# Application and Evaluation of Energy Conservation Technologies in Wastewater Treatment Plants
## 1 Introduction
### Current Energy Consumption of WWTPs
#### 1.2.2 Influencing Factors  
The relationship between influencing factors and the energy consumption is also significant. Many studies show that the scale, treatment processes, effluent discharge standards, and wastewater quality can affect energy consumption [28; 32]. Therefore, it is not advisable to study the energy consumption of wastewater treatment alone, and it is more practical to compare the energy consumption of wastewater treatment process horizontally [33].  
[PERSON] et al. made statistics on the factors affecting energy consumption. He found that process, scale, and water quality were the key factors affecting energy consumption [34]. The influence of effluent quality on energy consumption is intuitive and easy to understand. Energy consumption is positively correlated with effluent water quality standards [28]. The unit energy consumption of WWTPs with the same process and scale increases with the improvement of effluent quality, which is consistent with conclusion of [PERSON] [34]. Some researchers hold the opinion that the expansion of the WWTP scale helps to reduce unit energy consumption [35; 36]. However, [PERSON] et al. found that unit energy consumption would have a reverse increase if scale exceeded the boundary [28]. [PERSON] et al. attributed it to the friction between the wastewater and the pipeline when the wastewater was transported. There is no doubt that treatment processes have a great effect on energy consumption. A typical WWTP, where aerobic activated sludge treatment and anaerobic sludge digestion technology is applied, consumes 0.6 kWh/m\({}^{3}\) electrical energy for wastewater treatment [37]. Wastewater treatment using lagoons, trickling filters, activated sludge and advanced wastewater treatment requires 0.09-0.29, 0.18-0.42, 0.33-0.60, and 0.31-0.40 kWh/m\({}^{3}\), respectively [38]. The energy consumption of WWTPs under different factors (locations, processes) is shown in Table 1. Different countries and treatment methods will have a great impact on energy consumption.  
Similarly, the aging factor, climate, function, location, and other influencing factors were taken into consideration by researchers [41; 42]. However, these factors are less influential. [PERSON] et al. investigated energy consumption of WWTPs in different regions of China and found that there were significant differences among different regions [28]. They believe that this result is due to the difference in climate, treatment process, effluent standard, scale, and other related factors. Location is not a direct factor in energy consumption.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Countries** & **Processes** & **Consumption/Wastewater (kWh/m\({}^{3}\))** & **Reference** \\ \hline \multirow{3}{*}{China} & SBR & 0.22711 & [34] \\  & Activated sludge & 0.24408 & [34] \\  & Oxidation ditch & 0.26254 & [34] \\ \hline \multirow{2}{*}{Japan} & Oxidation ditch & 0.44–2.07 & [39] \\  & Activated sludge & 0.3–1.89 & [39] \\ \hline \multirow{2}{*}{Australia} & Oxidation ditch & 0.5–1.0 & [40] \\  & Activated sludge & 0.46 & [40] \\ \hline \multirow{2}{*}{USA} & Activated sludge & 0.33-0.60 & [40] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Energy consumption of wastewater treatment in different countries and processes.