# Application and Evaluation of Energy Conservation Technologies in Wastewater Treatment Plants
## 3 Wastewater Treatment System Optimization and Control
### Control Strategy and Decision-Making  
Choosing the appropriate decision-making factors is the premise of formulating control strategies. Different objectives will lead to completely different optimization results. [PERSON] et al. used NSGA-II, a multi-objective evolutionary algorithm, to study the potential of control strategy optimization for the reduction of greenhouse gas (GHG) emissions from wastewater treatment in a cost-effective manner [129]. They took GHG emissions, effluent quality and operational costs as trade-off objectives and found that water quality standards and GHG emissions are negatively correlated, while energy consumption does not have a significant impact on GHG emissions. Other researchers have used multi-objective optimization methods, such as genetic algorithms and particle swarm, to draw similar conclusions [130; 131; 132]. [PERSON] et al. proposed some suggestions to improve wastewater discharge standards with low greenhouse gas emissions by using multi-objective optimization [133]. [PERSON] et al. used multi-objective optimization techniques to balance processing costs and efficiency [134]. The wastewater treatment process which has obvious non-linearity and multi-objective optimization can help to make rational decisions and balance multiple objectives, such as effluent quality, energy consumption, operation cost, GHG emissions. Therefore, studying intelligent multi-objective optimization control technology for urban wastewater treatment is still an important research direction in the current wastewater treatment industry [132; 135]. It is worth noting that policies have direct impacts on the optimization objectives. For the EU, energy efficiency is not the only focus of attention, according to EU Urban Wastewater Treatment Directive (91/271) [21; 136]. Moreover, tax, cost, environmental impact, and other factors are the goals that need to be concerned.  
Modeling and simulation is a good technique to evaluate the condition of process control in WWTPs by providing reference data, which can help researchers to facilitate a control strategy development, make a decision and evaluate performance [137]. Activated Sludge Models (ASMs) released by International Water Association (IWA), have great significance in process design and simulation verification, which can show the working mechanism of the treatment process. The ASM1 includes the basic biotransformation processes of an activated sludge WWTP which is used to describe the denitrification process in a WWTP [138]. BSM1, which includes a simulation model, a control strategy, evaluation standards, and test procedures, is useful in testing control strategies [139; 103]. Many researchers use the modified model to save energy, reduce cost, and evaluate control strategies [137; 140; 141]. [PERSON] et al. made an extension of BSM1 to facilitate a control strategy development and performance evaluation [142]. [PERSON] et al. optimized the modified anaerobic, buffer, intermittently aerated, and oxic (ABA\({}^{2}\)) process with linearized ASM2 for saving aeration energy [143].