بهره وری فنی و تجزیه و تحلیل هزینه در فرایندهای تصفیه خانه فاضلاب: روش DEA

In light of the growing importance of water reuse as an alternative source of water resources in many regional areas, the objective of this paper is to analyse the efficiency of wastewater treatment plants as a basic requisite to improve the potential of the water reuse. The analytical benchmarking methodology Data Envelopment Analysis (DEA) is used to calculate efficiency measurements. An efficiency index is obtained for each plant by means of mathematical programming techniques, aiming to minimise the inputs used in the water treatment process. This indicator is used as a reference to analyse plants' activity through a series of variables including the size of the plant or its cost structure. Given the importance of wastewater treatment in the Valencia Region (Spain), empirical research has been carried out for 338 plants located in this area. We verify the fact that the largest plants run more efficiently than smaller plants, as was to be expected. At the same time, there is evidence that a series of representative variables in the treatment process are clearly linked to efficiency. Maintenance and waste management costs are the most important factors to explain the differences between plants in terms of efficiency. Finally, the benchmarking methodology (Data Envelopment Analysis) is confirmed as a very useful management tool for the study of wastewater sector.

It is common knowledge that water reuse is beneficial, not only because it enables water resources to be recovered, but also because it reduces environmental impacts. However, it is also true that some variables such as cost efficiency of the treatment process, the effluent quality and the risk existence, among others, condition its use, particularly in comparison to other available resources. In this sense, an in-depth analysis of the local water market is required in order to know the real possibilities to make water reuse an attractive option for a given sector, such as agriculture, industry and aquifer recharging. This analysis should bear in mind both the costs involved in the various water supply alternatives [1] and the type of crop, profit margins, social stance with respect to the environment, irrigation methods and guaranteeing supply, among other aspects. Any given analysis of the potential of water reuse in a particular region and for a series of specific uses requires an extensive knowledge of the wastewater treatment processes from technical and cost point of view [2], [3], [4], [5], [6] and [7]. A classification of the effluents depending of their respective quality parameters enables the most suitable water treatment technology for each potential use. Moreover, a growing use of reclaimed water for irrigation could allow a transfer of freshwater up to now used for agricultural purposes to human and industrial consumption. This would be a redistribution of available water resources in accordance with the quality required by each use and with a favourable effect on the environment. Farm crops would have a no conventional water resource of which supply would be guaranteed, even during droughts, and which would be sufficiently of high quality. This replacement of resources would occur at the same time as irrigation infrastructure was improved and, therefore, farms would use water more efficiently. This paper focuses on analysing efficiency in wastewater treatment processes. Efficient performance, both in technical and cost terms favours water reuse possibilities and, therefore, increases the supply of the so-called non-conventional resources. Empirical research is carried out for Spain (the Valencia Region) using an analytical benchmarking methodology known as Data Envelopment Analysis (DEA).

We have analysed the processes of treatment of wastewater by means of obtaining the technical efficiency index. This methodology allows us to characterise in detail the performance of each plant of the sample at cost level. This exhaustive knowledge associated to each wastewater treatment process is considered as a basic requirement when valuing the true potentiality of reclaimed water in any territory, particularly in terms of costs. In the context of the benchmarking methodology (Data Envelopment Analysis) the present paper sets out to measure the efficiency of wastewater treatment processes with the aim of obtaining efficiency indicators by plant. Once these indexes have been obtained, the next step has been to assess the possible relationships between these efficiency indicators and the size of the plant, expressed in terms of the volume of wastewater treated. The results obtained from empirical research show that the largest plants run more efficiently than smaller plants. A series of representative variables in the treatment process are clearly linked to efficiency. The most important factors to justify the differences between plants in terms of efficiency are maintenance and waste management costs. Finally, the DEA models are confirmed as a very useful tool for the study of wastewater sector. The use of this methodology provides an important knowledge about the activity of the wastewater treatment plants allowing an improvement of the global efficiency. In this context, the calculation of efficiency indicators for each input used in the treatment process will be a great challenge.