environmental opportunity [40].Moreover, in Quebec, using the biomass produced during the phytofiltration process to replace maize-based ethanol would also represent an economic opportunity [41].The process by which biomass is valorized for bioenergy or bioethanol production thus affects the whole system.

Producing biomass using phytofiltration an alternative to fertilization and irrigation
The biomass produced in addition to wastewater treatment by means of phytofiltration can supply different end-uses.Growing willows or poplars in short rotation coppice (SRC) for biomass production has the potential to provide a significant positive environmental impact for renewable energy systems [42,43] such as heating or bioethanol production.This process can also yield multiple different environmental benefits when used to alleviate problems such as aquatic ecotoxicity, terrestrial ecotoxicity, aquatic acidification or aquatic eutrophication, or when integrated into other agricultural or industrial activities [44,45].When looking at conventional and phytofiltration biomass production scenarios (BIOMASS + CONVENTIONAL and BIOMASS + PHYTOFILTRATION), there is no clear difference in impact either at damage points or midpoint.Compared to conventional production of biomass, primary wastewater treatment for phytofiltration increased the environmental impact when compared to fertilizer production and application.Consequently, a reduced contribution of the primary wastewater treatment impact is the key to making biomass production more  environmentally friendly for the phytofiltration process.Being an alternative solution for wastewater treatment, phytofiltration can also be an alternative solution to fertilization and irrigation [46][47][48] and further minimize any negative environmental impacts of producing willow biomass in SRC.

Using phytofiltration incentives can create lower selling prices for biomass
We have shown that municipal incentives could be an important driver for the expansion of phytofiltration as a biomass production process, since the economic viability of any such undertaking would then be less dependent on biomass selling price.We showed that NPV would increase by $54 153 with the addition of carbon tax credits.This could provide further incentives for the entire value chain, including the end-user stakeholders, who would be able to claim carbon tax credits.These new revenues could foster the creation of context-driven sustainable solutions aligned with local social, environmental and economic characteristics, using an integrated biorefinery approach [49][50][51][52][53][54].Looking at an integrated value chain, ethanol production from willow represents a real opportunity for CO 2 reduction depending on the carboneutrality of the electricity grid [55].Lower selling prices for biomass and new potential revenue streams could foster the development of other valorization streams, such as bioproducts or secondary metabolites for willow phytofiltration biomass to fit integrated biorefinery [11].
Phytofiltration can be an economic opportunity for locally-driven development High biomass production profits such as these could be important to encourage phytofiltration technology uptake by biomass producers.In this scenario, carbon tax incentives had little impact on NPV for biomass producers, but could potentially be an asset for end-users downstream willing to take advantage of either the opportunity to purchase carbon offsets or incentive regulations when replacing fossil feedstock [33].Because of municipal incentives, such an approach could positively impact biomass selling price and then facilitate market development [56,57].Its benefits for regional development by relocating economic activity have been demonstrated [58], but remain dependent on locally-driven environmental and economic conditions.Québec has already developed experience on developing partnerships between environmental organizations, cooperatives, municipalities and local investment funds [16].Various initiatives, based on cooperation between industries and municipalities, using biomass for bioproducts or as fossil fuels replacement for heating systems were created in Québec [59] and can represent a realistic alternative to the framework of macroeconomic policies needed for a willow-based value chain [60].Like nutrient removal and valorization systems [61][62][63], phytofiltration can create leverage for a more sustainable, locally integrated approach.The other main influencing parameter would be the biomass yield, which could influence the contribution of different key processes.Phytofiltration represents an alternative solution for wastewater treatment.Similarly, it could become a new alternative approach to fertilization and irrigation.Under the phytofiltration scenario, municipal incentives would enable a lower selling price for biomass within the local market.Such infrastructure development could have a beneficial impact on the environment and commodity chain development, depending on the biomass valorization option.Phytofiltration a multifunctional technology for local development an economic and environmental perspective, primary wastewater treatment options should be the focus of development in order to make an efficient multifunctional technology that will improve the efficiency of both wastewater treatment and biomass valorization needs to be developed (figure 10).It can then become a major contribution for local communities.The main challenge will be to work towards a common vision and ambition among all stakeholders, in order to make that new phytotechnology a good option for wastewater treatment and local development through biomass valorization routes.In order to make phytofiltration a viable solution and make its implementation a reality, expertise from both the local community and phytotechnology experts need to be mobilized.Knowledge mobilization is a way to combine local expectations and experience with scientific expertise [64].This approach can be an asset for the project social acceptance and sustainability.It could benefit all stakeholders and researchers to engage in a more effective way to transform scientific discoveries into local applications [65].

Conclusion
Wastewater management represents a major environmental challenge around the world, with many additional constraints in the context of developing countries and rural areas with low urban density.Due to the impacts on human health and ecosystems, wastewater treatment must be addressed globally.Our results show that the main constraints on development are economic viability and investment capital.Generating cooperation among local stakeholders and reducing reliance on high levels of investment by governments are among the promising strategies for the future.In Québec, wastewater treatment is a critical issue for rural areas where the lack of appropriate infrastructure is creating an environmental hazard.Phytofiltration has been found to be an effective and more environmentally process in a small rural municipality with both land availability and existing biomass valorization practices.However, stakeholders need tools and assessments to ensure it represents a potentially viable opportunity for them in their local context.
Phytofiltration has a more positive environmental impact than conventional wastewater treatment on climate change, ecosystem quality and human health, although the potential for improving that impact is dependent on biomass valorization or use.This highlights that willow biomass valorization is a sensitive factor in the environmental assessment of phytofiltration.The valorization of biomass for bioenergy or bioethanol production affects the whole phytofiltration system and provides avenues for greater improvement.Even though phytofiltration is an environmentally sound solution, specific and context related scenarios must be evaluated to gain a better understanding of the real environmental impact of the phytofiltration process.Phytofiltration is an economically viable solution for wastewater treatment but is still dependent on the cost of primary wastewater treatment.For a biomass producer using phytofiltration as a new approach to fertilization, the predominant environmental impact results from the primary wastewater treatment, versus harvesting for conventional production.Primary wastewater treatment thus seems the main area for environmental impact reduction.
Phytofiltration can be a multifunctional technology that solves a major environmental problem in rural Quebec and provides leverage for local economic development.In order to tackle the development of phytofiltration for rural communities, some barriers still need to be overcome.This involves both local governments and scientists.The lack of funding mechanisms or policy incentives can become barriers facing rural communities in Québec.It implies local communities to develop more cooperation between all local stakeholders involved in the chain value.Using current experience from stakeholders to ensure a sustainable development will be necessary.From a technological point of view, improvements must be made according to the need for contextual solutions.For that reason, knowledge mobilization can become a tool to build a common vision for local stakeholders while ensuring that technical improvements will help environmental and economical viability.Involving organizations to ensure coordination processes is one way to ensure that technology serves local interests.Phytofiltration is a sound solution for wastewater treatment in rural communities in Québec.It can contribute to the development of local biomass chains, but still needs stakeholder and community involvement to become an efficient and context-sensitive solution.

Figure 6 .
Figure 6.Impact comparison between conventional willow biomass production (BIOMASS + CONVENTIONAL) and willow biomass production using phytofiltration (BIOMASS + PHYTOFILTRATION) at endpoint and midpoint categories.

Figure 9 .
Figure 9. NPV with time for of biomass using phytofiltration.

Table 1 .
Willow cultivation process parameters concerning contamination and concentration removed using a phytofiltration process for wastewater treatment.

Table 2 .
Global parameters for each phytofiltration wastewater treatment scenario.

Table 3 .
Economic project evaluation parameters for phytofiltration wastewater treatment scenarios.

Table 4 .
Global project parameters for conventional willow cultivation and willow biomass production using phytofiltration.

Table 5 .
Economic project evaluation parameters for willow biomass production scenarios.

Table 6 .
Net present cost (NPC)for wastewater treatment using phytofiltration.

Table 7 .
Net present value (NPV) for the production of biomass with phytofiltration.