**2. Analysis of energy consumption and potential renewable energies**

Some projects in the world originated from the concept of the energy–water nexus, which is the coupling of energy, water, the environment including climate change, and food supply [1–9]. Studies conducted on WWTP and in collaboration with local governments and major organizations provide solid evidence of unit electricity for wastewater treatment or neutral energy. Electricity from renewable energy resources, such as wind or solar power, may be used to partially or completely replace electricity from the grid. Moreover, novel wastewater treatment processes have been employed in WWTPs to reduce the energy requirements per unit volume of treated wastewater in comparison with cases that depend on electricity only from renewable energy resources [10–15]. Some researchers illustrated that energy cannot be gained at all from aerobic digestion or organic substances at WWTPs and sludge treatment plants. The specific energy demand at these plants is still high, and too much energy is needed for far-reaching aerobic degradation of organic substances. However, biogas from anaerobic treatment from WWTPs or waste management may become a suitable way of improving energy efficiency. For alternative sanitation concepts, sewage and food waste management, or other environmental assessments of urban water systems [16, 17], life cycle assessments should be conducted to explore plant energy balance. Besides renewable energy, one potential candidate for compensating the consumption at WWTPs is wastewater heat recovery. Case studies show that technologies for heat recovery from wastewater also have been successfully implemented. However, heat recovery may harm the wastewater treatment process

Lithium-ion batteries contain precious metals such as lithium, cobalt, or manganese; therefore, recycling and recuperation of these batteries are highly advantageous. However, these processes use high levels of electricity in traditionally chemical methods [27–32]. Lithium-ion batteries are suitable as ancillary services or for supporting large-scale solar and wind integration in existing power systems by providing grid stabilization or frequency regulation [50]. Lithium-ion batteries are also classified as dangerous waste. If they are not properly treated, then they will damage the environment and cause harm to humans and the environment. By contrast, abundant electrical capacity remains in discarded lithium-ion batteries. Following an intensive review on advanced smart metering and communication infrastructures, a strategy for integrating electric vehicles (EVs) into the electric grid is presented [51]. Under the vehicle-to-grid phenomenon, the deployment of EV batteries in the energy market can compensate for fluctuations of the electric grid. A previous study [52] presented the optimization of electrical energy storage systems and improved control strategies based on hybrid power

To achieve energy self-efficient WWTPs, we consider several ways of ensuring positive energy balance of wastewater treatment such as renewable energies. In this study, automotive reused lithium-ion battery (RLIB) is used to accumulate electricity at night to shave peak power in the grid at noon as a prior phase before chemical separation of the RLIB pack. In general, RLIB packs might decay rapidly after being discarded, and the energy management system (EMS) is developed to address this issue. The performance of depth of discharge (DoD), which indicates the life cycle, is used to determine the effectiveness of EMS in bench test. Besides, an online scheme of estimating life cycle sensitized parameters is embedded in EMS for safety

and reduce the performance of WWTPs [18–26].

source and series.

164 Energy Systems and Environment

and performance guarantee.

After dividing a portion of effluent from the Dihua Sewage Pumping Station in Taipei, sewage enters the Dihua WWTP at an average of 434,349 m3 /day. It then passes through fine bar screens to remove coarse materials. It flows into primary clarifiers to remove the greater part of the suspended solids and a small portion of the organic matter in the sewage. Aeration basins and secondary clarifiers are used to remove organic matter in the sewage. The effluent from the secondary clarifiers is disinfected with sodium hypochlorite to remove pathogens before discharge into the Tamsui River. After sand filtration, 10,000 cubic meters per day of effluent become reused water for the plant. Night solids, combined with primary sludge and secondary sludge, is thickened, anaerobically digested, and dewatered to become sludge cake. It is then disposed in a landfill site or used as fertilizer for inedible vegetation by any organization that requests it. The energy consumption is listed in **Table 1**.

In the Dihua plant, the entire water treatment process consumes 120,526 kWh of electricity a day. Approximately 0.28kWh/m3 is required for wastewater treatment. This value is much lower than UNESCO's report (2014) of 0.62–0.87 kWh/m<sup>3</sup> excluding pumping to the treatment site and equipment efficiency. The average quantity of energy used varies considerably depending on the level of treatment, type of treatment, and size of plant, but it approximately doubles from primary to secondary and doubles again to tertiary levels of treatment (US EPA Office of Water 2013).

In Dihua's case, the outcome of biomass occupies 55.69% total unstable renewable energy as listed in **Figures 1** and **2**. Twenty percent of total area is assumed to be installed solar panel, and the reliable electricity capacity of 943.8 kW is obtained. Hydropower and wind power are not dominant energy resources in this plant.


**Table 1.** Usage of energy consumption in Dihua WWTP.

**Figure 1.** Unsteady renewable energies in Dihua WWTP.

**Figure 2.** Potential renewable energies in Dihua WWTP.
