Các quá trình về xử lý bằng đất Tưới nước: Tưới bằng nước thải, quá trình xử lý bằng đất được áp dụng phổ biến nhất hiện nay, bao gồm việc tưới nước thải vào đất và để đáp ứng các yêu cầu sinh trưởng của cây cối. Dòng nước thải khi đi vào đất sẽ được xử lý bằng những quá trình vật lý, hoá học và sinh học. Dòng nước thải đó có thể dùng tưới cho các loại cây bằng cách phun mưa hoặc bằng các kỹ thuật tưới bề mặt như là làm ngập nước hay tưới theo rãnh, luống. Có thể tưới cho cây trồng với tốc độ tiêu thụ từ 2,5 7,5 cm tuần. Thấm nhanh vào đất : Theo phương pháp này, dòng nước thải được đưa vào đất với tốc độ lớn (10 210 cm tuần) bằng cách rải đều trong các bồn chứa hoặc phun mưa. Việc xử lý xảy ra khi nước chảy qua nền đất (đất dưới mặt) ở những nơi mà nước ngầm có thể dùng để đảo ngược lại gradient thủy lực và bảo vệ nước ngầm hiện có ở những nơi chất lượng nước ngầm không đáp ứng với chất lượng mong đợi nước được phục hồi quay trở lại bằng cách dùng bơm để hút nước đi, hoặc là những đường tiêu nước dưới mặt đất, hoặc tiêu nước tự nhiên.
e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ecolmodel Design of a constructed wetland for wastewater treatment in a Sicilian town and environmental evaluation using the emergy analysis G Siracusa ∗ , A.D La Rosa Department of Physical and Chemical Methodologies for Engineering, Faculty of Engineering, University of Catania, Italy a r t i c l e i n f o a b s t r a c t Article history: This study examines and evaluates, by means of the emergy analysis, the use of environ- Received 30 September 2005 mental resources for wastewater treatment in a Sicilian town A traditional wastewater Received in revised form 20 treatment plant coupled with a surface flow constructed wetland was considered for water February 2006 purification The surface area of the wetland was calculated by using a first order plug flow Accepted 14 March 2006 kinetic model; the area’s value was a necessary parameter for the application of the emergy Published on line 24 April 2006 analysis Water is part of the natural capital but, as water is processed through purification processes for city use, there are additional emergy and money values added In the present Keywords: application, the additional emergy value of water purification was calculated The purpose Emergy analysis of the analysis was to determine whether or not the installation of a constructed wetland on Natural capital a Sicilian wastewater treatment plant may result in monetary savings and benefit the envi- Environmental accounting ronment The analysis done here shows that the proposed design not only results in savings Constructed wetlands by reducing electricity consumption, but also reduces pressure on the local environment by First-order plug-flow model providing the option of recycling clean water Furthermore, the emergy analysis which uses inputs both from natural ecosystems and the human economy, allows a quantitative evaluation of the environmental savings due to water reuse as well as the environmental impact due to the wastewater treatment process © 2006 Elsevier B.V All rights reserved Introduction Wetlands have been used to provide tertiary treatment to municipal wastewater as an alternative to conventional methods Wetland utilization generates economic savings: because they rely on more natural methods, they are less expensive to build and operate than conventional sewage treatment (e.g., less electricity consumption); furthermore the purified water is suitable for reuse Purified water for reuse is a very valuable asset as clean water is a scarce resource that is critical for human existence May be ∗ Corresponding author E-mail address: gsiracusa@dmfci.unict.it (G Siracusa) 0304-3800/$ – see front matter © 2006 Elsevier B.V All rights reserved doi:10.1016/j.ecolmodel.2006.03.019 important particularly in areas with large temporal variations in water availability, for example in semi-arid regions like Sicily, to focus on preserving or constructing manmade wetlands in order to increase water availability over time and gain benefits from the ecosystem services provided The project presented hereafter is an application of the environmental accounting method, developed by Odum (1996), to a small case study: the proposal of creating a constructed wetland (CW) to improve the performance of an existing wastewater treatment plant 491 e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 Table – Baseline data used for sizing the wastewater treatment plant Parameter Wastewater influent (average daily flow Q) Estimated water consumption rate per equivalent person per daya Equivalent population for urban sewage only Equivalent population including the olive crushers and the abattoir BOD5 per person per daya BOD5 of the influent wastewater Required BOD5 for the purified water Value Unit 1920; 80 250 1920000 (l/d)/250 (l/d) = 7680 11735 0.064 (11735 × 0.064) = 751; 391 20 m3 /d; m3 /h l/p.e d p.e p.e kg/p.e d kg/d; mg/l mg/l Source data: Original project provided by the municipality a Textbook: Luigi Masotti, Depurazione delle acque—Tecniche ed impianti per il trattamento delle acque di rifiuto, 1987 Scheme – Existing traditional treatment plant TP Methods 2.1 plant Description of the existing wastewater treatment The wastewater treatment plant under study is located near a little town called Canicattini Bagni, in Sicily, an area with a high environmental and archaeological value It collects domestic wastewaters from the village and waters from organic farming activities (an abattoir and few olive crushers) The baseline data used for sizing the plant is reported in Table The treated effluent is discharged in a water stream called “Cava Bagni” and not utilized This is because the effluent water does not comply with the law specifications and also because of the poor condition of the plant The treatment plant consists of a preliminary screen, a primary clarifier, two Imhoff septic tanks, two percolation beds (16 m diameter and m height), a biofilter, a secondary clarifier and a chlorination basin (see Scheme 1) The efficiency of each plant section is reported in Table The actual state of the plant is worrying as several actions are required to keep good efficiency: the septic tanks need to be cleaned; the percolation bed and the biofilter efficiency is very low compared with the cost of running As a possible solution to the problem, our proposal is to modify the original scheme of the plant by replacing the secondary treatment section (percolation beds and biofilter) with a constructed wetland (see Scheme 2) As mentioned before, wetland utilization generates economic savings while con- ventional sewage treatment plants are very capital-intensive Three-quarters of overall costs are involved in the pumping required to move raw sewage to the centralized sewage plant Electrical costs are high since much of the conventional sewage treatment plants system process relies on machinery 2.2 Constructed wetlands: an overview CWs for wastewater treatment facility involve the use of engineered systems that are designed and constructed to utilize natural processes These systems are designed to mimic natural wetland systems, utilizing wetland plants, soil and associated microorganisms to remove contaminants from wastewater effluents (EPA, 1993) CWs are classified according to the life form of the dominating large aquatic plant, or macrophyte, in the system Nutrient uptake capacities of a number of emergent, free-floating, and subemerged macrophytes have been reported by Brix (1994) and Kivaisi (2001) CWs with emergent macrophytes are widely used for Table – BOD removal efficiency for each plant sections Plant section Septic tank Percolation bed Biofilter Secondary clarifier BOD removal efficiency (%) 68 16.7 6.2 44 492 e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 Scheme – Proposed TP + CW system wastewater treatment in Europe and North America (Kadlec and Knight, 1996a,b) Various designs for emergent macrophyte (e.g., phragmites australis) CWs have been recently reviewed by Vymazal (1998), and are categorized according to surface (SF) or sub-surface (SSF) wastewater flow patterns CWs with free-floating macrophytes may contain large plants with well-developed submerged roots such as water hyacinth, or small surface floating plants with little or no roots such as duckweed (Greenway, 1997) Due to its large potential for nutrient removal from wastewater, the water hyacinth is the one that stimulated extensive experimentation The plant has been reported to double its biomass in days and to give a yield of 88–106 Mg ha−1 year−1 (Reddy and Sutton, 1984) 2.2.1 Water hyacinth CWs The capability of water hyacinth (WH) to purify wastewater is well documented (Reddy and Sutton, 1984; Reddy and DeBusk, 1985; DeBusk et al., 1989; Reddy and D’Angelo, 1990) The extensive root system of the weed provides a large surface area for attached microorganisms thus increasing the potential for decomposition of organic matter Plant uptake is the major process for nutrient removal from wastewater systems containing water hyacinth plants (Reddy and Sutton, 1984) Nitrogen is removed through plant uptake (with harvesting), ammonia is removed through volatilisation and nitrification/denitrification, and phosphorus is removed through plant uptake WH wastewater treatment systems produce large amounts of excess biomass given the rapid growth rate of the plant To sustain an effective treatment system based WH, the management plan must include provision for harvesting and use of the excess plant material 2.2.2 CWs with emergent macrophytes These systems have been tested for treating various wastewaters under various conditions in different countries Studies on purification of domestic wastewaters under semi-arid conditions are reported in literature Reed beds with phragmites australis in Morocco obtained organic removal of 48–62%, TSS of 58–67% and a parasitic removal of 71–95% (Mandi et al., 1998) In Egypt, Stott et al (1999) achieved a 100% removal of parasitic ova from domestic waters intended for agriculture use In Iran, a subsurface flow reed bed (ph australis) of 150 m2 was tested for treating municipal wastewaters (Metcalf and Eddy Inc, 1991) In Italy few different constructed wetlands have been monitored during the last few years, showing excellent removal efficiency (Conte et al., 2000; Barbagallo et al., 2003) 2.3 Design criteria and calculations The dimensioning tools utilised for the design of the system were based on published first order plug flow kinetic models (Reed et al., 1995; Kadlec and Knight, 1996a,b; Crites and Tchobanoglous, 1998) In our application we use the Reed method to calculate the area of a free water surface CW considering the BOD removal, as described by the “Guide lines for using free water surface constructed wetland to treat municipal sewage” (Knight Mertz, 2000) In his model Reed incorporated flow rate, wetland depth, wetland porosity, a temperature-based rate constant, and inflow and outflow concentrations The rate constant is a function of depth and porosity of the wetland Reed equation is the following: A= Q ln(Ci /Co ) KT dnv and KT = K20 (Tw −20) where A is the wetland treatment area (m2 ), Q the influent wastewater flow (m3 /d), Ci the influent pollutant concentration at wetland inlet (mg/l), Co the effluent pollutant concentration at wetland outlet (mg/l), d the water depth in wetland (m), nv the void ratio or porosity corresponding to proportion of typical wetland cross section not occupied by vegetation, KT the rate constant corresponding to water temperature in wetland (d−1 ), K20 the rate constant at 20 ◦ C reference temperature (d−1 ), Tw the wetland temperature (◦ C) and is the temperature coefficient for rate constant The first-order kinetic constant values at 20 ◦ C (K20 ) and the temperature coefficient ( ) depends on the pollutant removal For BOD removal K20 = 0.678 d−1 and = 1.06 while for NH4 + removal K20 = 0.218 d−1 and = 1.048 Wetland temperature Tw is a fundamental parameter for the designer because the removal of BOD and the various nitrogen forms are temperature dependent Winter temperatures correspond to lower reaction rates and should be used in the design calculations The calculation of winter water temperature was carried through an iterative routine applied to the following expressions (Kadlec and Knight, 1996b, Chapter 9): Rn = r m ET + Ha e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 493 Fig – Multiple wetland cells Geometrical conditions: minimum length/width ratio = 5:1; maximum width = 10–15 m where Rn is the net radiation reaching the ground (MJ/m2 /d), r the density of water (kg/m3 ), m the latent heat of vaporization of water (MJ/kg), ET the water lost to evapotranspiration (m/d) and Ha is the convective transfer to air (MJ/m2 /d): ET = Ke × [Psat w (Tw ) − Pwa ] where Ke is the water vapor mass transfer coefficient (m/d/kPa), Psat w (Tw ) the saturation water vapor pressure at Tw (kPa), Tw the water temperature (◦ C) and Pwa is the ambient water vapor pressure (kPa) The meteorological data were collected in a nearby area (Priolo) 2.4 Wetland calculations result In our study we use the following values: Q = 1920 m3 /d, d = 0.5 m, Ci = 64 mg/l, nv = 0.75, (14–20) KT = 0.678 × (1.06) Co = 20 mg/l, ◦ Tw = 14 C, = 0.478, A = [1920 × ln(64/20)]/(0.478) × (0.5) × (0.75) = 12.459 m2 The detention time is calculated as follows: t= nv × d × A 0.75 × 0.5 × 12.459 = = 2.4 days Q 1920 The hydraulic loading rate (HRT) that provides a measure of the volumetric application of wastewater into the wetland, is calculated using the following expression: HRT = 2.5 Q = 15.41 cm/d A Wetland geometry In our proposal, FWS constructed wetlands should have a number of flow paths operating in parallel Parallel flow paths help to balance the seasonal variation in treatment performance and water balances For example, high evapotranspiration rates in the dry season can be balanced by taking an individual flow path off-line and reducing the theoretical detention time Multiple flow paths also help break the system up into units that are easier to inspect and maintain The (length:width) ratio of the wetland flow path should be as long as is practical with a minimum of 5:1 In general, the longer the flow path, the closer the flow patterns approximate a plug flow The actual width of the flow path is probably best determined by the reach of mechanical earth-moving equipment that may be used for construction, maintenance or rehabilitation but is probably best limited to less than 10–15 m A general scheme of the wetland geometry is reported in Fig Background on environmental impact studies of wastewater treatment systems Municipal wastewater treatment systems have environmental impacts on different scales This implies that one has to consider not only the impact on the local environment of resource use at the wastewater treatment plant and of the discharged treated water, but also the impact on global and local scales of the production of external inputs used at the plant (e.g., changes in global climate caused by emissions from use of fossil fuels and local environmental impact from extraction of raw material used in machinery and buildings at the wastewater treatment plant) Resource use and emissions from construction and operation of municipal wastewater treatment systems have been studied by Ødegaard (1995) and Bengtsson et al (1997) Ødegaard (1995) evaluated the energy consumption, and the environmental impact due to the withdrawal of raw material for construction and due to emissions from treatment by using weighting factors employed in life cycle assessment (LCA), for the different treatment steps in conventional treatment plants Bengtsson et al (1997) studied differences in the environmental impact of alternative ways to treat wastewater, including conventional treatment, urine sorting and liquid composting, by using LCA and emergy analysis These studies mainly deal with the direct use of energy and other resources None of these studies included the indirect resource use due to human labour or an evaluation of the environmental work in the generation of the resources used 494 e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 In emergy analysis, all environmental work that sustains a specific system can be quantified (Odum, 1996) Emergy evaluation Emergy is an analysis tool to measure the work previously required to produce a product or service The analysis reveals the “embedded energy” or energy memory contained in the production process Emergy accounting (Odum, 1996) uses the thermodynamic basis of all forms of energy, materials and human services, but converts them into equivalents of one form of energy Emergy can be defined as the available energy that was used in the work of making a product and expressed in units of one type of energy The emergy of one type required to make a unit of energy of another type is defined transformity This gives a measure of how much one type of energy is worth in terms of every other; it is possible therefore to sum up in terms of one type of energy all the available energies used directly or indirectly to either create something or to offer a service That total is the emergy Emergy analysis may provide more complete accounting since it can evaluate both economic and environmental systems (Ulgiati et al., 1995) Emergy analysis differs from economic analysis because instead of using the money value of goods, services and resources, a measure of quality is used 4.1 Emergy evaluation of a conventional wastewater treatment plant completed with a constructed wetland (TP + CW) The emergy analysis has previously been used in analysis of wastewater treatment in wetlands (Flanagan and Mitsch, 1997; Nelson et al., 2001), in conventional treatment systems (Nelson, 1998) and in conventional wastewater treatment plants coupled with constructed wetlands (Geber and Bjorklund, 2001) In our study we analyse the benefits/costs ratio of using a TP + CW to obtain reusable water Scheme is a general diagram of emergy flows in the proposed TP + CW system In Annex A and B the emergy flows of respectively the existing traditional TP and the proposed TP + CW are reported Different inputs are considered for both the traditional plant and the constructed wetland (electricity; human labour; maintenance costs which includes chemicals, fuel, services, etc.; plant building price; renewable sources, lagoon building price, etc.) Each item values is multiplied by its own transformity to obtain the correspondent emergy value Scheme – Diagram of Emergy flows of wastewater treatment in a conventional treatment plant with a constructed wetland (TP + CW) 495 e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 The first observation from the analysis is that the proposed TP + CW system, although involving additional economic costs due to the wetland construction, has a minor emergy value (2.67E17 sej), which means a minor environmental cost, compared to the existing TP (2.7E17 sej) This is because of the reduction of electricity consumption due to the biofilter and percolation beds removal Furthermore, we have to remark that the product of the TP + CW system is purified water suitable for reuse, while the existing TP is not able to purify the wastewaters up to the law requirements We also analyse the benefits/costs ratio of using a TP + CW system to obtain reusable waters The total emergy value referred to the treated wastewaters was 2.65E17 sej; this represents the environmental cost of the TP + CW system to purify 7.04E11 g of wastewaters If we consider the same amount of surface water (solar emergy per unit = 5.12E5 sej/g, calculated for the Italian territory by Tiezzi et al., in Analisi di sostenibilita` ambientale della Provincia di Modena e dei suoi distretti, Siena, 1998) we can calculate the emergy value as: (5.12E5 sej/g × 7.04E11 g) = 3.58E17 sej This result means that if we use 7.0E11 g of surface waters (e.g., for irrigation) the emergy required is (5.12E5 sej/g × 7.0E11 g) = 3.58E17 sej which represents the benefit, in terms of natural capital, that our society can use from the environment without additional costs Now, instead of using surface water for irrigation, let’s hypothesize using the same quantity of treated waters The additional environmental costs necessary to depurate the same amount of wastewaters calculated for the TP + CW system is 2.67E17 sej This is an index of the environmental impact due to the wastewater treatment process The total emergy value of the purified waters is the sum of the emergy of the surface waters plus the emergy of the treated wastewaters (3.58E17 sej + 2.67E17 sej = 6.25E17 sej) Item Traditional plant Electricitya Human labourb Maintenance costsc : includes costs of—chemicals, fuels, services and sludge disposal Plant building priced Total emergy for treatment Outlet wastewater treatmente a b c d e If the purified waters are discharged (e.g., into the river) and not reused, there is an environmental waste of 2.67E17 sej (environmental cost to purify 7.04E11 g of wastewaters) If the waters are reused there is an environmental saving of the natural capital of 3.58E17 sej (6.25E17 sej − 2.67E17 sej = 3.58E17 sej) The benefit-costs ratio is 3.58E17 sej/ 6.25E17 sej = 0.6 which means that the order of magnitude of costs and benefits are similar Conclusion A sustainable use of a resource is when the resource use can be extended by society for a long time, because the use level and system design allow resources to be renewed by natural or human-aided processes When we use natural resources at a speed and in a manner which does not diminish them, so that we are not threatened with catastrophe as they run out, that use can be said to be sustainable Sustainability happens in the case of wetlands for wastewater treatment use as they collect and purify waters that can be used as a renewed resource for human activities especially for agricultural irrigation in an area (South Sicily) that suffers from a high risk of desertification In this contest, the project we propose, with the benefit/cost ratio = 0.6 (the order of magnitude of costs and benefits are similar) appears to be advantageous Furthermore, in terms of environmental renaturation a great advantage of using TP + CW is the increase of biodiversity that is a basis for many ecosystem services in the wetland and the surrounding landscape (e.g., biotic regulation, hunting, aesthetic values, pollination etc.) Appendix A Emergy analysis of the existing conventional wastewater treatment plant Raw unit/yr (g, J and D ) Solar emergy per unit (sej/unit) Solar emergy (×E15 sej/yr) 6.5E11 J 3.8E9 J 2.8E4 D 1.43E5 sej/J 7.38E6 sej/J 1.4E12 sej/D 92 sej 28 sej 26 sej 8.7E4 D 1.4E12 sej/D 120 sej 270 sej 3.8E5 sej/g 270 sej 7.04E11 g Emeuro EmD unit−1 Electricity = 500 × 365 kW h = 182,500 kW h = 6.5E11 J (per year) The transformity is 1.43E5 sej/J (Sviluppo di un modello di analisi emergetica per il sistema elettrico nazionale, 2000, Contabilita` Ambientale, Bastianoni, p 72) Human labour = 3.8E9 J (D 199,868.82) Three employees working h per day; 365 persons/yr × 2500 kcal/person × 4186 J/kcal = 3.8E9 J The transformity is 7.38E6 sej/J (Ulgiati et al., 1994) Maintenance costs = D 2.8E4 (31 December 2002) It includes the costs of chemicals, fuels, services and sludge disposal The solar emergy per unit is 1.4E12 sej/D according with Tiezzi’s evaluation (Tiezzi et al., Analisi di sostenibilita` ambientale della Provincia di Modena e dei suoi distretti, Siena, 1998) 7.26E8 sej/£ × 1.93627E3 £/D ; D = 1.93627 £ Plant building price = D 1.7E6/20 = 8.7E4 The yearly costs was evaluated dividing the total cost for 20 years (the average efficiency of a treatment plant is estimated to be 20 years) Treated wastewater = Q = 80 m3 /h × 8760 h/yr × 1000.000 g/m3 = 7.004E11 g/yr The total emergy value to obtain reusable water is 2.5E17 sej The solar emergy per unit of the treated wastewater is 2.7E17/7.004E11 = 3.8E5 sej/g 496 e c o l o g i c a l m o d e l l i n g ( 0 ) 490–497 Appendix B Emergy analysis of the proposed conventional wastewater treatment plant completed with a constructed wetland Item Changed traditional plant Electricitya Human labourb Maintenance costsc : includes costs of—chemicals, fuels, services and sludge disposal Plant building priced Total emergy for treatment Outlet wastewater treatmente Constructed wetland Sunlightf Wind, kineticg Rain, chemicalh Evapotraspirationi Wetland construction pricej Land moving Waterproof sheet Total emergy in purchased goods Wetland outlet waterk Raw unit/yr (g, J and D ) Solar emergy per unit (sej/unit) Solar emergy (×E15 sej/yr) 4.4E11 J 3.8E9 J 2.8E4 D 1.43E5 sej/J 7.38E6 sej/J 1.4E12 sej/D 63 sej 28 sej 26 sej 8.7E4 D 1.4E12 sej/D 120 sej 7.04E11 g 3.4E5 sej/g 237 sej 2.79E13 J 3.26E10 J 9.4E11 J 9.6E10 J 1496 sej/J 18199 sej/J 1.8 E4 sej/J 6.5E3 2.6E3 D 3.85E3 D 1.4E12 sej/D Emeuro EmD unit−1 0.03 sej 0.04 sej 17 sej 1.7 sej 9.1 sej 265 sej 7.04E11 g 3.76E5 sej/g 265 sej 0.27 EmD /m3 Wetland inlet water = Q (80 m3 /h) Q = 80 m3 /h × 8760 h/yr × 1000.000 g/m3 = 7.004E11 g/yr Benefit evaluation: If we consider the same amount of surface water (transformity 5.12E5 sej/g) the total emergy of that good would be (5.12E5 sej/g × 7.04E11 g) = 3.58E17 sej This value represents the real benefit obtained in terms of environmental saving when we use the same amount of water derived from wastewater treatment instead than from surface basins Environmental account: (2.65E17 sej/1.4E12 sej/D ) = 1.9E5 EmD /yr (environmental cost, expressed in EmD to purify 7E5 m3 /yr) 1.9E5 (Em/yr)/7E5 (m3 /yr) = 0.27 EmD /m3 a b c d e f g h i j k Electricity = 350 × 365 kW = 122,500 kW = 4.4E11 J (per year) The electricity reduction due to the biofilter and the percolation beds elimination was calculated being 30% the total energy consumption The transformity is 1.43E5 sej/J (Sviluppo di un modello di analisi emergetica per il sistema elettrico nazionale, 2000, Contabilita` Ambientale, Bastianoni, p 72) Human labour = 3.8E9 J (D 199.868.82) Three employees working h per day; 365 persons/yr × 2500 kcal/person × 4186 J/kcal = 3.8E9 J The transformity is 7.38E6 sej/J (Ulgiati et al., 1994) Maintenance costs = D 2.8E4 (31 December 2002) It includes the costs of chemicals, fuels, services and sludge disposal The solar emergy per unit is 1.4E12 sej/D according with Tiezzi’s evaluation (Tiezzi et al., Analisi di sostenibilita` ambientale della Provincia di Modena e dei suoi distretti, Siena, 1998) 7.26E8 sej/£ × 1.93627E3 £/D D = 1.936,27 £ Plant building price = D 1.7E6/20 = 8.7E4 The yearly costs was evaluated dividing the total cost for 20 years (the average efficiency of a treatment plant is estimated to be 20 years) Treated wastewater = Q = 80 m3 /h × 8760 h/yr × 1000.000 g/m3 = 7.004E11 g/yr The total emergy value to obtain reusable water is 2.5E17 sej The solar emergy per unit of the treated wastewater is 2.7E17/7.004E11 = 3.8E5 sej/g Sunlight = area*I*absorbed percentage (Brown, M.T., Bardi, E., Handbook of Emergy Evaluation (3), p 59) A is the pond area (1.25 ha) and I is the average solar radiation of Priolo (SR) = 101.5 W/m2 (average summer insulation 137.7 W/m2 ; average winter insulation 65.3 W/m2 , CIPA) Absorbed percentage = 70% Evaluation = 1.25E4 m2 × 101.5 J/s m2 × 31536E3 s/yr × 0.7 = 2.79E13 J/yr (*) This item is calculated only for the pond and not for the treatment plant because the plant surface is irrelevant respect to the pond surface Wind kinetic = rc(vg ) A, where r is the air density (1.23 kg/m3 ), c the drag coefficient (1E−3), v the average annual wind velocity (2.42 m/s), vg the geostrophic wind (10/6v) and A is the pond area (1.24E4 m2 ) (Brown, M.T., Bardi, E., Handbook of Emergy Evaluation (3), p 39) Evaluation = 1.23 kg/m3 × 1E−3 × (10/6 × 2.42 m/s)3 × 31536E3 s/yr × 1.25E4 m2 = 3.26E10 J/yr Rain, chemical potential energy = A × p × d × G, where G is the Gibbs free energy (4.94 J/g) (Odum, H.T., Environmental Accounting, p 42), p the yearly precipitation (340 mm), d the water density (1E6 g/m3 ) Evaluation = 140E4 m2 × 0.340 m/yr × 1E6 g/m3 × 4.94 J/g = 2.34E12 J/yr Evapotranspiration: ET × A × d × G, where ET is the evapotranspired water (1.46 m/anno), A the pond area (12.459 m2 ), d the water density (1E6 g/m3 ) and G is the Gibbs free energy (4.94 J/g) (Odum, H.T., Environmental Accounting, p 42) Evaluation = (1.56 m/yr) × (12.459 m2 ) × (1E6 g/m3 ) × (4.94 J/g) = 9.6E10 J The transformity is 1.8E4 sej/J (Brown, M.T., Bardi, E., Handbook of Emergy Evaluation (3), p 31) Wetland construction price/20 years = D 1.3E5/20 = D 6.5E3 Land moving: D 4.19 m−3 (Regione Siciliana, 2002) Land volume: 2.459 m2 × m = 12.459 m3 Total price = 5.2E4 D /20 = 2.6E3 D Waterproof sheet: D 6.20 m−2 (Regione Siciliana, 2002) Total price = D 7.7E4/20 = 3.85E3 D Wetland outlet water transformity = (2.97E17)/(7.04E11) = 4.2E5 sej/g ecological modelling references Barbagallo, S., Cirelli, G.L., Consoli, S., Faro, G., Giammanco, G., Indelicato, S., Pignato, S., Toscano, A., 2003 Constructed wetland systems for urban wastewater reuse: a case-study in Sicily Ingegneria Ambientale XXXII (1), 34–40 Bengtsson, M., Lundin, M., Molander, S., 1997 Life cycle assessment of wastewater systems, case studies of conventional treatment, urine sorting and liquid composting on three municipalities In: Technical Environmental Planning Chalmers University of Technology, Goteborg, Sweden Brix, H., 1994 Functions of macrophytes in constructed wetlands Water Sci Technol 29, 71–78 Conte, G., Martinuzzi, N., Giovannelli, L., Masi, F., Pucci, B., 2000 Constructed wetlands for wastewater treatment in central Italy In: Seventh International Meeting IWA, vol 2, Orlando, Florida, pp 869–872 Crites, R.W., 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constructed wetlands to remove parasite eggs from wastewater in Egypt Water Sci Technol., 117–123 Ulgiati, S., Odum, H.T., Bastianoni, S., 1994 Emergy use Environmental loading and sustainability An emergy analysis of Italy Eco-Model 73, 215–268 Ulgiati, S., Brown, M.T., Bastianoni, S., Marchettini, N., 1995 Emergy-based indices and ratios to evaluate the sustainable use of resources Ecol Eng 5, 519–531 Vymazal, J., 1998 Types of constructed wetlands for wastewater treatment In: A Paper presented at the Sixth International Conference on Wetland Systems for Water Pollution Control, Aguas de Sao Pedro, Brazil ... 1998 Application of constructed wetlands for domestic wastewater treatment in an arid climate Water Sci Technol 38, 379–387 Metcalf and Eddy Inc., 1991 Wastewater Engineering: Treatment, Disposal... of a conventional wastewater treatment plant completed with a constructed wetland (TP + CW) The emergy analysis has previously been used in analysis of wastewater treatment in wetlands (Flanagan... priced Total emergy for treatment Outlet wastewater treatmente Constructed wetland Sunlightf Wind, kineticg Rain, chemicalh Evapotraspirationi Wetland construction pricej Land moving Waterproof sheet