Investigation of Economic and Environmental Impacts of the Use of Solar and Biogas Resources in Urban Wastewater Treatment Plants
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As water and energy are the most basic needs for the well-being of people, the water-energy nexus is an area to be examined. A large share of the energy demand (ED) of the water sector is caused by Wastewater Treatment Plants (WWTP) and realizes in the form of electricity constituting a large share of their operating costs. Considering the world's dependence on fossil fuels, Green House Gases (GHGs) caused by electricity generation and the current climate change crisis, it is an important opportunity to meet ED of WWTPs by renewable energy sources (RES). The wastewater industry has developed rapidly in the last 20 years in Turkey. ED of the sector has increased as a result of the need for more advanced technologies and treatment methods due to the increasing number and capacity of WWTP, per capita wastewater and population. It will continue to increase due to plants in construction and the increase of population. In this study, together with the option of RES integration in WWTPs, ED to treat 1 m3 of wastewater (energy intensity-EI-kWh /m3) in the WWTPs in metropolitan municipalities, which are the source of 85% of the total wastewater produced and host 70% of the WWTPs in Turkey, was investigated. The main objective of this study is to calculate the EI based on type and process of WWTPs in Turkey and to analyze possible environmental and economic impacts of meeting the ED via photovoltaic (PV) panels and biogas generators. In the first stage of the study, an online survey was prepared to collect information from WWTPs. The first part of the survey has questions related to the ED of the plant; the second part focuses on the perception of WWTPs regarding the use of RES. In addition, data regarding WWTPs in metropolitan municipalities, treated wastewater, ED, (if available) biogas and electricity generation, population served, BOD/COD/SS, type of plant and treatment process were collected from various open sources. The data that cannot be obtained online has been completed via personal communication for 451 plants. Data collected for 2017 were analyzed based on plant type, the process used and the amount of treated wastewater. The analysis revealed that the EI of large-scale WWTPs is lower than that of small-scales. Furthermore, as expected, the EI of the primary treatment (0.07 - 0.34 kWh / m3) is lower than that of secondary (0.08 - 1.36 kWh / m3) and advanced treatment (0.15 - 0.99 kWh / m3). In the second stage of the study, 25 WWTPs were selected according to the completeness of their data and representing different capacities. The possibility of meeting their ED by biogas and solar power and the economic and environmental impacts of this integration were investigated. HOMER simulation software was used in six scenarios defined based on CO2 emission penalty (0 and 16 $/ton) and electricity selling price (0.000, 0.050 and 0.133 $/kWh). The results were examined under five WWTP capacities. The analysis has shown that RES integration is not cost-effective for WWTPs having a capacity of below 1 million m3. It was observed that CO2 penalty and electricity selling have a major impact on the generation from the RES and the in-use of generated electricity for WWTPs having a capacity of above 1 million m3. In the case of electricity selling price of 0.133 $/kWh, RES can meet 88% of the ED, while PV panel can generate an amount equal to 3.1 times the ED. In the scenario where there is no electricity selling and emission penalty, CO2 emissions can be mitigated by 15% while production from RES reached up to 23%.