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The life cycle analysis (LCA) offers a holistic approach to the environmental assessment of the various options of re-use

Use of LCA methodology for the environmental assessment of alternatives for water reuse

Montse Meneses, group of systems engineering and Automatics (UAB)

Jorgelina C. Pasqualino and Francesc Castells, Department of engineering automatic (URV)

Josep Flores and Raquel lawns, water Technology Center (Agbar)

Lluis room and Maribel Marin, Consorci de la Costa Brava

14/07/2011

July 14, 2011

Implementation of tertiary treatment for the reuse of water stations purification of waste waters (WWTP) output, is the subject of growing interest in recent years. Re-use of treated water strategies seek to solve the problem of water scarcity without other environmental problems. In this context, the life cycle analysis (LCA) offers a holistic approach to the environmental assessment of the various options of re-use.

In this work the LCA methodology is used to assess different technologies of tertiary treatment and assess the advantages and disadvantages of the reuse of urban waste water in applications other than the use of mouth. They have been compared the environmental impact of the production of 1 m³ of water for non-potable uses reused water of drinking water from the ETAP and desalinated water. This analysis has also accompanied an economic study and sensitivity analysis. The calculation has been considering current data of operation of a wastewater treatment plant located in the Mediterranean area, although the results can be applied to any other plant. The use of reused water for use as non-potable water is beneficial both from economic and environmental point of view.

Introduction

The regeneration of the waste water is a tool which allows to improve the management of water resources. Although the reuse of reclaimed water is being promoted as one of the possible solutions to the problems of water supply, there are few countries in which it is actually implemented. Several Mediterranean countries suffer continuously from episodes of drought, once they find it difficult to implement reuse in their treatment plants for water or sewage stations of Residual water (WWTP).

The applications in which reclaimed water can be used include irrigation, industrial use, urban cleaning, extinction of fires, recreational activities, resupply of surface water, recharge of aquifers, etc. In addition, use of reclaimed water reduces the consumption of drinking water (and therefore avoids the consumption of electricity and reagents required to purify her) (Hall and Serra, 2004).

The reuse of waste water can become an alternative resource of water. However, the social opposition is significant, leading to the rejection of the appeal by the end-user. In addition to the concept of risk, need a good predisposition of the end user will consume the final product (for example, the vegetables irrigated with reclaimed water, the turf of golf courses, services of cleaning of streets, etc.). Some of the reasons for this rejection are the potential effects of remains of pollutants in water, which can damage human health or pollute the environment (pollution dangerous, remains of pharmaceutical products and cleaning products, etc.).

Despite the fact that wastewater reuse strategies intended to deal with the problem of water scarcity, is must ensure, on the other hand, that the actions implemented to solve this problem carry no other environmental damage. For this reason, the completion of an environmental assessment of the alternatives for waste water reuse is necessary, using a methodology objective. In this context, the methodology of life cycle analysis (LCA) is a right approach to the environmental assessment of products, processes or services, and for the assessment of different alternatives.

Materials and methods

To assess the environmental benefit of using water regenerated into non-potable uses, it has compared the environmental profile of the following alternatives to the production of 1 m³ (Figure 1):

(a) regenerated water, to be applied in agricultural irrigation: in calculations only stages of treatment for tertiary treatment of wastewater, as well as the environmental benefit because of the savings of fertilizer have referred.
(b) reclaimed water to be applied in non-agricultural uses: in calculations have provided only the stages of treatment for tertiary treatment of wastewater.
(c) water, obtained from conventional treatment of drinkable water: environment from environmental profile of different purification plants previously studied and generic plants obtained in database has been obtained.
(d) water desalted, obtained from the desalination of seawater using reverse osmosis (Meneses et al., 2010): half from environmental profile of different desalination plants studied previously has been obtained.

In addition, has been an economic these alternatives analysis, when the water produced in each one of them is used for agricultural or non-agricultural uses.

Figure 1: Diagram of the alternatives for production of 1 m3 of water for non-potable uses

Figure 1: Diagram of the alternatives for production of 1 m³ of water for non-potable uses.

The LCA methodology has been developed according to international standards (ISO 14040 and ISO 14044). As a functional unit we have selected 1 m³ of water regenerated, produced in the WWTP for non-potable uses. Within the limits of the system it has included only the phase of operation of the plant, excluding infrastructure and the dismantling of the same. Traditional a WWTP, evaluated primary and secondary treatments in earlier studies (Pasqualino et al., 2009), are mandatory and are essential to minimize the environmental impact of download the residual water in the watercourse, natural, regardless of the fact that this water is then regenerated or not. For this reason, environmental and economic burdens related to the traditional treatment of residual water not be allocated to reclaimed water. Therefore, the environmental profile of the production of regenerated water includes only tertiary treatment. Current data of operation of a WWTP situated on the Mediterranean coast have been used for the purposes of calculation.

However, the results may be applicable to other similar plants. All consumption of matter and energy of the plant were related to pollution inventory data provided by the database ecoinvent v2.1. These data were adapted to the Spanish electric mix and the European model of water and transport. In this study,

We have evaluated climate change indicator (GWP Global Warming Potential, kg CO₂ eq.), calculated in accordance with the CML2000 methodology, as well as two additional environmental indicators: water use, (Water Use,³m WU) and the accumulated demand of energy (CED, Cumulative Energy Demand, MJ). Water use indicator indicates the consumption of water from different origins (freshwater, surface water, groundwater, etc) throughout the cycle of life.

Results and discussion

Table 1 shows the environmental profile and economic evaluation of the production of 1 m³ of water for non-potable uses (agricultural uses such as non-agricultural). The use of water reused in agriculture is the most favourable option environmentally because it reduces fertilizer requirements. The content of N in the reused water replaces an important part of the necessary fertilizer for agriculture. For non-agricultural applications use of reused water and drinking water has similar environmental profiles, while the production of desalinated water is the biggest environmental impact. The most important difference between reused water and drinking water is water savings.

The impact of the tertiary treatment in a WWTP where the raw material is a regenerated waste (domestic waste water) may be comparable to the impact of drinking water in a company's treatment of Potable water (ETAP), while the latter may present problems of supply (River, Lake or well water).

Table 1: environmental profile of the production of 1 m³ of water for non-potable applications.

The use of reclaimed water in non-potable uses such as irrigation of parks and gardens and the cleaning of streets, implies the use of a residual current that otherwise would have dumped the medium without use.

For non-potable water applications, if not reclaimed water is used, are usually water of 3 types of sources: well water (energy consumption due to its uptake and transport, as well as consumption of fresh water resources), ETAP water (energy consumption and items in his collection and treatment, as well as consumption of fresh water resources) and water IDAMSea water desalination installation (consumption of energy and reactive in its catchment and treatment).

The use of water regenerated in these applications, therefore, saves the consumption of energy, reactive and freshwater resources derived from the 3 previous sources, and therefore avoids their environmental impacts. On the other hand it should be noted that the residual water is a continuous source, which does not depend on the weather.

Indicator of water use, measures the consumption of fresh water (rivers, lakes, underground water, etc) and salted throughout the process life cycle, including water used in the generation of electrical energy to produce different types of electricity (e.g. water used in hydroelectric power). This indicator measures the consumption accumulated in all stages of the process without specifying neither the place nor the time of consumption. Not should therefore confused with local water consumption, very significant in times of drought. For this reason, water use indicator indicates that for 1 m³ of drinking water for uses non-potable, from the tertiary of a WWTP, less amount of water (1,3 - 1.45 m³, depending on the application) that is required to produce it in an ETAP (2.74 m³), whereas in an IDAM will consume 18 times that amount of water (26.2 m³). However, most of the water included in this indicator is water used without consuming it (water of power plants or equipment cooling water), or that it comes from sources regarded as inexhaustible (sea water). On the other hand, the indicator of the use of freshwater as local resource consumption of a resource, which is limited in certain places, becomes more important.

Conclusions

The application of water both regenerated in agricultural applications such as non-agricultural shows the advantage of including a tertiary in the process of a WWTP to thus obtain a valuable resource that can replace drinking water desalinated, especially in areas with water stress. Where agricultural applications, the environmental benefits achieved by the replacement of fertilizer are very relevant due to the saving of fertilizer.

To compare water drinking and reused for non-agricultural applications, despite presenting similar environmental and economic impacts, the use of reused water to replace drinking water helps to preserve a very valuable resource (fresh water).

The use of water desalted for non-potable uses must not allow, that the environmental and economic impact of its production is significant, when compared with other options.

Awards

This work is part of the project Sostaqua ("' technological developments towards the urban cycle of self-sustaining water"', led by Aguas de Barcelona (Agbar) and funded by the Centre for Industrial technological development (CDTI) through the Ingenio 2010 program within the zenith call.) We appreciate the data acquisition process to all the treatment plant equipment and especially to Maribel Marin, head of management of the southern part of the d'Aigües joint enterprise of the Costa Brava.

Bibliographic references

-Meneses M, Pasqualino JC, Céspedes R, Castells f. 2009. Alternatives for reducing the environmental impact of the main residue from a desalination plant. J Ind Ecol (DOI: 10.1111/j.1530-9290.2010.00225.x).

-Pasqualino JC, Meneses M, Abella M, Castells f. 2009. LCA as a decision support tool for the environmental improvement of the operation of at municipal wastewater treatment plant. Environ Sci technology 43: 3300-3307.

-Sala L, Serra M. 2004. Towards sustainability in water recycling. Water ski technology 50: 1-7.