# Application and Evaluation of Energy Conservation Technologies in Wastewater Treatment Plants
## 4 Performance Evaluation of Energy Conservation Technologies and WWTPs
### Evaluation Methods  
Appropriate evaluation methods can help managers to understand the energy utilization of the entire process through various data of the wastewater treatment plant, and to find opportunities for energy efficiency optimization. Only when the above objectives are achieved, can the results of energy research and technical analysis be used to guide technological transformation and engineering practice. [PERSON] et al. study three benchmark methods: normative method, statistical method, and programming method, and conducted energy efficiency evaluation [150]. The Key Performance Indicators (KPIs) method is the most common and simplest evaluation method. KPIs, the most commonly used evaluation method in WWTPs, is usually expressed as the ratio of output to input. The KPIs method is simple and easy to implement, but it can only evaluate specific parts, and it cannot systematically evaluate the status of WWTPs [16; 150]. Although the KPIs can be created by weighting, the complexity of the WWTPs process makes the method unsuitable [162]. Similarly, the KPIs method ignores the differences in WWTPs (location, size, process). Data Envelopment Analysis (DEA) is a tool using mathematical programming technology for performance evaluation. It can be used to evaluate energy performance in complex systems such as wastewater treatment because it can deal with multiple inputs and outputs problems [163; 164; 165]. The BCC model and the CCR ratio model are two types of DEA models [166]. The CCR model can evaluate the overall efficiency of a unit while the BCC model evaluates the pure technical efficiency of a unit. [PERSON] et al. used DEA to study the relationship between sewage characteristics and energy efficiency [167]. They gave some suggestions for efficient operation. Statistical methods such as ordinary least squares (OLS) and stochastic frontier analysis (SFA) are commonly used evaluation methods. These methods are mainly used to explore the influence of factors on energy efficiency and identify its determinants [162]. These methods regard the difference between the reference value and the actual value as a measure of efficiency. OLS uses the fitted regression line to express evaluation efficiency. In the OLS method, all treatment plants with below-average ratings are considered efficient [168]. SFA, which needs to determine the specific form of the production frontier, is a method of frontier analysis. Its advantage is to consider the impact of random factors on the results. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Objectives** & **Indexes** & **Reference** \\ \hline Environment & Risk quotient, Quantitative microbial risk assessment, Changes in ecosystem distribution, Soil productivity and permeability & [156; 157; 158] \\ \hline Water supply safety & Probability of a threat, Material losses, Human losses, security category, Four-Parameter risk matrix & [159] \\ \hline Treatment capacity & Removal efficiency, Toxic Units & [160] \\ \hline Comprehensive indexes & Process advancement, Process maturity, Process stability, Construction costs, Operating costs, Floor area, Operations’ personnel, Facility operations, Dependence on the downstream environment, Dependence on the upstream environment & [161] \\ \hline ENERWATER & Water treatment energy index (WTEI), Energy consumption, Pollutant concentration, Flow rate & [162] \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Cont. SFA separates inefficient components from incorrect components to make efficiency measurements more accurate, which is significant in the energy efficiency analysis of wastewater treatment [150]. Life Cycle Assessment (LCA) is an important framework in the evaluation process. LCA involves the whole process of a product life cycle, including the input of energy and raw materials, the output of wastewater, waste gas and solid waste, etc. LCA is an important tool for wastewater treatment assessment, which can be used to evaluate energy utilization and pollutant discharge [169; 170]. [PERSON] et al.