# Measuring the Performance of Wastewater Treatment in China
## 1 Introduction
[PERSON] [29] proposed a dynamic activity analysis model based on the directional distance function to forecast the possibility of win-win development in China's industry between 2009 and 2049. [PERSON] [30] calculated regional efficiency of environmental technology with the data of 30 provinces in China in order to evaluate the coordination of environmental and industrial growth based on the directional distance function. The radial output angle efficiency models used above ignore the variance of the variables and can lead to estimation errors. To overcome this defect, [PERSON] et al. [31] set up a nonradial directional distance function which, compared with other methods, is better because it provides more reasonable and accurate estimation results. Other studies have applied nonradial directional distance functions to energy and environmental (CO\({}_{2}\)) efficiency analyses, such as [PERSON] et al. [32] and [PERSON] et al. [33]. [PERSON] et al. [34] measured the performance of industrial green development using a nonradial distance function approach on the Jiangxi Province in China. [PERSON] et al. [35] used a global M-L productivity index based on the directional distance function (DDF) to dynamically evaluate energy efficiency. [PERSON] and [PERSON] [36] measured and decomposed the total factor green efficiency and productivity of 30 provinces in China over the period from 1998 to 2013 under the basis of resource and environment constraints in the nonradial directional distance function. Our study shall thus apply the nonradial directional distance function to measure the wastewater treatment performance of 31 provinces of China from 2011 to 2015. Simultaneously, researchers recently analyzed the methods of water treatment adopted by China. [PERSON] et al. [37] investigated the occurrence, removal, and risk of 42 organic micro pollutants (MPs) in 14 municipal wastewater treatment plants (WWTPs) distributed across China. They provided useful information for better control of the risks associated with MPs. [PERSON] et al. [38] investigated the occurrence and fate of pharmaceuticals and personal care products (PPCPs) in seven wastewater treatment plants (WWTPs) in Xiamen City in China. It was found that PPCPs were widely detected. This indicates that water treatment has become a critical topic for every country. There are few specific studies on wastewater treatment efficiency measurement that cover overall China. Regarding wastewater discharge research on China, some studies focus on single-year factors or compare three large areas within the country. The assessment of wastewater treatment plants' efficiency neglects undesired output in the process of water pollution control, which may lead to a bias in the evaluation results. This present study uses the directional distance function model to assess the development of 31 regions in China from 2011 to 2015. The model considers relatively directional distance concepts. We consider complete economic growth factors that produce good economic growth effects, but which also cause bad wastewater discharge issues. We also examine whether there is an effective comparison measure for wastewater treatment expenses in each region. The purpose of this study is to measure the performance of wastewater treatment and efficiency in order to help to provide a path for maintaining balanced and sustainable progress in China. We also note the importance of the government's water policy and the improvement in efficiency of some regions. Government urbanization policy and new corporate establishments must consider the costs of sewage treatment before any new investments. There should be a balance between economic development and protection of any country's natural ecology. This paper thus particularly focuses on the DDF method to offer a complete discussion of efficiency issues in 2011-2015 (that is, the 12 th Five-Year Plan).