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.
Trang 1a v a i l a b l e a t w w w s c i e n c e d i r e c t c o m
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / e c o l m o d e l
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
Article history:
Received 30 September 2005
Received in revised form 20
February 2006
Accepted 14 March 2006
Published on line 24 April 2006
Keywords:
Emergy analysis
Natural capital
Environmental accounting
Constructed wetlands
First-order plug-flow model
a b s t r a c t This study examines and evaluates, by means of the emergy analysis, the use of environ-mental resources for wastewater treatment in a Sicilian town A traditional wastewater treatment plant coupled with a surface flow constructed wetland was considered for water purification The surface area of the wetland was calculated by using a first order plug flow kinetic model; the area’s value was a necessary parameter for the application of the emergy 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 application, the additional emergy value of water purification was calculated The purpose
of the analysis was to determine whether or not the installation of a constructed wetland on
a Sicilian wastewater treatment plant may result in monetary savings and benefit the envi-ronment The analysis done here shows that the proposed design not only results in savings
by reducing electricity consumption, but also reduces pressure on the local environment by 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 evalu-ation 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
1 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)
important particularly in areas with large temporal varia-tions in water availability, for example in semi-arid regions like Sicily, to focus on preserving or constructing man-made wetlands in order to increase water availability over time and gain benefits from the ecosystem services pro-vided
The project presented hereafter is an application of the environmental accounting method, developed byOdum (1996), to a small case study: the proposal of creating a con-structed wetland (CW) to improve the performance of an exist-ing wastewater treatment plant
0304-3800/$ – see front matter © 2006 Elsevier B.V All rights reserved
doi:10.1016/j.ecolmodel.2006.03.019
Trang 2Table 1 – Baseline data used for sizing the wastewater treatment plant
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 1 – Existing traditional treatment plant TP.
2 Methods
2.1 Description of the existing wastewater treatment
plant
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
crush-ers) The baseline data used for sizing the plant is reported in
Table 1 The treated effluent is discharged in a water stream
called “Cava Bagni” and not utilized This is because the
efflu-ent 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
2 m height), a biofilter, a secondary clarifier and a
chlorina-tion basin (seeScheme 1) The efficiency of each plant section
is reported inTable 2 The actual state of the plant is
worry-ing 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
run-ning As a possible solution to the problem, our proposal is to
modify the original scheme of the plant by replacing the
sec-ondary treatment section (percolation beds and biofilter) with
a constructed wetland (seeScheme 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 pump-ing 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 capac-ities of a number of emergent, free-floating, and subemerged macrophytes have been reported byBrix (1994)and Kivaisi (2001) CWs with emergent macrophytes are widely used for
Table 2 – BOD removal efficiency for each plant sections
Trang 3Scheme 2 – Proposed TP + CW system.
wastewater treatment in Europe and North America (Kadlec
and Knight, 1996a,b) Various designs for emergent
macro-phyte (e.g., phragmites australis) CWs have been recently
reviewed byVymazal (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 6 days and to give
a yield of 88–106 Mg ha−1year−1(Reddy and Sutton, 1984)
The capability of water hyacinth (WH) to purify
wastewa-ter 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
sur-face 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
har-vesting), ammonia is removed through volatilisation and
nitri-fication/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
These systems have been tested for treating various
wastew-aters under various conditions in different countries Studies
on purification of domestic wastewaters under semi-arid
con-ditions 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
agricul-ture use In Iran, a subsurface flow reed bed (ph australis) of
150 m2was tested for treating municipal wastewaters (Metcalf
and Eddy Inc, 1991) In Italy few different constructed
wet-lands 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 mod-els (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 sur-face 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)
KTdnv and KT= K20(T w −20)
where A is the wetland treatment area (m2), Q the influent
wastewater flow (m3/d), Cithe influent pollutant
concentra-tion at wetland inlet (mg/l), Cothe effluent pollutant
concen-tration 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 tem-perature (d−1), Twthe 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−1and = 1.048
Wetland temperature Twis a fundamental parameter for the designer because the removal of BOD and the various nitrogen forms are temperature dependent Winter tempera-tures correspond to lower reaction rates and should be used in the design calculations The calculation of winter water tem-perature was carried through an iterative routine applied to the following expressions(Kadlec and Knight, 1996b, Chapter 9):
R = r ET+ H
Trang 4Fig 1 – Multiple wetland cells Geometrical conditions: minimum length/width ratio = 5:1; maximum width = 10–15 m.
where Rnis the net radiation reaching the ground (MJ/m2/d), r
the density of water (kg/m3), mthe latent heat of vaporization
of water (MJ/kg), ET the water lost to evapotranspiration (m/d)
and Hais 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), Twthe water temperature (◦C) and Pwais 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, Ci= 64 mg/l, Co= 20 mg/l,
d = 0.5 m, nv = 0.75, Tw= 14◦C,
KT= 0.678 × (1.06)(14–20)
= 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
Q =0.75 × 0.5 × 12.4591920 = 2.4 days
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=Q
A= 15.41 cm/d
2.5 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
perfor-mance and water balances For example, high
evapotranspi-ration 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 sys-tem 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 deter-mined by the reach of mechanical earth-moving equipment that may be used for construction, maintenance or rehabilita-tion but is probably best limited to less than 10–15 m A general scheme of the wetland geometry is reported inFig 1
3 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 con-sider 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 wastew-ater treatment plant)
Resource use and emissions from construction and opera-tion 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 mate-rial 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 treat-ment plants.Bengtsson et al (1997)studied differences in the environmental impact of alternative ways to treat wastewa-ter, including conventional treatment, urine sorting and liq-uid 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
Trang 5In emergy analysis, all environmental work that sustains a
specific system can be quantified (Odum, 1996)
4 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
transfor-mity 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
eco-nomic 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 sys-tems (Nelson, 1998) and in conventional wastewater treat-ment 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 3 is a gen-eral diagram of emergy flows in the proposed TP + CW system In Annex A and B the emergy flows of respec-tively 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 3 – Diagram of Emergy flows of wastewater treatment in a conventional treatment plant with a constructed wetland (TP + CW).
Trang 6The 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,
com-pared 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
suit-able for reuse, while the existing TP is not suit-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
ter-ritory by Tiezzi et al., in Analisi di sostenibilit `a 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
ben-efit, 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
environmen-tal costs necessary to depurate the same amount of
wastew-aters 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)
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 wastew-aters) 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
5 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 do run out, that use can be said to be sustainable Sustainabil-ity 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 agricul-tural irrigation in an area (South Sicily) that suffers from a high risk of desertification In this contest, the project we pro-pose, 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, aes-thetic values, pollination etc.)
Appendix A Emergy analysis of the existing conventional wastewater treatment plant
(g, J andD )
Solar emergy per unit (sej/unit)
Solar emergy (×E15 sej/yr)
Emeuro
EmD unit−1
Traditional plant
Maintenance costsc: includes costs of—chemicals,
fuels, services and sludge disposal
aElectricity = 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, Contabilit `a Ambientale, Bastianoni, p 72)
bHuman labour = 3.8E9 J (D 199,868.82) Three employees working 8 h per day; 365 persons/yr× 2500 kcal/person × 4186 J/kcal = 3.8E9 J The trans-formity is 7.38E6 sej/J (Ulgiati et al., 1994)
cMaintenance costs =D2.8E4 (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 sostenibilit `a ambientale della Provincia di Modena e dei suoi distretti, Siena, 1998) 7.26E8 sej/£× 1.93627E3 £/D; 1D= 1.93627 £
dPlant building price =D1.7E6/20 = 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)
eTreated 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
Trang 7Appendix B Emergy analysis of the proposed conventional wastewater treatment plant completed with a constructed wetland
(g, J andD )
Solar emergy per unit (sej/unit)
Solar emergy (×E15 sej/yr)
Emeuro
EmD unit−1
Changed traditional plant
Maintenance costsc: includes costs of—chemicals,
fuels, services and sludge disposal
Total emergy for treatment
Constructed wetland
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 EmDto purify 7E5 m3/yr) 1.9E5 (Em/yr)/7E5 (m3/yr) = 0.27 EmD/m3
aElectricity = 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, Contabilit `a Ambientale, Bastianoni, p 72)
bHuman labour = 3.8E9 J (D199.868.82) Three employees working 8 h per day; 365 persons/yr× 2500 kcal/person × 4186 J/kcal = 3.8E9 J The trans-formity is 7.38E6 sej/J (Ulgiati et al., 1994)
cMaintenance costs =D2.8E4 (31 December 2002) It includes the costs of chemicals, fuels, services and sludge disposal The solar emergy per unit
is 1.4E12 sej/Daccording with Tiezzi’s evaluation (Tiezzi et al., Analisi di sostenibilit `a ambientale della Provincia di Modena e dei suoi distretti, Siena, 1998) 7.26E8 sej/£× 1.93627E3 £/D 1D= 1.936,27 £
dPlant building price =D1.7E6/20 = 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)
eTreated 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
f 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
gWind kinetic= rc(vg)3A, 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) Evalua-tion = 1.23 kg/m3× 1E−3 × (10/6 × 2.42 m/s)3× 31536E3 s/yr × 1.25E4 m2= 3.26E10 J/yr
hRain, 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
i 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)
j 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×
1 m = 12.459 m3 Total price = 5.2E4D/20 = 2.6E3D Waterproof sheet:D6.20 m−2(Regione Siciliana, 2002) Total price =D7.7E4/20 = 3.85E3D
kWetland outlet water transformity = (2.97E17)/(7.04E11) = 4.2E5 sej/g
Trang 8r e f e r e n c e s
Barbagallo, S., Cirelli, G.L., Consoli, S., Faro, G., Giammanco, G.,
Indelicato, S., Pignato, S., Toscano, A., 2003 Constructed
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in Sicily Ingegneria Ambientale XXXII (1), 34–40
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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
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