Conditional Order-m Efficiency of Wastewater Treatment Plants: The Role of Environmental Factors

Abstract

Abstract:The growing economic and environmental importance of managing water resources at a global level also entails greater efforts and interest in improving the functioning and efficiency of the increasingly more numerous wastewater treatment plants (WWTPs). In this context, this study analyzes the efficiency of a uniform sample of plants of this type located in the region of Valencia (Spain). The type of efficiency measure used for this (conditional order-m efficiency) allows continuous and discrete contextual variables to be directly involved in the analysis and enables the assessment of their statistical significance and effect (positive or negative). The main findings of the study showed that the quality of the influent water and also the size and age of the plants had a significant influence on their efficiency levels. In particular, as regards the effect of such variables, the findings pointed to the existence of an inverse relationship between the quality of the influent water and the efficiency of the WWTPs. Also, a lower annual volume of treated water and more modern installations showed a positive influence. Additionally, the average efficiency levels observed turned out to be higher than those reported in previous studies.

Identifying the performance drivers of wastewater treatment plants through conditional order-m efficiency analysis

“…For other variables, the results are quite conflicting. In some cases, the plant's age seems to exert a negative effect on efficiency, as demonstrated by Fuentes et al (2015) and Molinos-Senante et al…”

“…First, the existing studies on WWTP efficiency are limited to specific geographic areas: Spain (Lorenzo-Toja et al, 2015) and, in particular, the Valencia and Catalonia regions (e.g., Hernández-Sancho and Sala-Garrido, 2009;Hernández-Sancho et al, 2011a, 2011bMolinos-Senante et al, 2014a, 2014bSala-Garrido et al, 2011Fuentes et al, 2015). Only two do not involve the Iberian Peninsula: Hsiao et al, (2007) in Taiwan and Frequelli and Giandrone (2003) The evidence from prior literature is consistent when examining some variables, such as size and plant capacity, which positively affect efficiency.…”

“…Finally, the pollution concentration of input wastewater has a negative effect, according to Fraquelli and Giandrone (2003) and Lorenzo-Toja et al (2015). This can be explained by the higher costs incurred to remove an intense pollutant load, although other scholars have demonstrated the opposite effect (Fuentes et al, 2015), probably because of the larger amount of pollutants that can be removed from a cubic meter of concentrated wastewater than from a more diluted one. Many studies have tried to address this issue through parametric and nonparametric approaches.…”

“…The studies that observe the performance of different technologies consistently show the dominance of activated sludge and anaerobic digestion, but conflicting evidence arises when the effects of aeration systems are observed (Hernández-Sancho et al, 2011a;Fuentes et al, 2015). The greatest efficiency in anaerobic digestion is given by the production of biogas, which is used to generate energy.…”

Computing Economies of Scope Using Robust Partial Frontier Nonparametric Methods

“…These recent nonparametric methods use only part of the sample to compute efficiency scores, thereby reducing the influence of outliers and extreme observations [18]. They do not face the problem of the "curse of dimensionality" and have important statistical features and interesting econometric interpretations [19], which makes them more robust than the traditional full-frontier nonparametric methods, such as DEA [20] and the non-convex free-disposal hull (FDH) [21].…”