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ENCUENTRO INTERNACIONAL EN FITODEPURACIÓN (Julio del 2005, Lorca)
INTERNATIONAL MEETING ON PHYTODEPURATION (July 2005, Lorca, Murcia, Spain)
TÍTULO DEL TRABAJO
“Sustainable Indicators of Treatment Solutions for Small Agglomerations”
TÍTULO RESUMIDO
“Sustainability Indicators”
NOMBRE DE AUTORES
Espadinha, C.; Marcão, A.; Fàbregas, A.; Galvão*, A.; Matos, J.
NOMBRE Y DIRECCIÓN DE LAS INSTITUCIONES
Instituto Superior Técnico. Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
NÚMERO DE TELÉFONO, FAX Y E-MAIL
Tfno: +351218418371; Fax: +351218418371; e-mail: [email protected];
[email protected]
FIGURAS Y TABLAS
8 figuras
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Sustainable Indicators of Treatment Solutions for Small Agglomerations
Espadinha, C.; Marcão, A.; Fàbregas, A.; Galvão*, A.; Matos, J.
Instituto Superior Técnico
SUMMARY:
Evaluating sustainable treatment solutions is especially relevant in Portugal due the number of this type of wastewater
treatment plants serving small agglomerations and the lack of qualified human resources in rural communities. In the first
stage of the study, several indicators were applied in order to evaluate the sustainability of different types of wastewater
treatment plants. The facilities analysed are located in Odemira, Penacova, Penamacor, Sabugal, Fundão and Viseu
Municipalities. The types of biological treatments to be compared were conventional systems (extended aeration and
trickling filters) and non conventional treatment systems (constructed wetlands and ponds) for small agglomerations.
A conventional system for the wastewater treatment of small agglomerations is, usually, an appropriated and sustainable
option, because they have ol wer energy consumptions and lower chemical products and concrete consumptions per
inhabitant. The higher needs of such systems are associated to the extended area required for their implantation. Nevertheless,
wetlands are still a valid option in rural communities, where area availability is not usually a restriction.
KEY WORDS : Constructed wetlands; Sustainability indicators; treatment; wastewater.
Indicadores de Sostenibilidad de Soluciones de Tratamiento para Pequeñas
Aglomeraciones
RESUMEN
La evaluación de la sostenibilidad de sistemas de tratamiento para pequeñas poblaciones es especialmente relevante en
Portugal debido a la gran proporción de este tipo de sistemas en nuestro país y a la escasez de recursos humanos cualificados
en zonas rurales. En base a estaciones de tratamiento de aguas residuales en funcionamiento, se analizaron los distintos
indicadores de sostenibilidad propuestos en una primera fase del trabajo. Las estaciones de tratamiento de aguas residuales
objeto de estudio se encuentran en los Concelhos de Odemira, de Penacova, de Penamacor, de Sabugal, de Fundão y de
Viseu. El tratamiento biológico de estas estaciones de tratamiento de aguas residuales divididse en sistemas convencionales
(fangos activados y filtros percoladores) y no convencionales (humedales construidos y lagunaje).
La elección de sistemas no convencionales (humedales construidos y lagunaje) para el tratamiento de aguas residuales
provenientes de pequeñas poblaciones es, generalmente, apropiada y sostenible, en la medida en que presentan menores
consumos energéticos, de productos químicos y de hormigón por habitante equivalente. Las mayores exigencias por parte de
estos sistemas no convencionales, se reflejan a nivel del área necesaria para la implantación de los mismos. A veces, esa
situación no constituye una limitación en las regiones rurales, donde predominan las pequeñas poblaciones.
PALABRAS -CLAVE: Humedales construidos; Indicadores de sostenibilidad; tratamiento; aguas residuales.
1. INTRODUCTION
In order to improve sanitation levels in Portugal, the Portuguese government published, in the
beginning of this century, a document intituled “Strategic Plan of Water Distribution and
Wastewater Sewage” (PEAASAR), where a main goal of providing drainage and wastewater
treatment to 90% of Portuguese population was set.
According to MATOS et al. (2002), 70% of Wastewater Treatment Plants (WWTP), expected
to be built or improved in Portugal, are intending to serve agglomerations with less than 2000
habitants. This percentage is relevant taking into account that approximately 42% of the
Portuguese population lives in agglomerations with less than 2000 habitants (INE, 2001). In
this study, this population size was considered to be the limit for the definition of “small
agglomeration”. Therefore, this paper intends to support the decisions to be taken concerned
with building and improving WWTP serving small agglomerations, by analysing the
sustainability of different treatment systems.
In accordance with “The Brundtland Report”, sustainable development is defined as the
“development that satisfied the needs of the present, without compromising the future
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generations’ abilities of satisfying their own needs” (IA, 2002). Based on this concept, a
WWTP with lower consumptions associated with the used materials for building and
operation of the system, lower installed power, lower costs associated with the operation,
maintenance and monitoring and that presents an effluent suitable with the receiving waters,
should be considered the more sustainable system.
According to the Directive n ° 91/271/CEE, the wastewater treatment required for populations
lower than 2000 inhabitants is defined as “appropriate treatment”, that is, a treatment level
that guarantees the quality standards of the receiving waters.
The wastewater treatment applied to small agglomerations usually includes a septic tank or an
Imhoff tank followed, in some cases, by a biological treatment or soil disposal. Tertiary
treatment can be necessary, in some cases, due to the receiving environment’s requirements,
such as bathing areas or water bodies subject to eutrophication.
In Portugal, the facilities for wastewater treatment of small agglomerations are included in the
following types: septic tanks, Imhoff tanks, extended aeration, trickling filters, lagoons and
constructed wetlands. Nevertheless, there is a tendency, namely in the centre of the country,
for the construction of horizontal flow constructed wetlands, because they are generally
considered more sustainable solutions.
In the context of this paper, the conventional systems analysed include biological treatment by
extended aeration or trickling filters. On the other hand, the non conventional systems
considered are constructed wetlands and ponds.
An important aspect when analysing sustainable development, is the development and
monitoring of indicators. In accordance with the Organisation for Economic Co-operation
and Development an indicator is defined as: “a parameter, or a value derived from
parameters, which points to, provides information about, describes the state of a
phenomenon/environment/area, with a significance extending beyond that directly associated
with a parameter value”. The indicators are classified as measuring instruments and they
should yield certain criteria, and their application must be defined and structured in order to
be a useful tool.
2. MATERIAL AND METHODS
In order to evaluate the sustainability of several wastewater treatment systems (conventional
and non conventional), sustainablility indicators were developed. The indicators can be
divided in three domains: environmental, economical and social. Then, these indicators were
applied to WWTP of several municipalities located in the centre of Portugal (Penacova,
Penamacor, Sabugal, Fundão and Viseu Municipalities), and in the south of country (Odemira
Municipality).
The total number of WWTP analysed comprised 27 facilities, from which project data was
available. Data regarding operational parameters, like the number of employees, was only
available for 8 of the WWTP (all of them from Odemira Municipality).
The sustainable indicators calculated were the following:
Environmental
?? Installed power per inhabitant vs. served population
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?? Annual energy consumption per inhabitant vs. served population
?? % of energy consumed in the WWTP comparing to the total energy consumed by the
population
?? Concrete used in WWTP per inhabitant vs. served population
?? Total area per inhabitant vs. served population
Economical
?? Civil construction costs per inhabitant vs. served population
?? Mechanical and electric equipment costs per inhabitant vs. served population
?? Annual operation costs per inhabitant vs. served population (only data from WWTP of
Odemira Municipality).
Social indicators, like the number of complaints or odour nuisance, were not possible to
evaluate due to the lack of enough data.
When performing the calculations, the following assumptions and considerations were taken
into account:
for a comparative and economical analysis the preliminary treatment was not
considered. All the works and materials associated with upstream pumping and
screens were not considered, because the need for these infrastructures is usually
determined by the upstream topography;
the energy consumptions were estimated based on the installed power and on the
operation time;
the concrete used on WWTP refers to primary, secondary, tertiary and sludge
treatment infrastructures and to operation building;
the civil construction costs gather the material and labour;
the investments costs include civil construction, mechanical equipments and land
movement;
the operation costs include labour, chemical products, energy, chemical analysis and
transportation and sludge disposal.
3. RESULTS
For a comparative analysis of conventional and non conventional systems, figures were
developed in order to give a large and intuitive vision of the two kinds of treatment systems.
A distinction was made between conventional and non-conventional systems.
Each indicator was plotted against the corresponding served population, in order to evaluate
the scale effect of the different systems.
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Annual energetic
consumption per inhabitant
(kWh/inh./year)
Installed power per
inhabitant (kW/inh.)
70,0
Conventional
systems
Non conventional
systems
0,050
0,045
0,040
0,035
0,030
0,025
0,020
0,015
0,010
0,005
0,000
60,0
50,0
Conventional
systems
40,0
Non conventional
systems
30,0
20,0
10,0
0
500
1000
1500
2000
0,0
0
Served population
Figure 1 – Installed power per inhabitant vs. served
population
1,5
1,0
0,5
0,0
0
500
1000
1500
2000
3
2,0
1500
2000
Conventional
systems
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
Non conventional
systems
(m /inh.)
2,5
Concrete per inhabitant
Conventional
systems
Non conventional
systems
3,0
1000
Served population
Figure 2 – Annual energy consumption per
inhabitant vs. served population
4,0
3,5
500
0
Served population
500
1000
1500
2000
Served population
Figure 4 – Concrete used in WWTP
per inhabitant vs. served population.
Conventional
systems
Non conventional
systems
30,0
25,0
2
(m /inh.)
Total area per inhabitant
35,0
20,0
15,0
10,0
5,0
0,0
0
500
1000
1500
Civil construction costs
per inhabitant (€/inh.)
Figure 3 – % of energy consumed in the WWTP
comparing to the total energy consumed by the
population.
700,0
Conventional
systems
600,0
Non conventional
systems
500,0
400,0
300,0
200,0
100,0
0,0
0
2000
500
Conventional
systems
Non conventional
systems
100,0
80,0
60,0
40,0
20,0
0,0
0
500
1000
1500
2000
1500
2000
Served population
Figure 7 – Mechanical and electric equipment costs
per inhabitant vs. served population.
Figure 6 – Civil construction costs per
inhabitant vs. served population.
800,0
Civil construction and
mechanical and electric
equipment costs per
inhabitant (€/inh.)
Mechanical and electric
equipment costs per
inhabitant (€/inh.)
Figure 5 – Total area per inhabitant vs. served
population.
120,0
1000
Served population
Served population
Conventional
systems
700,0
600,0
Non conventional
systems
500,0
400,0
300,0
200,0
100,0
0,0
0
500
1000
1500
2000
Served population
Figure 8 – Annual operation costs per inhabitant
vs. served population (only WWTP from Odemira
Municipality).
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4. DISCUSSION AND CONCLUSIONS
Figure 1 shows a higher need of installed power per inhabitant for conventional systems, what
was already expected. Conventional WWTP presents, generally, higher energy consumptions
per inhabitant.
According to the presented data (Fig. 3), the energy consumption per inhabitant with
treatment facilities is lower than 4% of the total consumption per inhabitant of the served
community. When the effluent is treated with constructed wetlands, the percentage of energy
consumption in the WWTP is lower than 2% of the total.
Figure 5 shows a higher area requirement per inhabitant for the implantation of non
conventional systems, due the extensive nature of these systems.
Although trickling filters are classified as conventional systems, this particular type of
treatment may have characteristics similar to non-conventional systems, in what respects low
energy costs and concrete used per inhabitant. The operation costs associated with low rate
trickling filters are generally also very low, as illustrated in Figure 8.
In general, it is expected that annual costs with treatment systems will be lower when
considering wetlands and lagoons. In this study, as it can be observed from Figure 8, a
significant part of the existing conventional systems (the low rate trickling filters) present
very low operation costs, due to the characteristics of the facilities (without pumping or
lighting) and poor operation. On the other hand, in certain cases, the constructed wetlands
included lighting, responsible for additional energy consumption.
A global analysis performed for the group of indicators presented, and from the available
data, seems to show that non-conventional systems have the following characteristics, when
compared to conventional systems:
?? Less average energy consumption per inhabitant
?? Less average concrete consumption per inhabitant,
?? Similar civil construction costs per inhabitant,
The major disadvantage regarding conventional systems seems to be associated with the
extended area required for their implantation.
Taking also these limited results into account, the selection of non conventional systems for
the wastewater treatment from small agglomerations may be considered, generally, an
appropriated and sustainable option, especially in sites where land availability is not a
problem and when its cost are low.
5. ACKNOWLEDGEMENTS
This paper has been developed under the “ICREW Project – Improvement of Coastal and
REcreational Waters for all”, funded by INTERREG IIIB Program. Part of the results
presented where developed under a final thesis of the Environmental Engineering Course at
Instituto Superior Técnico, Universidade Técnica de Lisboa.
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6. REFERENCES
INSTITUTO DO AMBIENTE (IA) – Estratégia Nacional de Desenvolvimento Sustentável,
ENDS 2002, Junho de 2002.
INSTITUTO NACIONAL DE ESTATÍSTICA (INE) - Recenseamento Geral da População e
Habitação - 2001 (Resultados Definitivos).
MATOS, J.; SANTOS, S.; DIAS, S., Sistemas de Tratamento para Pequenos Aglomerados
em Portugal: desafios, estratégias e tendências para o futuro, Lisboa, 2002.
MINISTÉRIO DO AMBIENTE E ORDENAMENTO DO TERRITÓRIO (MAOT) – Plano
Estratégico de Abastecimento de Água e de Saneamento de Águas Residuais. MAOT, Lisboa,
Abril 2000.
ORGANIZAÇÃO PARA A COOPERAÇÃO E DESENVOLVIMENTO ECONÓMICO,
OCDE Environmental Indicators – development, measurement and use, 2003.
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